The increasing reliance on renewable energy sources presents challenges due to their intermittent and variable nature, necessitating efficient energy storage solutions. Underground Mechanical Energy Storage (UMES) has emerged as a promising approach, utilizing subsurface reservoirs to store pressurized fluids. However, the deployment of UMES systems is constrained by the availability of suitable natural subsurface formations. This study explores a novel concept of forming impermeable CO₂ hydrate geo-capsules within porous soil deposits at depths of 50–400 m for fluid-based UMES applications, leveraging gas hydrate-bearing sediments’ unique properties of extremely low permeability and increased stiffness. An analytical mechanical model is developed to describe the overall capsule response to energy storage, incorporating a spherical multi-layered elasto-plastic solution for internal fluid injection. The analytical model is validated through numerical simulations, which are also used to extend the investigation to varying lateral earth pressure conditions (k₀≠1). A solution space mapping is then performed to evaluate the influence of key geometrical and stiffness parameters on the mechanical response of hydrate geo-capsules, followed by an assessment of pressure retention over time. The framework is further extended to estimate the energy storage capacity of a single or multiple capsules, considering a hybrid Pumped-Hydro Compressed Gas Energy Storage (PH-CGES) configuration. This study provides a first-step assessment of hydrate-based UMES feasibility and establishes a baseline for future investigations.

Acoustic waves are introduced to a silicon nitride photonic integrated circuit. The acoustic waves are generated through thermo-elastic actuation in a metallic grating and monitored using photo-elastic modulation in a racetrack resonator readout waveguide. The stimulation of three acoustic modes of the layers structure is observed. The frequencies and group velocities of the three modes agree with calculations. The acoustic frequency reaches 1.3 GHz. The concept introduces high-frequency modulation to the otherwise passive silicon nitride platform. The efficiency of photo-elastic modulation is modest: estimated as 6 × 10⁻⁸ refractive index units for 1 W of optical pump power. With future work, the concept may find applications in microwave photonic signal processing, optical and mechanical sensors, and characterization of materials and layers.

The intermittency of renewable energy sources and the increase in renewable energy shares require energy storage capability to sustain the green transition. One promising solution for underground energy storage is the use of subsurface CO₂ hydrate capsules, which act as impermeable vessels that store compressed fluids and discharge them upon need. However, as part of the proof-of-concept study of this technology, the feasibility of constructing such vessels, e.g. CO₂ hydrate capsules, has yet to be demonstrated. This work employed CO₂ gas injection assisted by chemical solution into partially water-saturated sand sediments to synthesize CO₂ hydrate capsules. The concentrations of chemical solutions (THF, CP and DIOX) were screened out in the gas/liquid/sand system in terms of kinetic promotion, using a rocking cell. Separately, experiments were carried out with a new high-pressure chamber set-up that quantified the effects of water saturation and chemical promoters on the efficiencies of CO₂ hydrate synthesis in confined partially water-saturated sand. Results on the gas/liquid/sand system showed that 0.025 water/CP weight ratio CP solution and 1.3mol% THF solution induced the largest pressure drops of 18.4 ± 0.2 bar and 16.7 ± 0.1 bar, respectively, indicating the most promoted CO₂ hydrate formation kinetics. Results with the pressure chamber showed three stages during slow CO₂ gas injection: (1) initial pressure “build-up stage”; subsequent (2) CO₂ gas “uptake stage”; and (3) CO₂ injection “closing stage”. CO₂ hydrate formation kinetics of CO₂ hydrate retention percentage (S_CO2) and CO₂ hydrate density (ρ_CO2) were directly proportional to the initial water saturation (6.0–76.7%). Injection of THF or CP solutions increased S_CO2 by 16.5% or 18.5%, and ρ_CO2 by 74.5% or 128.3% compared to injection of water. The best performances were obtained at a fluid pressure of 27.0 bar, with a 0.025 water/CP solution-assisting CO₂ gas injection, in sediment with an initial water saturation of 32.6% and porosity of 44.6%, giving rise to S_CO2 of 67.2% and ρ_CO2 of 80.6%. These findings demonstrated that the injection of THF or CP solution with CO₂ gas facilitated the possibility of the formation and stabilization of subsurface CO₂ hydrate capsules.

Open-ended pre-stressed high-strength concrete (PHC) pipe piles are susceptible to progressive distortion and even failure in the vicinity of the pile toe during driving into stiff soil or rock strata. This paper presents an experimental investigation conducted as part of a power plant construction in Huainan, China. After 50 piles were driven in the initial phase, the toe of 9 piles were detected as damaged using the sonic echo testing method. In the second construction phase, four piles were instrumented with longitudinal and circumferential fiber optic cables, as well as discrete strain gauges. The recorded responses of pipe piles throughout their driving process are analyzed to reveal the causes of damages. The results show that a maximum circumferential tensile stress developed at a distance of 1/6 pile length above the pile toe, with its value three times greater than that in other cross-sections. This high circumferential stress results in transverse cracks and the failure of open-ended PHC piles and is believed to be related to the formation of soil plugs. The findings provide valuable insights into performance evaluation of driven open-ended PHC piles.

Confinement of rock bolts by the surrounding rock formation has long been recognized as a positive contributor to the pull-out behavior, yet only a few experimental works and analytical models have been reported, most of which are based on the global rock bolt response evaluated in pull-out tests. This paper presents a laboratory experimental setup aiming to capture the rock formation effect, while using distributed fiber optic sensing to quantify the effect of the confinement and the reinforcement pull-out behavior on a more local level. It is shown that the behavior along the sample itself varies, with certain points exhibiting stress drops with crack formation. Some edge effects related to the kinematic freedom of the grout to dilate are also observed. Regardless, it was found that the mid-level response is quite similar to the average response along the sample. The ability to characterize the variation of the response along the sample is one of the many advantages high-resolution fiber optic sensing allows in such investigations. The paper also offers a plasticity-based hardening load transfer function, representing a “slice” of the anchor. The paper describes in detail the development of the model and the calibration/determination of its parameters. The suggested model captures well the coupled behavior in which the pull-out process leads to an increase in the confining stress due to dilative behavior.

Ribbed bars are known for their enhanced bond to concrete. Their ribs make bar section variable along the axis and the strain profile is variable as well, under any given applied force. Such variable strain profile has not been measured so far, thus the stress profile and its effect on the global behavior of the bar cannot be determined. Though optical fibers are an effective means to measure the strains in structural members, their application to the study of bond behavior is still in its infancy. Such an application is the objective of this research project. Specially manufactured partly smooth and partly ribbed bars with optical fibers were tested in pure tension (bare bars) and in the pullout from concrete to investigate the strain profile variability. In the bare bars, the strain measured in the smooth part was constant (as expected), while in the ribbed part higher strains were measured but no localized effects were detected, and the location of the ribs was not identified. Similar behavior was obtained by 3D finite-element analysis, which merely yielded slight ups and downs at ribs' locations, with an average strain that is similar to the measured strain. However, in the pull-out tests, the strains were constant in the unbonded smooth part and exhibited an undulating profile in the bonded ribbed part, where the peaks were related to the locations of the ribs. Such promising results motivate further studies to improve the resolution of the proposed technique.

Geomechanical aspects of methane hydrate (MH) bearing sediments constitute a major factor in MH reservoirs exploitation. One important element to be analyzed and quantified is the hydrate dissociation effect on the soil response, which may be critical for understanding the overall sediment response to gas hydrate production. This paper investigates the effect of MH dissociation on stresses and strains using the discrete element method (DEM). Both thermal-induced and depressurization-induced dissociation are considered in the paper. The sediment response is investigated under stress control and strain control loading conditions (one leading to excessive deformation while the other to stress relaxation), with examination of the resulting strain path and stress path, respectively. The effect of the stage in which the hydrate is formed and stressed is also investigated. Based on the DEM investigation, a simplified model entailing an interpolation between two states of the sediment (with and without hydrate) is suggested for potential use in continuum based formulations.

Energy storage needs to account for the intermittence of solar radiation if solar energy is to be used to answer the heat demands of buildings. Energy piles, which embed thermal loops into the pile body, have been used as heat exchangers in ground source heat pump systems to replace traditional boreholes. Therefore, it is proposed to store solar thermal energy underground via energy piles. To investigate the performance of such systems, a laboratory-scale coupled energy pile-solar collector system was built for this study. Experiments were performed to evaluate the effects of various controlling parameters on the short-term performance of the system. These include the degree of saturation of the soil, the flowrate of the heat-carrying fluid, the intensity of solar radiation, and their interaction. The results showed that under abundant solar radiation, the daily average rate of energy storage per unit pile length increases by about 150 W/m when the soil condition changes from being dry to saturated, with a maximum value of about 200 W/m. As the intensity of solar radiation drops, it becomes the dominant factor. Compared to the laminar flow, the turbulent flow contributes more to the underground solar energy storage as the soil is more saturated. This suggests a technique to minimise the electricity consumption by the system and thus optimise its performance through regulating the flowrate. In addition, a mathematical model of the coupled energy pile-solar collector system was validated against the measurements. Long-term simulations in prototype using the validated model further confirm the above conclusions.

This paper deals with the problem of tunneling effects on existing jointed pipelines. It extends a recently developed Fourier-based elastic continuum approach which has been applied to continuous pipelines. Unlike the continuous pipeline solution, in which the response in the spatial frequency domain is orthogonal (that is, each frequency response is independent of other frequencies), the joints lead to coupling between the spatial frequencies. Within the paper, closed form expressions are provided for the set of equations describing the coupling and interaction between the spatial frequencies. These expressions can directly be used to solve the global response of the jointed pipeline. The development is based on energy principles, and involves full cross-sectional as well as longitudinal compatibility, and hence may be regarded as more rigorous than previously published elastic continuum solutions which involve various assumptions regarding the distribution of interaction forces and discretization. The results of the suggested solution are compared against previous published, matrix based, solutions, where it is shown that the current method is well suited for the jointed pipeline problem. Finally, the condition of the more simplified Winkler system is addressed and various subgrade reaction models are discussed and compared with the more rigorous elastic continuum solution.

The Mobilisable Strength Design (MSD) philosophy has been used in various applications related to underground construction, e.g. for analysis of deep foundation and retaining wall performance. MSD requires simple models for the stress-strain behaviour of soils. The use of a mobilisation factor on undrained strength to limit soil mobilisation was introduced in BS8002 in 1994. To assist with MSD calculations, the mobilisation strain framework (MSF) has been developed to allow geotechnical engineers to account for the non-linear behaviour of fine-grained soils in routine geotechnical design. In this paper, triaxial and pressuremeter test data from the London Clay deposit are analysed, using the MSF, to study the effects of anisotropy on both the mobilisation strains and non-linearity exponent. The implications for design of underground constructions are also discussed.

This study offered a novel method for characterizing the soil support in slab-on-grade constructions such as rigid pavements and raft foundations. The method applies to slabs that are instrumented with fiber-optic cables for distributed strain sensing; it is based on analyzing the spatial profiles of slab bending strains generated by randomly applied surface loads. The concept was demonstrated for a synthetic case involving an infinite plate resting on a Pasternak support model. The method was shown to deliver non-destructive, non-disruptive, and load-independent quantitative information on the prevailing soil support. Therefore, it is deemed well suited for long-term health monitoring applications of slab-on-grade constructions. Such monitoring can help facility owners evaluate and intercept external events that undermine the integrity of the structure. In the long-term, continued monitoring of soil support can help the engineering community improve analysis approaches and design decisions concerning soil-structure interaction.

Seismically-induced permanent displacements of slopes are commonly evaluated using the Newmark sliding block approach. The conventional Newmark approach, while convenient in application, is often applied to a singular potential failure mechanism, omits consideration of the spatial distribution of potential failure mechanisms, neglects complex yet realistic failure geometry, and does not consider the temporal evolution of the critical mechanism. The proposed diagnostic tool applies the Newmark approach within a rigorous limit equilibrium framework to produce spatial distributions of yield accelerations and seismically-induced permanent displacements, or yield maps and surface-associated displacement maps, respectively. In this study, the application and utility of these diagnostic tools are demonstrated through a sensitivity analysis considering various soil strength parameters, horizontal and vertical motions, and complex slope and failure geometries. Additionally, it is shown that the proposed diagnostic tool reasonably estimates post-seismic geometry, shown by a comparison to an experimental shake table study. Using yield and displacement maps, both coseismic displacement and the range of potentially unstable geometry may be constrained. Moreover, the spatial and temporal evolution of possible seismically-induced displacements may be considered. This tool provides a rational means of applying sliding block approaches that reduces the need to assume the surface of maximum displacement a priori while retaining the simplicity that has facilitated the application of the sliding block approach versus more complex numerical models. The proposed diagnostic tools also provide a framework for future potential analyses, as it can be modified to incorporate other slope stability methods or seismic analyses.

This paper presents an approach for evaluating the horizontal stresses that develop in geotechnical Direct Simple Shear (DSS) tests through the use of high-resolution distributed fiber optic sensing. For this aim, fiber optics were embedded in 3D printed rings used for confining the soil in the test procedure. An analytical approach linking the measured spatially-distributed strain profile and the internal soil-ring contact stresses is developed in the paper. The method is based on representation of the contact stresses by a Fourier series expansion, and determining the coefficients of the series by minimizing the difference between the measured strain and the analytical strain within the linear elastic ring. The minimization problem results in a linear set of equations that can easily be solved for a given measurement. The approach is demonstrated on a set of drained DSS tests on clean sand specimens. Stress paths using the evaluated horizontal stresses are plotted together with Mohr circles at failure. These illustrate how, in these specific tests, the horizontal stress increases and principal stress direction rotates, until failure occurs along horizontal planes.

The evaluation of soil reaction in geotechnical foundation systems such as concrete pavements, mat- and raft foundations is a challenging task, as the process involves both the selection of a representative mechanical model (e.g., Winkler, Continuum, Pasternak, etc.) and identify its prevailing parameters. Moreover, the support characteristics may change with time and environmental situation. This paper presents a new method for the characterization of plate foundation support using high-resolution fiber-optic distributed strain sensing. The approach involves tracking the location of distinct points of zero and maximum strains, and relating the shift in their location to the changes in soil reaction. The approach may allow the determination of the most suited mechanical model of soil representation as well as model parameters. Routine monitoring using this approach may help to asses the degradation of the subsoil with time as part of structural health monitoring strategies. In this paper, fundamental expressions that relate between the location of distinct strain points and the variation of soil parameters were developed based on various analytical foundation support models. Finally, as an initial validation step and to underpin the idea basics, the proposed method was successfully demonstrated on a simple mechanical setup. It is shown that the approach allows for load-independent characterization of the soil response and, in that sense, it is superior to common identification methods.

Past experience of gas production from methane-hydrate-bearing sediments indicates that sand migration is a major factor restricting the production of gas from methane-hydrate reservoirs. One important geotechnical aspect of sand migration is the influence of grain detachment on the existing stresses. This paper focuses on understanding and quantifying the nature of this aspect using different approaches, with a focus on discrete element method (DEM) simulations of sand detachment from hydrate-bearing sand samples. The investigation in the paper reveals that sand migration affects isotropic and deviatoric stresses differently. In addition, the existence of hydrate moderates the magnitude of stress relaxation. Both of these features are currently missing from continuum-based models, and therefore, a new constitutive model for stress relaxation is suggested, incorporating the research findings. Model parameters are suggested based on the DEM simulations. The model is suitable for continuum mechanics-based simulations of gas production from hydrate reservoirs.

The paper aims to develop an approximated analytical solution to model the bending moment profile in a sewage pipe, buried within an unsaturated soil, which occurs as a result of a leak. The solution involves evaluation of the greenfield displacements due to a buried point source, and its use as an input to a soil-pipeline interaction problem. The solution is extended for a general wetted sphere (having different degree of saturation with the radial distance). The final model is tested against finite element simulations of the coupled problem without the simplified assumptions and approximations, and is found to be satisfactory. The work may be considered a first step towards realization of a distributed fiber optic sensing system that, together with an appropriate spatial signal analysis, could identify leaks at their early stage. The current analysis indicates that the developed strain signal (and its profile) could be detectable for leaks having liquid loss as little as 300 to 500 liters.

Proper representation and understanding of the mechanical response of the sediment is a prerequisite for successful future gas production from gas hydrate-bearing sediments, in view of the geotechnical issues encountered in recent field trials. Recent investigations have indicated that the increase of sediment strength, due to hydrate existence, is of frictional nature and associated with changes in the kinematic response, and not necessarily due to cementation. Following this idea, this paper presents a non-cohesive micro model for methane-hydrate-bearing sediments, where the hydrate is represented as solid particles precisely positioned between sand particles, contributing to the skeleton response even for small strains. Analytical expressions relating between the geometry, inter-particle properties, and the mechanical response of the hydrate-bearing sediment are developed in the paper. Global stress-strain response is evaluated under simulated triaxial loading, exhibiting stiffer, stronger and more dilative response compared to pure sand samples. It is shown that a trade-off exists between the particle size and the inter-particle friction, which can be unified using a participation factor related to the pore size distribution. As observed in recent experimental investigations, the suggested model results in a cohesionless response when analyzed using Rowe’s stress dilatancy theory.

The paper presents a formulation for evaluating the effect of tunneling on existing buildings. The formulation involves the matrix condensation method to represent the response of a linear elastic building and macroelements to represent the nonlinear elastoplastic soil behavior. The formulation includes new features that allow interaction between macroelements, both through the soil continuum and the structure, to result in the final displacements of the foundations due to tunneling. One of the advantages of the formulation is its ability to incorporate a general input of a greenfield field displacement for the interaction analysis, allowing consideration of various tunneling scenarios. The formulation is evaluated by a comparison with a continuum-based solution obtained using the finite difference method. The formulation is then used to conduct a parametric analysis of tunneling–soil–superstructure interaction, considering three different approaches: (i) the suggested elastoplastic formulation, (ii) purely elastic analysis, and (iii) simplified analysis in which the foundations are forced to displace as a greenfield. It is shown that the vertical settlements of the foundations, due to tunneling, are the greatest when the first approach is considered. This is an outcome of the combined vertical and horizontal yielding, depicted in the formulation by the coupled yield function and plastic flow potential. Yet damage, which relates to differential settlement, appears to be smaller in the elastoplastic formulation.

Although significant advancement has been made over recent years with respect to three-dimensional upper bound calculations of tunnel facing, a considerable difference still exists between analytically and empirically based stability values. The current work suggests that the difference may well be the outcome of the traditional use of Tresca yield criterion for the upper bound calculations, which, by definition, does not distinguish among the shearing modes (compression, extension, plane strain). Consequently, this paper suggests and discusses a new yield function, which allows for asymmetric yielding. Such yielding is only beneficial in the case of three-dimensional and continuous velocity fields, and therefore a numerical procedure that generates relevant kinematically admissible fields for classical upper bound calculation is suggested. The procedure involves conversion from a load controlled boundary value problem to a velocity controlled problem at the limit state of collapse. The analysis results in significantly lower upper bound values than those presented earlier (for Tresca material), and the values are much closer to the stability curves of Kimura and Mair (1981), which are commonly used in design.

This paper presents an analytical solution for the effect of tunneling-induced ground displacements on buried pipelines within an elastic continuum. The greenfield ground displacement is decomposed into an infinite series of trigonometric functions. The response of the soil and the pipeline to these trigonometric functions is then established and used to derive a solution for the global pipeline response using the superposition principle. The approach is used first with the commonly used barrel load for interaction between the pipe and the soil, under the requirement for longitudinal soil-pipe compatibility. To avoid the a priori assumption of barrel load interaction forces, the solution is then extended to consider a more general interaction load pattern based on the requirement for cross-sectional compatibility (in addition to the longitudinal compatibility). This is achieved by an additional Fourier series expansion describing the load variation along the pipe cross section. The cross-sectional Fourier expansion is solved as a minimization problem to achieve the compatibility. Previous solutions of the elastic continuum problem involved discretization along the pipeline (or the use of shape functions) with compatibility requirements at specific points, without any requirements for exact longitudinal and cross-sectional compatibility, as in the present solution. The derived solutions are presented in a normalized manner and compared with previous solutions. Various aspects of the present and previous solutions are discussed and examined.

The geomechanical behavior of gas hydrate-bearing sediments is strongly coupled to the other processes involved in the behavior of gas hydrates. This chapter focuses on the geomechanical characteristics of gas hydrate-bearing sediments and on the methods by which they can be represented, and coupled numerically for complete thermo-hydro-mechanical-chemical (THMC) simulations. It presents a general, but unique, characterization of gas hydrate-bearing sediments, followed by both continuum-based and discrete-based approaches for modeling the mechanical behavior of these materials. The mechanical behavior is represented either using a constitutive model, which expresses changes in stresses due to strain increments, or by discrete element method (DEM) simulations, in which each soil particle is modeled individually as it interacts with the other particles and with the solid hydrate in the pores. The chapter also presents the simulation of the world’s first offshore gas production test from gas hydrate-bearing sediments conducted at the Eastern Nankai Trough, Japan.

The effect of tunnel construction on ground displacements is an important problem for tunnelling engineers. Numerical methods, including continuum and discrete element methods, have been used to evaluate tunnelling induced ground displacements. In this paper, the ability of numerical methods to replicate the response to tunnelling of a real soil is evaluated by comparing results from numerical analyses with experimental data obtained from geotechnical centrifuge tests. The centrifuge tests include two types of tunnel boundary condition: pressure-controlled (water extracted from model tunnel within a flexible membrane) or displacement controlled (rigid boundary model tunnel undergoing an eccentric contraction). Centrifuge measurements are compared against discrete element method (DEM) and finite element method (FEM) analyses which replicate the conditions of the experiments: pressure controlled boundary for FEM and DEM; displacement controlled boundary for FEM only. The effects of tunnel boundary condition on the soil displacement mechanisms are illustrated and the performance of the numerical analyses to replicate salient features of ground response are discussed.

The sudden collapse of sinkholes in the Dead Sea area represents a serious threat to infrastructure in the area. The formation of these sinkholes has been shown to be directly correlated with the drop in the Dead Sea water level which is accompanied by a corresponding lowering of the groundwater level and permits the penetration of low-salinity groundwater into coastal areas. This water causes dissolution of the salt layers which results in the formation of subsurface voids that develop into collapse sinkholes. Various tools and measurement methods have been investigated in order to attempt to detect the formation of sinkholes, but to date, there is no method capable of providing early warning of possible collapse. This paper investigates the use of fiber-optic Brillouin optical time-domain reflectometry (BOTDR) or Brillouin optical time-domain analysis (BOTDA) for such detection. Brillouin optical time-domain reflectometry or analysis (BOTDR/A) is an optical measurement technique that provides distributed measurements of strain along tens of kilometers of conventional optical fibers, based on the Brillouin frequency shift of backscattered light. The rationale for this approach is that the formation of an underground cavity causes strains in the soil which can be detected using a fiber-optic cable buried at a shallow depth. A closed-form solution for the expected surface sinkholeinduced strain profile attributable to spherical voids in elastic-plastic soil is developed, validated, and evaluated against more realistic conditions. The model is then used to develop a procedure that can differentiate between signals induced by a sinkhole and signals caused by disturbances. The suggested procedure uses wavelet decomposition to filter out the disturbances and extract the sinkhole contributions. This procedure is evaluated with signals measured in the field during a 50-day period on which were superimposed theoretical strains based both on the closed-form model and finite-difference analysis of more realistic cases. This analysis showed that in the depth range investigated (up to 50 m), detection can be achieved while the subsurface cavities are still stable and early enough to enable the implementation of countermeasures.

The full potential of pile optimization has not been realized as the interactions between superstructures and foundations, and the relationships between material usage and foundation performance are rarely investigated. This paper introduces an analysis and optimization approach for pile group and piled raft foundations, which allows coupling of superstructure stiffness with the foundation model, through a condensed matrix representing the flexural characteristics of the superstructure. This coupled approach is implemented within a multi-objective optimization algorithm, capable of providing a series of optimized pile configurations at various amounts of material. The approach is illustrated through two case studies. The first case involves evaluation of the coupled superstructure-foundation analyses against field measurements of a piled raft-supported building in London, UK. The potential benefits of pile optimization are also demonstrated through re-analyses of the foundation by the proposed optimization approach. In the second case, the effects of a soft storey on the superstructure-foundation interactions are investigated. These cases demonstrate the importance of properly considering the superstructure effects, especially when the building consists of stiff components such as concrete shear walls. The proposed approach also allows engineers to make informed decisions on the foundation design, depending on the specific project finances and performance requirements.

This paper explores the possibility of using high-resolution fiber-optic distributed sensing for in situ geotechnical estimation of soil shear modulus distribution with depth. It is shown that a recursive analysis of an elastic problem together with a measured vertical strain can assist in evaluating the sought stiffness values. It is suggested that high-resolution fiber-optic distributed sensing can provide the necessary strain for the proposed process. The approach was demonstrated in a field trial, entailing a stratified soil profile including a thin sand layer encapsulated between two clay layers. Results of the suggested profiling method are compared against data from a geophysical survey and against correlations with conventional in situ testing. Excellent agreement is exhibited between the different methods, indicating aptitude and viability of the idea for implementation as a geotechnical investigative tool.

This paper provides a comprehensive analytical formulation that entails the features of sand production in gas hydrate-bearing sediments, including grain detachment, migration, sediment deformation and hydrate dissociation. The formulation is thermo-hydro-mechanically coupled such that grain detachment causes stress reduction, sediment shear deformation induces grain detachment and grain flow alters multiphase fluid pressure and temperature profiles. Through a series of analyses, the sensitivity of sand production related parameters on resulting solid volume changes is evaluated. Furthermore, the effect of various operational methods on mitigating sand production in hydrate-bearing sediments during gas production is numerically investigated. It is found that, out of the different operational methods investigated, lowering depressurization rate was the most effective in reducing sand production for a given gas production.

This paper presents a systematic approach for relating fundamental (soil element) strength-degradation models with cyclic fullflow penetration tests. The approach is then employed to enhance the commonly-used exponential strain-softening model by adding a parameter that regulates the slope of degradation. Using the developed methodology, a new relationship between ξ95 and N95 (the shear strain and cycle number associated with 95% degradation in strength and penetration resistance, respectively) is established for the enhanced strainsoftening model. The additional parameter of the enhanced model is optimized against various cyclic field test results and found to be roughly constant. It is demonstrated that the new model independently reproduces the field test results when introduced into advanced numerical analyses of cyclic penetration tests.

The process of tunneling is associated with ground movements which may lead to stressing of nearby existing buried infrastructure, and potentially poses a risk of damage. The need for an effective evaluation method of the potential risk increases with the ongoing expansion of underground space utilization. This paper presents a new approach for evaluating the interaction between an assumed input of greenfield tunneling displacements and an existing buried pipeline. The approach integrates new developments with previous research findings to establish a practical interaction analysis methodology that can be used in design. It involves the use of an elastic-continuum analysis to solve the soil-pipeline interaction together with an iterative calculation of the equivalent stiffness in order to consider soil nonlinearity. A set of simplified closed-form expressions, which can be used to evaluate maximum pipeline bending moments within the suggested framework, are presented in the paper. A comparison of the new method results against centrifuge test data and advanced discrete element-method simulations is presented in the paper. The obtained agreement provides validation of the new method over a wide range of tunneling-induced volume losses and pipeline parameters.

A better understanding of the behavior of gas hydrate-bearing sediments during gas extraction is a vital step towards realization of long-term gas production for the future. In March 2013, the world first trial of gas production from offshore hydrate-bearing sediments by depressurization method was conducted at the Eastern Nankai Trough site, Japan. While the operation was successful in producing gas, after six days it suddenly encountered a large amount of sand migration into the well, a phenomenon known as sand production, leading to a premature termination of the operation. This incident has highlighted the importance of development of sand migration model within hydrate-bearing sediments and understanding of the geomechanical behavior of hydrate-bearing sediments with the effect of sand migration during gas extraction. This paper presents the overview of the recently developed thermo-hydro-mechanically coupled formulation that entails sand migration in gas hydrate-bearing sediments. The formulation is then applied to simulate the 2013 Nankai production test in wellbore scale, including history matching of produced water and gas. The amount of produced sand at the end of the test is also matched and the effects of sand migration on geomechanical behavior are investigated.

Two parallel, yet complimentary, paths are being pursued by the scientific community with respect to the future of smart infrastructure. The first focuses on sensor technology and deals with advancing the capabilities and performance of the sensory gear. The second focuses on engineering applications and targets the development of interpretation models capable of transforming raw readings into information of engineering worth. This paper presents advancements made within various Israeli universities along these two paths. Firstly, innovations in the field of Brillouin distributed fiber optic sensing are discussed, together with presentation of prospective applications and future research directions. This is followed by an overview of recent advancements in the field of wireless embedded sensors, called Wisdom Stones, for civil engineering applications. It is concluded that expediting a smart infrastructure future requires a multi-disciplinary approach in which engineering needs are involved in the development of the sensing techniques.

This report provides an overview of the reviewed papers presented at the Conference under the theme of design using in-situ tests. The papers cover a breadth of topics spanning from estimation of specific soil properties through determination of their spatial distribution, and up to global direct design which encompass both the old and new.

Gas production from gas hydrate-bearing sediments has been attracting global interests because of its potential to meet growing energy demand. Methane (CH₄) gas can be extracted from CH₄ hydrates by depressurization, thermal stimulation or chemical activation. However, it has never been produced on a commercial scale and the past field trials faced premature termination due to the technical difficulties such as excessive sand flow into the well, a phenomenon known as sand production. One exception is the trial at the Ignik Sikumi, Alaska in 2012, which was conducted by chemical activation followed by depressurization. During the trial, initial sand production ceased after two weeks while CH₄ gas production continued for five weeks. The mitigation of sand production is deemed attributed to mechanical or hydraulic effects through formation of CO₂-rich gas hydrates. This incident has highlighted the favorable effect of CO₂ hydrate formation and needs to incorporate the chemo-processes into existing thermo-hydro-mechanical formulations. This paper presents an analytical formulation to capture the coupled thermo-hydro-chemo-mechanical behavior of gas hydrate-bearing sediments during gas production via CO₂ injection. The key features of the formulation include hydrate formation and dissociation, gas dissolution and multiphase flow for both CH₄ and CO₂, facilitating CH₄-CO₂ hydrate conversion.

Tunnel excavation causes ground movements which have the potential to cause damage to other buried infrastructure, including pipelines. This note examines the tunnel–pipeline interaction problem from the context of an elastic-continuum based approach. A theoretical proof is provided which shows that there is a constraint of volume loss equality between the greenfield displacement input and the resulting deformed pipeline shape. In addition, for an assumed Gaussian curve fit for the input greenfield displacements, it is shown that the deformed pipeline also fits well to a Gaussian shape. These two features are used to develop simple expressions for the prediction of pipeline bending moments. An interesting outcome of the analysis, whereby displacement and bending moment ratios can be related using a simple power law expression, is demonstrated and shown to agree well with experimental data.

The paper explores the possibility of the use of high spatial resolution fiber optic distributed sensing technology for on-specimen strain measurements in laboratory element testing. The approach provides the means to evaluate specimen surface deformation through a novel conjuncture helical envelope configuration of a single optical fiber ribbon. Given that this technology has yet to be applied in the area of material characterization, the paper investigates the most basic setup of a uniaxial compression test. It is shown that the approach provides a full-field view of surface strains with a resolution and accuracy level that is comparable with traditional deformation sensors. It enables the evaluation of small-strain mechanical properties as well as visualization and quantification of any indication of non-uniform test conditions. Because of the relative ease and low-cost for instrumentation, the suggested approach has a great potential to be a routine application for element testing.

Distributed Optical Fiber Sensing is a mature technology given its strong record of over 20 years. Nevertheless, underground utilities are yet to embrace it as an everyday tool despite its enormous capability. One dimensional long buried utilities and tunnels offer the best application for the use of this technology. Research studies around the world offer the promise of this technology in monitoring the impact of ground movements on underground utilities and tunnels. No application standards existed that governed the use of this technology within any jurisdiction in the world in September 2012. A global task group on optical fiber sensing systems (OFSS) was born to become a unique pool of talent and experience on the subject with over 40 leading experts from 17 countries, which went on to author two companion standards American Society for Testing and Materials (ASTM) F3079-14 and F3092-14, within ASTM Technical Committee F36. This paper provides a brief overview of how OFSS work, what is in these standards, why OFSS is poised to become the most versatile innovation among all measurement tools for field monitoring, what problems the task group faced during the development of the standards and how the members of the task group resolved these problems, what the benefits are of such global standards and the future plans for the global OFSS task group. The most paramount goal of the authors is to share the lessons they learned during the development of the standards with the delegates of this conference.

The geomechanical behaviour of gas hydrate-bearing sediments is unique. Since gas hydrate exists as a solid in pores, it effectively densifies the host sand and bonds surrounding grains together. As a result, hydrate-bearing sediments exhibit stiffer, stronger and more dilatant behaviour than hydrate-free sediments. The uniqueneb of hydrate-bearing sediments becomes more prominent during gas production. Unlike conventional oil and natural gas, gas production from hydrate-bearing sediments involves phase change of the gas hydrate from solid to gaseous. This implies not only that the aforementioned characteristics diminish accordingly to the remaining hydrate in pores, but also that the solid (i.e. hydrate) that has been carrying the effective strebes disappears, resulting in release of the effective strebes. The release of the effective strebes upon hydrate dibociation, referred to as hydrate dibociation-induced streb relaxation, causes streb redistribution as well as plastic deformation. Neglecting the streb relaxation term could therefore lead to inaccurate deformation prediction. This paper presents the formulation for hydrate dibociation-induced streb relaxation and demonstrates the importance of the term for an accurate wellbore deformation prediction.

The paper presents a three-dimensional mobilised strength design formulation for evaluating the face ‘take’ volume loss of an advancing tunnel in clays. A closed-form analytical expression for an incremental displacement field per unit advancement of the tunnel is obtained. This displacement field is integrated to result in normalised (by volume loss) three-dimensional settlement trough and cumulative strain field for the mobilised strength design calculation. Using energy conservation, an expression for the expected volume loss is obtained. Normalised solutions, relating the volume loss and load factors, are derived and presented for idealised stress-strain curves of the form of power and exponential functions. The practical use of the developed model is demonstrated using several tunnelling cases in London Clay. The predictions of the model are found to be in fair agreement with the observed volume losses in the field.

The relation between the strength law rate parameter and the observed rate effect from full-flow penetrometer soundings performed at different penetration velocities is discussed and examined herein through an analytical investigation. It is shown, using numerical results of steady-state (continuous) penetrations, that the shear strength and global penetration resistance follow a similar law in which the shear strength and penetration resistance increase linearly with the logarithm of shear strain and penetration velocity, respectively. However, the strain rate parameter that is associated with the in situ penetration is found to be different from the conventional laboratory-based strain rate factor when considering the logarithmic relation between strength and rate. Consequently, previous suggestions to estimate the laboratory-based strength rate parameter as equal to the in situ rate parameter can only be considered a first-order approximation. Analytical examination of the energy terms involved in the plasticity solution, under the relaxing assumption of a constant plastic flow field, has led to the development of a simplified expression that resulted in an in-situ-based rate parameter of µ/(1 + 5µ) (where µ is the conventional laboratory-based strength rate parameter). Comparison of the numerically derived values with the simplified analytical expression shows good agreement, suggesting that this relation may help establish the soil rate strength parameter from full-flow penetration tests.

Determination and monitoring of tunneling induced ground displacement is an important component in tunneling design and construction. In recent years several technologies for distributed strain measurement along fiber optics have been developed, namely the Brillouin Optical Time Domain Reflectometry (or Analysis) - BOTDR/A and the Rayleigh backscatter wavelength interferometry (OBR). This paper presents how these technologies could be used to monitor and define ground displacement models through an appropriate 2D and 3D optimization and signal analysis of information derived from a horizontally laid fiber above the tunnel. The suggested approach is evaluated in two field investigations, one involving excavation of a 3. m diameter tunnel by TBM at depth of 18. m, and the other installation of a 1. m diameter water main by pipe-jacking at depth of 6. m. Comparison between the results obtained by the different technologies shows that they are equally suitable for the suggest approach. The suggests approach allows reliable determination of the parameters involved in empirical ground displacement models, and allows field validation that the tunneling process lies within the design bounds. An interesting observation, supported by the analytical models, is that non-perpendicular alignment of the fiber, relatively to the tunnel line, results in a shift in the peak strain location as the tunnel advances. It was demonstrated that the rate of change in peak strain location, with tunnel advancement, can be used to obtain the settlement trough length parameter, without the need for complete evaluation of all other model parameters.

Brillouin optical time domain reflectometry or analysis (BOTDR/A) is one of the strain measurement technologies that is suitable for smart monitoring of civil engineering infrastructures. Although the technology has the advantage of supplying spatially distributed data, it is currently limited to a spatial resolution of approximately 1 m. This infers that the technology may lack the ability to identify the exact type and source of damage; that is, different geometrical configurations of cracking within a concrete beam may lead to similar BOTDR/A readings, and hence, the exact nature of cracking might not be resolved. This study suggests different crack indicators and analytically and experimentally examines their correlations with BOTDR/A readings of damaged RC beams. The analytical part entails a finite-element based statistical analysis of hundreds of cracking cases in fractured RC beams and their effects on the simulated BOTDR/A readings. It is found from the analysis that the increase of curvature measured by BOTDR/A is best correlated with the sum of ratios of crack size to the remaining healthy cross section within 1 m. This finding is supported by an experimental study of a cracked RC beam. The correlation, by itself, is only valid when the increase of curvature is associated with the damage and does not involve a curvature increase as a result of redistribution of moments. This, however, would be the case only in statically determinate beams. To facilitate the use of the correlation for statically indeterminate beams, this paper suggests an iterative algorithm that evaluates the different contributors to the increase of the curvature.

Earthquake accelerations cause many problems for structures on the ground surface. Ground improvement may be carried out to reduce or otherwise modify shear waves before they reach the structures, which can be more cost-effective than structural strengthening. This paper investigates the response of a simple structure whose foundation has been completely enclosed by a layer of soft material. Physical and numerical models of this are presented. Based on these, it is seen that not only is linear acceleration significantly attenuated by such a system, but the foundation-structure system is able to rock in antiphase to the translational motion to further reduce acceleration. A simple two degree of freedom spring model is presented that can match the behaviour of the more sophisticated models. Recorded strong motion data applied to this simple model suggests that improvement can be achieved provided caisson modes and structural modes occur at different frequencies.

The mathematical solution for the two-dimensional linear problem of acoustic-gravity waves in a compressible ocean with an elastic bottom is presented. The physical properties of these waves are studied, and compared with those for waves over rigid ground. The solutions for constant water depth, together with the assumption of constant energy flux, are used to study the shoaling of acoustic-gravity waves over a slowly-varying bathymetry. The present work enriches our knowledge about acoustic-gravity waves in a way that could assist, among others, in the early detection of tsunami.

This paper presents an explicit time-marching formulation for the solution of the coupled thermal flow mechanical behavior of gas- hydrate sediment. The formulation considers the soil skeleton as a deformable elastoplastic continuum, with an emphasis on the effect of hydrate (and its dissociation) on the stress-strain behavior of the soil. In the formulation, the hydrate is assumed to deform with the soil and may dissociate into gas and water. The formulation is explicitly coupled, such that the changes in temperature because of energy How and hydrate dissociation affect the skeleton stresses and fluid (water and gas) pressures. This, in return, affects the mechanical behavior. A simulation of a vertical well within a layered soil is presented. It is shown that the heterogeneity of hydrate saturation causes different rates of dissociation in the layers. The difference alters the overall gas production and also the mechanical-deformation pattern, which leads to loading/ unloading shearing along the interfaces between the layers.

There are several geotechnical problems for which the formulation of large deformations is vital for their solution. Among these problems are in-situ penetration tests. In this paper, a new numerical approach is used to solve such problems efficiently with the aim to calibrate fundamental soil properties to fit the global penetration resistance obtained from experimental studies. The utilized numerical method treats the continuum as rigid plastic with a non-uniform strength field, where the spatial distribution of strength is determined by converting time changes into spatial distributions using the governing equation of steady state flow. For this purpose, the method employs an upstream weighting technique for determination of information flow within the domain. Using the suggested method, the resistance factors for in-situ T-bar and ball penetrometers were obtained under a various soil conditions. These included the rate effect on the soil, strain softening and anisotropy, all of which affect the shear strength of the soil. General expressions for the resistance factors of the T-bar and ball penetrometers are finally suggested for engineering use.

Cross-border smuggling tunnels enable unmonitored movement of people and goods, and pose a severe threat to homeland security. In recent years, we have been working on the development of a system based on fiber- optic Brillouin time domain reflectometry (BOTDR) for detecting tunnel excavation. In two previous SPIE publications we have reported the initial development of the system as well as its validation using small-scale experiments. This paper reports, for the first time, results of full-scale experiments and discusses the system performance. The results confirm that distributed measurement of strain profiles in fiber cables buried at shallow depth enable detection of tunnel excavation, and by proper data processing, these measurements enable precise localization of the tunnel, as well as reasonable estimation of its depth.

A method for the analysis of reinforced earth walls which includes the interaction between the three components of the system (i.e. soil, reinforcement and the wall facing) was recently introduced by Klar and Sas [1], [2]. The statical indeterminacy of the system was solved using minimization requirements on the kinematical compatibility between the reinforcement layers and the wall. The method entailed a genetic type algorithm, which required significant computational effort. The main drawback of the original method is that it is limited to inextensible reinforcement. The current paper treats the aforementioned limitation by improving the method through the use of an alternative algorithm which involves the solution of the differential equations representing the reinforcement deformation. The suggested algorithm involves a repetitive linear solution of the wall's deformation equations in a matric form, using an input vector based on a non-linear top-down procedure which represents the soil and the reinforcement behavior.

The bullet train from Be'er-Sheva to Eilat in Israel is planned to be built in great vicinity to the Dead Sea Fault (DSF) and therefore susceptible to different seismic risks. Bullet trains are especially vulnerable to differential deformations and one of the engineering tasks associated with the train design is to evaluate the expected serviceability level with time. The paper presents statistical analyses conducted for the prediction of the anticipated deformation of the railway caused by multiple and single earthquake events as function of the exposure period. The analyses incorporate both a probabilistic seismic hazard analysis (PSHA) and statistical disaggregation to select controlling events, using local seismicity data. The highlight of the analyses is its comprehensive approach to include four main features, from viewpoints of geotechnical engineering and earthquake engineering. Firstly, the soil constitutive model considers the effects of nonlinearity and plastic compaction due to cyclic loading. Plastic deformations during earthquakes are widely known phenomena and thus important to be taken into account for accurate deformation prediction. Secondly, the soil properties are distributed heterogeneously so that differential deformations can be evaluated, which are likely to occur in natural sediments. Thirdly, using an attenuation model, a potential cumulative absolute velocity (CAV) is evaluated at different return period based on Israeli local seismic zones and levels. Using statistical disaggregation, well representative earthquakes are selected and used for geomechanical analyses in order to predict deformation patterns. Forth, based on the results of 81 cases investigated, the fragility curves for the serviceability of the train are plotted. The resulting curves can be used as guideline to build the railway track for given exposure period of the structure and deformation tolerance.

A better understanding of the behavior of hydrate-bearing sediments during gas extraction is a vital step towards realization of commercially viable gas production for the future. In 2007, the world first trial of gas production from hydrate-bearing sediments by depressurization method was conducted at the Mallik gas hydrate site, located in the Mackenzie Delta of Northwest Territories, Canada. However, the operation encountered a large amount of sand migration into the well, a phenomenon known as sand production, and thus was terminated after 24 hours. This incident highlights the importance of development of hydro-mechanical sand production model within hydrate-bearing sediments and understanding of the behavior of hydrate-bearing sediments with the effect of sand production during gas extraction. This extended abstract provides a formulation for the sand production including grain flow and hydraulic dispersion effect. A formulation is fully-coupled such that the sand production affects fluid pressures, saturations and temperature. In addition, the effective stress reduction due to grain detachment is incorporated. This results in further deformation of hydrate-bearing sediments, which may need to be considered for stability of the wellbore.

This paper examines the effect that tunnel size, depth and volume loss have on greenfield soil displacements above tunnels in sandy ground. The results of a series of plane-strain centrifuge tests performed on tunnels in a dry silica sand are examined. The cover-to-diameter ratio, C/D, of the tunnels ranged from 1.3 to 4.4. Features of greenfield settlement trough shape, both surface and subsurface, are illustrated by examining soil displacement data obtained using an image-based deformation measurement technique. The effects of tunnel size, depth and volume loss are demonstrated, and the suitability of typical fitting curves is discussed. The complex volumetric behaviour of drained soil is illustrated by comparing tunnel volume loss with the volume loss experienced by the soil. A set of equations is developed that provide a method of evaluating the change of settlement trough shape with tunnel size, depth and volume loss.

A remarkable field observation is that landslides of different sizes, from different locations around the globe and triggered by different mechanisms, all seem to follow a single relation, with their volume to surface area ratio following a power law of ∼1.4. This paper presents an analytical examination of the shape of landslides on the basis of limit equilibrium principles involving the exact mathematical solution of the failure mode. The obtained analytical relation between the volume and the surface area of a landslide agrees well with the function obtained from the field observations, and hence a mechanical basis is given to the previously poorly understood field observations. In addition, this paper presents a new graphical interpretation of the factor of safety associated with slope stability analysis and its relation to the probability of failure.

BOTDR is one of the strain measurement technologies that is suitable for smart monitoring of civil engineering infrastructures. While the technology has the advantage of supplying spatially distributed data, it is currently limited to a spatial resolution of about 1 m. In a previous work, it was found that curvature increase along the beam can be related to the crack configuration. This, however, only appropriate to statically determinate beams, where no redistribution of internal forces is induced by the damage. Consequently, the use of the previously suggested relation to statically indeterminate beams may result in inaccurate estimation of the damage. In order to overcome this problem the current paper suggests an iterative identification algorithm which deals with statically indeterminate beams.

Pile reuse has become an increasingly popular option in foundation design, mainly due to its potential cost and environmental benefits and the problem of underground congestion in urban areas. However, key geotechnical concerns remain regarding the behavior of reused piles and the modeling of foundation systems involving old and new piles to support building loads of the new structure. In this paper, a design and analysis tool for pile reuse projects will be introduced. The tool allows coupling of superstructure stiffness with the foundation model, and includes an optimization algorithm to obtain the best configuration of new piles to work alongside reused piles. Under the concept of Pareto Optimality, multi-objective optimization analyses can also reveal the relationship between material usage and the corresponding foundation performance, providing a series of reuse options at various foundation costs. The components of this analysis tool will be discussed and illustrated through a case history in London, where 110 existing piles are reused at a site to support the proposed new development. The case history reveals the difficulties faced by foundation reuse in urban areas and demonstrates the application of the design tool to tackle these challenges.

Methane hydrate is estimated to be present in substantial amounts below deep sea floors. Particular scientific and engineering interests that encourage studies of mechanical behaviour of methane hydrate soils include submarine geohazards, such as the initiation of marine landslides through hydrate dissociation, wellbore stability and estimation of future gas production from wells. To study these problems, a formulation of a multi-physics model of methane hydrate flow coupled to soil deformation is developed. By assuming deformable porous media (soil matrix) that accommodate non-movable but dissociable hydrate, a two-phase flow formulation of water and methane gas is suggested according to Darcy's law and capillary pressure law. A single-phase elastic-perfectly plastic constitutive model for hydrate soil sediments, based on the concept of effective stress, is developed to account for the effect of hydrate saturation on mechanical strength and stiffness. The formulation is incorporated into the explicit scheme of finite-difference code FLAC by solving three boundary value problems in parallel. The code is used to simulate the behaviour of horizontal unsupported and supported wells in hydratebearing sediments under different in situ stress conditions during methane hydrate extraction. Axial force, bending moment and well displacements were compared for supported and unsupported wells.

Cross-borders smuggling tunnels enable unmonitored movement of people, drugs and weapons and pose a very serious threat to homeland security. Recent advances in strain measurements using optical fibers allow the development of smart underground security fences that could detect the excavation of smuggling tunnels. This paper presents the first stages in the development of such a fence using Brillouin optical time domain reflectometry (BOTDR). Two fiber optic layouts are considered and evaluated in a feasibility study that includes evaluation of false detection and sensitivity: (1) horizontally laid fiber buried at a shallow depth, and (2) fibers embedded in vertical mini-piles. In the simulation study, two different ground displacement models are used in order to evaluate the robustness of the system against imperfect modeling. In both cases, soil-fiber and soil-structure interactions are considered. Measurement errors, and surface disturbances (obtained from a field test) are also included in the calibration and validation stages of the system. The proposed detection system is based on wavelet decomposition of the BOTDR signal, followed by a neural network that is trained to recognize the tunnel signature in the wavelet coefficients. The results indicate that the proposed system is capable of detecting even small tunnel (0.5. m diameter) as deep as 20. m (under the horizontal fiber) or as far as 10. m aside from the mini-pile (vertical fiber), if the volume loss is greater than 0.5%.

This paper compares linear-elastic and nonlinear pile group analysis methods through settlement analyses of hypothetical scenarios and real case studies, and elaborates on the implications for interpretation of pile load test data. Comparisons between linear-elastic and nonlinear methods justify the proposition that pile-to-pile interaction is dominated by linear elasticity, characterized by the small-strain soil stiffness. As the size of a pile group increases, nonlinearity in individual pile behavior becomes overwhelmed by the interaction effects. In such cases, similar estimates will be achieved by both linear and nonlinear methods if the soil modulus is derived from the initial tangent, rather than some secant stiffness, assessed from the load test data. The study clarifies the capabilities and limitations of linear elasticity in pile group analysis and provides guidance on pile test interpretation for analysis of pile group response.

The paper examines the problem of tunneling beneath buried pipelines and the relationship between soil strains and pipeline bending behavior. Data are presented from centrifuge tests in which tunnel volume loss was induced in sand beneath pipelines of varying stiffness properties. The model tunnel and pipelines were all placed at a Perspex wall of the centrifuge strong box such that image-based deformation analyses could be performed. The method provided detailed data of subsurface soil and pipe displacements and illustrated the soil-pipe interaction mechanisms that occurred during tunnel volume loss, including the formation of a gap beneath the pipes. The relationship between tunnel volume loss, soil strain, and pipe bending behavior is illustrated. Experimental results of pipe bending moments are compared against predictions: (1) assuming the pipe simply follows greenfield displacements; (2) using an elastic continuum solution; and (3) using a new method in which an "out-of-plane" shear argument, due to soil-pipe interaction, is introduced into the elastic continuum solution. It is shown that the new method gives the best prediction of experimental pipe bending moments.

This paper suggests a new method for obtaining steady-state solutions for 'full-flow' penetrometers. The method is based on the numerical solution of the small strain plastic-flow problem (i.e. rigid plastic material) with an inhomogeneous strength field, which is determined by converting changes of material properties over time in a stationary frame of reference into spatial distribution of strength in a moving frame of reference. Rather than building streamlines from back integration of soil element distortion, as previous methods have suggested, the method treats the domain as continuous with the associated field equations. The method employs an upstream weighting technique for the determination of information flow within the domain. The execution order for the calculation is based on topological ordering. This results in the calculation having a complexity of O(N), as compared with O(N1.5) for the strain path or streamline methods (N is the number of discretized points), which significantly reduces the calculation time. The formulation is presented for the cylindrical (T-bar) penetrometer, and includes aspects of soil strength degradation, strain rate effects, strength anisotropy, and interface strength law. Comparison to previously published values, based on large displacement finite element simulations with remeshing, showed good agreement, indicating on the correctness of the suggested approach. Investigation into the soil rigid-body rotation and the remolding effect on anisotropy characteristics showed an interesting behavior, where the decrease of strength anisotropy due to remolding has a greater influence when the soil strength is higher in the vertical direction.

Reinforced soil walls commonly include facing elements which affect the mechanical behavior of the system. However, the design procedures involved in the existing codes and manuals (e.g. FHWA, BS8006, AASHTO, etc.) do not consider the structural contribution of the facing to the wall stability. Recently, a new computer based method for the analysis of reinforced soil walls which takes into account the interaction between the facing and the soil reinforcement layers was presented [Klar A and Sas T. Rational approach for the analysis of segmental reinforced soil walls based on kinematic constraints. Geotextiles and Geomembranes 2009;27:332-340]. This method demands full compatibility between the reinforcement layers and the deforming wall, and is solved as an optimization problem on this constraint. This kinematic compatibility (KC) method entails several assumptions regarding the interaction between the three components of the system (soil, wall, and reinforcement). This paper compares the KC method to a more rigorous continuum analysis. Results show that the KC method is capable of replicating the behavior of the more rigorous system, with a good agreement on both the value of maximum tensile forces in the reinforcement and shear and bending moment distributions along the wall. The KC method has a certain advantage over continuum methods, such as finite element or finite difference, since it requires limited input data that can easily be obtained from field tests.

Pile groups are frequently designed with equal or similar pile lengths. However, the significant interaction effects among equal-length piles imply that this may not be the optimized configuration. This paper presents the optimization analyses of piled rafts and freestanding pile groups, where pile lengths are varied across the group to optimize the overall foundation performance. The results of the analyses are applicable in cases where the piles derive a majority of the capacity from the frictional resistance. It is demonstrated that, with the same amount of total pile material, an optimized pile length configuration can both increase the overall stiffness of the foundation and reduce the differential settlements that may cause distortion and cracking of the superstructure. The benefits of the optimization can be translated to economic and environmental savings as less material is required to attain the required level of foundation performances. The reliability of the optimization benefits in relation to construction-induced variability is also discussed.

The paper presents centrifuge test data of the problem of tunnelling effects on buried pipelines and compares them to predictions made using DEM simulations. The paper focuses on the examination of pipeline bending moments, their distribution along the pipe, and their development with tunnel volume loss. Centrifuge results are obtained by PIV analysis and compared to results obtained using the DEM model. The DEM model was built to replicate the centrifuge model as closely as possible and included numerical features formulated specially for this task, such as structural elements to replicate the tunnel and pipeline. Results are extremely encouraging, with deviations between DEM and centrifuge test bending moment results being very small.

This paper proposes a simple method to include superstructure stiffness in foundation analyses. The method involves extracting a small "condensed structural matrix" from finite element models of the superstructure, which can then be incorporated into pile group or piled raft analyses using common approaches such as elastic continuum or load transfer methods. The matrix condensation method directly couples structural and geotechnical analyses, and eliminates the need for iterative analyses between structural and geotechnical engineers. Effectiveness of the approach is illustrated through analyses of several buildings designed with a typical floor plan but with varying heights. The parametric study illustrates that superstructure stiffness can have a significant influence on foundation settlement estimates, and the stiffening effects are dominated by the lower stories of the superstructure. The proposed method aims to bridge the gap between structural and geotechnical analyses. Also, being a computationally simple and accurate approach, it is applicable to parametric or optimization studies that would otherwise involve large amounts of analyses.

This paper deals with the problem of tunneling effects on existing buildings. The direct solution, using the condensation method, is presented. This method allows the structural and geotechnical engineers to treat the problem separately and then assemble a relatively small matrix that can be solved directly, even within a spreadsheet. There are certain concerns that the resultant matrix may be ill-conditioned when the structure is very stiff. This paper suggests an alternative method that essentially relaxes the system from an infinitely rigid structure solution. As such, it does not encounter the problems associated with stiff systems. The two methods are evaluated for an example problem of tunneling below a framed structure. It is found that while the direct method may fail to predict reasonable values when the structure is extremely rigid, the alternative method is stable. The relaxation method can therefore be used in cases where there are concerns about the reliability of a direct solution.

This paper evaluates a new analysis approach for reinforced soil walls which considers the structural role of the facing. The three component (soil - reinforcement - wall) system is statically indeterminate, and hence cannot be solved by equilibrium equations alone. In the new approach, this indeterminacy is resolved using kinematic constraints on the compatibility between the reinforcement layers and the wall. The resultant system is fully coupled whereby upper reinforcement layers are affected by the behavior of lower layers. The method has a certain advantage over sophisticated analysis methods, such as finite elements, since it requires fewer input parameters. This paper evaluates the capability of the method to reliably predict the values of tensile forces, bending moment, shear forces and displacement along the wall. The evaluation is conducted through a comparison to sophisticated finite different analyses. The method is also compared to design codes, where it is shown that the design codes may be overconservative.

BOTDR is one of the strain measurement technologies that is suitable for smart monitoring of civil engineering infrastructures. While the technology has the advantage of supplying spatially distributed data, it is currently limited to a spatial resolution of about 1m. This infers that the technology may lack the ability to identify the exact type and source of damage; that is, different geometrical configurations of cracking within a concrete beam may lead to similar BOTDR readings, and hence the exact nature of cracking might not be resolved by the BOTDR. This study suggests different crack indicators, and examines, both analytically and experimentally, their correlation with BOTDR readings of damaged reinforced concrete beams. The analytical part entails statistical analysis of hundreds of cracking cases in fractured reinforced concrete beams and their effect on the simulated BOTDR readings. The analysis is conducted within COMSOL-Multiphysics, and is aimed to understand the correlation between different crack indicators and the beam curvature as would be obtained by the BOTDR. The experimental part consists of a controlled load test of a reinforced beam instrumented by BOTDR fibers, and is aimed to support the analytical findings.

The paper presents a formulation for evaluating the effects of tunneling induced displacement on existing buildings. Using the matrix condensation method, the building behavior is represented by a relatively small matrix, associated with the foundations of the superstructure. In the formulation, each foundation (with up to 6 degrees of freedom) is represented by a macro-element that captures the elasto-plastic behavior of the soil, using a yield function, a plastic flow potential, and a hardening law. The formulation includes new features that allow interaction between macro-elements, and the effects of the tunneling induced displacements. Since the solution depends on the foundations force level before tunneling (due to the soil nonlinear behavior), the construction process of the building is taken into account in the solution scheme. The formulation is used for the solution of an example problem of a tunnel excavation underneath a six story 3D frame structure. It is shown that vertical plastic displacement may increase even when there is vertical unloading of the foundation, as an outcome of the coupling between the degrees of freedom in the plastic flow potential.

Cross-border smuggling tunnels enable unmonitored movement of people, drugs and weapons and pose a very serious threat to homeland security. Recently, Klar and Linker (2009) [SPIE paper No. 731603] presented an analytical study of the feasibility of a Brillouin Optical Time Domain Reflectometry (BOTDR) based system for the detection of small sized smuggling tunnels. The current study extends this work by validating the analytical models against real strain measurements in soil obtained from small scale experiments in a geotechnical centrifuge. The soil strains were obtained using an image analysis method that tracked the displacement of discrete patches of soil through a sequence of digital images of the soil around the tunnel during the centrifuge test. The results of the present study are in agreement with those of a previous study which was based on synthetic signals generated using empirical and analytical models from the literature.

The paper presents an analytical method for the solution of reinforced soil walls in which the wall facing has a structural role. The three-component (soil-reinforcement-wall) system is statically indeterminate, and hence cannot be solved by equilibrium equations alone. The paper follows up on the work of Baker and Klein [2004. An integrated limiting equilibrium approach for design of reinforced soil retaining structures part I - formulation. Geotextiles and Geomembranes 22, 119-150] where an interaction model, incorporating factors that divide forces between the reinforcement layers and the wall, was introduced to solve the statically indeterminate system. In the current work, the division factors are resolved such that the kinematic constraints of compatibility between the reinforcement layers and the wall are satisfied. This is achieved by solving an optimization problem in which the objective function includes the relative displacement between the reinforcement layers and the wall. The resultant system is fully coupled whereby upper reinforcement layers are affected by the behavior of lower layers. As such, the method overcomes the limitation of the original framework in which the top-down procedure omits such coupling. A non-dimensional parametric study was conducted on walls with 10 face blocks (9 reinforcement layers). Results are given in a normalized manner for cases in which the reinforcement pullout stiffness is uniform and linearly increasing with depth. Analysis results show that in cases where the wall is relatively stiff compared to the reinforcement, the upper reinforcement layers are clearly affected by the lower layers (this is a direct outcome of the fully coupled system). On the other hand, when the relative stiffness of the wall is low, the system behavior tends towards that of a hinged system, which is statically determinate. In this case the solution becomes independent of the reinforcement pullout stiffness. Analysis results indicate that current design codes, which do not explicitly consider the structural role of the facing in the calculation procedure, may be overconservative in certain cases. This result supports the argument for introducing the structural role of the facing into design procedures.

Cross-borders smuggling tunnels enable unmonitored movement of people, drugs and weapons and pose a very serious threat to homeland security. Recent advances in strain measurements using optical fibers allow the development of smart underground security fences that could detect the excavation of smuggling tunnels. This paper presents the first stages in the development of such a fence using Brillouin Optical Time Domain Reflectometry (BOTDR). In the simulation study, two different ground displacement models are used in order to evaluate the robustness of the system against imperfect modeling. In both cases, soil-fiber interaction is considered. Measurement errors, and surface disturbances (obtained from a field test) are also included in the calibration and validation stages of the system. The proposed detection system is based on wavelet decomposition of the BOTDR signal, followed by a neural network that is trained to recognize the tunnel signature in the wavelet coefficients. The results indicate that the proposed system is capable of detecting even small tunnel (0.5m diameter) as deep as 20 meter.

This note presents a method for predicting nonlinear response of pile groups in clays, subjected to vertical loads. The method is based on mobilizable strength design (MSD) concepts, in which the mobilized strength is associated with the shear strains developed in the soil. The suggested procedure is incremental, and requires evaluation of a displacement field. A simple procedure of superposition of pattern functions is suggested for the construction of a complete displacement field. The incremental procedure allows for the variation of the displacement field throughout the loading process, according to principles of minimum energy and compatibility requirements among the piles. Essentially, the procedure allows consideration of a nonlinear continuum between the piles. The pattern functions are an adaptive form of the logarithmic function suggested by Randolph and Wroth in 1979. Under small load levels, when the soil is essentially elastic, the procedure yields values comparable to those from the elastic solution of Randolph and Wroth. At larger strain levels, nonlinear pile group response is simulated based on the soil constitutive models specified by the practitioner. The method is applicable to cases where shaft loading does not induce volume changes in the soil. The method is compared with three dimensional finite difference simulation of undrained loading of pile groups with a nonlinear soil constitutive model. Fair agreement is observed.

The paper presents an energy approach for the prediction of non-linear foundation behaviour. The formulation entails three main stages: (a) assumption of admissible pattern functions from which displacement fields can be assembled; (b) equating external work to internal work; and (c) minimisation of internal work by variation of the displacement field using the different pattern functions. The approach is demonstrated on two problems: (a) a vertically loaded shallow foundation; and (b) laterally loaded piles. The approach is evaluated by comparison with finite difference analyses using three different constitutive models. It is shown that the approach provides a fair estimation of the overall foundation response. Under large displacements the method degenerates into conventional upper-bound calculations.

The problem of tunneling effects on pipelines is approached in the paper. Previous solutions treated the pipeline as a simple Euler-Bernoulli beam. Strictly speaking, this treatment cannot be rigorous as the pipe itself is actually a three dimensional structure loaded all around. It is therefore possible that the Euler-Bernoulli beam representation is not suitable for all cases. The current paper examines this issue by comparing analysis results of soil-pipe-tunnel interaction based on two different formulations. In one formulation the pile is represented as a Euler-Bernoulli beam, while in the other it is treated as a three dimensional structure composed of shell elements. The soil behavior and the tunneling induced displacements are identical in the two formulations, thus any variation in behavior is solely a function of the employed pipe representation method. It is found that when the relative material stiffness of the pipe and soil is small, the pipeline does not behave as a beam, and the results of the two theories differ. As the relative pipe-soil material stiffness increases the two solutions approach each other and eventually coincide for large relative pipe-soil material stiffness values. It is shown that typical concrete and steel pipes can be well represented as simple beams, while polyethylene pipes may require the shell element representation for more accurate predictions.

This paper deals with the problem of T-bar penetration. New kinematically admissible velocity fields are derived from elastic solutions of incompressible material using Airy stress function. These velocity fields are used to obtain upper bounds to collapse loads. Two particular solutions are presented, one for a rough contact surface between the T-bar and soil and the other for a smooth contact surface. The merit of the solutions is that within the boundaries of the velocity field, the soil is required to shear compatibly and continuously. Therefore, these solutions can easily be combined with the strain path method to estimate rate and softening effects. Analysis including consideration of strain rate effect showed that the new mechanisms predict, under certain conditions, lower values than previously published upper bound solutions.

The problem of tunneling effects on existing jointed pipelines is studied using the boundary integral method. Normalized solutions to evaluate the maximum bending moments and rotations are presented. They depend on tunnel-induced ground settlements at pipeline level, relative soil-pipe stiffness, relative pipe-joint stiffness, and the location of the joints in relation to the tunnel centerline. A jointed pipeline generally experiences smaller bending moments than a continuous one owing to the joint rotation. The solutions indicate that there are certain cases where hinged systems result in greater bending moments than continuous ones. However, these cases rarely occur in reality.

A new upper bound failure mechanism for the problem of rigid cylinder motion is presented. The velocity field associated with the mechanism is derived from a known elastic solution by similitude of the deformation field. The obtained upper bound value is 21% higher than the exact solution. However, the failure mechanism is continuous, involving no discontinuity, not even on the cylinder perimeter. The solution has a certain advantage if one, for example, wishes to combine its mechanism with a strain path approach to investigate the T-bar penetration problem. The absence of discontinuities in the mechanism also allows evolution of deformation under serviceability conditions, by associating a mobilized strength as a function of an average strain. Based on this approach, a load transfer function for lateral loading of piles in an undrained clay is suggested. This load transfer function involves nonlinear scaling of a stress-strain curve obtained from a triaxial compression test. An analytical, closed form, solution is given for the case of a hyperbolic stress-strain curve.

This paper presents 2D and 3D upper bound solutions for the problem of tunnel excavation in soft ground. The solution invokes the use of incompressible flow fields derived from the theory of elasticity and the concept of sinks and sources. Comparison is made with previously published results. For some geometries the current calculation results in lower (better) upper bound values; however, the results were generally close to previously published values.

Solutions for the problem of tunneling effects on existing pipelines are given. The solution utilizes a boundary integral formulation for describing the elastic continuum, in conjunction with a limiting force to consider relative pullout failure. The solution requires estimation of soil and pipe elastic properties, relative pipe-soil uplift capacity, and the green field soil settlement profile given in the current paper as a modified Gaussian curve. Normalized graphs for the solution are given as a function of these input parameters. The solution method is compared and evaluated against a limited number of finite-element analysis.

Methane hydrate soil is a natural soil deposit that contains methane hydrate in its pores. Methane hydrate is a metastable solid material and it bonds the soil particles together. Methane hydrate soil can only develop and exist under a condition of high pressure and low temperature. Hence, natural methane hydrate soils are usually found under deep seabed or permafrost regions. This paper synthesises the available data of engineering properties of natural methane hydrate soil samples retrieved at four different sites; Nankai Trough, Mallik-Mackenzie Delta, Blake Ridge and Hydrate Ridge. The geotechnical data are obtained from index tests, oedometer tests, triaxial compression tests and wave velocity measurements. The effects of hydrate growth pattern and hydrate saturation on their mechanical properties are discussed.

An optical fiber strain sensing technique, based on Brillouin Optical Time Domain Reflectometry (BOTDR), was used to obtain the full deformation profile of a secant pile wall during construction of an adjacent basement in London. Details of the installation of sensors as well as data processing are described. By installing optical fiber down opposite sides of the pile, the distributed strain profiles obtained can be used to give both the axial and lateral movements along the pile. Measurements obtained from the BOTDR were found in good agreement with inclinometer data from the adjacent piles. The relative merits of the two different techniques are discussed.

Ageing infrastructure such as pipelines are often subjected to third party activities, such as tunnelling. If engineers are unable to confidently judge the effects on the pipeline in question, this may result in costly and possibly unnecessary diversions to avoid the problem. Current methods of assessing the effect of tunnelling on buried pipelines are mostly based on elasticity and although extremely useful for parametric studies and preliminary evaluation of the problem, may contradict true behaviour. The aim of this paper is to discuss the underlying mechanisms governing pipeline response to tunnelling based on results from centrifuge testing.

Recent advances in strain measurement using optical fibres provide new opportunities for monitoring the performance of piles. Brillouin optical time-domain reflectometry (BOTDR) is an innovative technique that allows measurement of full strain profiles using standard optical fibres. Distributed optical fibre strain sensors were installed at two sites, and the details of the installation methods are presented. A theoretical analysis that compares pile behaviour evaluated from localised strain measurement at discrete locations and from distributed strain measurements is conducted for the case of a vertically loaded pile in layered soil. Two problems are considered: a load test aiming to establish the load transfer function, and changes in pile-soil interface stress due to nearby tunnelling. Advantages of such a distributed reading for monitoring the performance of pile foundations in layered soils are demonstrated from the results of both cases. Cost analysis results show that the BOTDR measurement is a cost-effective pile monitoring method compared with discrete strain measurement methods such as vibrating-wire strain gauges and fibre Bragg gratings.

The seismic behavior of driven piles in sand is being studied, using small models attached to a shaking table and subjected to downward hydraulic gradient. In these models, the drag forces applied by downward flow have the same effect as the increased acceleration field in centrifuge models. The paper describes the experimental set-up used in the study, including a laminar model box, a one-directional shaking table, and a closed loop hydraulic flow system. The model pile is made of brass tube, with strain gauges attached internally, along the length, allowing measurement of moment distribution along the pile during seismic excitation of the base. In addition, displacements and accelerations of different sections of the laminar box are recorded. Some of the early results of free-field and pile tests under sinusoidal base excitation are presented and discussed.

The objective of this paper is to consider the use of an "isolated" pipe system for mitigation of damage caused by ground deformation induced by surface fault rupture. The concept of an "isolated" pipeline, as introduced in the paper, refers to a system in which an inner pipe is isolated from a protective outer casing pipe by a relatively soft packing material. An analytical solution for the behavior of the "isolated" pipeline is derived and used for comparison to that of conventional pipelines. The solution assumes linear Winkler soil. It is demonstrated that the "isolated" pipeline experiences less strain than a conventional pipeline under the considered conditions. Copyright ASCE 2006.

Methane hydrate, which is usually found under deep seabed or permafrost zones, is a potential energy resource for future years. Depressurization of horizontal wells bored in methane hydrate layer is considered as one possible method for hydrate dissociation and methane extraction from the hosting soil. Since hydrate is likely to behave as a bonding material to sandy soils, supported well construction is necessary to avoid well-collapse due to the loss of the apparent cohesion during depressurization. This paper describes both physical and numerical modeling of such horizontal support wells. The experimental part involves depressurization of small well models in a large pressure cell, while the numerical part simulates the corresponding problem. While the experiment models simulate only gas saturated initial conditions, the numerical analysis simulates both gas-saturated and more realistic water-saturated conditions based on effective stress coupled flow-deformation formulation of these three phases.

Previous published elastic solutions for ground displacement due to tunneling ground loss ignore the effect of tunnel buoyancy. This note discusses this issue and quantifies the buoyancy contribution to the surface ground settlement in elastic soil. Solutions are given both for homogenous and Gibson's soils.

This paper describes the use of fibre optic sensing with Brillouin Optical Time-Domain Reflectometry (BOTDR) for near-continuous (distributed) strain monitoring of a large diameter pipeline, buried in predominantly granular material, subjected to a pipe jack tunnelling operation in London Clay. The pipeline, buried at shallow depth, comprises 4.6 m long sections connected with standard bell and spigot type joints, which connect to a continuous steel pipeline. In this paper the suitability of fibre optic sensing with BOTDR for monitoring pipeline behaviour is illustrated. The ability of the fibre optic sensor to detect local strain changes at joints and the subsequent impact on the overall strain profile is shown. The BOTDR strain profile was also used to infer pipe settlement through a process of double-integration and was compared to pipe settlement measurements. The close approximation of the measured pipe settlement provides further confidence in fibre optic strain sensing with BOTDR to investigate the intricacies of pipeline behaviour, pipe-soil interaction and interaction between pipe sections when subjected to ground movement. Copyright ASCE 2006.

One of the challenges facing civil engineers in the 21 ^st century is the maintenance, upgrading and safe operation of ageing infrastructure. Buried pipelines in the urban environment are frequently affected by ground movement caused by construction activities such as tunnelling. The interpretation of pipeline safety is, however, often hindered by a lack of understanding of complicated pipe-soil interaction, the state and effect of joints on pipe strain and interaction between individual pipe sections. This paper describes the use of fibre optic sensing with Brillouin Optical Time-Domain Reflectometry (BOTDR) for near-continuous (distributed) strain monitoring of a large diameter pipeline subjected to a pipe jack tunnelling operation in London Clay. The pipeline, buried at shallow depth, comprises 4.6 m long sections connected with standard bell and spigot type joints, which connect to a continuous steel pipeline. In this paper the suitability of fibre optic sensing with BOTDR for monitoring pipeline behaviour is illustrated. In particular, the ability of the fibre optic sensor to detect local strain changes due to changing rotational and/or axial resistance at joints and the impact on the overall strain profile are shown. The paper illustrates that the ability to detect joint behaviour aids in the interpretation of the state of the buried pipeline, taking account of the intricacies of joint behaviour, pipe-soil interaction and interaction between individual pipe sections when a pipeline is subjected to ground movement.

A method is presented for estimating the maximum bending moment for continuous (or rigidly jointed) pipelines affected by tunnel-induced ground movement. The estimation can be made based on the knowledge of tunnel and pipeline geometries, the stiffness of soil and pipeline, and tunnel-induced ground deformation at the pipeline level. The method takes account of soil nonlinearity by an equivalent linear approach, in which the stiffness of the soil is evaluated based on an average deviatoric strain developed along the pipeline. The approach is conservative and promises that the bending moment is not underestimated. The validity of the method as an upper bound approximation is evaluated against centrifuge test results. Journal of Geotechnical and Geoenvironmental Engineering

Experimental and numerical simulations are performed to evaluate the modification of ground response resulting from either the presence of soft layers or occurrence of partial liquefaction. Results from two densely instrumented dynamic centrifuge tests are presented to show the ambiguous role played by the presence of a soft layer. It was found that the lateral extent of the soft layer has significant influence on the overall response of the layered strata and any structure founded on it. The experimental observations are supported by simplified numerical analysis. The amplification or deamplification of the input motion is found to be a function of the ratio of the width of soft layer to the wave length. Based on the numerical analysis, a general function describing the site amplification is presented which may be used as a guide in seismic design of foundations in such layered strata.

Experimental and numerical simulations are performed to evaluate the modification of ground'response resulting from either the presence of soft layers or occurrence of partial liquefaction. Results from two densely instrumented dynamic centrifuge tests are presented to show the ambiguous role played by the presence of a soft layer. It was found that the lateral extent of the soft layer has significant influence on the overal1 response of the layered strata and any structure founded on it. The experimental observations are supported by simplified numerical analysis. The amplification or dearnplification of the input motion is found to be a function of the ratio of the width of soft layer to the wave length. Based on the numericd analysis, a general function describing the site amplification is presented which may be used as a guide in seismic design of foundations in such layered strata.

An elastic continuum solution and a Winkler solution of the problem of tunnelling effects on existing pipelines are given. A comparison is made between an elastic continuum solution and a closed-form Winkler solution with Vesic subgrade modulus. Although applying the Vesic expression results in the same moments and displacements under external loading in a Winkler system and the elastic continuum, it is found that its use is not necessarily adequate for the problem of tunnelling effects on pipelines and may not be conservative owing to possible underestimation of bending moments. An alternative expression for the subgrade modulus is provided, resulting in similar maximum bending moments in the Winkler and elastic continuum systems.

A formulation for coupled flow-deformation analysis of methane-hydrate extraction problems is presented. By assuming that the hydrate does not flow, a two phase flow formulation is considered, based on Darcy's law and capillary pressure relation. The formulation is implemented in the finite difference code FLAC. The code was used to investigate the stability of a methane extraction well by depressurizing the well.

Numerical analysis of an infinite pile group in a liquefiable soil was considered in order to investigate the influence of pile spacing on excess pore pressure distribution and liquefaction potential. It was found that an optimal pile spacing exists resulting in minimal excess pore pressure. It was also found that certain pile group configurations might reduce liquefaction potential, compared to free field conditions. It was observed that for closely spaced piles and low frequency of loading, pile spacing has little influence on the response of the superstructure.

Numerical analysis of seismic soil-pile interaction was considered in order to investigate the influence of flow mechanisms. Two models were employed-a simplified model, where the pore pressure at any depth is that of the free field, and a more complete model in which the pore pressure is associated with three-dimensional flow. The soil behavior was modeled by a nonlinear, quasi-hysteretic constitutive relation. A parametric study was carried out, varying the superstructure mass and soil permeability. It was found that there is a pore pressure threshold below which both models yield similar results, but that this threshold cannot be quantified a priori, as it depends strongly on soil-pile interaction.

A novel Lagrangean approach for the analysis of nonlinear contact surface for rotationally motioned rigid body to deformable body was described. The integration forces the contact grid points to move along a predefined shape function that represented the contact surface, unless separation occurs. The applicability of the formulation to geotechnical engineering was demonstrated in the numerical simulation of pile installation where the tip was described by a nonlinear surface. It was found that the shape of the pile affects the resulted stress path in the soil domain when the upper end of the tip passes the depth of the adjacent points.

A procedure for exploiting a two-dimensional (2D) explicit, numerical computer code for the 3D formulation of dynamic lateral soil-pile interactions is considered. The procedure is applied to two models using simultaneous computation of a series of plane strain boundary value problems, each of which represents a horizontal layer of soil. The first model disregards the shear forces developed between the horizontal layers, and may be considered as a generalized Winkler model. The second model takes account of these forces by coupling the behavior of the horizontal layers. Several verification problems for a single pile and pile groups in a homogeneous soil layer modeled as a viscoelastic material were solved and compared to known solutions in order to assess the reliability of the models. Excellent agreement was observed between results of the present analyses and existing solutions.