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1.
Cyclic shearing and liquefaction of soil under irregular loading: an incremental model for the dynamic earthquake-induced deformation 总被引：1，自引：0，他引：1
V. A. Osinov 《Soil Dynamics and Earthquake Engineering》2003,23(7):535-548
The paper presents a mathematical model for the deformation of soil under irregular cyclic loading in the simple-shear conditions. The model includes the possible change in the effective pressure in saturated soil due to the cyclic shearing, the reciprocal influence of the effective pressure on the response of the soil to the shear loading, and the pore pressure dissipation due to the seepage of the pore fluid. The hysteresis curves for the strain–stress relationship are constructed in such a way that they produce both the required backbone curve and the required damping ratio as functions of the strain amplitude. At the same time, the approach enables the constitutive functions involved in the model to be specified in various ways depending on the soil under study. The constitutive functions can be calibrated independently of each other from the conventional cyclic shear tests. The constitutive model is incorporated in the boundary value problem for the dynamic site response analysis of level ground. A numerical solution is presented for the dynamic deformation and liquefaction of soil at the Port Island site during the 1995 Hyogoken-Nambu earthquake. 相似文献
2.
Zhi-Fan Xia Guan-Lin Ye Jian-Hua Wang Bin Ye Feng Zhang 《Soil Dynamics and Earthquake Engineering》2010
It is known that a series of aftershocks might follow a mainshock, which may cause further damages on civil engineering structures. So it is necessary to investigate the dynamic response of structures undergone several shocks. This study presents a numerical analysis of repeated shake-consolidation process for an earth embankment founded on liquefiable foundation soils. Analysis is carried out using an effective stress-based, fully coupled, finite element method. The behaviors of the foundation soils are described by means of a cyclic mobility constitutive model which was developed at the bases of modified Cam-clay model by introducing concepts such as stress-induced anisotropy, over-consolidation, and structure. Results show that the cyclic mobility constitutive model can reflect the dynamic response of liquefiable soils. Special emphasis is given to analyze the result of excess pore water pressures, stress path, acceleration, and deformations during the two seismic excitation and consolidation process. 相似文献
3.
This paper presents results of a series of centrifuge models of dry, sandy slopes excited by earthquakes and cyclic waves
under 50g centrifugal acceleration to investigate the dynamic performance of slopes. Test results of four model slopes with different
profiles stimulated by the adjusted El Centro earthquakes with various peak accelerations reveal the response amplification
mechanism of the slope. By calculating the response spectra of recorded acceleration time histories, it was observed that
the different frequency contents of the input event were amplified to different degrees. The model slope showed a completely
different response under the cyclic wave with a constant frequency and amplitude in that the spectral amplification factor
curves had no prominent peak values. These findings suggest that dynamic centrifuge tests excited with a real ground motion
are able to better reflect the response characteristics of a slope rather than the tests with cyclic loading. 相似文献
4.
Assessment of liquefaction triggering using strain energy concept and ANN model: Capacity Energy 总被引：3，自引：0，他引：3
In the present study, an artificial neural network (ANN) model was developed to establish a correlation between soils initial parameters and the strain energy required to trigger liquefaction in sands and silty sands. A relatively large set of data including 284 previously published cyclic triaxial, torsional shear and simple shear test results were employed to develop the model. A subsequent parametric study was carried out and the trends of the results have been confirmed via some previous laboratory studies. In addition, the data recorded during some real earthquakes at Wildlife, Lotung and Port Island Kobe sites plus some available centrifuge tests data have been utilized in order to validate the proposed ANN-based liquefaction energy model. The results clearly demonstrate the capability of the proposed model and the strain energy concept to assess liquefaction resistance (capacity energy) of soils. 相似文献
5.
Physical modeling and visualization of soil liquefaction under high confining stress 总被引：1，自引：0，他引：1
Lenart González 《地震工程与工程振动(英文版)》2005,4(1):47-57
The mechanisms of seismically-induced liquefaction of granular soils under high confining stresses are still not fully understood. Evaluation of these mechanisms is generally based on extrapolation of observed behavior at shallow depths. Three centrifuge model tests were conducted at RPI‘s experimental facility to investigate the effects of confining stresses on the dynamic response of a deep horizontal deposit of saturated sand. Liquefaction was observed at high confining stresses in each of the tests. A system identification procedure was used to estimate the associated shear strain and stress time histories. These histories revealed a response marked by shear strength degradation and dilative patterns. The recorded accelerations and pore pressures were employed to generate visual animations of the models. These visualizations revealed a liquefaction front traveling downward and leading to large shear strains and isolation of upper soil layers. 相似文献
6.
A one-dimensional constitutive model, developed for the nonlinear ground response analysis of layered soil deposits, is calibrated and validated experimentally in this paper. The small number of parameters renders the model easily implementable, yet quite flexible in effectively reproducing almost any type of experimentally observed hysteretic soil behavior. In particular, the model generates realistic shear modulus and damping curves as functions of shear strain, as well as stress–strain hysteresis loops. The model is calibrated against three sets of widely-used published shear modulus and damping (G : γ and ξ : γ) curves and a library of parameter values is assembled to facilitate its use. The model, along with a developed explicit finite-difference code, NL-DYAS, for analyzing the wave propagation in layered hysteretic soil deposits, is tested against established constitutive models and numerical tools such as Cyclic1D [12] and SHAKE [42], and validated against experimental data from two centrifuge tests. Emphasis is given on the proper assessment of the Vs profile in the centrifuge tests, on the role of soil nonlinearity, and on comparisons of two inelastic codes (NL-DYAS and Cyclic1D) with equivalent linear (SHAKE) analysis. 相似文献
7.
Dynamic response of dams is significantly influenced by foundation stiffness and dam-foundation interaction. This in turn,
significantly effects the generation of hydrodynamic pressures on upstream face of a concrete dam due to inertia of reservoir
water. This paper aims at investigating the dynamic response of dams on soil foundation using dynamic centrifuge modelling
technique. From a series of centrifuge tests performed on model dams with varying stiffness and foundation conditions, significant
co-relation was observed between the dynamic response of dams and the hydrodynamic pressures developed on their upstream faces.
The vertical bearing pressures exerted by the concrete dam during shaking were measured using miniature earth pressure cells.
These reveal the dynamic changes of earth pressures and changes in rocking behaviour of the concrete dam as the earthquake
loading progresses. Pore water pressures were measured below the dam and in the free-field below the reservoir. Analysis of
this data provides insights into the cyclic shear stresses and strains generated below concrete dams during earthquakes. In
addition, the sliding and rocking movement of the dam and its settlement into the soil below are discussed. 相似文献
8.
Lateral spreads are complex dynamic phenomena that are challenging to represent numerically. In this paper numerical models are developed and calibrated using the displacement, acceleration, and pore water pressure time histories recorded in a free-field lateral spreading centrifuge test. The calibrated numerical model then is used to predict another free-field lateral spreading centrifuge test using the same soil profile but different input acceleration time history. The computed response shows good agreement with the centrifuge test measurements. This paper demonstrates that even in a large strain problem, such as lateral spreading, small strain damping plays an important role in numerical simulation results; it also shows the need to have pressure dependent dilation parameters in the employed soil constitutive model implemented in order to simultaneously reproduce measurements of pore water pressure, acceleration and lateral displacement. 相似文献
9.
Validation of a new endochronic liquefaction model for granular soil by using centrifuge test data 总被引：1，自引：0，他引：1
The application of a new liquefaction constitutive model, based on the endochronic theory applied to densification of sandy soil, to a set of centrifuge tests from the University of British Columbia, is presented in this paper. The model employed herein takes into account, in a unified formulation, contractive and dilative behaviours, and considers the soil collapse as well. First of all, the model is calibrated by means of undrained cyclic simple shear stress test data. The constitutive law of the soil is implemented in the bidimensional coupled finite element code CMLIQ (Cyclic Mobility and LIQuefaction), developed by the authors. Three centrifuge tests are analysed, the seismic loading and the geometry being the same for all of them, namely an improved slope with drain devices or denser soil at some locations. Comparisons between the data provided by the numerical model and the experimental measurements are shown, and, as a result, the accuracy of the model is explored and evaluated. 相似文献
10.
Konstantinos I. Andrianopoulos Achilleas G. Papadimitriou George D. Bouckovalas 《Soil Dynamics and Earthquake Engineering》2010
This paper presents the constitutive relations and the simulative potential of a new plasticity model developed mainly for the seismic liquefaction analysis of geostructures. The model incorporates the framework of critical state soil mechanics, while it relies on bounding surface plasticity with a vanished elastic region to simulate the non-linear soil response. Key constitutive ingredients of the new model are: (a) the inter-dependence of the critical state, the bounding and the dilatancy (open cone) surfaces on the basis of the state parameter ψ, (b) a (Ramberg–Osgood type) non-linear hysteretic formulation for the “elastic” strain rate, (c) a discontinuously relocatable stress projection center related to the “last” load reversal point, which is used for mapping the current stress point on model surfaces and as a reference point for introducing non-linearity in the “elastic” strain rate and finally (d) an empirical index of the directional effect of sand fabric evolution during shearing, which scales the plastic modulus. In addition, the paper outlines the calibration procedure for the model constants, and exhibits its accuracy on the basis of a large number of laboratory element tests on Nevada sand. More importantly, the paper explores the potential of the new model by presenting simulations of the VELACS centrifuge tests of Models No 1 and 12, which refer to the free-field liquefaction response of Nevada sand and the seismic response of a rigid foundation on the same sand, respectively. These simulations show that the new model can be used successfully for the analysis of widely different boundary value problems involving earthquake soil liquefaction, with the same set of model constants calibrated on the basis of laboratory element tests. 相似文献
11.
This paper presents a non-linear finite element study to back-interpret the free field seismic response recorded at the Lotung Large-Scale Seismic Test site. The study is carried out in the time domain by the Finite Element (FE) code PLAXIS 3D, considering the vertical wave propagation of both the horizontal components of motion. The non-linear soil behaviour is simulated through a constitutive model, the Hardening Soil model with Small-Strain Stiffness (HSsmall), capable of describing the cyclic response of the material at different strain levels. In the paper, the constitutive response of the HSsmall model is firstly investigated through numerical simulations of strain-controlled cyclic shear tests under single and multi-directional conditions at low strain levels. Then, it is adopted to back-analyse the recorded free field seismic response, comparing the FE numerical results to the in-situ down-hole and surface signals recorded during two earthquakes occurred on May 20th and July 17th 1986, characterized by different peak ground accelerations. 相似文献
12.
Two correctly-scaled model cantilever retaining walls of different stiffnesses were tested under dynamic loading conditions in a centrifuge. A medium-dense fine sand was retained with a range of backfill slopes. For the centrifuge model, an earthquake-generating mechanism was designed to produce seismic shaking equivalent to that generated at ground surface in the epicentral area of an earthquake of approximate magnitude 5–5. The response of the model retaining walls to the input dynamic motion was measured by strain gauges, pressure transducers and accelerometers. From the measurements plots were constructed of moment, shear, pressure and displacement over the height of the walls as a function of time. The results are compared with calculations based on the quasi-static Mononobe-Okabe theory. Although the calculated resultant force is in reasonable agreement with the experiments, the moments can be substantially different. Residual values of all parameters at the end of shaking are considerably greater than the initial static values. It is recommended that dynamic behaviour be incorporated in the earthquake design of retaining walls. 相似文献
13.
为研究卵石土场地地震反应特征,基于四川成都典型卵石土场地,通过振动台模型试验研究卵石土场地在不同地震波、不同地震强度激励下的加速度峰值放大系数、加速度频谱反应及动土压力反应,并且对其场地地震反应非线性效应及土体动剪应力-动剪应变关系进行分析。结果表明：卵石土场地表层土层对地震波具有明显的放大效应,加速度峰值放大系数介于1～1.4之间,下部土层放大效应较小,加速度峰值放大系数介于0.9～1.2之间。卵石土场地对地震波具有低频放大,高频滤波的作用,滤波频率上、下限随激励强度的增大逐渐向低频方向移动。激励强度较小时,土体尚未破坏,动土压力在地震过程中逐渐增大;随着激励强度的增大,动土压力反应明显增大,表现出骤减后逐渐增大的现象。在激励强度较小时(SN1),中部土体最先进入非线性反应阶段,地震波在中部土层能量损耗最大;激励强度较大时(EL3),土体均发生了较大变形,土体最大动剪应变达到1.7%,此时卵石土场地对地震波的放大作用明显减弱。 相似文献
14.
A laboratory study on the undrained dynamic behavior of saturated clays in cyclic triaxial tests with a variable confining pressure (VCP tests) is presented. Tests were performed on remolded clayey samples using a dynamic triaxial device where the deviatoric stress and confining pressure can be varied simultaneously. Various cyclic stress paths have been applied on the specimens through varying the ratios or phase differences between the cyclic deviatoric stress and cyclic confining pressure. Specifically, the stress paths used in the present study were designed to simulate the coupling effects of simultaneously varying shear and normal stresses in clays due to earthquakes and other vibration sources. Test results obtained from this study show that the undrained response of saturated clays is strongly influenced by the variation of confining pressure, in terms of pore water pressure, development speed of cyclic strain and magnitude of cyclic strength. It is found that when strong P-waves are propagating in soil layers, VCP tests are more appropriate for the simulation of in situ stress fields than the conventional cyclic triaxial tests with a constant confining pressure (CCP tests). 相似文献
15.
Laboratory study of seismic free-field response of sand 总被引：2，自引：0，他引：2
This paper describes a new soil-structure interaction test box for use on a moderately large shaking table. The test box is designed to replicate, as nearly as possible, the free-field seismic response of a soil layer overlying a rigid base. Results from shaking table testing are presented which demonstrate the ability of the test box to serve as a large-scale shear device. The test box is unique in its ability to determine dynamic shear modulus for both high- and low-amplitude shear strain, and also to study the dynamic response of sand under low levels of confining stress. Dynamic shear modulus for standard Ottawa sand was measured over a wide range of shear strain amplitude and compared with data from the existing literature. Finally, based on results from the test box, a constitutive model is proposed which describes the free field response of a sand layer overlying bedrock and subjected to vertically propagating SH waves. The model is simple in form with a single parameter uniquely related to the friction angle of the sand. 相似文献
16.
Experimental investigations and modeling of nonlinear elasticity of fiber-reinforced soil under cyclic loading at small strain are conducted in this paper. The investigations include three aspects. First, cyclic shear tests are conducted using conventional triaxial apparatus. Twenty-seven specimens with three different fiber contents are employed to conduct triaxial cyclic shear tests under different confining pressure and loading repetition. Effects of geofiber, confining pressure and loading repetition on elastic shear modulus of reinforced soil are studied and analyzed. Second, a hyperbolic function is introduced to describe the nonlinear stress–strain skeletal curve under cyclic loading. Nonlinear elastic modulus is expressed as a function of shear strain and two variables A and B that are related to the initial tangential modulus and ultimate cyclic loading stress, respectively. In the present paper, variables A and B both are further assumed to be functions of geofiber content, confining pressure and loading repetition. Finally, eight constitutive coefficients of the nonlinear elastic model are calibrated using stress–strain curves from cyclic triaxial shear tests. The calibration of parameters is conducted using the technique of the linear regression for multiple variables. Impacts and effects of geofiber, confining pressure and loading repetitions on soil nonlinear elastic behavior are discussed. 相似文献
17.
地震波是一种随机的、不规则作用的动荷载脉冲,可分为振动型和冲击型。不同类型的地震波会对砂土液化和变形等产生重要影响,而传统的砂土震陷计算方法往往忽视这种因素,只考虑最大加速度幅值。通过编写UMAT子程序,在非线性有限元软件ABAQUS中开发亚塑性砂土边界面模型,对不同地震波类型下不同相对密度的砂土进行动单剪试验模拟,得到一系列砂土剪应变及竖向应变的时程曲线,并与室内试验结果进行对比分析。研究表明:在同一工况下,同类型的地震波引起的砂土竖向应变相近,不同类型引起的竖向应变差异明显;振动型地震波比冲击型引起的竖向应变更大。 相似文献
18.
Centrifuge modeling of seismic response of layered soft clay 总被引：1，自引：0，他引：1
Centrifuge modeling is a valuable tool used to study the response of geotechnical structures to infrequent or extreme events
such as earthquakes. A series of centrifuge model tests was conducted at 80g using an electro-hydraulic earthquake simulator mounted on the C-CORE geotechnical centrifuge to study the dynamic response
of soft soils and seismic soil–structure interaction (SSI). The acceleration records at different locations within the soil
bed and at its surface along with the settlement records at the surface were used to analyze the soft soil seismic response.
In addition, the records of acceleration at the surface of a foundation model partially embedded in the soil were used to
investigate the seismic SSI. Centrifuge data was used to evaluate the variation of shear modulus and damping ratio with shear
strain amplitude and confining pressure, and to assess their effects on site response. Site response analysis using the measured
shear wave velocity, estimated modulus reduction and damping ratio as input parameters produced good agreement with the measured
site response. A spectral analysis of the results showed that the stiffness of the soil deposits had a significant effect
on the characteristics of the input motions and the overall behavior of the structure. The peak surface acceleration measured
in the centrifuge was significantly amplified, especially for low amplitude base acceleration. The amplification of the earthquake
shaking as well as the frequency of the response spectra decreased with increasing earthquake intensity. The results clearly
demonstrate that the layering system has to be considered, and not just the average shear wave velocity, when evaluating the
local site effects. 相似文献
19.
20.
This paper is concerned with the modelling of the behaviour of steel under cyclic and dynamic loading conditions. After a general discussion regarding the requirements for accurate and efficient modelling in dynamics, two models are described and implemented. The bilinear stress-strain constitutive relationship with kinematic hardening is widely used in many computer codes, hence is used for ‘control’ purposes. The multisurface plasticity model is said to exhibit the important qualities of strain hardening, softening and relaxation to a mean stress. This model is described in detail and notes on model parameter evaluation are given. A number of validation examples are presented, due to the complexity of implementation of the multisurface formulation. This is followed by comparisons between the bilinear response predictions and those of the multisurface model for cyclic and dynamic tests on beam-columns. It is concluded that in the absence of material test data under cyclic loading, the bilinear model provides acceptably accurate response predictions. However, the multisurface model provides a significantly closer fit to experimental results, due to its ability to model a yield plateau and a non-linear strain-hardening regime as well as cyclic degradation. It can also be used for new types of steel where no distinct yield point is observed. 相似文献