Dynamic Soil Behavior Research Articles

Implementation of a hydromechanical elastoplastic constitutive model for fully coupled dynamic analysis of unsaturated soils and its validation using centrifuge test results

Prediction of unsaturated soil behavior during earthquake loading has received increasing attention in geotechnical engineering research and practice in recent years. Development of a fully coupled analysis procedure incorporating a coupled hydromechanical elastoplastic constitutive model for dynamic analysis of unsaturated soils has, however, been limited. This paper presents the implementation of a coupled hydromechanical elastoplastic constitutive model into a fully coupled dynamic analysis procedure and its validation using a centrifuge test. First, the fully coupled finite element equations governing the dynamic behavior of unsaturated soils with the solid skeleton displacement, pore water pressure, and pore air pressure as nodal unknowns are briefly presented. The closest point projection method is then utilized to implement the coupled hydromechanical elastoplastic constitutive model into the finite element equations. The constitutive model includes hysteresis in soil–water characteristic curves, cyclic elastoplasticity of the solid skeleton, and the coupling mechanisms between the SWCCs and the solid skeleton. Finally, the analysis procedure is validated using the results from a dynamic centrifuge test on an embankment constructed of compacted unsaturated silt subjected to base shaking. Reasonable comparisons between the predicted and measured accelerations, settlements, and deformed shapes are obtained.

Seismic response and damage analysis of underground structures considering the effect of concrete diaphragm wall

This paper investigates the effect of concrete diaphragm wall on the seismic response of underground structures using numerical simulation. The seismic response of a two-story subway station supported by concrete diaphragm walls located in Nanjing, southeast China was analyzed. A finite element model was developed to simulate the soil-diaphragm wall-underground structure interaction during earthquakes. This model simulated the nonlinear dynamic behavior of soils using a visco-plastic model and concrete damage using a plastic-damage constitutive model. The effect of the diaphragm wall was explored related to the burial depth of the subway station. The simulation results showed that during a strong earthquake, the diaphragm wall reduced the lateral deformation of the lower story of the structure. However, the effect was very limited to the upper story of the structure. In contrast, during a small earthquake, the diaphragm wall increased the lateral deformation of the upper story of a deeply buried structure. The concrete diaphragm wall also increased the settlement of a deeply buried structure. The earthquake damage to the underground structure increased with the increase of the burial depth. The seismic tensile damage to the diaphragm wall was found adjacent to the invert of the structure. The damage to the diaphragm wall increased the uplift potential of a shallowly buried structure during earthquakes. Findings from this paper provide guidance to the seismic design of large underground structures buried in similar grounds.

Effect of the confining method on the cyclic undrained behaviours of sand

Cyclic Simple Shear (CSS) test is widely considered to best simulate vertically propagating shear waves and in-situ stress conditions. CSS test is always performed to generate reliable laboratory data for development and calibration of models in Geotechnical Earthquake Engineering design. Soil sample is laterally confined to simulate in-situ stress condition (k0). Stacked rings (SR) and Wire-reinforced membranes (WR) are the two widely used confining methods. Studies have been conducted on the effect of the two confinement methods on the static behavior of soil. In this paper, the effect of the SR and WR confinement methods on the dynamic soil behavior is studied. Undrained cyclic stress controlled tests were performed on loose and medium dense samples of Ottawa sand laterally confined by SR and WR. The comparison of the tests results showed that the dynamic behavior of the two confinement methods is mostly similar.

Modelling approach for soil displacement in tillage using discrete element method

The majority of studies dedicated to the dynamic behaviour of agricultural soils are basically focused on prediction of physical conditions within the soil-tool interface whereas the dynamic soil response, such as soil displacement, has not attracted sufficient attention. Considering its importance for engineering applications, the objective of the presented study was to develop a modelling approach to study the soil displacement due to soil interaction with operating tool during sweep cultivation. The developed approach employs the similarity criteria to account for the effect of scaling-up soil particle sizes on model quality and combines (i) an empirical study of soil displacement during a sweep operation and (ii) related numerical simulations using a discrete element model. Soil displacement for three different soil types in soil bins was measured using a tracer methodology. The discrete element model was formulated for cohesive soils with parallel bond contacts between aggregates. The model allows simulation of mechanical tests (used for calibration purposes) and simulation of soil interaction with operating tool during sweep cultivation. This work shows that due to the necessary change in particle sizes of model soil, the conditions of physical equivalence between the model and natural soil can be difficult to satisfy. Such condition can cause significant dissimilarity between measured and simulated soil displacement. However, this can be overcome if the model scaling does not exceed a certain limit which is determined by soil structure and the potential contact density on a tool’s contact surface during the soil-tool interaction. By using these findings, our simulations demonstrate that prediction of soil displacement is possible within the suggested approach with sufficient accuracy.

Soil characterization of Bornova Plain (Izmir, Turkey) and its surroundings using a combined survey of MASW and ReMi methods and Nakamura’s (HVSR) technique

Structural damage which occurs during earthquakes is related to both the soil dynamic behavior attributes and soil response spectrums. Therefore, soil characterization based of S-wave velocity (Vs) is one of the prime factors to estimate damage and hazards. In this study, multi-channel analysis of surface waves (MASW) and refraction microtremor (ReMi) methods have been applied to estimate Vs values of the area located east of Izmir Bay. Based on the estimated Vs values, two- and three-dimensional shear-wave velocity and the maximum shear modulus maps at various depths down to 50 m were prepared. To study the relationship between the predominant period of the soil and shear-wave velocity values, a horizontal-to-vertical (H/V) spectral ratio method using Nakamura’s technique has been applied. Groundwater level, standard penetration test (SPT-N30) and Poisson ratio values were also obtained from previous geotechnical borehole data in the study area. In addition, we calculated building periods using the empirical relationship between height (or number of floors) of buildings and predominant period of the buildings to examine soil-structure resonance. According to the National Earthquake Hazard Reduction Program (NEHRP; 1997) soil classification, the study site consists of B-, C- and F-type soils. Risk maps were created using dynamic properties of the soil.

Local Site Investigation of Liquefied Soils Caused by Earthquake in Northern Thailand

ABSTRACT Ambient noise measurements and spectral analysis of surface waves were performed in Mae Lao to investigate the local site effects of the May 5, 2014 Mae Lao earthquake in Northern Thailand. Site investigations were conducted to determine horizontal to vertical spectral ratio, predominant frequency, and shear wave velocity profile. The results showed that the liquefied locations were classified as Site Class D. The low Vs profile at the shallow depth confirmed evidences of liquefaction in this area. The results could bring an understanding of site response and dynamic behavior of soils during earthquake in the Northern Thailand.

Response of saturated cohesionless soil subjected to irregular seismic excitations

Irregular stress waves generated during an earthquake induce irregular shear stresses in the soil, which affect the dynamic behaviour of soil significantly. Laboratory investigations on the response of soils during real earthquake scenario are very limited. This paper reports about the response of saturated sandy soils subjected to irregular cyclic stress histories using stress-controlled cyclic triaxial tests. Tests were conducted at different relative densities (30–90%) and confining stresses (50–150 kPa) representing varying compactness of soil obtained from different confining depths. Cyclic loading was applied as per the three different earthquake motions considered having different peak ground accelerations (PGAs). The responses are presented in terms of stress–strain variations, excess pore-water pressure ratio and shear strain accumulation in the soil specimen. The results indicated that the accumulated shear strains and excess pore-water pressures get significantly affected by the increase in confining stress and simultaneous changes in the relative density. Further, the study emphasized that the strong motions scaled to the same PGA levels produce substantially differing soil responses due to the variation in the associated strong-motion parameters.

The Effects of Dam–Reservoir Interaction on the Nonlinear Seismic Response of Earth Dams

ABSTRACTThe objective of this study is to investigate the effects of dam–reservoir interaction (DRI) on the nonlinear seismic response of earth dams. Although DRI effects have for long been considered as insignificant for earth dams, that conclusion was mainly based on linear elastic investigations which focused only on the acceleration response of the crest without examining the seismic shear stresses and strains within the dam body. The present study explores further the impact of DRI focusing on the nonlinear behavior of earth dams. The effects of reservoir hydrodynamic pressures are investigated in terms of both seismic dam accelerations and nonlinear dynamic soil behavior (seismic shear stresses and strains). It is shown that although dam crest accelerations are indeed insensitive to DRI, the stress and strain development within the dam body can be significantly underestimated if DRI is ignored.

Field Investigation of Maximum Dynamic Shear Modulus of Clay Deposit Using Seismic Piezocone

The maximum dynamic shear modulus (Gmax) of soils is a fundamental parameter used in the evaluation of soil dynamic behavior and seismic design in geotechnical engineering. In this study, seismic piezocone (SCPTU) and resonant column (RCT) test methods were adopted for measuring soil shear wave velocity (Vs) in Jiangsu Province of China. Then, the relationship between the Gmax and SCPTU test parameters was established based on the test data of shear wave velocity. The results show that using the correlation between the cone resistance (qt) and void ratio (e) or pore pressure parameter (Bq) to evaluate Gmax was better than using the single-cone tip resistance parameters. The Gmax of the soft soil can be determined more accurately using the cone tip resistance and pore pressure parameters measured by the SCPTU test method, and corrected based on the laboratory test data. The evaluation of Gmax based on the RCT test results was not satisfactory due to the soil disturbance induced during sampling and testing processes.

Shear Modulus and Damping Ratio for Normally Consolidated Peat and Organic Clay in Hokkaido Area

This paper presents that the shear modulus at small strain (G0) for peat and organic clay in normally consolidated state, as well as the strain dependence of the shear modulus and the damping ratio (dynamic property). In analyzing dynamic ground behavior, G0 and dynamic property of soils should be accurately determined. Therefore, eight types of peat and two types of organic clay, which were all different in terms of engineering property, were given a series of cyclic torsional shear tests in the normally consolidated state, to clarify effects of physical properties of the soils and effective confining pressure on G0 and dynamic properties. Finally, based on the test results, empirical equations to determine G0 and dynamic property of peat and organic clay are proposed.

Undrained dynamic behaviour of peaty organic soil under long-term cyclic loading, Part I: Experimental investigation

To investigate the undrained cyclic behaviour of peaty organic soil under long-term cyclic loading, a series of undrained cyclic triaxial compression tests was conducted. The permanent axial strain, accumulated excess pore pressure as well as secant shear modulus during the loading cycles were studied and their dependencies on variables such as confining pressure, cyclic deviator stress and static deviator stress were summarized. Distinctive characteristics of the peaty organic soil under long-term cyclic loading were presented in comparison to a soft clay from Wenzhou. For a given stress state, the permanent strain over the initial limited loading cycles was smaller for the peaty organic soil than for the inorganic soft clay for the higher static strength of peaty organic soil. The peaty organic soil displayed distinct viscous nature and higher permanent strain rate under long-term cyclic loading. Due to the highly decomposed and often amorphous organic components in the peaty organic soil, which results in a weak structure strength, the development of permanent strain was found to be insensitive to confining pressure. In addition, for a given shear strain, the secant modulus of peaty organic soils increased with decreasing organic content and degree of decomposition or with increasing confining pressure. While the equivalent damping ratio was found to generally decrease as the confining pressure, organic content or degree of decomposition increased.

Long-term dynamic behaviour of Coode Island Silt (CIS) containing different sand content

The foundations of nearshore and offshore structures are always subjected to long-term cyclic loading which is often a one-way, with low amplitude and a large number of cycles. Hence, the long-term dynamic behaviour of shoreline soils and sediments should be understood to avoid excessive deformation and liquefaction. As one of the most problematic soft soils in Melbourne, Coode Island Silt (CIS) at the northern shoreline of Port Phillip Bay contains a considerable but variable amount of sand. This paper explores the dynamic response of CIS containing different sand content subjected to a large number of cycles. To determine the liquefaction potential, and the effect of sand content on the resilient modulus and permanent strain of CIS, a series of long-term cyclic triaxial tests at a sinusoidal loading frequency of 1 Hz is performed. Based on the test results, it is found that CIS with varying sand content up to 30%, does not liquefy under the cyclic stress ratios and frequency applied in this study. Also, a sand content of 10% causes CIS to degrade more under cyclic loading. In the end, an empirical model to predict the permanent strain of CIS with a variable sand content is calibrated.

Dynamic Behavior of Soft Subgrade Soils Treated with Boron Waste

A series of laboratory tests using resonant column and dynamic torsional shear tests were conducted on kaolinite and montmorillonite clays treated with boron waste. The effect of the boron waste on the dynamic characteristics of two clays was studied considering the effects of the plasticity index. Pulverized boron waste was mixed with the clay soils in different proportions. It has been seen that treatment with boron waste improved the dynamic properties of the two clays. However, increasing the amount of boron waste does not affect the dynamic characteristics of the samples in the same proportions. Increasing the amount of boron waste in the mixture increased the initial shear modulus of the montmorillonite clay up to 300% compared to untreated samples, whereas the reaction of the kaolinite clay with boron waste treatment was moderate. Degradation curves of treated and untreated soils in regard to shear strain are presented. In general treatment, success is dependent on the amount of boron waste and the clay type. The continuous increase with the amount of boron waste in the shear modulus and damping ratio is apparent on both clays.

Effect of geotextile reinforcement on cyclic undrained behavior of sand

Dynamic behavior of reinforced soil are evaluated relative to a number of factors including: strain level, density, number of cycles, material type, fine content, geosynthetic inclusion, saturation, and effective stress. This paper investigates the dynamic behavior of saturated reinforced sand under cyclic stress condition. The cyclic triaxial tests are conducted on remolded specimens under various cyclic stress ratios (CSR) which reinforced by different arrangement of non-woven geotextile. Aforementioned tests simulate field reinforced saturated deposits during earthquake or other cyclic loadings. This analysis revealed that the geotextile arrangement played dominant role on dynamic soil behavior and as geotextile close to top of specimen, the liquefaction resistance increased. Meanwhile, the results demonstrate that the effects of arrangement of reinforcement layers on deformation and shear modulus are considerable.

Local site effect of a clay site in Shiraz based on seismic hazard of Shiraz Plain

Propagation of seismic waves through soil layers would drastically change the frequency content and amplitude-based features of ground motions at the surface. These alterations are known as seismic site effects. Computation of site effects of high-populated areas such as large cities is of great importance (e.g., it is used in development of seismic microzonation of a region). Shiraz is one of the most populous cities of Iran and is located in a high seismic hazardous region. A representative clay site in this city is selected to assess local site effects. The time series and random vibration theory procedure in the frequency domain are implemented to analyze the aforementioned site. Furthermore, the nonlinear dynamic soil behavior is simulated by the equivalent linear method and the nonlinear method via DEEPSOIL program. Three types of soil column uncertainties such as shear wave velocity, modulus reduction, and damping ratio of soil layers as well as depth of underlying rock half-space (D bed) are considered herein. The mean amplification and standard deviation of natural logarithm of amplification factors are computed for a variety of analysis types. The results of the current study show that the computed mean and standard deviation of amplification factor in ln units by considering only V S uncertainty are in good agreement with the corresponding ones by considering V S and modulus reduction and damping ratio variabilities simultaneously for the studied site. Furthermore, it seems that the effect of bedrock depth in definition of spectral shapes of the Iranian seismic building code should be taken into account.

Determination of shear wave velocity of Yangtze Delta sediments using seismic piezocone tests

Abstract Shear wave velocity is one of the most important parameters in the evaluation of soil dynamic behavior and seismic design of geotechnical structures. In this study, a comprehensive geotechnical in situ and laboratory investigation into the predominantly intermediate soils deposited in the upper Quaternary basin of the Yangtze Delta (YD) was carried out. It is indicated that uncertainty may be introduced when applying existing empirical shear wave velocity correlations from the literatures due to the heterogeneous and highly stratified nature of such sediments, and the issue of change of drained, partially drained and undrained conditions during penetration. The applicability of six existing CPT-V s correlations for YD mixed soils, relied on direct CPT measured data or other indirect parameters incorporated, has been first compared and evaluated. The results show that all the selected correlations tend to be biased to varying degrees, demonstrating the need for a YD-specific V s prediction correlation. Hence, new prediction models are proposed through multiple linear regression based on the YD SCPTU database, which relies on CPT-based variables (q t , f s , B q , I c , z) and additional laboratory data. The performance of these models is evaluated through comparisons of predicted and measured V s values. Moreover, several significant influencing factors are analyzed including the initial effective stress, void ratio and pore pressure ratio. It is found that the coefficients of determination are generally larger when cone resistance, overburden stress, void ratio or pore pressure ratio are considered in the regression equations rather than cone resistance solely. Additionally, an appropriate CPT-V s model is suggested from a practical standpoint, which depends on terms directly measured by the CPT (q t or q c , f s and z). Although situated in the Chinese context, the proposed correlations can be helpful in preliminary estimate of the stiffness at small strain of similar deltaic deposits encountered in other countries.

Dynamic Properties of Soils at Large Strains in Roorkee Region Using Field and Laboratory Tests

The evaluation of the dynamic properties of natural soil deposits is important to study the site response, to predict the ground motion and to proceed to seismic zonation. In this paper, dynamic behavior of soils in Roorkee (India) region has been investigated. The study focuses primarily on four sites: Solani Riverbed site, Bhagwanpur site, Bahadrabad site, and Haridwar site. The soil samples were collected from different depths at these four sites using SPT. Soil samples collected were tested in the laboratory for index properties and subjected to bender element tests to measure the maximum shear wave velocity. Dynamic behavior of soil samples collected from all sites was investigated by a series of cyclic triaxial tests. Strain controlled undrained cyclic triaxial tests were carried out as per ASTM D3999 for determination of dynamic soil properties (i.e., shear modulus and damping ratio). The effects of shear strain (in the range 0.03–2%) on shear modulus and damping ratio have been investigated at different depths. The results show that the variation in shear modulus and damping ratio with shear strain is greater for the samples collected from greater depths as compared to the samples collected from shallower depths. Variation in shear modulus and damping ratio with shear strain were compared with the published literature and found to be in good agreement.

Theory of a Time Domain Boundary Element Development for the Dynamic Analysis of Coupled Multiphase Porous Media

This paper presents an advanced formulation of the time-domain two-dimensional (2D) boundary element method (BEM) for an elastic, homogeneous unsaturated soil subjected to dynamic loadings. Unlike the usual time-domain BEM, the present formulation applies a convolution quadrature which requires only the Laplace-domain instead of the time-domain fundamental solutions. The coupled equations governing the dynamic behavior of unsaturated soils ignoring contributions of the inertia effects of the fluids (water and air) are derived based on the poromechanics theory within the framework of a suction-based mathematical model. In this formulation, the solid skeleton displacements [Formula: see text], water pressure [Formula: see text] and air pressure [Formula: see text] are presumed to be independent variables. The fundamental solutions in Laplace transformed-domain for such a dynamic [Formula: see text] theory have been obtained previously by authors. Then, the BE formulation in time is derived after regularization by partial integrations and time and spatial discretizations. Thereafter, the BE formulation is implemented in a 2D boundary element code (PORO-BEM) for the numerical solution. To verify the accuracy of this implementation, the displacement response obtained by the boundary element formulation is verified by comparison with the elastodynamics problem.

Dynamic behavior of fiber-reinforced soil under freeze-thaw cycles

This research presents the dynamic behavior of fiber-reinforced soil exposed to freeze-thaw cycles. The series of dynamic triaxial tests were conducted on fine-grained soil mixed with different percentages of basalt and glass fibers subjected to freeze-thaw cycles. The results showed that after freeze-thaw cycles, with the addition of basalt and glass fibers, the damping ratio and the shear modulus increased at a constant confining pressure because of the increase of stiffness, but the shear modulus decreased with increasing shear strain. Moreover, the theoretical analytical formulations were developed to define for dynamic shear stress and dynamic shear modulus. The parameters were predicted by Hardin-Drnevich model and Kondner-Zelasko model. The shear modulus was expressed as a function of freeze-thaw cycles, fiber contents, confining pressure and initial water content. Finally, ten coefficients were calibrated by analyzing the experimental results and then employed to describe dynamic shear modulus of the fiber-reinforced soil.

Dynamic properties of soils at low strains in Roorkee region using resonant column tests

In this paper, dynamic behaviour of soils in Roorkee (India) region has been investigated. The soil samples were collected from the four different sites from different depths using standard penetration tests and tested in the laboratory for index properties. Dynamic behaviour of soil samples collected from all sites was investigated in low strain range using resonant column tests. The effect of shear strain on shear modulus and damping ratio has been investigated at different depths. The results show that the variation in shear modulus and damping ratio with shear strain are greater for the samples collected from higher depths as compared to the samples collected from shallower depths. Variation in shear modulus ratio and damping ratio with shear strain were also compared with the published literature and found to be in good agreement. This is the first ever study, where modulus reduction and damping ratio curves in low strain range is presented for Roorkee region at different depths. There is hardly any literature which presents effect of depth on these curves.