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1.
Results from a benchmark test on full-scale piles are used to investigate the response of piles to lateral spreading. In the experiment, two single piles, a relatively flexible pile that moves together with the surrounding soil and a relatively stiff pile that does not follow the ground movement have been subjected to large post-liquefaction ground displacement simulating piles in laterally spreading soils. The observed response of the piles is first presented and then the results are used to examine the lateral loads on the pile from a non-liquefied soil at the ground surface and to evaluate the stiffness characteristics of the spreading soils. The measured ultimate lateral pressure from the crust soil on the stiff pile was about 4.5 times the Rankine passive pressure. The back-calculated stiffness of the liquefied soil was found to be in the range between 1/30 and 1/80 of the initial stiffness of the soil showing gradual decrease in the course of lateral spreading.  相似文献   

2.
The present study aims to obtain p-y curves(Winkler spring properties for lateral pile-soil interaction) for liquefied soil from 12 comprehensive centrifuge test cases where pile groups were embedded in liquefiable soil. The p-y curve for fully liquefied soil is back-calculated from the dynamic centrifuge test data using a numerical procedure from the recorded soil response and strain records from the instrumented pile. The p-y curves were obtained for two ground conditions:(a) lateral spreading of liquefied soil, and(b) liquefied soil in level ground. These ground conditions are simulated in the model by having collapsing and non-collapsing intermittent boundaries, which are modelled as quay walls. The p-y curves back-calculated from the centrifuge tests are compared with representative reduced API p-y curves for liquefied soils(known as p-multiplier). The response of p-y curves at full liquefaction is presented and critical observations of lateral pile-soil interaction are discussed. Based on the results of these model tests, guidance for the construction of p-y curves for use in engineering practice is also provided.  相似文献   

3.
An interest in the behavior of liquefied sand during seismic flow failure led the authors to conduct shaking table tests in which an embedded pipe was pulled laterally and the required drag force was monitored. Test results showed that the amplitude of shaking acceleration affected the behavior of sand in both dry and water-saturated conditions. In dry sand, the induced inertia force decreased the shear strength and consequently the magnitude of the drag force. When the sand was saturated, a special consideration was made of the similitude of dilatancy between 1-G model tests and the in-situ situation. This goal was attained by employing very loose sand in model tests. The rate-dependency in which the drag force increased with the rate of pipe movement was focused on, leading to an apparently viscous behavior of sand. This is consistent with what several former studies reported.  相似文献   

4.
汶川地震砾性土液化场地特征解析   总被引：1，自引：0，他引：1       下载免费PDF全文
通过成都平原砾性土场地勘察测试,研究汶川地震中大量砾性土液化场地的基本特性,找出一般规律,对砾性土场地液化发生主客观原因提出解释,并修正以往若干认识偏差.分析表明:汶川地震液化砾性土层粒径范围宽,含砾量5%~85%甚至更大,同时其实测剪切波速140~270 m·s~(-1),修正剪切波速160~314 m·s~(-1),都远超历史记录;液化砾性土场地1/2集中在Ⅷ度区内,表明如砂土层液化一样,砾性土场地大规模液化需要较强地震动触发,但超过触发强度后液化规模增长均有限;成都平原浅表地层二元基本结构是汶川地震中出现大量砾性土场地的客观条件之一,该结构可使饱和砾性土层处于封闭状态,构成了砾性土液化的基本条件;虽然液化砾性土层剪切波速很高,但实际上大多松散状态,是此次地震大量砾性土场地发生液化的客观条件之二;地震中地表(井中)喷出物与地下实际液化土类大相径庭,且液化层埋深大多小于6.0 m,以往以地表喷出物反推地下液化层土性类型的做法不再成立;认为砾性土层波速大、透水性好而不会液化的传统认识也不再成立,但砾性土层液化条件与砂土层液化条件不同,前者要求更高.  相似文献   

5.
Liquefaction of saturated loose sand is a major cause of extensive damage to buildings and infrastructures during large earthquakes. A better understanding of the behaviour of liquefied soil is becoming increasingly necessary to mitigate earthquake damage, and the fluid method has become an increasingly popular means to study the behaviour of liquefied soils. The purpose of this study is to determine the fluid characteristics of liquefied fine sand. In this paper, the apparent viscosity was measured as an index of fluid characteristics using the shaking table tests of pre-liquefaction behaviour of saturated fine sand at approximately 45 % relative density; the relationship of apparent viscosity and shear strain rate on liquefying fine sand was indicated as a power-law shear-thinning non-Newtonian fluid; and liquefying fine sand has the alternating behaviour of shear dilatancy and compressibility during cyclic loading. Additionally, a series of a monotonic axial compression loading tests in an undrained manner were performed to measure the shear stress and excess pore pressure ratio relationship on the post-liquefaction saturated fine sand at approximately 50 % relative density. The fluid characteristics of post-liquefaction fine sand exhibits rate dependence and can be described by a combined fluid model of time-independent and time-dependent power-law functions; the time-independent viscous resistance is not relevant to the excess pore pressure ratio; but the time-dependent frictional resistance is closely related to the excess pore pressure ratio. Furthermore, the results of the verification tests demonstrate that the proposed fluid model has good applicability for the fluid behaviour of the post-liquefaction fine sand.  相似文献   

6.
The 1995 Kobe earthquake seriously damaged numerous buildings with pile foundations adjacent to quay walls. The seismic behavior of a pile group is affected by movement of quay walls, pile foundations, and liquefied backfill soil. For such cases, a three-dimensional (3-D) soil–water coupled dynamic analysis is a promising tool to predict overall behavior. We report predictions of large shake table test results to validate 3-D soil–water coupled dynamic analyses, and we discuss liquefaction-induced earth pressure on a pile group during the shaking in the direction perpendicular to ground flow. Numerical analyses predicted the peak displacement of footing and peak bending moment of the group pile. The earth pressure on the pile in the crustal layer is most important for the evaluation of the peak bending moment along the piles. In addition, the larger curvatures in the bending moment distribution along the piles at the water side in the liquefied ground were measured and predicted.  相似文献   

7.
液化土中桩基础动力反应试验研究   总被引：3，自引：0，他引：3  
本文设计完成了包括三种密度饱和砂土和非液化干砂的多工况桩-土相互作用振动台动力试验,研究液化对土体和桩-承台动力反应的影响。通过试验和分析,得到了液化和非液化土层中土体水平加速度、侧向位移和桩-承台的水平加速度、侧向位移、桩身弯矩等指标的反应过程和模式,对比了液化和非液化条件对这些指标的影响方式,提出了各因素影响大小的分析结果。  相似文献   

8.
Collapse and/or severe damage to pile-supported structures are still observed in liquefiable soils after most major earthquakes. Poor performance of pile foundations remains a great concern to the earthquake engineering community. This review paper compares and contrasts the two plausible theories on pile failure in liquefiable soils. The well established theory of pile failure is based on a flexural mechanism; where the lateral loads on the pile (due to inertia and/or lateral spreading) induce bending failure. This theory is well researched in the recent past and assumes that piles are laterally loaded beams. A more recent theory based on buckling instability treats the piles as laterally unsupported slender columns in liquefiable soils and investigates the buckling instability (bifurcation). The objective of this paper is to investigate the implications to practical pile foundation design that flow from both these theories. Provisions for design made by major international codes of practice for pile design including the Japanese Highway Code (JRA) will be considered. The necessity for such codes to consider alternative forms of failure mechanisms such as the buckling instability of piles in liquefied ground will be discussed. S. Bhattacharya–Previously Departmental Lecturer in Engineering Science, University of Oxford, UK and Fellow of Somerville College, Oxford. S. P. G. Madabhushi–Fellow of Girton College, Cambridge.  相似文献   

9.
This paper presents an experimental study on the lateral resistance of a pile subjected to liquefaction-induced lateral flow. To observe the soil surrounding the pile during liquefaction, it was modeled as a buried cylinder that corresponded to a sectional model of the prototype pile at a certain depth in the subsoil. In order to create a realistic stress condition in the model ground, the model was prepared in a sealed container and the overburden pressure was applied to the ground surface by a rubber pressure bag. The model pile was actuated back and forth through rods attached on each side by an electro-hydraulic actuator.This paper focuses on observing the deformation of the liquefied soil surrounding the pile when a large relative displacement between the pile and the soil is induced. The loading rate effect on the lateral resistance of the pile in the liquefied sand and the influence of the relative density are also investigated.Test results show that a larger resistance is mobilized as the loading rate becomes higher. When the loading rate is higher, the cylinder displacement required for the lateral resistance becomes smaller. It has been also observed that as the relative density of the soil increases, dilatancy of the soil in front of the pile also increases.  相似文献   

10.
通过给饱和砂土层施加反压,模拟地震荷载作用下具有残余孔压的饱和弱化、液化土层。选择粉质细砂与细砂,进行了18组水平荷载作用下桩与饱和弱化、液化土层相互作用的模型试验,研究了饱和弱化、液化土层水平极限抗力随土层残余孔压增加的变化规律。结果表明,随土层中残余孔压增加,水平极限抗力逐渐降低,土层液化后的水平极限抗力大约降低80%~90%。通过定义饱和弱化、液化土层的强度,定量分析了饱和弱化、液化砂土的强度参数与水平极限抗力之间关系。又通过引入土层的残余孔压比折减系数,建立了确定饱和弱化、液化土层等效强度的关系式,进而提出了一种按等效强度确定饱和弱化、液化土层水平极限抗力的方法。  相似文献   

11.
In liquefied ground, lateral flow is sometimes much larger than surface settlement and may exceed several meters even in a gentle slope of less than a few percent. It occurs not only during but also after earthquake shaking. Conventional laboratory soil tests using uniform sand cannot reproduce this phenomenon. Its mechanism is still poorly understood. In this paper, there is a major focus on the mechanism involving void redistribution or water film effects in layered sand deposits using recent findings obtained by different researchers on void redistribution and the associated lateral flow movement that potentially occurs in layered sand deposits. 1G shake table tests, 1D tube tests, torsional simple shear tests, in situ soil investigations, case history studies, etc. are used to develop an understanding of the lateral flow mechanism during liquefaction. Some of the major findings are; sand deposits in the field consist of sublayers with different particle sizes and permeability and readily develop water films by post-liquefaction void redistribution at sublayer boundaries. The water films may have served as sliding surfaces for large flow during the 1964 Niigata earthquake without the constraint of the dilatancy effect because the water films serve as shear stress isolators. The potential of this type of flow failure will be high for loose sand with relative density around 40% or less.  相似文献   

12.
This paper intended to evaluate the behavior of saturated sand and sloped ground subjected to flow failure with seepage of pore water in the ground after earthquake and the resultant liquefaction. Triaxial compression tests of sand with constant deviator stress but changing of pore pressure and volume of the specimens were conducted in this study. It was revealed that the relation between the volume change and the amount of shear strain during deformation depended on the initial density of the sand but it did not much depend on shear stress and initial confining stress levels. Based on this test results and numerical analysis of the seepage of pore water in liquefied ground, a methodology was proposed to predict the deformation of inclined ground due to liquefaction.  相似文献   

13.
To investigate the seismic response of a pile group during liquefaction, shaking table tests on a 1/25 scale model of a 2 × 2 pile group were conducted, which were pilot tests of a test project of a scale-model offshore wind turbine with jacket foundation. A large laminar shear box was utilized as the soil container to prepare a liquefiable sandy ground specimen. The pile group model comprising four slender aluminum piles with their pile heads connected by a rigid frame was designed with similitude considerations focusing on soil–pile interaction. The input motions were 2-Hz sinusoids with various acceleration amplitudes. The excess pore water pressure generation indicated that the upper half of the ground specimen reached initial liquefaction under the 50-gal-amplitude excitation, whereas in the 75-gal-amplitude test, almost entire ground was liquefied. Accelerations in soil, on the movable frames composing the laminar boundary of the shear box, and along the pile showed limited difference at the same elevation before liquefaction. After liquefaction, the soil and the movable-frame accelerations that represented the ground response considerably reduced, whereas both the movable frames and the piles exhibited high-frequency jitters other than 2-Hz sinusoid, and meantime, remarkable phase difference between the responses of the pile group and the ground was observed, all probably due to the substantial degradation of liquefied soil. Axial strains along the pile implied its double-curvature bending behavior, and the accordingly calculated moment declined significantly after liquefaction. These observations demonstrated the interaction between soil and piles during liquefaction.  相似文献   

14.
For sites susceptible to liquefaction induced lateral spreading during a probable earthquake, geotechnical engineers often need to know the undrained residual shear strength of the liquefied soil deposit to estimate lateral spreading displacements, and the forces acting on the piles from the liquefied soils in order to perform post liquefaction stability analyses. The most commonly used methods to estimate the undrained residual shear strength (Sur) of liquefied sand deposits are based on the correlations determined from liquefaction induced flow failures with SPT and CPT data. In this study, 44 lateral spread case histories are analyzed and a new relationship based on only lateral spread case histories is recommended, which estimates the residual shear strength ratio of the liquefiable soil layer from normalized shear wave velocity. The new proposed method is also utilized to estimate the residual lateral displacement of an example bridge problem in an area susceptible to lateral spreading in order to provide insight into how the proposed relationship can be used in geotechnical engineering practice.  相似文献   

15.
To understand the post-liquefaction behavior of liquefied ground, it is important to get a better understanding and a more suitable characterization of the variation of excess pore pressure after liquefaction. In this paper, the soil permeability is considered as one of the key soil parameters for clarifying the mechanism of post-liquefaction behavior of liquefied ground. For this reason, a series of shaking table tests were conducted for a Toyoura sand deposit with different soil permeability values. Polymer fluid was used in model tests to vary the permeability of sand deposits. Excess pore pressures and settlements were measured in each test. A basic mechanism in post-liquefaction behavior and the solidification phenomenon after liquefaction were discussed based on these test results. Also, a new method for predicting the dissipation of excess pore pressure was developed. This study provides evidence of the important effect of soil permeability on the velocity with which the solidification front moves upward in liquefied ground. It is suggested that the value of coefficient of permeability of liquefied sand can increase to about 4.0 times the initial value. This variation of permeability after liquefaction should be taken into account in post-liquefaction analysis.  相似文献   

16.
Compaction or densification of loose saturated soils has been the most popular method of reducing earthquake related liquefaction potential. Such compaction of a foundation soil is only economical when limited in extent, leading to a case of an ‘island’ of improved ground (surrounded by unimproved ground). The behavior of the densified sand surrounded by liquefied loose sand during and following earthquakes is of great importance in order to design the compacted area rationally and optimize both safety and economy. This problem is studied herein by means of dynamic centrifuge model tests. The results of three heavily-instrumented dynamic centrifuge tests on saturated models of side-by-side loose and dense sand profiles are discussed. The test results suggest the following concerns as relates to ‘islands’ of densified soil: (1) there is a potential strength degradation in the densified zone as a result of pore pressure increase due to migration of pore fluid into the island from the adjacent loose liquefied ground; (2) there is a potential for lateral deformation (sliding) within the densified island as the surrounding loose soil liquefies.  相似文献   

17.
Earthquake Engineering and Engineering Vibration - In this study, centrifuge model tests of vertical and batter pile groups in liquefied sand were conducted on a centrifuge shaking table. The...  相似文献   

18.
Two full-scale experiments using controlled blasting were conducted in the Port of Tokachi on Hokkaido Island, Japan, to assess the behavior of piles and pipelines subjected to lateral spreading. Test specimens were extensively instrumented with strain gauges to measure the distribution of moment during lateral spreading. This allowed us to compute the loading condition, as well as to conduct damage and performance assessments on the piles and pipelines. This paper presents the test results and discussions on the response of single piles and pipelines observed from the full-scale experiments. Based on the test results, it can be concluded that using controlled blasting successfully liquefied the soil, and subsequently induced lateral spreading. The movements of the single pile, as well as the transverse pipelines, were approximately the same as the free field soil movement. Observed moment distribution of the single pile indicated that global translation of the liquefied soil layer provided insignificant force to the pile. In addition, the degree of fixity at the pile tip significantly affected the moment along the pile as well as the pile head displacement. The pile with a higher degree of fixity at the pile tip had smaller pile head displacement but larger maximum moment.  相似文献   

19.
桩-液化土相互作用p-y关系分析   总被引：2，自引：0，他引：2  
基于多工况的桩-液化土体动力相互作用振动台试验,研究地震荷载作用下液化土层中桩土间侧向相互作用力p与桩身和土体间侧向相对位移y之间的关系。将试验得到的实际p-y曲线与采用拟静力法和以API规范为基础的折减系数法计算出的p-y曲线进行对比,结果表明:(1)液化土层中试验得到的桩真实p-y响应及由拟静力法和折减系数法得到的结果都呈非线性变化,三者极限状态有接近一致的趋势,但变化过程差异明显;(2)采用拟静力法和折减系数法都会使液化土层桩基础侧向反力迅速增长,很快达到屈服极限,远远超过实际情况,会导致相当保守的结果;(3)液化进程中控制桩p-y响应的是土体位移而非惯性力,因而拟静力法和折减系数法的原理不适合桩-液化土体动力相互作用分析,不能用于液化土层中桩基础地震响应的计算。  相似文献   

20.
Horizontal earth pressures on rigid vertical walls in liquefied soils have extensively been studied by many researchers for the level ground surface condition. In this paper, a series of centrifuge tests was conducted to investigate the effects of embankments resting on ground surfaces on the pressure on the rigid vertical walls. In the tests, earth pressures on the rigid walls were successfully measured with built-in earth pressure cells with small accelerometers attached on them. The earth pressure cells are capable of measuring both normal and shear stresses simultaneously with a good accuracy. It appears that dynamic component of the earth pressure of liquefied sand is in proportion to the acceleration of the rigid wall irrespective of amplitude and frequency of the input motion, and increases with increasing average embankment load. On the other hand, the residual component of the earth pressure is found to be well estimated from FEM assuming the liquefied soil as an incompressible elastic body. A practical formula of the earth pressures is established for the purpose of practical use.Another series of centrifuge tests was carried out on models with solidification or densification zones below embankment toes as a remedial countermeasure against liquefaction-induced embankment failure. It was found that the proposed formulae holds valid independently of the movement of walls as long as the liquefied soil behaves as a heavy fluid, and the countermeasure does not soften significantly.  相似文献   

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