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The damage caused by seismic shaking and liquefaction-induced permanent ground deformation has conventionally been assessed as two separate problems often by different engineers. However, the two problems are inherently linked, since ground shaking causes liquefaction, and liquefaction-induced soil softening affects ground shaking. Modelling both problems within a single numerical model is complex for both the engineer and the software, and most finite element software only have the capabilities to address one of them. To improve the estimates of the seismic performance of buildings on liquefiable soil, a new sub-structuring approach is proposed called the macro-mechanism approach. This approach allows the soil-liquefaction-foundation-structure interaction to be considered in a series of sub-models accounting for the major nonlinear mechanisms of the system at a macro level. The proposed approach was implemented in the open-source finite element software OpenSees and then applied to a case study of a building where significant liquefaction- and shaking-induced damage was observed after the 1999 Mw 7.4 Kocaeli Earthquake. The case study building was also simulated using two different commercial software programs, the finite difference software FLAC, and the finite element software PLAXIS, by two different research teams. A comparison between the results from the macro-mechanism approach compared to full numerical models shows that the macro-mechanism approach can capture the extent of the foundation deformation and provide more realistic estimates of the building damage than full approaches since the FLAC and PLAXIS models consider elastic elements for the building. [ABSTRACT FROM AUTHOR]

Evaluation of ground failure potential in geotechnical practice is typically based on demand parameters that solely consider vertically propagating shear waves in the free-field. Soil–structure interaction (SSI) modifies demands beneath foundations, and observations from recent earthquakes, physical modeling studies, and numerical modeling simulations indicate that SSI contributes significantly to ground failure. We present a methodology that utilizes elastic solutions to define SSI-induced stresses imposed on the soil beneath shallow foundations during earthquake shaking. Input parameters include a free-field ground surface motion as well as static and dynamic base shear, moment, and axial stresses imposed on the soil by a shallow foundation. The resulting stresses in the soil are analyzed in terms of the deviatoric stress invariant and the mean effective stress, which represents the states of stress leading to shear failure more accurately than the traditional use of stresses on horizontal planes. The invariant-based cyclic stress ratio (CSRq) is introduced to quantify demands, which is equivalent to the conventional CSR in the free-field. The ratio of the corresponding cyclic resistance parameter, CRRq , to CSRq is the factor of safety against ground failure at a point. Application of this methodology to results of centrifuge modeling of shallow foundations resting on low-plasticity fine-grained soils shows that the factor of safety computed from the proposed methodology at a location in the soil below the edge of the foundation correlates strongly to measured permanent settlements and rotations, whereas the free-field factor of safety underpredicts ground failure potential. [ABSTRACT FROM AUTHOR]

Analytical solutions for axial displacement, strain, and stress in a single semifloating energy pile embedded in a layered soil profile subjected to thermal and mechanical loads were derived. An analytical solution for the location of zero displacement, also known as a null point, was derived for a pile subjected to thermal load. It was shown that the location of the thermal null point corresponds to the location of the maximum magnitude of thermal axial stress. It also was shown that the location of the null point moves toward the pile tip as the stiffness of the bedrock below the pile tip increases. The analytical solutions were validated against in situ full-scale energy pile tests. The solutions along with the validation process delineated the load transfer mechanism in energy piles subjected to thermal, mechanical and combined thermomechanical loads embedded in a four-layer soil profile. Flowcharts delineating the procedures for obtaining the analytical solutions for a single energy pile embedded in an arbitrary number of layers, and subjected to thermal and mechanical loads are provided. Although the continuity of stresses and displacements at the interface of different soil layers is maintained, displacement, strain, and stress diagrams exhibit a lack of smoothness, the amount of which depends on the difference in the stiffness of these layers. In summary, the presented solutions provide a rational, mechanics-based framework for advancing the understanding of thermomechanical response of energy piles that not only is essential for analysis and design, but ultimately contributes to a wider use of energy piles and increased sustainability of civil engineering infrastructure. [ABSTRACT FROM AUTHOR]

Excavation-induced ground movements can have a detrimental influence on adjacent structures and services. These complex soil–structure interactions are affected by a range of factors such as ground conditions, excavation sequence, and the characteristics of the structures. Considerable prior research has been concerned with understanding the ground response during excavation and in evaluating the potential damage to adjacent facilities. A number of case histories have been reported worldwide. Finite-element analysis can be effective in providing insight into the response of the ground and adjacent structures during the entire construction process. Previous studies have shown that observed excavation behavior (e.g., ground movements and retaining wall deformations) can be captured reasonably well in finite-element analysis, provided that certain key modeling aspects are appropriately addressed. This paper extends a previous deep excavation case study in greenfield conditions (i.e., without adjacent buildings and utilities included in the analysis), focusing particularly on the excavation-induced settlements of nearby buildings and buried pipelines. Sensitivity analyses have been conducted to investigate the effects of several aspects on the computed settlements of buildings and pipelines, such as (1) building weight, (2) building stiffness, (3) building foundation type, (4) ground improvement measures, and (5) geometries and material properties of pipelines. Conclusions are drawn for future applications. [ABSTRACT FROM AUTHOR]

This paper reports the development of a particle breakage model within a finite-element (FE) framework based on the modified Mohr–Coulomb model (MMC). A modified form of the strength-dilatancy relationship is used to incorporate additional energy consumed due to particle breakage. A new particle breakage index is introduced and constitutively linked to the mobilized friction angle. The model is verified against carefully conducted drained triaxial tests on medium-dense calcareous sand obtained from offshore Australia as well as other published data. The model is implemented in the FE program ABAQUS for both small strain and large deformation FE analyses in practical field problems. Several important microscopic observations can be made from the proposed model that are not limited to identifying soil regions where particle breakage is maximized. Due to its inherent simplicity, the newly developed model can provide reasonable predictions for soil-structure interaction problems in calcareous sands. [ABSTRACT FROM AUTHOR]

Considerable bridge-ground interaction effects are involved when evaluating the consequences of liquefaction-induced deformations. Due to seismic excitation, liquefied soil layers may result in substantial accumulated permanent deformation due to the sloping ground near the abutments. Ultimately, global response of the bridge is dictated by soil-structure interaction considerations of the entire bridge-ground system. Of particular interest is the scenario of narrow waterways where interaction between downslope deformations at both ends of the bridge takes place. In order to highlight the involved salient mechanisms, this study investigates the longitudinal response of an overall bridge-ground system. For that purpose, a full three-dimensional (3D) finite-element (FE) model is developed, motivated by details of an existing narrow waterway bridge-ground configuration. As such, a realistic multilayer soil profile is considered with interbedded liquefiable/nonliquefiable strata. Specific attention is given to global response of the bridge structure as an integral entity due to ground deformation in the vicinity of the abutments. The overall results indicated that downslope deformations at both ends of the bridge may result in significant interference within the narrow waterway central section. As such, assessment of deformations at each slope separately might lead to unrealistic outcomes. Generally, the analysis technique as well as the derived insights are of significance for the seismic response of bridge systems with downslope ground deformations. [ABSTRACT FROM AUTHOR]

Energy piles, a new type of heat exchanger that serves dual purposes, have gained increasing attention due to the growing energy demand and corresponding carbon emissions. Depending on intended operational requirements or by accident, energy pile groups may be subjected to cyclic and variable thermal loadings. This study presents the results from a series of full-scale field tests of a 2×2 energy pile foundation. The energy pile group was operated partially or fully during the tests to investigate the potential effects of cyclic nonuniform thermal loadings. The results indicated that the cyclic thermal loadings could induce an increase in compressive stress of piles at the end of the experiments. Further comparative analysis showed that the residual compressive stress was attributed mainly to the drag-down effects of the surrounding soil. The compressive stress induced by drag-down effects will overlap with the thermally induced stress, and thus lead to a more significant effect on the energy piles. If the drag-down effects are presented, the stress change may exceed the theoretical upper bound of thermal stress and may be underestimated. In addition, cyclic nonsymmetrical thermal loadings could induce accumulation of differential settlement and group tilt in the energy pile group. It was shown that the group tilt caused by cyclic and variable thermal loadings can be acceptable for general engineering structures. The group tilt will not accumulate further when subjected to symmetrical thermal loadings. A reasonable arrangement of operational piles still can be used to avoid unwanted group tilt generation. [ABSTRACT FROM AUTHOR]

Recently, progress has been made toward understanding the seismic response of structures placed on unsaturated soil layers. A missing link, however, involves the influence and assessment of the underlying soil saturation conditions on the expected superstructure seismic demands. Simplified soil–structure interaction procedures that can be used to predict superstructure seismic demands have not been explicitly extended to incorporate the influence of unsaturated soil on the system response. In this paper, results from a series of six centrifuge tests are compared. In each test, an inelastic single-degree-of-freedom physical model was shallowly embedded in a sandy silt with a distinct water table elevation or a completely dry soil condition. The soil-structure system was subjected to a series of earthquake motions. The response of the system was evaluated to assess the influence of the soil saturation condition on the seismic response. Specifically, a conventional analytical procedure for predicting the influence of inertial interaction on the seismic response of the structure was extended to consider the water table elevation and underlying soil saturation condition and evaluated for its reliability. Analytical flexible-base modal parameters were compared with those determined from experimental results to judge the potential of the analytical procedure to be used in practice. Experimental results suggest that as the water table elevation was lowered from the fully saturated condition, both the flexible-base system period and damping ratio reduced. Therefore, the system behaved stiffer in the unsaturated soil compared with the dry and fully saturated conditions. The stiffer response reduced the seismically induced foundation settlements and rotations but amplified superstructure seismic demands in the form of accelerations, flexural drifts, and bending strains. [ABSTRACT FROM AUTHOR]

This paper proposes a new simple approach for assessing dynamic soil–structure interaction effects on structures supported by embedded massive foundations. The classical substructure method was revisited by proposing an exact decomposition approach which allows performing the inertial interaction analysis of the superstructure without modeling foundation and soil, which are replaced by properly defined impedances. The proposed approach requires redefinition of simplified formulas for both the dynamic stiffnesses and the kinematic interaction factors, which are referred to the top of the massive foundation. Accurate expressions for the complex impedances were derived based on rigorous finite-element results. The same formulas were used to calibrate a four-spring model for the analysis of the kinematic interaction problem, resulting in different expressions for the kinematic interaction factors depending on the adopted assumptions. The proposed approach, in conjunction with the novel formulas for impedances and kinematic factors, was applied to the case of bridge piers on caisson foundations, and the results were more accurate than those of the existing simplified procedures. [ABSTRACT FROM AUTHOR]

Yard loads may induce slope deformation and compress the piles of pile-supported wharfs, resulting in structural damage. In this paper, centrifuge tests were conducted to investigate yard load induced performances of pile-supported wharfs reinforced with T-shaped and F-shaped soil cement mixing (TSCM and FSCM, respectively) retaining walls. The TSCM and FSCM walls were located in the bent-yard connecting section and wharf performances were presented in terms of soil movements, bent displacements, soil and pore pressures, and pile bending moments. The results show that the slope soil migrated toward the waterside as the soil cement mixing (SCM) walls tilted, inducing tilting failure of the pile-supported wharf. The FSCM wall–reinforced bent showed greater displacements than the TSCM wall–reinforced bent at the same load intensities. Pore pressures were registered immediately after yard loads were applied but dropped to constant values or kept decreasing over time during the unloading period. Soil pressures generally increased with yard loading in the upper part but exhibited increasing-decreasing tendencies in the lower part. The soil pressures on the FSCM side were generally greater than those on the TSCM side in the upper and middle parts but smaller in the lower part. The bending moments on the FSCM side were generally larger than those on the TSCM side on landside because the structure-soil interaction was more intense. SCM walls are feasible and beneficial for reinforcing pile-supported wharfs under yard loads, and TSCM walls seem to be superior to FSCM walls considering their improved performance and economic efficiency. [ABSTRACT FROM AUTHOR]

Removal of soil around a bridge foundation due to scour results in a reduction of the lateral and vertical foundation capacity due to the loss of soil support. The common approach in modeling the scour phenomenon of removal of soil springs without modifying the parameters of the remaining soil fails to consider the change of stress state of the remaining soil and the formation of scour hole geometry around the pile foundation. In practice, both of these factors impact the mechanical properties of the remaining soil and the resulting expected structural response of the pile under loadings. This paper proposed a methodology to comprehensively evaluate the combined effects of stress history and scour hole dimensions on piles under scour conditions in uniform soil. It enabled the examination of the lateral and axial behaviors of a loaded pile subject to scour and is applicable for both cohesive and cohesionless soils. The methodology was validated with results from field tests for no-scour scenarios and verified with existing numerical models for scour scenarios. Quantification of the soil effects was investigated through lateral pile deflection and load-settlement curves for lateral and axial behaviors, respectively. Load-settlement curves demonstrated that including the effect of stress history results in increases of up to 34.1% and 61.1% in estimated pile settlement for sand and clay, respectively, leading to potential unconservative designs if soil effects are not properly included in the analysis. [ABSTRACT FROM AUTHOR]

In this paper, we present a probabilistic predictive procedure for a foundation's permanent average settlement on liquefiable soils improved with ground densification. The proposed procedure is based on 770 three-dimensional (3D), fully coupled, effective-stress, finite-element analyses designed through quasi-Monte Carlo sampling of key input parameters. The numerical models are themselves calibrated and validated with centrifuge model studies, and they consider realistic, nonlinear, 3D structures on shallow foundations, seismic soil–structure interaction, interlayering and layer cross interactions, ground densification properties and geometry, and ground motion characteristics. We use nonlinear regression with lasso-type regularization to estimate model coefficients. The primary predictors of a foundation's settlement are identified as the cumulative absolute velocity of the outcropping rock motion; total thickness of the soil deposit above bedrock and cumulative thickness of the critical liquefiable layer(s); the foundation's bearing pressure, size, and embedment depth; the structure's total height; the achieved density and size of ground improvement; and the thickness of the remaining undensified susceptible soils within the foundation's influence zone. In the end, the predictive model is shown to capture the trends in a limited number of centrifuge and field case histories collected from the literature. The insight from the numerical database and the first-of-its-kind predictive model aims to guide the design of liquefaction mitigation strategies that improve the performance of the soil–foundation–structure system holistically and reliably. [ABSTRACT FROM AUTHOR]

The role of spatially variable soil stiffness and strength on structural performance has been increasingly recognized with the rapid development of geotechnical reliability-based design tools. Performance criteria linked to the angular distortion between foundations and the probability of exceeding certain limit states as a function of linear-elastic soil property autocorrelation have shed light on the link between foundation soils and potential structural damage. However, the role of soil-structure interaction (SSI), especially considering nonlinearity in soil and structural elements, to redistribute shear and flexure within structures that result from differential foundation movements, has been largely neglected. This study presents a critical examination of the effect of nonlinear SSI to redistribute flexural demands within a steel structure founded in soils exhibiting spatial variability and the corresponding differential settlements through a comparison of uncoupled and coupled Monte Carlo simulations (MCS). This study shows that the differential settlement, Δs , computed using coupled (i.e., SSI) analyses are significantly smaller than those derived from the uncoupled analyses for the random field models (RFMs) used to simulate soil spatial variability. The effect of SSI is to substantially reduce the probability of exceeding selected limit state criteria due to differential movements that vary in magnitude with the level of stringency of the limit state criteria; the most significant reduction corresponds to the structural ultimate limit state (ULS). Furthermore, the effect of SSI on structural performance and the critical scale of fluctuation, δcrit , becomes more apparent and beneficial as the severity of differential movement increases. Smaller and/or "allowable" angular distortions are governed by the local footing-to-footing distance, whereas the probability of exceeding the ULS (i.e., yielding of beams) is controlled by the entire structure working to redistribute the flexural demands. Limit state severity appears to control the critical soil autocorrelation length for angular distortion, indicating that the role of SSI in the performance of structures in spatially varying soils cannot be ignored. [ABSTRACT FROM AUTHOR]

Ground densification is a common countermeasure against soil liquefaction. The state-of-practice for designing ground densification is typically based on empirical estimates of liquefaction triggering and ground settlement in the free field, ignoring seismic soil-structure interaction (SSI) near building structures. The existing guidelines for the geometry of ground densification also do not take into account constraints introduced by the presence of a neighboring foundation, or the impact of densification on seismic structure-soil-structure interaction (SSSI) and performance of adjacent buildings in urban settings. In this paper, three-dimensional (3D), fully-coupled, nonlinear finite-element analyses, validated with centrifuge experimental results, are used to evaluate the influence of ground densification on the seismic performance of isolated and adjacent, similar and dissimilar, inelastic structures on liquefiable soils. The response is evaluated for treatment of varying dimensions (depth [dDS] and width [WDS]), location (e.g., below one or both neighboring buildings), and symmetry configurations. Ground densification is shown to effectively reduce the permanent settlement of isolated structures when covering the full depth of the critical layer, while potentially amplifying column strains and structural deflections. Depending on the properties of the structure and symmetry of treatment, densification could also adversely impact a foundation's permanent tilt. The influence of densification on SSSI is shown to depend strongly on the geometry of densification, dynamic properties of the neighboring structures, and building spacing. For the spacings (S) considered, ground densification effectively reduced the permanent settlement of two adjacent mitigated structure(s). However, the combination of SSSI and ground densification typically notably amplified asymmetrical deformations below the foundations (hence, permanent tilt) as well as column strains, particularly for an unmitigated neighbor. This effect was strongest when closely spaced and when WDS=S. The results indicate that ground densification location and geometry must be designed with extreme care in urban settings, particularly when near a taller and weaker neighboring structure. [ABSTRACT FROM AUTHOR]

Heat transfer from/to energy piles can cause plastic contraction of soft clay with a low overconsolidation ratio (OCR) during heating and cooling. This can lead to thermally induced excess pore water pressure and changes in the lateral stress acting on a pile. These thermally induced phenomena cause additional plastic settlement of the soil and pile. Irreversible settlement may cause serviceability or ultimate limit state problems for floating energy piles whose capacity is mainly derived from shaft resistance. Due to intended operational needs or by accident, cyclic nonsymmetrical thermal loads may be applied to floating energy pile groups and piled rafts. The thermomechanical interaction among nonsymmetrical loaded piles is not well understood. In this study, a series of cyclic nonsymmetrical thermally loaded centrifuge model tests were conducted on floating pile groups and piled rafts in soft kaolin clay with an OCR of 1.7 at the pile toe. The performance of floating 2×2 elevated energy pile groups and energy piled rafts was investigated. Three piles in each group were subjected to 15 cycles of ±14°C in temperature change. The thermally induced irreversible settlement and tilting of the elevated pile groups exceeded serviceability and ultimate criteria. The piled rafts similarly settled but to a smaller extent than the elevated group. Their tilting, however, did not exceed the serviceability criterion. It is recommended that energy piled rafts be used in soft clay instead of elevated energy piles. [ABSTRACT FROM AUTHOR]

Tunneling can compromise the safety and serviceability of existing buried infrastructure because of settlements, crack openings, dislocations, and material strains. A continuum-based soil-structure interaction model, implementing an equivalent Timoshenko beam, is used to evaluate the excavation-induced settlements and longitudinal deformations of existing tunnels and pipelines. Both single and twin tunneling scenarios are examined. The shear flexibility of shield and sprayed concrete lining tunnels may be significant. This increases tunneling-induced settlements while it decreases tilt, curvature, and the associated bending moment, with implications for optimal monitoring installations. In this work, a new dimensionless shear factor is introduced, governing the relative importance of shear and bending deformations and accounting for the settlement trough width. This can be used to evaluate if a pure-bending, shear-dominated, or mixed deformation mode should be expected. Design charts to assess existing infrastructure affected by either single or twin tunnels are proposed. [ABSTRACT FROM AUTHOR]

This study presents an analytical framework to estimate the change in ultimate bearing capacity of energy piles in unsaturated fine-grained soils under drained mechanical loading conditions after drained heating. The framework was developed by extending conventional methods for the ultimate bearing capacity of piles in unsaturated soils to temperature-dependent conditions, where thermally induced changes in the characteristics of the unsaturated soil and soil–pile interface are considered. Specifically, the thermally induced variations in matric suction and effective saturation profiles with depth were incorporated into calculations of the shaft capacity and the end bearing capacity of piles in unsaturated soils. The proposed ultimate bearing capacity model is validated against experimental data for an energy pile loaded to failure in unsaturated Bonny silt, and a good match between measured and predicted values was obtained. A parametric study was carried out to evaluate the effects of infiltration rate and pile aspect ratio (i.e., pile embedment length/pile diameter) on the ultimate bearing capacity of energy piles in unsaturated clay and silt layers subjected to temperatures ranging from 5°C to 45°C. For both soils, the shaft, end bearing, and ultimate bearing capacities vary with an increase in temperature. At the reference temperature, the shaft, end, and ultimate bearing capacities vary monotonically with pile embedment length, while at elevated temperatures they vary nonmonotonically with pile embedment depth. At a given temperature, the parametric study shows that the bearing capacity of energy piles in clay decreases with increasing downward infiltration of water into the soil profile surrounding the energy pile, while in silt it may decrease or increase depending on pile embedment length. The ultimate bearing capacity increases with a decrease in pile aspect ratio at all temperatures. Estimates of the ultimate bearing capacity of energy piles in unsaturated fine-grained soils from the framework are a critical part of thermomechanical soil–structure interaction analyses needed to design energy piles, so this study contributes toward the widespread application of this emerging technology in practice. [ABSTRACT FROM AUTHOR]

The stability of pile-supported structures under earthquake loads involves complex dynamic soil–structure interaction (SSI). A series of large-scale shaking table experiments was performed to investigate the seismic performance and SSI of pile-supported structures considering different ground conditions. Lateral soil resistance and dynamic displacements of superstructures located in nonliquefiable and liquefiable sites as well as a rigid foundation were measured during shaking tests. The measured responses were analyzed to investigate the P- Δ effect on structural stability. It was observed that the soil lateral resistance to the pile cap at the nonliquefiable site was large and represented the main component of the lateral bearing capacity resisting structure overturning. On the other hand, the lateral resistance of liquefied soil on piles was insignificant and the lateral bearing capacity was derived primarily from soil resistance to pile cap. The analysis of the measured dynamic displacements demonstrated that the seismic instability of the structure was mainly due to the P- Δ effect caused by the rotation of the foundation, especially in liquefied sites. In addition, comparison with the results of base shears and bending moments with the rigid base assumption allows for an in-depth discussion of the effect of SSI on structural seismic design. [ABSTRACT FROM AUTHOR]

Oversimplifying structural modeling in the analysis of the seismic performance of tall buildings introduces variability and biases in the computed seismic response. Engineering demand parameters (EDPs) from coupled soil–structure interaction (SSI) systems can only be realistically determined when nonlinear constitutive soil and structural behaviors are adopted in the numerical formulation. Large-magnitude earthquakes mobilize soil and structural demands that are beyond the elastic response of both materials. This paper aims at evaluating the influence of the structural modeling assumptions in the computed soil response due to seismic excitations using a direct fully coupled nonlinear SSI approach. Numerical analyses are conducted on elastic and nonlinear inelastic-degrading tall building models supported on a mat foundation-to-soil continuum domain using a multiple-yield surface plane-strain constitutive model. The models were subjected to multiple ground motion scenarios representative of broadband frequency content. Large discrepancies occur between linear and nonlinear inelastic tall buildings in terms of interstory drifts, peak horizontal accelerations, structural displacements, hysteretic energy, foundation rotation, and soil settlements. The results show how using nonlinear inelastic-degrading structural models of tall buildings largely affect the computed seismic response of the entire SSI system relative to linear elastic structural modeling approaches. More realistic responses are obtained using nonlinear degrading building models including SSI effects, because energy distribution and tradeoff among both the supporting soils and structure vary significantly as the seismic demands induce stresses and strains in the building beyond the onset of structural yielding. [ABSTRACT FROM AUTHOR]

This technical note investigates the effect of footing embedment depth on tunnel–structure interaction using geotechnical centrifuge testing. A 2-story framed building on separate footings, either resting directly on the surface or embedded in the soil, and subjected to tunneling-induced displacements is modeled. Measurements of the displacements of the footings and underlying soil, ground deformations, and structural distortions are presented. Results show that footing embedment increases foundation differential settlements and horizontal displacements, thereby causing a greater level of distortion within the frame. Furthermore, the embedded footings result in a larger magnitude of ground displacements and shear strains of the soil. Finally, modification factors and relative stiffness parameters are presented, indicating a greater effect of the embedment on horizontal deformations than the angular distortion of the bays. [ABSTRACT FROM AUTHOR]

EICP (enzyme induced carbonate precipitation) and MICP (microbially induced carbonate precipitation) treatments were applied through pervious concrete model piles to cement soil around the piles and enhance soil-pile interaction and pile capacity. The behaviors of the pervious concrete piles treated by EICP and MICP when subjected to axial compression loading were compared with each other and with an untreated pervious concrete pile. These tests were performed on 1/10th-scale model piles in the soil-structure interaction (SSI) testing facility at Lehigh University. The piles and surrounding soil were instrumented with strain gauges, bender elements, in-soil null pressure sensors, and a tactile pressure sheet. The responses of the pervious concrete piles and surrounding soil were compared through analysis of shear wave (S-wave) velocities in the treated and untreated soil zones, load transfer along the piles at the ultimate load condition, soil moisture content, calcium carbonate (CaCO3) content and ammonium (NH4+) concentration in soil, and the characteristics of the precipitated CaCO3 crystals along the soil-pile interface. In addition, comparisons with consolidated drained (CD) triaxial test results were made among sand without treatment and with EICP and MICP treatments. The results presented in this paper demonstrated that both EICP and MICP treatments can create a cemented soil zone surrounding the pervious concrete pile and improve the pile capacity and load transfer under compression loading. [ABSTRACT FROM AUTHOR]

In urban environments, structures are often built in close proximity to each other. Seismic coupling and structure-soil-structure interaction (SSSI) are known to affect system accelerations, settlement, and tilt with consequential impact on structural damage. Yet, the extent and nature of these interactions are poorly understood, particularly on ground susceptible to liquefaction. In this paper, we use dynamic centrifuge and numerical modeling of isolated and neighboring, similar and dissimilar, shallow-founded structures on layered, level, saturated, and liquefiable soils to provide insight into (1) the mechanisms of SSSI; and (2) the relative influence of key parameters on system performance. Fully-coupled, nonlinear finite-element analyses of the centrifuge experiments indicated that in addition to a comprehensive calibration of the soil constitutive model parameters, use of higher-order elements and a sufficiently large domain size in three dimensions (3D) were critical ingredients to predicting the general trends in system response compared to centrifuge recordings. A limited numerical sensitivity analysis was performed subsequently. The results identified the key parameters affecting SSSI as spacing between the two foundations (S) in relation to their width (W) as well as the contact stress and geometry of the neighboring foundation-structure system. SSSI slightly decreased the permanent settlement of structures at the expense of a notable increase in their permanent tilt, particularly when S≤W. The foundation's spectral accelerations were observed to amplify at shorter periods when near a taller and heavier building at S≤W/3 , which was attributed to the added confinement. Increasing the uniform thickness of the critical liquefiable layer increased both adjacent structures' permanent settlement, while not affecting their residual tilt or SSSI. Importantly, the impact of SSSI on foundation tilt and accelerations remained significant for building spacings exceeding 2.5W. The results point to the importance of considering the impact of SSSI on structure's key engineering demand parameters and the urgent need for improved guidelines when assessing and treating liquefaction in urban settings. [ABSTRACT FROM AUTHOR]

Centrifuge modeling has been considered as an effective means of studying flexural soil–pile interaction, yet the conventional use of elastic material to model an RC pile prototype is unable to reproduce the important nonlinear quasi-brittle behavior. It also remains a challenge to numerically model the soil–pile interaction due to the nonlinearity of both the soil and pile materials. This paper presents a small-scale model RC pile for testing soil–structure interaction under lateral pile head loading in sand within a centrifuge. Accompanying nonlinear finite-element numerical modeling is also presented to back-analyze the centrifuge observations and explore the influence of the constitutive models used. The physical model RC pile is able to (1) reproduce the pile failure mechanism by forming realistic tension crack patterns and plastic hinging and (2) give hardening responses upon flexural loading. Comparisons of measured and predicted results demonstrate that for the laterally loaded pile problem, the load–displacement response can be well approximated by models that do not incorporate strain softening, even though the soil behavior itself exhibits a strong softening response. [ABSTRACT FROM AUTHOR]

This paper proposes simple numerical models that simulate the influence of tunneling-induced ground movements on masonry buildings founded on shallow strip footings. The focus is on developing an improved understanding of the impact of structural discontinuities due to pre-existing cracks and joints between adjacent buildings. The soil–structure system is idealized with equivalent Timoshenko beams connected to a homogenous elastic half-space with rigid links. The flexibility of the equivalent beam at the location of the crack or building interface is determined using linear-elastic fracture mechanics. The proposed models are first applied to a generic numerical example. Then, they are used to interpret the detailed displacement and strain measurements gathered from a masonry church during nearby tunneling. The results show that pre-existing cracks can have variable influence on the soil–structure interaction depending on their extent and position relative to the building and settlement trough. For the investigated case study, the proposed models illustrate how pre-existing large cracks in the hogging zone localized deformations and how the interaction between adjacent buildings drastically altered response mechanisms. [ABSTRACT FROM AUTHOR]

Design of column-supported embankments (CSE) requires the evaluation of global stability using the conventional limit equilibrium method (LEM). Yet, for CSEs using unreinforced concrete columns and load transferring geogrids, the failure mechanisms and corresponding soil-structure interactions are not well understood. There is increasing evidence pointing to large bending moments in columns and failure of columns in flexure, as opposed to a failure by shear as assumed in limit equilibrium analyses. In response to these design uncertainties, the failure height, failure mode, and deformations of eight column-supported embankment scenarios were investigated using three-dimensional (3D) numerical analyses. For the same embankment scenarios at failure height, factors of safety (FS) were then calculated using the two-dimensional (2D) LEM for investigating its applicability in evaluating global stability of CSEs. The 3D numerical analyses examined CSE stability for the limiting conditions at undrained end-of-construction and after long-term dissipation of excess pore water pressures. The numerical model included representations of flexural tensile failure in the concrete columns and tensile failure in the geosynthetic reinforcement. Scenarios consisted of a base case with typical concrete column design, five single-parameter variations using base case conditions, and two multiparameter variations using base case conditions. The undrained condition was the most critical, and two failure modes were found: (1) multisurface shearing in the embankment coupled with bending failure of columns and near-circular shear failure in the clay, and (2) multisurface shearing in the embankment coupled with bending failure of columns and shearing in the upper portion of the soft foundation clay. Both failure modes were accompanied by a rupture of the geosynthetic when included in the load transfer platform. Soil-column interactions were complex, and many columns failed in bending at lower embankment heights than those that produced collapse. The factors of safety calculated using the LEM were overstated. This is because the LEM assumes failure by shear, which has limited applicability for examining the complex mechanisms by which CSEs fail. The practical implication is that the LEM should not be used for evaluating global stability of this system type and, by extension, other system types in which soil-structure interactions result in failures controlled by mechanisms other than shear. [ABSTRACT FROM AUTHOR]

The deep vertical bearing capacity of rectangular foundations of varying aspect ratios (0.2–10) are explored within a coupled Eulerian–Lagrangian (CEL) finite element modeling framework. The CEL model is verified against existing numerical and theoretical solutions. For accurate shallow bearing capacity assessment, large deformation finite element (LDFE) solutions were found to be suitable if penetration resistance is extracted at normalized penetration depths of less than 5% of the foundation width. The deep bearing capacity factor for a circular foundation was predicted within ∼2% for a smooth foundation and ∼5% for a rough foundation. Soil weight and stiffness were found to have no impact on the penetration resistance at shallow depths but to influence the resistance at deeper depths. The relative foundation thickness has a profound influence on the deep bearing capacity factor (Nc). Increasing the normalized foundation thickness from 0.1 to 0.5 increased the bearing factor by more than 20%. An alternate soil flow mechanism was discovered responsible for this increase. The deep bearing capacity factor for a rectangular foundation was found to nonlinearly increase with the footing aspect ratio. An exponential form of equation was shown to capture well the effects of varying aspect ratio and footing thickness. The effect of the common assumption of a rigid foundation on bearing capacity in geotechnical numerical analyses has been revisited. [ABSTRACT FROM AUTHOR]

A set of dynamic centrifuge experiments was performed to assess the effect of the depth of the groundwater table on the seismic site response and kinematic interaction of a foundation on unsaturated sandy soil. The experimental program consisted of centrifuge tests on dry soils, saturated soils, and soils having groundwater level at various depths. Results show that as the groundwater level was lowered, (1) seismically induced soil settlement, the mean period of the free-field motion, and the midperiod amplification factor generally decreased; (2) the lateral incoherence parameter, soil strain–dependent natural frequency, and amplification factors for peak ground acceleration, Arias Intensity, and short period roughly increased; while (3) the rocking incoherence parameter stayed approximately constant. Assuming soils in a fully saturated state for seismic design may either over- or underpredict different aspects of the seismic soil–foundation response, in comparison with partially unsaturated ground. Thus, this assumption may not always lead to safe or economical designs, especially with regard to seismically induced soil settlement, seismic site response analysis, and kinematic soil–foundation interaction. [ABSTRACT FROM AUTHOR]

The paper examines the problem of the soil-structure interaction for buildings founded on piles throughout the comparative analysis between the seismic demand in compliant base and fixed base models. The aim of the work is to introduce a simple approach for evaluating the effects of soil-foundation-structure interaction (SFSI) for buildings founded on piles and, hence, to quantify the relevance of SFSI effects for this kind of structure. Inertial interaction analyses are carried out by idealizing the complete system as a linear SDOF on a deformable base represented by frequency dependent springs and dashpots. An application of the proposed methodology to a case study of a nine-story building resting on two well-studied subsoils, a deep clay layer from Piana del Fucino (Italy) and a pyroclastic deposit from Napoli, is presented and discussed. Reference is made to a complete seismic risk analysis in which the input signals are grouped into strips according to the conditional spectrum method. As a further objective, the effect of wall infills on the seismic demand in the reference buildings is investigated. The results show that for the pyroclastic deposit the seismic demand in the compliant model is comparable with that in the fixed base. By contrast, SFSI leads to a relevant reduction of the seismic demand for buildings on the clay layer. It is concluded that, contrary to the common belief, SFSI may also be relevant for tall buildings if they rest on soft soils. [ABSTRACT FROM AUTHOR]

In cities, seismic coupling between structures is known to influence ground motions, settlement patterns, and demand on superstructures. Yet the effects of interactions between soil and building clusters on structural performance are poorly understood, particularly on ground susceptible to liquefaction. Existing analytical methods cannot capture the nonlinearity and complexity of seismic interactions between adjacent buildings and softened soil, while advanced numerical tools that can capture such complexities have not been validated. Consequently, liquefaction mitigation measures designed assuming no interaction between structures may perform poorly. To evaluate the appropriateness and effectiveness of a common mitigation strategy--prefabricated vertical drains--in urban environments, a series of experiments were conducted on a geotechnical centrifuge. Closely spaced, dissimilar, realistic model structures were placed on a layered liquefiable soil deposit and subjected to realistic earthquake motions. Mechanistic consequences of seismic coupling due to the use of drains around the shorter structure were evaluated. The results show that the use of drains around one structure may have drastic consequences for the performance of an adjacent unmitigated structure, even causing its collapse. Engineers and planners must consider integrated mitigation strategies in dense urban environments with the goal of improving performance in building clusters rather than individual buildings. [ABSTRACT FROM AUTHOR]

Pile foundations in earthquake-prone areas are subject to overturning moments in which the behavior is dependent on the fixity of the pile tips and characteristics of the stratigraphy of the formation into which the piles are embedded. Further, the bending moment caused by the overturning moment cannot be ignored because the bending moments resulting from the lateral loads and deformation do not cause significant differences in moments irrespective of pile tip fixity. Each model test consisted of four piles identified as Pile A, Pile B, Pile C, and Pile D as shown in Fig. [Extracted from the article]

An extensive suite of three-dimensional finite-element simulations was carried out to examine the response of pile-raft-soil systems under seismic excitation representative of far-field events. The numerical procedure was first validated by a series of seismic centrifuge tests performed mainly on 4 × 3 pile-raft systems embedded in soft clays and was subsequently extended to study the influence of various factors on the computed raft acceleration and maximum bending moment near the pile head. The factors considered were pile length, pile flexural stiffness, peak base acceleration, superstructural mass, soil stiffness, soil frictional angle, pile density, and soil-layer thickness. With the help of dimensional analysis, the results of the parametric studies were processed and interpreted using regression analysis to derive correlations for predicting the maximum pile-group bending moment and peak raft acceleration. Such correlations are highly useful in the practical seismic design of pile-raft systems embedded in soft soils, because they provide quick first-order predictions for making initial engineering judgments prior to performing more-detailed and rigorous numerical simulations. [ABSTRACT FROM AUTHOR]

A practically oriented analytical procedure for determining the dynamic stiffness and damping (impedance coefficients) of a laterally loaded pile in soil exhibiting different types of inhomogeneity with depth, is presented. To this end, an energy method based on the Winkler model of soil reaction in conjunction with pertinent shape functions for the deflected shape of the pile are employed. A new elastodynamic model for the wave field around a pile is also introduced. The method is self-standing and free of empirical formulas or constants. Dimensionless closed-form solutions are derived for (1) the distributed (Winkler) springs and dashpots along the pile; (2) dynamic stiffness and damping coefficients at the pile head; (3) active length, beyond which the pile can be treated as infinitely long; and (4) relative contributions to the overall head stiffness and damping of the soil and the pile media. Swaying, rocking, and cross swaying-rocking impedances are considered for parabolic, exponential, and multilayered inhomogeneous soil. The predictions of the model compare favorably with established solutions, while new results are presented. An illustrative example is provided. [ABSTRACT FROM AUTHOR]

The seismic response of underground reservoir structures is a complex soil-structure interaction problem that depends on the properties of the earthquake motion, surrounding soil, and structure. More experimental and field data of the response of these structures under different boundary conditions are needed to validate analytical and numerical tools. This paper presents the results of four centrifuge experiments that investigate the seismic performance of reservoir structures, restrained from rotational movement at their roof and floor, buried in dry, medium-dense sand and compacted, partially saturated, silty sand. This study focuses on the influence of backfill soil properties, cover, and slope on accelerations, strains, lateral distortions, and lateral earth pressures experienced by the buried structure. The structure to far-field acceleration spectral ratios were observed to approach unity with added soil confinement, density, and stiffness. Both dynamic thrust and accelerations on the structure showed a peak near the effective fundamental frequency of the backfill soil. The addition of a shallow soil cover and stiffness slightly increased seismic earth pressures and moved their centroid upward, hence slightly amplifying seismic moments near the base. The added stiffness, density, and apparent cohesion of the compacted site-specific soil did not influence the magnitude of dynamic earth pressures significantly but often moved their centroid upward. A sloping backfill reduced the earth pressures and bending moments near the top of the wall because of the reduced soil mass. The trends in the experimental results indicate that new analytical procedures and design guidelines are needed to account for the backfill soil conditions and ground motions for which these underground structures must be designed. [ABSTRACT FROM AUTHOR]

This paper presents an innovative grouted ground improvement pile alternative (biogrouted pervious concrete pile). Biogrouting is a potential ground improvement technique that utilizes soil bacteria to induce calcium carbonate (CaCO3) precipitation to cement soil particles. The most commonly investigated biogrouting method is microbial-induced carbonate precipitation (MICP). Previous large-scale applications of MICP have encountered practical difficulties including bioclogging, which results in a limited zone of cemented soil around injection points and heterogeneous distribution of CaCO3. The research presented in this paper focuses on evaluating the feasibility of MICP biogrouting of a limited soil zone surrounding permeable piles to improve their responses when subjected to axial compression loading. To investigate this, two instrumented pervious concrete piles with diameters of 76 mm and lengths of 1.07 m with and without MICP biogrouting were subjected to compression loading at the Soil-Structure Interaction (SSI) facility at Lehigh University, Bethlehem, Pennsylvania. The pervious concrete pile serves as an injection point during the MICP biogrouting. The mechanical responses of the pile and surrounding soil were analyzed, along with shear wave (S-wave) velocity, moisture content, and CaCO3 and ammonium contents of the surrounding soil. The results presented in this paper demonstrated that the limited MICP-improved zone around pervious concrete piles improved the load-displacement response, load transfer, and pile capacity under compression loading. [ABSTRACT FROM AUTHOR]

The results of fully coupled, three-dimensional (3D), nonlinear finite-element analyses of structures founded on liquefiable soils are compared with centrifuge experiments. The goal is to provide insight into the numerical model's capabilities in predicting the key engineering demand parameters that control building performance on softened ground for a range of structures, soil profiles, and ground motions. Experimental and numerical observations will also guide future analyses and mitigation decisions. The numerical model captured excess pore pressures and accelerations, the dominant displacement mechanisms under the foundation, and therefore building's settlement, tilt, and interstory drift. Both experimental and numerical results showed that increasing the structure's contact pressure and height=width (H=B) ratio generally reduces net excess pore pressure ratios in soil but amplifies the structure's tilting tendencies and total drift. The settlement response of a structure with a greater pressure and H=B ratio was also more sensitive to soil-structure-interaction induced forces, which could at times amplify on a denser soil with less softening. A denser soil profile also increased building's flexural drift in all cases by reducing excess pore pressures and rocking drift, while amplifying foundation accelerations and total drift. Numerical simulations captured these trends well. These experimental and numerical results point to the importance of taking into account a building's dynamic properties and overall performance in mitigation design. [ABSTRACT FROM AUTHOR]

This paper focuses on elastic stiffness parameters for axial, horizontal, and vertical motions of a pipeline relative to the seabed, with the aim of expressing these parameters in terms of fundamental elastic properties of the soil. Limited information exists in the literature on the axial elastic response of on-bottom pipelines, particularly for nonhomogeneous soil. Therefore, an approximate analytical approach was developed for axial stiffness, focusing on the case of shear modulus proportional to depth. The solution was then verified through numerical analysis. Further numerical analysis was carried out to obtain relationships for horizontal and vertical elastic stiffnesses of on-bottom pipelines. Finally, relationships among elastic stiffnesses were developed. Here recommendations are made for the selection of proper elastic stiffnesses in all three directions of motion. These recommendations allow consistent and rigorous modeling of elastic pipe-seabed interactions with application to the analysis of pipeline laying, buckling, walking, and on-bottom stability. [ABSTRACT FROM AUTHOR]

A series of centrifuge tests were performed to investigate the behavior of laterally loaded pile groups in improved and unimproved soft clay. The soil profile consisted of four lightly overconsolidated clay layers overlying a dense layer of sand. The pile groups had a symmetrical layout consisting of 2 × 2 piles spaced at 3.0 and 7.0 pile diameters (D). After improving the soft clay in situ using simulated cement deep soil mixing (CDSM), pile foundations were driven into the improved ground. Centrifuge tests revealed that CDSM is an effective method to increase the lateral resistance of pile foundations. The lateral resistance of the improved pile group at 7D spacing increased by 157%. Due to pile-soil-pile interactions, the lateral resistance in the 3D pile group increased by only 112%. In both improved and unimproved pile groups with 3D spacing, the leading row of piles carried larger loads and bending moments than the trailing row of piles. No group interaction effects were observed in all pile groups with 7D spacing. At very large deflections, cracks developed and tension failure occurred in the CDSM block of the improved 3D pile group. Values for p-multipliers were back-calculated and incorporated into a computer code to perform a parametric study on improved pile groups with 3D spacing. It was seen that for CDSM block depths greater than 9D, increases in lateral resistance are practically negligible. At deflections less than 8 cm, lateral resistance of the improved pile groups is not sensitive to undrained shear strength of the improved clay representing typical cement contents. [ABSTRACT FROM AUTHOR]

This study presents 3M, an analytical method to estimate the skin friction of bored piles in sands. It is based on the fundamental mechanic behavior of sands and keeps track of the major mechanisms occurring in the soil close to the pile during loading. These include the development of a shear band, its potential expansion as induced by soil dilatancy, and the ensuing increment of horizontal stresses owing to the restraining effect of surrounding soils. The resulting analytical equations are easy to apply and insert in a worksheet. The procedure to evaluate the shear band expansion is calibrated against results of direct shear tests at constant normal load, whereas the increment of horizontal stresses is evaluated by the closed-form solution for the expansion of a cylindrical cavity into a dilatant elastic-perfectly plastic medium. The effectiveness of the 3M method in predicting shaft friction has been checked against numerical results, centrifuge, and full scale pile load tests. Nevertheless, prior to use in design practice, preliminary validation is required with more well-documented experimental data from load tests on instrumented bored piles. [ABSTRACT FROM AUTHOR]

The nonlinear response of shallow foundations when subjected to combined loading has attracted the attention of the research engineering community over the last few decades, providing promising evidence for incorporation of such response in design provisions. Failure in the form of soil yielding or foundation uplifting may accommodate high ductility demand and increase the safety margins of the whole structure. However, increased permanent displacement and rotation may occur. This paper explores the concept of shallow soil improvement as a means to locally increase soil strength and thus limit rocking-induced settlement. Bearing in mind that the rocking mechanism is relatively shallow, failure may be contained in a soil layer of known properties that extends to a shallow depth beneath the foundation. The performance of a system in poor soil conditions, on an ideal soil profile, and on improved soil profiles was explored through a series of centrifuge tests at the Center for Earthquake Engineering Simulation at Rensselaer Polytechnic Institute. The shallow soil improvement, evaluated in terms of moment-rotation and settlement-rotation response, proved quite effective even when its thickness was limited to 25% of the footing width. Some interesting similarities between poor, improved and ideal systems were observed in terms of cyclic moment capacity, contact pressure at the soil-foundation interface, and soil-foundation effective contact area. It is shown that even when uplifting is substantial and only 25% of the footing surface remains in contact with the soil, behavior in all four examined cases is quite stable--an important finding in seismic design of rocking foundations. [ABSTRACT FROM AUTHOR]

However, there are many possible factors that affect a pile's stress, such as soil deformation, rotation constraint of a pile head, pile spacing effects, bending rigidity of a pile depending on axial loads, and vertical displacement of piles, as well as the horizontal reaction under combined loads. I agree that determining the stratigraphy and modulus of the various soil layers within which the pile is embedded and their characteristics are important for estimating the bending moment of the pile. [Extracted from the article]

The writers would like to thank the discussers for their discussion, providing analytical insights and practical considerations on the response of existing pipelines and tunnels to tunneling-induced settlements, and reply with four main comments: • The shear factor HT ht was presented to facilitate the description of the mechanical response of pipelines and tunnels in practical applications. • Concerning the observation that the published article is limited to (vertical) contact soil resistance, the writers agree with the discussers that it strictly applies to perfectly smooth pipeline/tunnel-soil interface conditions, considering either coupled or uncoupled vertical springs only for the soil model. Further research is needed for more sophisticated two-stage interaction models capable of considering both contact and frictional resistance of the soil in the context of pipeline or tunnel response to vertical and horizontal ground movements. [Extracted from the article]

To evaluate the effect of soil-foundation interaction on the earthquake response of structures, centrifuge tests were performed using an in-flight earthquake simulator. The test specimen was composed of a single-degree-of-freedom structure model, a shallow foundation, and subsoil deposits in a centrifuge container. The test parameters were the dynamic period of the structure model, the centrifugal acceleration level, and the type and level of input earthquake accelerations. The test results showed that the lateral forces of the structures were limited by the soil-bearing strength (i.e., ultimate moment capacity of the foundation) and the damping effect owing to the rocking motion of the foundation. Thus, even when the periods of the structures were close to the site periods, the lateral forces did not significantly increase. However, it should be noted that, because of the damping effect of the foundation, the maximum seismic lateral load of the structures exceeded the load statically determined by the soil-bearing strength. This issue should be addressed for the safe design of structures and members. In this test, the maximum damping ratio for rocking due to the rocking motion was estimated to be 0.31. [ABSTRACT FROM AUTHOR]