Non-liquefiable Soil Research Articles

Numerical analysis of the tunnel uplift behavior subjected to seismic loading

Seismic loading has always been a major concern for any engineering structures, and thereby, underground facilities (e.g., tunnels) are not exceptional. It is due to the seismically induced uplift and instability of tunnels caused by the large deformation of liquefiable soils. Therefore, the tunnel uplift behaviors subjected to seismic loading are always taken into account in any designing stages of tunnels. This study's main goal was to evaluate how a tunnel buried in liquefiable and non-liquefiable soils would behave when subjected to seismic stress. Seismic and liquefaction potential assessments of the soils surrounding the tunnel were carried out using the finite-element method. In this study, PM4sand, an advanced constitutive model was adopted in all finite-element models. In addition, the uplift displacement and excess pore pressure of liquefiable soils were studied, under a typical earthquake. Investigations were also conducted into how the thickness of the non-liquefiable soil affected seismic loading, tunnel uplift displacement, and the buildup of excess pore water pressure. As a result, during the earthquake, liquefaction was triggered in most parts of the sand layer but not in the clay layer. In addition, the tunnel uplift displacement was triggered due to the relative motion and interaction at both sides of the tunnel. In addition, this study found that the thickness of the non-liquefiable soil layer (sand layer) had a significant impact on the build-up of excess pore water pressure and, consequently, the tunnel uplift displacement. The uplift displacement and excess pore water pressure build-up were higher the thinner the non-liquefiable layer was.

Nonlinear Solid–Fluid Coupled Seismic Response Analysis of Layered Liquefiable Deposit

A seismic response analysis of layered, liquefiable sites plays an important role in the seismic design of both aboveground and underground structures. This study presents a detailed dynamic site response analysis procedure with advanced nonlinear soil constitutive models for non-liquefiable and liquefiable soils in the OpenSees computational platform. The stress ratio controlled, bounding surface plasticity constitutive model, PM4Sand, is used to simulate the nonlinear response of the liquefiable soil layers subjected to two seismic ground motions with different characteristics. The nonlinear hysteretic behavior of the non-liquefiable soil under earthquake excitations is captured by the Pressure Independent Multi Yield kinematic plasticity model with a von Mises multi-yield surface. The soil elements are modelled utilizing the solid–fluid fully coupled plane-strain u-p elements. The seismic response of the layered liquefiable site in terms of the development of excess pore water pressure, acceleration, ground surface settlement, and stress–strain and effective stress path time histories under two representative earthquake excitations are investigated in this study. The numerical results indicate that both the characteristics of ground motions and the site profile have a significant influence on the dynamic response of the layered liquefiable site. Under the same intensity of ground motion, the loose sand layer with a 35% relative density is more prone to liquefaction and contractive deformation, which causes irreversible residual deformation and vertical settlement. The saturated soil layer can effectively filter the high-frequency components and amplify the low-frequency components of ground motions. Moreover, the liquified site produces a 40% post-earthquake consolidation settlement after the excess pore pressure dissipation.

Sıvılaşan Zeminlerde Kazık Davranışına Dair Parametric Bir Çalışma

Liquefaction in saturated sandy soils under cyclical loads has a significant part in the structural damage cases. Pile foundations, used for soils with bearing capacity problems, might get exposed to various liquefaction-based damages. The finite element program FLAC2D is utilized to understand the pile behavior in liquefied soils under dynamic loads. The 1999 Kocaleli earthquake record was used in the numerical analysis for a single pile element in the layered soil profile with liquefied and non-liquefied soil. The pile-head of the model used in the layered soil sample was left free for rotation. Calculations for a single pile profile where axial load and horizontal load are affected simultaneously were performed by considering both the kinematic and inertial effect. Finite difference analyzes were performed by changing the embedded lengths of pile socket according to the existence and absence of a non-liquefying crust layer on the liquefied soil in the layered soil profile. As the results of the pile-head displacement and maximum moment value output were assessed.

Seismic resilience of extra-large LNG tank built on liquefiable soil deposit capturing soil-pile-structure interaction

Assessment of seismic resilience of critical infrastructure such as liquefied natural gas (LNG) storage tanks, is essential to ensure availability and security of services during and after occurrence of large earthquakes. In many projects, it is preferred to build energy storage facilities in coastal areas for the ease of sea transportation, where weak soils such as soft clay and loose sand with liquefaction potential may be present. In this study, three-dimensional finite element model is implemented to examine the seismic response of a 160,000 m3 full containment LNG tank supported by 289 reinforced concrete piles constructed on liquefiable soil overlaying the soft clay deposit. The seismic soil-structure interaction analysis was conducted through direct method in the time domain subjected to the 1999 Chi-Chi and the 1968 Hachinohe earthquakes, scaled to Safe Shutdown Earthquake hazard level for design of LNG tanks. The analyses considered different thicknesses of the liquified soil deposit varying from zero (no liquefaction) to 15 m measured from the ground surface. The key design parameters inspected for the LNG tank include the acceleration profile for both inner and outer tanks, the axial, hoop and shear forces as well as the von Mises stresses in the inner tank wall containing the LNG, in addition to the pile response in terms of lateral displacements, shear forces and bending moments. The results show that the seismic forces generated in the superstructure decreased with increasing the liquefied soil depth. In particular, the von Mises stresses in the inner steel tank exceeded the yield stress for non-liquefied soil deposit, and the elastic–plastic buckling was initiated in the upper section of the tank where plastic deformations were detected as a result of excessive von Mises stresses. However, when soil liquefaction occurred, although von Mises stresses in the inner tank shell remained below the yield limit, localised stress concentrations were observed in the lower section of the tank near the base, increasing the risk of the elephant foot buckling. The lateral displacements, shear forces and bending moments in the piles increased with increasing depth of the liquefied soil. Indeed, increasing the pile lateral displacement amplified the bending moment at the pile head, thus resulting in increases in the pile bending moments especially when the liquefied soil depth exceeded one third of the entire soil deposit. In particular, the bending moment at the pile head exceeded the yield moment capacity of the pile and subsequent plastic hinges were formed. Moreover, when the thickness of the liquefied soil was more than half of the entire soil depth, the mobilised bending moments in the piles exceed the ultimate moment capacity of the pile and thus total failure of the piles were observed. In addition, in the absence of liquefied soil layer, the inertial interaction had a dominant impact on the pile response in this study. However, with increasing the thickness of the liquefied layer, further loads were developed in the piles due to amplified kinematic interaction, while the inertial interaction-induced loads decreased.

A Simplified Approach of Design Pile Foundation on Liquefiable Soil in India

In India piles are designed as per IS 2911:2010 (Part 1) for different soil conditions considering all the load criteria. But there is no such provision in Indian Standard Codes for designing piles in potentially liquefiable soils. In this paper, the design of pile foundation in liquefiable soil is discussed. The provisions for design of pile foundations in liquefiable soil from different codes of practice from different countries are studied and the design approaches for the same are discussed based on those studies (Puri et al. 2008). The load bearing capacity of a pile in liquefied soil and non-liquefied soil is made based on the force equilibrium approach. A standardize graph which may be useful for practicing engineers has been plotted. Further, a comparative study is made based on the force equilibrium approach in Indian conditions.

The slenderness ratio effect on the response of closed-end pipe piles in liquefied and non-liquefied soil layers under coupled static-seismic loading

AbstractThis study presents the findings of a 3D finite element modeling on the performance of a single pile under various slenderness ratios (25, 50, 75, 100). These percentages were assigned to cover the most commonly configuration used in such kind of piles. The effect of the soil condition (dry and saturated) on the pile response was also investigated. The pile was modeled as a linear elastic, the surrounded dry soil layers were simulated by adopting a modified Mohr-Coulomb model, and the saturated soil layers were simulated by the modified UBCSAND model. The soil-pile interaction was represented by interface elements with a reduction factor (R) of 0.6 in the loose sand layer and 0.7 in the dense sand layer. The study was compared with the findings of 1g shaking table tests which were performed with a slenderness ratio of 25. In the validation case, there was a clear correlation between the laboratory findings and the numerical analyses. It was observed that the failure mechanism is influenced by the soil condition and the slenderness ratio to some extent. Under the dry soil condition, no base pile deformation was observed; However, tip pile movement was observed under the saturated soil condition with pile slenderness ratios of 25 and 50. The findings of this study are also aimed to include an approximation of the long-term deformations at the ground surface which has experienced shaking.

Buckling analysis of pile foundation in liquefiable soil deposit with sandwiched non-liquefiable layer

Many past earthquakes have shown failure of structures with pile foundations attributed to liquefaction. Various experimental tests have also shown that buckling is one of the credible reasons for the failure of such pile foundations, which gets insignificant lateral support due to seismic liquefaction of surrounding soil. In nature, liquefiable and non-liquefiable soil can occur in alternate layers. However, while estimating the buckling capacity of a pile, there are no specific guidelines available, to the best of the author's knowledge, to reasonably estimate its buckling capacity considering the effect of sandwiched non-liquefiable layer. Some studies recommend to ignore the sandwiched non-liquefiable layer present within a liquefiable deposit and consider it as a full liquefiable layer, which can become too conservative in many situations when both the strength and the depth of non-liquefied sandwiched soil layer are high.In the present work, a rational method of estimating the buckling capacity of pile foundation in liquefiable soil with a sandwiched non-liquefiable layer is proposed through a detailed numerical investigation. The developed numerical model (using Beam on Non-linear Winkler Foundation approach) is validated against the centrifuge results. The model considers the initial imperfection of pile and material nonlinearity of pile and soil. The P-delta effect is also considered in the analysis. Detailed parametric study for major influential parameters on the buckling capacity of the pile foundation has been considered in terms of (a) sandwiched non-liquefiable soil layer's type, thickness, and position, (b) pile length above the ground level, and (c) liquefiable soil's initial relative density and thickness. Based on this study, an effective length factor (β) has been introduced, which can be easily used in standard Euler's buckling equation to find out the buckling capacity of the pile in such layered soil profile. A simple chart has been developed for β, and a step-wise methodology has been proposed with explanatory examples for the estimation of buckling capacity of pile foundation in liquefiable soil having sandwiched non-liquefiable layer, with reference to various influential parameters.

Seismic behaviour of piles in non-liquefiable and liquefiable soil

This paper investigates the nonlinear soil–pile–structure interaction employing three-dimensional nonlinear finite element models verified with the results of large-scale shaking table tests of model pile groups-superstructure systems. The responses of piles in both liquefiable and non-liquefiable soil sites to ground motion with varying intensities were evaluated considering both kinematic and inertial interaction. The calculated piles and soil responses agreed well with the responses measured during the shaking events. The numerical models correctly predicted the different pile deformation modes that were exhibited in the experiments. The finite element analysis was then employed to perform a parametric study to evaluate the kinematic and inertial effects on the piles' response, considering different ground motion Intensity and piles characteristics. It was found that the bending moment of piles in the liquefiable site increases significantly, compared to the non-liquefiable site, due to the loss of lateral support of the liquified soil, and the maximum bending moment occurs at the interface between the loose and dense sand layers. The inertial interaction contributes the most to the bending moments at the pile top and the interface between the top clay and liquefied loose sand layers. For piles with a larger diameter, the bending moment due to kinematic interaction increases significantly, and the bending moment distribution corresponds to short (rigid) pile behaviour. In addition, the piles at the saturated site displace laterally as a rigid body during strong ground motions because the pile base loses the lateral support due to the soil liquefaction. Finally, the kinematic interaction effect becomes more significant for piles with higher elastic modulus.

Seismic axial behaviour of pile groups in non-liquefiable and liquefiable soils

This paper investigates the axial load transfer during seismic events for pile groups installed in loose and dense sand layers. The analysis was conducted employing three-dimensional (3D) nonlinear finite element models (FEM) that were validated using the results from shaking table tests of a model superstructure supported by a pile group installed in saturated (liquefiable) and dry (non-liquefiable) soil profiles. The FEM was employed to explore the axial load transfer at the liquefiable and non-liquefiable tests. The results of the liquefiable test demonstrated that the excess pore water pressure and associated liquefaction during the shaking caused dramatic decrease in the shaft friction resistance. Nonetheless, positive shaft friction was observed through the loose sand layer until the soil becomes fully liquefied. In addition, the end bearing forces decreased dramatically, and the pile exhibited excessive settlement, which mobilized additional end bearing resistance. At the non-liquefiable test, the pile experienced compression and tension loading cycles, but the loads were less than its static capacity. The effects of ground motion intensity, pile diameter, and thickness of the loose sand layer on the load transfer mechanism were also evaluated. It was found that as the pile diameter increased, higher excess pore water pressure developed in the dense sand, which reduced the bearing pressure. Also, as expected, the reduction in shaft resistance was higher as the thickness of the loose (liquefiable) sand layer increased, especially for piles with a small diameter. For the non-liquefiable soil, the strain in the soil increased for larger pile diameters, and consequently, the bearing forces decreased but later increased as the pile settlement mobilized higher resistance.

Effect of soil permeability on soil–structure and structure–soil–structure interaction of low-rise structures

Earthquake-induced soil liquefaction can generate excessive damage to building structures due to significant reduction in soil effective stress. With increasing urbanisation and population growth, the performance of closely spaced buildings, such as those in towns and cities, is of greater concern where structure–soil–structure interaction (SSSI) may occur in conjunction with full or partial liquefaction. This study investigates the seismic performance of isolated and adjacent structures built on shallow foundations on soils of different permeability (i.e. with different amounts of drainage and therefore generating different amounts of excess pore water pressure) using a combination of dynamic centrifuge modelling and finite-element modelling. The results demonstrate that the reduction in free-field ground surface intensity measure (specifically, Housner intensity) due to increasing liquefaction can be correlated to an index which is the normalised integral of excess pore pressure ratio (ru) with depth. This index can express the amount of liquefaction uniquely, even when full liquefaction occurs to only partial depth, or where excess pore water pressures are increased but below the level of full liquefaction at all depths. This underlying correlation means that structural demand reduction (e.g. reduction in inter-storey drift ratio) with liquefaction (SSI effect) can be linked to either: (a) the ru–depth index; (b) the depth of the liquefaction front, which can be estimated from a liquefaction triggering analysis; or (c) the ground surface intensity amplification/attenuation in the free field from the results of one-dimensional free-field soil column analyses. Where there are adjacent structures, a strongly beneficial SSSI effect on co-seismic settlement and a detrimental effect on drift in non-liquefied soil, as observed in this and previous studies, reduced towards a null effect in both cases with increased liquefaction, with liquefaction appearing to isolate the structures from each other (at least for the configuration considered herein). This has also been linked to the amount of amplification/attenuation of surface ground motion in the free field (or amount of liquefaction) as a simple indicator of the likely importance of SSSI effects in liquefiable soil.

An extended probabilistic demand model with optimal intensity measures for seismic performance characterization of isolated bridges under coupled horizontal and vertical motions

Intensity Measures (IMs) provide the relationship between Engineering Demand Parameters (EDPs) and seismic hazard characteristics for different structures and hence, their role in performance-based bridge design is significant. A few studies have investigated the optimal IMs for bridges under horizontal ground motions, however, detailed studies to explore the optimal IMs for isolated-bridges under the coupled vertical and horizontal records are very rare. This paper presents a procedure for the selection of optimal IMs for seismic-isolated bridges under the combined strong Horizontal Component (HC) and Vertical Component (VC) seismic excitations. Soil-Structure-Interaction (SSI) effects, the high level of uncertainties for soil properties, uncertainties for structural and geotechnical issues and advanced plasticity model for non-liquefied soil are included to explore the optimal vector-valued IMs. Four individual situations are considered to investigate the geometry effects on the selected optimal IMs. Optimal IMs criteria including efficiency, practicality, proficiency and sufficiency are investigated and developed to achieve a set of optimal vector-valued IMs for critical EDPs: drift ratio, pile-cap displacement and bearing displacement, which are affected by both HC and VC in isolated Soil-Pile-Bridge (SPB) systems. The results show that velocity-related IMs: peak ground velocity (PGVH), Housner spectrum intensity (HIH) and root mean square of velocity (VRMSH) are optimal IMs as representative of HCs. In addition, structure-dependent spectral IMs: vertical spectral acceleration at T = 0.2 s ( $${\text{S}}_{\text{a}0.2}^{\text{V}}$$ ) and square-root-of-the-sum-of-square of vertical spectral acceleration at the first and second vertical periods ( $${\text{S}}_{\text{a}}^{\text{V}}\left({\text{T}}_{\text{s}}\right)$$ ) are the appropriate optimal IMs as representative of VCs. However, the displacement-related IM, peak ground displacement of HCs (PGDH), may be treated as optimal IMs for SPB system supported by inclined pile foundations to investigate pile-cap displacement. In addition, the sufficiency term is investigated extensively with respect to seismological parameters.

Understanding of subsurface conditions controlling flow liquefaction occurrence during the 2018 Palu earthquake based on resistivity profiles

The 7.4 Mw earthquake on 28th September 2018 in Palu City triggered a flow liquefaction phenomenon in the Balaroa and Petobo areas, contributing to significant casualties and building damage. This paper presents the results of a liquefaction study to map subsurface conditions in these areas using the multi-electrode resistivity method with the dipole-dipole configuration. The objective of this study is to understand factors controlling the flow liquefaction phenomenon. Based on the interpretation of 2-D resistivity images, the liquefied soil layers are characterized by lower resistivity values than the non-liquified layers. These contrasts of resistivity values form a gently sloping boundary between the liquefied and non-liquefied soil layers. The resistivity image perpendicular to the flow direction indicates the presence of a subsurface basinal morphology in the Balaroa area, suggesting that a shallow groundwater zone is present within the liquefiable soil layer. Thus, the subsurface topographical condition is the main governing factor of flow liquefaction phenomena during the 2018 Palu earthquake.

Shaking table testing of two single piles of different stiffnesses subjected to liquefaction-induced lateral spreading

Lateral spreading is the main cause of pile foundation damage in liquefaction-prone areas during earthquakes. A soil profile in which a non-liquefied soil is on top of a liquefied soil is a critical design scenario. To investigate the influence of lateral spreading on pile responses in this type of soil profile, a shaking table test was performed on two single piles in the ground with a 2° slope. Considering different pile stiffnesses, an aluminum pile (Al pile) and a polypropylene pile (PP pile) were tested. The piles were embedded in multilayered soil comprising a clay layer sandwiched between dry sand above and saturated sand below it. The two piles had considerably different displacement and moment responses to an input motion based on a 1999 Taiwan Chi-Chi earthquake record. The experimental lateral spreading soil displacement profile approximated the cosine profile proposed by Tokimatsu and Asaka. Compared with the upper non-liquefied soil, the magnitude of the lateral spreading pressure of the liquefied soil was small. The experimental lateral spreading pressure from the non-liquefied soil layer was approximately 2.1 and 4.5 times Rankine's passive earth pressure for the PP and Al piles, respectively. The difference between the derived p-y curves of the Al and PP piles for the non-liquefied soil layer may have been due to the contribution of downhill soil reactions. To reflect the influence of pile stiffness, both the downhill and uphill p-y curves of the non-liquefied crust layer should be considered in lateral spreading analysis.

Dynamic behavior of a breakwater triggered by seepage, earthquake action, and wave pressure

The dynamic stability analysis of the breakwater is investigated under the actions of seepage, earthquakes, and waves. The research indicates that a non-liquefiable layer is a useful way to prevent the adverse effects of soil liquefaction and to improve the stability of the breakwater. Because of a covering layer of thicker non-liquefied soil, the breakwater will not undergo large liquefied deformation under the coupled actions of seepage, earthquakes, and waves. The dynamic soil pressure response on both sides of the breakwater is more noticeable as the soil depth increases.

Numerical analysis of seismic performance of inclined piles in liquefiable sands

Previous post-earthquake damage investigations have indicated that inclined piles have either performed satisfactorily or poorly during seismic events; hence their effectiveness is still questionable. This paper aims to clarify the performance of inclined piles installed in the liquefiable ground during earthquakes. To this end, a three-dimensional finite element model has been developed using the OpenSees program. The effects of soil-pile interaction have been evaluated by applying interface elements between the soil and the pile. Subsequently, the behavior of sand is described with the help of a multi-yield-surface plasticity constitutive relation. By changing the pile configurations and the amplitude of loading patterns, a series of parametric analyses are conducted, and the system responses (i.e., soil, cap, and pile responses) are compared. The results clearly illustrate that the presence of inclined piles has a beneficial effect on the dynamic response of the soil-pile-cap system in non-liquefied soils and of the cap response in liquefied soils. However, highly detrimental effects of inclined piles on the soil and pile responses have been observed as the soil liquefies. Based on the results, the conditions wherein inclined piles may perform satisfactorily or poorly are highlighted.

Large shaking table tests of pile-supported structures in different ground conditions

This study investigates the dynamic response of structures and the effect of soil-structure interaction for flexible structures supported by pile foundations located in non-liquefiable and liquefiable sites as well as a rigid foundation. A series of large-scale shaking table experiments were performed, and accelerations and dynamic displacements of model superstructures were recorded during the shaking events. It was observed that the structure in non-liquefiable soil deposits had the highest accelerations due to the amplification of ground motion within the soil. On the other hand, the accelerations of the structure in liquefied site was small due to the increased dissipation of seismic energy. The structures founded on soil experienced residual (permanent) lateral displacements, with the permanent lateral displacement and tilting of the structure in the liquefied site being much larger. The structure on rigid foundation (i.e. foundation on rock or fixed base) experienced high accelerations and oscillatory displacement as the seismic energy could not be dissipated. Therefore, structures in liquefiable soil are prone to overturning damage due to failure of their foundations. Furthermore, the base shear force of the structure in the non-liquefied site was significantly larger than that in the liquefied site and fixed-base, indicating it would be more susceptible to shear failure. On the other hand, the fixed-base structure experienced relatively large acceleration and dynamic displacement responses, which indicates increased seismic demands on its structural members.

Seismic performance of pile group-structure system in liquefiable and non-liquefiable soil from large-scale shake table tests

Observations from previous strong earthquakes reported severe damage of piles installed in different soils, particularly liquefiable saturated sand deposits. This paper examines the seismic performance of pile group-structure system in liquefiable and non-liquefiable sand deposits using large-scale shaking table tests, and discusses the possible failure modes of pile foundation in liquefied site and non-liquefied site. Accelerations and strains of piles, and lateral displacements and accelerations of model soil were recorded. The measured piles’ accelerations and strains were used to calculate their bending moment profiles during the shaking, while the soil dynamic shear strain – shear stress curves were obtained using measured soil accelerations. In addition, characteristics of dynamic responses for liquefied and non-liquefied sites were evaluated by comparing trends of acceleration and lateral displacements of model soil. Furthermore, the failure mode for pile foundations in liquefiable and non-liquefiable site were elucidated from the observed responses of the structure-pile foundation. It was found that (1) the stiffness of liquefied site degraded more significantly (compared to non-liquefies site) due to increase in pore water pressure, but the non-liquefied site experienced higher amplification of acceleration; (2) large lateral spreading did not occur in the liquefiable site experiment due to the horizontal surface of the underlying stable (non-liquefied) soil; (3) profiles of pile bending moment differed for liquefied and non-liquefied sites for the same excitation, which impacted the permanent deformation of the piles. The test results in this study can be used to validate related numerical models.

Insight into the Effect of Fine Content on Liquefaction Behavior of Soil

The present paper presents different approaches which includes plasticity based criteria that helps in distinguish between liquefiable and non-liquefiable soils deposits having fine content. A brief review of the previous work has been mentioned to emphasise on the need of new parameters for liquefaction susceptibility of clayey soils. Clay content, liquid limit and water content are considered as key parameters that helps in liquefaction assessment. Several recommendations proposed by prominent researchers are described here to present wide range of plasticity index, liquid limit and other parameters that affects liquefaction behaviour of clayey soil significantly. But the differences in the range of plasticity index leads to confusion and misperception in determination of liquefaction susceptibility of fine grained soil. One of the high seismic zone site is analyzed using different approach which consider fine content of soil mass. It is found that for a better and proper segregation of the layers Bray and Sancio criteria may be adopted which uses plasticity as one of its input parameter and clearly differentiate site in between liquefiable, non-liquefiable and sites that may liquefy i.e. moderately liquefiable. This summarizes that plasticity is one of the significant criteria which draws a clear differentiating line between liquefiable and non-liquefiable soil deposits.

P-y Curves of 2x2 pile group in liquefiable soil under dynamic loadings

The seismic analysis of pile groups subjected to lateral and axial loads is often implemented separately. As a result, the calculated bending moment and deflection are found to be nonrealistic in nature, as compared with conditions where a combined analysis is carried out. In reality combined loadings are encountered in almost all situations and the occurrence of pure loadings (either lateral or vertical) is either nonexistent or scarce. In the present study, the numerical analysis of a 2 × 2 pile group under the action of combined loadings (lateral load, vertical load, and seismic ground motions) and embedded in a layered soil is carried out using the FLAC3D computer program. The liquefiable soil layer is modeled using the Mohr-Coulomb with Byrne constitutive model, while the non-liquefiable soil layers are modeled with the conventional Mohr-Coulomb constitutive model. The pile group is considered an elastic model. The proposed numerical model is validated with the existing dynamic centrifuge test results and good agreement between the results is observed. Finally the dynamic P-y (P denotes the lateral load applied at the pile cap and y is the lateral pile group deflection at the pile head) curves are generated for different combinations of vertical load, lateral load, and input seismic ground motions in liquefiable and non-liquefiable soil. It is observed that for a constant vertical load (V) having a magnitude equal to 0.50 times the ultimate pile load capacity (0.50Vult), the pile group deflection increases by 36% when the lateral load increases from 300 to 900 kN, while the increase is by 48.5% for V = Vult and for the same increase in the lateral load. Similarly 2001 Bhuj and 2011 Sikkim motions caused an amplification of deflection by 8.4 and 9 times, respectively. The influence of vertical loads increases the pile head displacement and should be considered for determining the dynamic P-y curves. The proposed dynamic P-y curves will be beneficial to geotechnical engineers for understanding the qualitative response of pile groups under combined loading conditions.

On the deep soil mixing method in the mitigation of liquefaction-induced bearing capacity degradation of shallow foundations

ABSTRACT Bearing capacity degradation in shallow foundations due to subsoil liquefaction is not a new challenge in earthquake geotechnical engineering. Thus far, limited mitigation measures against this problem were suggested in the literature. In this paper, mitigation of liquefaction-induced bearing capacity degradation of shallow foundations using Deep Soil Mixing (DSM) method was investigated numerically. A 3D finite difference model has been developed via FLAC3D. It was explored whether liquefaction effects on static and seismic bearing capacity of shallow foundations were diminished, and may be effectively overlooked, for DSM column diameter and length and also shallow foundation width variation. It was found that an artificial non-liquefiable soil layer made by DSM method improves the seismic bearing capacity of shallow foundations remarkably. Therefore, in terms of excess pore water pressure generation decreases and bearing capacity ratio increases. It was also concluded that by increasing the diameter and length of the DSM columns, the seismic bearing capacity of shallow foundations increases. However, as shallow foundation width increases, along with an increase in DSM column diameter and length, the performance of DSM columns and accordingly shallow foundation decreases.