Layered Soil Deposits Research Articles

Torsion of end-bearing pile foundations in layered anisotropic geomaterials

ABSTRACT An analysis for the torsional dynamic response of end-bearing pile foundations embedded in a layered transversely isotropic geomaterial (soil/rock) is presented. The deformation of the transversely isotropic soil or rock is described by the method of separation of variables. The elasticity theory for a viscoelastic medium with frequency independent hysteretic material damping, and the Extended Hamilton’s Principle are utilised to derive the differential equations describing pile and soil motions. The differential equations are solved analytically in an iterative algorithm. The accuracy of the analysis is verified with existing studies reported in the literature for pile foundations embedded in a homogeneous and layered soil deposit. The effect of the degree of anisotropy on the pile-soil response – dynamic pile-head stiffness, distribution of pile rotation and torque with depth, dimensionless soil displacement function for various values of pile slenderness and pile-soil stiffness ratios in a homogenous soil deposit is investigated. Design charts of static pile-head stiffness in a homogeneous soil deposit for a wide range of pile-soil stiffness and pile slenderness ratios, and degree of anisotropy are also reported. The effect of soil layering for a pile embedded in a two-layered soil deposit is also studied.

Influence of spatial variability of soil shear-wave velocity considering intralayer correlation on seismic response of engineering site

Shear-wave velocity uncertainty significantly impacts seismic response analysis at engineering sites. Previous studies focused on the correlations of shear-wave velocities within soil layers. However, the influence of the vertical spatial variability of shear-wave velocity within individual soil layers was not considered. This study selected a typical Site Class II engineering site to investigate this influence based on the equivalent linear seismic response analysis method of layered soil deposits. Existing field test data on shear-wave velocity were used to discretize the shear-wave velocity within soil layers into a one-dimensional (1D) random field through covariance matrix decomposition and local average process theory. Monte Carlo simulations generated random shear-wave velocity profiles with different vertical correlation distances. Three artificial records with different earthquake return periods were used as input motions at the engineering bedrock for the 1D free-field model. Considering soil shear-wave velocity uncertainty, the peak shear strain increased by 19–27% with the input ground motion amplitude. Moreover, the site peak shear strain variability increased by 25–34% with the vertical correlation distance. The proposed 1D random field model effectively simulated the interlayer correlation and spatial variability of shear-wave velocity within soil layers, demonstrating its significance in seismic response analysis.

A MPM Lagrangian‐Eulerian hydrocode for simulating buried explosions in transversely isotropic geomaterials

AbstractShock waves in geological materials are characterized by a sudden release of rapidly expanding gas, liquid, and solid particles. These shock waves may occur due to explosive volcanic eruptions or be artificially triggered. In fact, underground explosions have often been used as an engineering solution for large‐scale excavation, stimulating oil and gas recovery, creating cavities for underground waste storage, and even extinguishing gas field fires. As such, hydrocodes capable of simulating the rapid and significant deformation under extreme conditions can be a valuable tool for ensuring the safety of the explosions. Nevertheless, as most of the hydrocodes are often formulated in an Eulerian grid, this setting makes it non‐trivial to track the deformation configuration of the materials without a level set. The objective of this paper is to propose the use of the material point method equipped with appropriate equation of state (EOS) models as a hydrocode suitable to simulate underground explosions of transverse isotropic geomaterials. To capture the anisotropic effect of the common layered soil deposits, we introduce a new MPM hydrocode where an anisotropic version of the Mie‐Gruneisen EOS is coupled with a frictional Drucker‐Prager plasticity model to replicate the high‐strain‐rate constitutive responses of soil. By leveraging the Lagrangian nature of material points to capture the historical dependence and the Eulerian calculation of internal force, the resultant model is capable of simulating the rapid evolution of geometry of the soil as well as the high‐strain‐rate soil mechanics of anisotropic materials.

Assessing the effect of input motion duration on seismic site responses of layered soil deposits using spectrally equivalent records

The characteristics of input motions at bedrock have a significant impact on the dynamic behavior of soils at various sites. This study aims to statistically analyze the conditions under which the long-duration (LD) seismic responses of layered soil deposits differ from those common short-duration (SD) responses. Furthermore, this study provides thresholds for the amplification prediction of sites where the differences caused by the duration effect are large enough to be practically significant. To investigate the duration effect of input motions, a series of LD and SD record pairs are assembled from earthquake databases, specifically focusing on records with VS30 > 500 m/s. Each pair of records is carefully selected to ensure that the amplitude and frequency content are equivalent. Subsequently, numerous site response simulations are conducted using the time-domain nonlinear method for a range of soil profiles under all selected records. The relative differences in spectral accelerations at the surface between LD and SD motions are subsequently evaluated. The results indicate that the occurrence of LD/SD response differences strongly depends on the site condition, selected frequency (or period), and intensity level of input motions. For smaller peak ground acceleration levels (PGAinput), both LD and SD input motions with equivalent spectral shapes yield consistent site responses. However, for larger PGAinput levels, significant differences emerge for frequencies >0.5 Hz, especially at softer sites. Finally, frequency-dependent thresholds of PGAinput with 20 % differences are proposed as the conditions in which the duration effect of input motions cannot be ignored in site response analysis.

Dynamic installation of torpedo anchors in slightly overconsolidated clay-overlaying-sand deposit

Torpedo anchor installation involves uncertain design and construction parameters, especially in layered soil deposits. Large deformation finite element and coupled Eulerian–Lagrangian (LDFE/CEL) analyses are performed in this study to elucidate the dynamic installation of torpedo anchors in an over consolidated clay-overlaying-sand deposit. The parametric analysis is conducted after model verification to explore the effect of upper clay layer thickness, anchor impact velocity, anchor submerged weight, soil properties and anchor geometric dimensions. The soil failure patterns and dynamic installation behaviour in the clay-overlaying-sand soil deposit are found to differ substantially from those in single-layer clay and sand deposits, which exhibit a squeezing flow pattern at the clay-sand soil layer interface. As the demarcation of the two velocity phases during the anchor penetration process (acceleration and deceleration phases) falls below the interface of two soil layers, the contribution of the internal friction angle of sand to the anchor final penetration depth exceeds that of the clay undrained shear strength. Based on intensive modelling data, an empirical method for predicting the anchor penetration depth in single and layered soil deposits is derived for engineering applications.

A meta-heuristic optimization-based approach for 3D simplified parametric analysis of embedded soil-foundation systems undergoing coupled horizontal-rocking vibrations

This paper presents a novel modeling approach based on meta-heuristic optimization for constructing adaptive lumped-parameter models to approximate the dynamic response of a shallow foundation in layered soil considering coupled horizontal and rocking vibrations. The developed model is adaptive to complexities of impedance functions for different types of layered soil deposits. The optimal parameters of the proposed model are computed using three optimization algorithms, with the forensic-based investigation outperforming the others and being chosen as the best optimization strategy for numerical investigations. A parametric study of foundation characteristics and soil properties on frequency response curves, including magnification factors and phase angle, is performed to comprehensively verify the proposed model’s appropriateness. The findings reveal that dynamic responses of the proposed simplified systems are perfectly consistent with those computed using existing impedances and worldwide-recognized software in both frequency and time domains. It shall be concluded that the proposed model is compatible with different soil profiles and more effective than existing models in approximating the unbounded behavior of layered soil. Furthermore, it offers great potential to implement the time-history analysis of interacting systems subjected to forced vibrations and seismic motions in commercial software based on the proposed model for engineering practice.

Effects of axial loading on dynamic response of laterally loaded single piles in liquefiable layered soil of Kolkata city considering nonlinearity of soil

In the present study, an advanced nonlinear finite-element based 3D numerical study has been carried out to investigate the effects of axial loading on dynamic response of soil-pile system in liquefiable layered soil deposits of Kolkata city. An advanced soil constitutive law based on multi-yield surface plasticity model implemented in fully-coupled u-p formulation is adopted for soil-fluid interaction and pore water pressure development reasonably. The present model is validated with the past experimental results. Then, a detailed systematic parametric study is performed for numerical simulation of pile failures in layered soil deposit under axial loading by taking into account various soil conditions, pile and ground motion parameters. It is seen that the depth of liquefaction (DL) is decreased from 11.5 to 1.5 m adjacent to the pile when the axial load on pile increases from 0 to 1327 kN. Parametric studies also reveal that the bending moment response of pile under axial loading can be higher in non-liquefiable condition, with reference to the liquefiable condition. The peak lateral displacement decreases by 83.2% in non-liquefiable condition and 60.71% in liquefiable condition due to decrease of axial load from 1327 to 0 kN. Also, peak bending moment developed in the pile decreases by 97.2% in non-liquefiable condition and 82.7% in liquefiable condition when the axial load reduces from 1327 to 0 kN. So, the designer should be considered both extreme scenarios for safe and economical design. Also, it is noticed that the buckling capacity of pile is improved significantly by using larger diameter pile and the bending capacity is increased by selecting higher grade of concrete. It is concluded that the bending and buckling failure mode may be avoided by selecting a suitable combination of material strength and pile geometry.

Seismic response of a layered soil deposit with inclusions

It is known that soil massifs can amplify or weaken seismic waves generated by earthquakes. Therefore, the problem of studying the impact of soil deposits on the passage of seismic waves is important in terms of the facilities in operation and the design of new earthquake-resistant objects. Soil deposits, which are allotted for building, are mainly layered. In addition, the materials in these layers are also significantly heterogeneous. To describe the dynamics of inhomogeneous soil massif, the model of an elastic continuum with oscillating non-interacting inclusions is used. Within the framework of this model, the resonant properties of multi-layered soil deposit are analyzed at the conditions of harmonic perturbations applied to the bedrock. On the basis of the solution to the boundary value problem concerning oscillations of the system subjected to the free surface and conjugation conditions on the boundaries between layers, it is derived the transfer function which characterizes the amplification of shear displacements by the layered system. Within the framework of problems on the oscillations of two- and five layered systems, the analytical studies were confirmed by numerical evaluations of transfer functions. In particular, using the built-in functions of the system «Mathematica», it is developed the numerical procedure for evaluating the frequency dependencies of amplification factor for layered Kelvin—Voigt media and media with oscillating inclusions. Moreover, for the two-layered system, it is analyzed the effect on the transfer function for the ratio of layers’ shear moduli and the ratio of the inclusions’ natural frequencies. It is also shown that the maxima in the transfer function correspond to the eigenfrequencies of the boundary value problem.The obtained results and the proposed approach to the study of the response of the layered inhomogeneous medium to vibrational perturbations can serve as a theoretical basis for earthquake-resistant design and construction.

Centrifuge and numerical modelling of the seismic response of tunnels in two-layered soils

Soil deposits inevitably affect the seismic performance of underground structures, and underground tunnels are commonly constructed on sites composed of layered soil deposits. In this study, dynamic centrifuge tests and numerical modelling are conducted to enhance the fundamental understanding of the kinematic soil-tunnel interaction for tunnels constructed in layered soils that consist of muddy clay and silty clay. The site seismic response and tunnel seismic performance between the centrifuge and numerical modelling are compared. The acceleration time histories, amplification factors of the input motions, and the Fourier spectra between free field and structural field are experimentally and numerically investigated. For comparative purposes, parametric studies of tunnels in a single muddy clay and a single silty clay using verified numerical modelling are carried out. In addition, the dynamic bending moment and axial forces obtained by centrifuge and numerical modelling are compared with the solutions predicted by analytical methods in prior studies.

Development and Use of a Minicone for Liquefaction Risk Evaluation in Layered Soil Deposits

AbstractThis paper shows and compares the experimental results obtained by using a standard cone (10 cm2) and a mini piezocone (2 cm2). Tests were carried out at Calendasco (Piacenza, Italy) in a...

Elastic stiffness of circular footings on clay overlying sand under general loading

Foundations are commonly situated on layered soil deposits, where the elastic stiffnesses may differ from values calculated using solutions for single-layer elastic media. This paper reports elastic stiffness coefficients for a rigid circular footing subjected to vertical, horizontal and moment loads bearing on a clay layer above a stiffer sand layer. Three-dimensional finite-element analyses considered various shear modulus ratios of top to bottom soil layers, as well as the thickness of the top layer below the footing. The elastic stiffnesses are presented as dimensionless coefficients and are bounded by published solutions for circular footings on a single-layer elastic half-space. Analytical expressions that capture the numerical results well are also proposed. The results can be used in the assessment of the elastic response of circular foundations on clay overlying sand, with applications in soil–structure interaction analyses of offshore structures among others.

Site-specific ground response analysis at a site in the affected area of the 2016 Pidie Jaya earthquake

Analytical models have demonstrated that they are able to simulate reasonably well the seismic motions at the ground level. The most widely used model is the equivalent linear approach. This equivalent linear model was used to compute the free-field response of Meureudu-Pidie Jaya, Aceh Indonesia’s soft soils during the 2016 Pidie Jaya earthquake. The model computes the ground response of horizontally layered soil deposits subjected to transient and vertically propagating shear waves through the one-dimensional soil column. Each soil layer is assumed to be homogeneous, visco-elastic and infinite in the horizontal extent. The equivalent linear estimation of soil properties is taken to express the nonlinearity of the soil’s shear modulus and damping values. These values are assumed to be a function of shear strain amplitude and determined by an iterative process that must be consistent with the level of the effective strain induced in each sub-layer. Starting with the highest shear modulus and a low damping value, the shear modulus and the damping ratio of each sub-layer are modified. The modification is based on the applicable relationship between both properties and the shear strain. The calculation is repeated until strain-compatible modulus and damping values converge within a tolerance of 1%. This research reveals the ground motions of Pidie Jaya’s soils. The results of the analysis are presented.

Evaluating liquefaction induced settlement of shallow foundation on layered soil deposit

The occurrence of liquefaction in saturated layered soil deposit underlying the shallow foundation can cause a wide range of problems from settlement to tilting of structures and foundations. It this study in order to evaluate the liquefaction induced settlement of shallow foundation on the ground surface of layered soil deposit, numerical studies have accomplished. The soil deposit involves a continuous saturated fine sand that is sandwiched between two dense continuous sand layers and the whole system had been subjected to a base shaking. The settlement of shallow foundation has been evaluated by considering the influence of relative density (Dr) of middle sand layer. The variation of relative density of middle continuous soil layer was examined by using the finite element method in OpenSEES software. It was observed that the liquefaction has occurred up to the depth of 6 m. In addition, by examining the slope of the settlement–relative density curve, it was found that in continuous fine sand layer for relative densities higher than 60% the effect of this layer on settlement of shallow foundation can be neglected, but for relative densities less than 60% the slope of curve is sharper and as a result, the shallow foundation is experienced higher settlement with 17 cm for Dr = 40% in compare with settlement 10 cm for a uniform soil deposit with Dr = 75%.

Effects of layering on triggering mechanisms of rainfall-induced landslides in unsaturated pyroclastic granular soils

Rainfall-induced landslides are widespread in shallow layered granular soil deposits. In many cases, slope instability is related to the decrease of suction during rainwater infiltration. However, the contrasts in the unsaturated hydraulic properties of the soils deeply affect the infiltration process, thus influencing slope failure. Coarse-textured soil layers embedded between finer ones may initially confine the process within the overlying finer layers, delaying the infiltration and eventually inducing lateral flow diversion. Nonetheless, depending on the state variables at the beginning of rainfall as well as on rainfall characteristics, the coarser layers may or may not have a positive effect on stability. The results of research based on advanced geotechnical characterization, physical and numerical modeling, and field monitoring have been analyzed to investigate the effects of layering on slope stability.

Geotechnical installation design of suction buckets in non-cohesive soils: A reliability-based approach

This study presents a probabilistic analyses of suction bucket installation in cohesionless soils. The spatial variability of soil properties is quantified using a representative survey dataset from practice. Vertical random field modelling is used to model cone resistance variability and probability density functions are fitted using drained parameter estimates. Conventional installation analysis methods are adapted for layered soil deposits. The effect of varying permeability is included through the incorporation of a finite element seepage model. Parametric uncertainties are considered through a Monte Carlo analysis and the results are interrogated through a variety of feasibility and sensitivity studies. Performing such an analysis allows a designer to gain insights into governing failure mechanisms and objectively quantify the impact of uncertainty regarding parameter estimates.

Seismic performance of outrigger\u2013belt truss system considering soil\u2013structure interaction

The focus of this study is to investigate the seismic behavior of outrigger-braced building considering the soil–structure interaction based on finding the best location of outrigger and belt truss system. For this purpose, a central outrigger-braced frame of a steel tall building is considered. A layered soil deposit underlied this frame and the resulting soil–structure system is subjected to seismic excitation. To analyze this system, direct method is employed in OpenSees. Also, elastic and in-elastic analyses are both considered and a comparison is made between current results and the results related to the system with fixed base. The best location of outrigger–belt truss system is determined by considering the maximum roof displacement, base moment and base shear with and without soil–structure interaction. It is shown that considering SSI affects the location of outrigger–belt truss system. Elastic analysis of both systems, namely with fixed base and with soil–structure interaction, showed that locating the belt truss at higher stories caused lower amounts of roof displacement.

Investigation of Soil Layers Stochasticity Effects on the Spatially Varying Seismic Response Spectra

The present study investigates the contribution of the stochasticity of a layered soil deposit on the seismic ground motion spatial variability via the random vibration theory. The seismic response evaluation is based on the 1-D shear wave propagation through random media. The soil layers stochasticity is introduced as spatial random fields of mass density and shear modulus of the soil deposit. The stochastic variation of these two parameters results in random natural frequency and damping ratio of an equivalent single degree of freedom oscillator modelling the soil deposit. Under the assumption of stationary Gaussian random process of the incident motion, the ground surface response spectra are obtained from the cross power spectral density of the total ground surface motion. The efficiency and the validity of the present approach are conducted via some applications. Numerical results showed that, the shape of the global coherency is controlled by that of the incident motion. The stochastic aspect of the soil layers causes disturbances in the surface motion and affects the coherency and the variability of the ground surface response spectra.

Kinematic bending of single piles in layered soil

A continuum solution is proposed for the kinematic bending of single piles embedded in a layered soil deposit. A displacement model is proposed to represent the displacement of the model of interest incorporating soil–pile interaction. The displacement functions and the attenuation function are obtained in the coupled form by means of Hamilton’s principle. Then an iterative procedure is applied to solve the coupled functions. The contributions of the proposed model are threefold: (1) The continuity of the Winkler springs is considered. (2) The effects of the inertial force of the surrounding soil on the kinematic response of the piles are taken into account. (3) An improved formula is proposed for the kinematic pile bending strain at the interface of two-layer soil deposit. A parametric study is performed to investigate the influence of the soil inhomogeneity on the kinematic bending of single piles. The results highlight that the stiffness discontinuity significantly influences the kinematic bending of single piles. There is a critical depth considering the effect of the pile head estimated as a non-dimensional length of the pile.

Mode-based equivalent multi-degree-of-freedom system for one-dimensional viscoelastic response analysis of layered soil deposit

Discrete models such as the lumped parameter model and the finite element model are widely used in the solution of soil amplification of earthquakes. However, neither of the models will accurately estimate the natural frequencies of soil deposit, nor simulate a damping of frequency independence. This research develops a new discrete model for one-dimensional viscoelastic response analysis of layered soil deposit based on the mode equivalence method. The new discrete model is a one-dimensional equivalent multi-degree-of-freedom (MDOF) system characterized by a series of concentrated masses, springs and dashpots with a special configuration. The dynamic response of the equivalent MDOF system is analytically derived and the physical parameters are formulated in terms of modal properties. The equivalent MDOF system is verified through a comparison of amplification functions with the available theoretical solutions. The appropriate number of degrees of freedom (DOFs) in the equivalent MDOF system is estimated. A comparative study of the equivalent MDOF system with the existing discrete models is performed. It is shown that the proposed equivalent MDOF system can exactly present the natural frequencies and the hysteretic damping of soil deposits and provide more accurate results with fewer DOFs.

Site response analysis for estimating seismic site amplification in the case of Banda Aceh - Indonesia

The city of Banda Aceh is potentially exposed to a significant seismic hazard of seismic site amplification. Estimation of seismic site amplification of the city is urgently required for any mitigation efforts as the city is founded on a thick, soft layer. This study aims to estimate seismic site amplification of Banda Aceh's soil. Analytical models have demonstrated that they can simulate reasonably well the seismic ground motions amplification. The most widely used model is the equivalent linear approach. The approach computes the ground response of horizontally layered soil deposits subjected to transient and vertically propagating shear waves through a one-dimensional soil column. As aforementioned, this study focuses on Banda Aceh-Indonesia which is founded on thick alluvium. Three actual historical time histories and three developed sub-surface models were used to estimate the seismic site amplification of Banda Aceh's soft soil. The used time histories are of 2012 M8.1 Simeulue earthquake, 2013 M6.0 Mane-Geumpang earthquake and 2013 M6.2 Bener Meriah earthquake. Three sub-surface models of three separate sites across the city of Banda Aceh were developed. The site response analysis results reveal the ground motions amplification of Banda Aceh's soils of up to 4.3. Thus, applying the seismic site amplification for structural design at Banda Aceh can be further works.