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1.
利用土工静力-动力液压-三轴扭转多功能剪切仪,针对相对密度为30 %的福建标准砂,进行了复杂初始固结条件下应力路径变化的应力控制式单调排水与不排水剪切试验。控制试验过程的平均主应力保持不变,变化中主应力系数和主应力方向,分别探讨在不同排水条件下中主应力系数和主应力方向对饱和砂土剪切特性的影响。通过对比表明：与排水条件无关,中主应力系数对归一化的应力-应变关系具有影响,但对体变或孔压的影响并不明显。初始条件相同,偏应力比随中主应力系数的增大而降低。主应力方向的影响同样显著,排水试验的主应力方向角不同时应力-应变关系所表现出的变化规律取决于水平面与竖直面上受到的剪应力作用。不排水试验的峰值有效偏应力比随着主应力方向角的增大而减小。 相似文献
2.
连云港软黏土的不排水强度试验研究 总被引：1，自引：0，他引：1
对连云港软黏土不扰动样和重塑样进行三轴CU对比试验研究。结果表明,不扰动样的不排水强度包线是由以屈服压力为界的双折线组成,而重塑样的不排水强度包线可以用通过圆点的直线表示。屈服前阶段,不扰动样由于受结构性影响产生的抵抗作用,其不排水强度包线高于重塑样;屈服后阶段,不扰动样的不排水强度包线介于具有不同初始含水率的重塑样的包线之间。通过对比分析,发现不扰动样与重塑样的不排水强度包线存在差异的主要原因是由于试样的不同初始含水率引起的。不扰动样在屈服后阶段的含水率变化规律与不排水强度增长规律与重塑土相一致,采用Burland提出的孔隙指数Iv,可将不同初始含水率重塑样及屈服后阶段不扰动样的压缩性状较好地归一化。 相似文献
3.
Peijun Guo 《国际地质力学数值与分析法杂志》2013,37(4):353-373
By taking into account the continuity of stresses and pore pressure across the boundaries of a shear band, it is theoretically shown that incipient localization may take place in saturated loose contractive sand in the regime of decreasing deviator stress under undrained conditions. The undrained shear band orientation primarily depends on the Poisson's ratio and the dilatancy characteristics of the material. However, under strict isochoric constraint, localization is precluded in dense dilative sand with deviator stress increasing only. If any local volume change takes place with a certain mechanism, undrained shear band would be possible in dense sand, most likely in the regime of decreasing friction angle after the peak friction angle is mobilized. Numerical examples are given to demonstrate the variation of shear band inclinations with void ratios and initial consolidation pressures. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
4.
Wissem Frikha Mounir Bouassida Jean Canou 《Geotechnical and Geological Engineering》2013,31(2):739-752
The paper describes the behavior of remolded kaolin clay reinforced by stone column as investigated in laboratory. The installation of stone column was simulated by performing lateral expansion at different rates within hollow cylindrical remolded kaolin specimens initially subjected to K0 consolidation path. These specimens were, then, subjected to classical consolidated undrained triaxial tests while recording excess pore pressure values. The objective of the experimental programme was to quantify the effects of consolidation stress and stone column on the undrained Young’s modulus and shear strength of kaolin clay. Obtained results showed a significant improvement in Young’s modulus when the cavity expansion ratio and the consolidation stress increase. It was also found that the increase in undrained shear strength of improved kaolin clay mainly occurred at lower consolidation stress. Another important finding of this study is that the ratio of undrained Young’s modulus to undrained shear stress increases when the consolidation stress decreases. Finally, the paper presents a model developed for the design of stone columns. 相似文献
5.
In this study the effect of the temperature increase on the hydro-mechanical properties of sheared Boom clay samples is investigated. Two samples of Boom clay are resaturated in a new hollow cylinder triaxial cell with a short drainage path and then sheared by performing an axisymmetric triaxial loading. The effect of the undrained heating under deviatoric stress is studied on the first sample. It is shown that undrained temperature increase leads to an increase of pore water pressure and consequently to a decrease of the effective mean stress which brings the sample to failure. For an initially sheared sample, the failure occurs along the existing shear band which behaves as a weakness plane in the sample. The responses of the local strain measurement transducers clearly show the sliding of rigid blocks when failure occurs in the sample.The effect of the presence of a shear band on the permeability of the other Boom clay sample is investigated at ambient temperature and at 80 °C. It is shown that the presence of a shear band does not affect significantly the permeability. These results confirm the good self sealing properties of Boom clay at ambient and at high temperature. 相似文献
6.
针对取自于长江口的海洋原状饱和软黏土,利用土工静力-动力液压三轴-扭转多功能剪切仪,在控制不同初始固结参数的三向非均等固结状态和不排水条件下,分别进行了轴向和扭转双向耦合循环剪切以及循环扭剪等多种复杂循环剪切试验。分别研究了初始大主应力方向角、初始偏应力比、初始中主应力系数以及循环剪切应力模式等因素对门槛循环应力比的影响。试验结果表明,在三向非均等固结条件下,初始大主应力方向角、初始偏应力比对门槛循环应力比影响显著,门槛循环应力比随着初始大主应力方向角与初始偏应力比的增大而明显减小;而初始中主应力系数对门槛循环应力比基本没有影响。循环剪切应力模式对门槛循环应力比具有显著影响,在相同的初始固结应力条件下,循环耦合剪切试验确定的门槛循环应力比明显小于循环扭剪试验所确定的门槛循环应力比。 相似文献
7.
通过室内三轴试验研究美国中部密西西比河流域低塑性粉土的液化重固结后剪切强度。研究成果表明,正常固结低塑性粉土液化后不排水剪切强度Su随重固结度的增加而提高,而且呈现类固结现象。类似于未受震动的情况,液化完全重固结后不排水剪切强度比Su,OC/Su, NC与固结比OCR呈幂指数关系,只是幂指数相对于未受震动情况稍大。随着OCR的增加,完全重固结引起的不排水剪切强度变化?Su, recon先提高后降低,当OCR =3.42时,?Su, recon达到最大值。液化完全重固结后不排水剪切行为不具有准稳态现象,随着轴应变增加,应力逐渐增加直至达到临界状态。另外,液化完全重固结后不排水剪切应力-应变曲线可被有效固结应力? ′c归一化。最终提出了计算液化完全重固结后低塑性粉土不排水剪切强度的计算公式。 相似文献
8.
9.
中主应力对饱和松砂不排水单调剪切特性的影响 总被引：7，自引：0，他引：7
利用土工静力-动力液压-三轴扭转多功能剪切仪,针对相对密度为30 %的福建标准砂,在不排水条件下控制主应力方向、中主应力系数、平均主应力保持不变,进行了单调剪切试验。以此着重探讨了中主应力系数对相变有效内摩擦角、峰值有效内摩擦角及有效应力路径的影响。研究表明,中主应力系数对在不排水单调剪切条件下饱和松砂的强度参数具有显著的影响,而对有效应力路径及应力-应变关系发展模式影响较小。基于广义双剪强度准则,从理论上探讨了土的强度参数对于中主应力的依赖性,并与试验结果进行了对比。 相似文献
10.
Michinori Honda Shintaro Ohno Atsushi Iizuka Katsuyuki Kawai Hideki Ohta 《Geotechnical and Geological Engineering》2011,29(2):171-180
An evaluation method for the mechanical behavior of unsaturated soils is studied in this paper. Although the mechanical behavior
of unsaturated soils is complicated, a simple modeling is preferable in practice. This is because the soil properties are
not homogeneous and ground data is limited when structures are being designed. In addition, in order to evaluate the reliability
of the design, the physical meanings of the parameters applied in the prediction model should be clear. Firstly, the authors
study the relationship between compaction curves and compression indexes in the unsaturated state that is used in the proposed
constitutive model. Based on the constitutive model, the stress paths for constant volume shear tests are formulated under
a constant void ratio condition and the stress paths for undrained shear tests are calculated under a constant water content
condition. In the case of unsaturated specimens, the volume of these specimens changes with the shear deformation and the
stress paths depend on the initial degree of saturation. The results of the calculation qualitatively describe the test results
by considering the changes in effective confining pressure in the undrained condition and the water retention curves. 相似文献
11.
Tests on specimens of reconstituted illitic clay have examined the influence of temperature on the mechanical behaviour of clay soils. The program involved consolidation to effective confining pressures up to 1.5 MPa, heating to 100°C, and tests on normally consolidated and overconsolidated specimens with OCR = 2. The tests included isotropic consolidation, undrained triaxial compression with pore water pressure measurement, drained tests along controlled stress paths to investigate yielding behaviour, and undrained tests which involved heating and measurement of the resulting induced pore water pressures. The large strain strength envelope is independent of temperature. However, peak undrained strengths increase with temperature because smaller pore water pressures are generated during shearing. An important contribution from the study is a series of results for the yielding of illitic clay at three different temperatures. For the first time, there is clear evidence of yield loci decreasing in size with increasing temperature. An associated flow rule can be assumed without serious error. The results contribute to the confirmation of a thermal elastic-plastic soil model developed by the authors from cam clay following the addition of a small number of extra assumptions. Depending on the initial stress state, heating under undrained conditions may produce shear failure. 相似文献
12.
Owing to imperfect boundary conditions in laboratory soil tests and the possibility of water diffusion inside the soil specimen in undrained tests, the assumption of uniform stress/strain over the sample is not valid. This study presents a qualitative assessment of the effects of non‐uniformities in stresses and strains, as well as effects of water diffusion within the soil sample on the global results of undrained cyclic simple shear tests. The possible implications of those phenomena on the results of liquefaction strength assessment are also discussed. A state‐of‐the‐art finite element code for transient analysis of multi‐phase systems is used to compare results of the so‐called ‘element tests’ (numerical constitutive experiments assuming uniform stress/strain/pore pressure distribution throughout the sample) with results of actual simulations of undrained cyclic simple shear tests using a finite element mesh and realistic boundary conditions. The finite element simulations are performed under various conditions, covering the entire range of practical situations: (1) perfectly drained soil specimen with constant volume, (2) perfectly undrained specimen, and (3) undrained test with possibility of water diffusion within the sample. The results presented here are restricted to strain‐driven tests performed for a loose uniform fine sand with relative density Dr=40%. Effects of system compliance in undrained laboratory simple shear tests are not investigated here. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
13.
基于有效固结应力法确定结构性黏性土不排水抗剪强度 总被引：3，自引：0，他引：3
由于结构性的存在使得很多天然黏性土的强度和变形特性不同于重塑土和非结构性土。首先回顾了适用于确定重塑土和非结构性土不排水抗剪强度的有效固结应力法,并推导了相应的方程。在此基础上,对于结构性黏性土,采用两段不同斜率（内摩擦角正切）和截距（黏聚力）的直线模拟其抗剪强度包络线,建立了确定其不排水抗剪强度的有效固结应力法方程;当有效应力小于结构屈服应力时,有效固结应力方程中有效应力部分需乘以0.8的修正系数;只要已知剪切前的有效应力,利用相应的有效固结应力法公式,可确定结构性土体的不排水抗剪强度。利用连云港结构性软黏土的等压固结三轴试验数据,验证了有效固结应力法的适用性。分析表明：对于连云港软黏土的不排水抗剪强度,有效固结应力法的计算结果与试验结果吻合较好;对于结构屈服应力,有效固结应力法的预测结果与试验数据点的拟合结果有一定偏差,但并不明显。 相似文献
14.
Yu Haizhen Zhao Wenguang Wang Ren Li Jianguo He Yang 《中国地质大学学报(英文版)》2005,16(4):340-344
INTRODUCTION Theexploitationofoffshorenaturalresourcesin thetropichaspresentedgeotechnicalengineerswith theproblemofdealingwithinsitucarbonatesedi mentsinharshconditionsforwhichfewengineering dataareavailable.Thecarbonatesedimentsaresub jectedtolargestaticstressesduetotheweightof foundationstructuresaswellascyclicstressesdueto waveaction,andinsomecases,earthquakeloading.Ithasbeenprovedthatthenatureofcyclicstresschangesoccurringintheseabeddepositduetowave loadinginvolvesacontinuousrotationo… 相似文献
15.
沿海沿江城市地下开挖产生的工程渣土含泥量大、含水率高且较松散,主要运往渣土场进行堆填处置。由于产量巨大而处置场地有限,许多渣土场在运营过程中存在堆填速度快、缺乏排水设施、超高超库容堆填等问题,容易引发堆填体失稳事故。目前对于非饱和工程渣土堆体在快速堆填过程中的失稳机制认识尚不清晰,尤其是对这一过程中的高饱和度工程渣土强度增长规律缺乏足够的认识。以深圳红坳渣土场填料——花岗岩风化料(CDG)填土为研究对象,对不同初始饱和度土样进行三轴不排水不排气等向压缩和剪切试验,结果表明:非饱和CDG填土不排水抗剪强度随围压增大呈非线性增长,增长速率与试样初始饱和度密切相关;当土样压缩后的饱和度超过0.7,不排水强度随围压的增长速率显著降低。基于有效固结应力法的原理,结合Hilf孔压公式和修正剑桥模型,提出了一种工程渣土不排水抗剪强度估算方法,并通过与试验结果对比验证了该方法对初始饱和度高于0.6的CDG填土的适用性。利用该方法确定的不排水强度cu与正应力σn的关系可应用于高饱和度工程渣土快速堆填中的稳定性分析。 相似文献
16.
An analysis of the vane test using an Arbitrary Lagrangian–Eulerian formulation within a finite element framework is presented. This is suitable for soft clays for which the test is commonly used to measure in situ undrained shear strength. Constitutive laws are expressed in terms of shear stress–shear strain rates, and that permits the study of time effects in a natural manner. An analysis of the shear stress distributions on the failure surface according to the material model is presented. The effect of the constitutive law on the shear band amplitude and on the position of the failure surface is shown. In general, the failure surface is found at 1–1·01 times the vane radius, which is consistent with some experimental results. The problem depends on two dimensionless parameters that represent inertial and viscous forces. For usual vane tests, viscous forces are predominant, and the measured shear strength depends mainly on the angular velocity applied. That can explain some of the comparisons reported when using different vane sizes. Finally, the range of the shear strain rate applied to the soil is shown to be fundamental when comparing experimental results from vane, triaxial and viscosimeter tests. Appart from that, an experimental relation between undrained shear strength and vane angular velocity has been reproduced by this simulation. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
17.
天津市区第一海相层粉质黏土卸荷路径下强度特性的试验研究 总被引：1，自引：0，他引：1
土的强度特性与土体中应力变化过程、固结状态有关,常规的三轴试验并不能真实地反映土体经历的应力路径对其强度特性的影响。采用自制的应力-应变联合控制式三轴试验仪,对天津市区地层中第一海相层的粉质黏土原状饱和试样进行一系列特殊三轴试验,研究了排水卸荷条件对其强度特性的影响。试验结果表明：经历排水卸荷路径的土体的加荷剪切总应力强度指标大于常规试验结果,也大于前人在不排水卸荷路径下的试验结果,但几种应力路径下土体的有效应力强度指标基本相等。研究成果对天津市区基坑开挖及支护结构设计计算、软土隧道施工研究及其他相关岩土工程问题的研究均有较大的实用价值。 相似文献
18.
Many geotechnical problems involve undrained behavior of clay and the capacity in undrained loading. Most constitutive models used today are effective stress based and only indirectly obtain values for the undrained shear strength. To match the design profiles of undrained shear strengths, in active (A), direct simple shear (D) and passive (P) modes of loading are complicated. This paper presents the elastoplastic constitutive model NGI‐ADP which is based on the undrained shear strength approach with direct input of shear strengths. Consequently, exact match with design undrained shear strengths profiles is obtained and the well‐known anisotropy of undrained shear strength and stiffness is accounted for in the constitutive model. A non‐linear stress path‐dependent hardening relationship is used, defined from direct input of failure strains in the three directions of shearing represented by triaxial compression, direct simple shear and triaxial extension. With its clear input parameters the model has significant advantages for design analysis of undrained problems. The constitutive model is implemented, into finite element codes, with an implicit integration scheme. Its performance is demonstrated by a finite element analysis of a bearing capacity problem. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
19.
火山岩坡残积土地区暴雨滑坡泥石流的形成机理 总被引：8，自引：0，他引：8
暴雨条件诱发的浅层坡残积土质斜坡破坏的机理受控于土体在低有效围压条件下的应力应变特性。1993年11月4～5日,香港大屿山地区特大局部性暴雨导致在120km2范围内产生自然滑坡泥石流800余处,且绝大多数发生于火山岩风化坡残积土地区。本文对火山岩风化坡残积土开展了室内偏压固结不排水剪和偏压固结常剪应力排水剪试验,揭示了该类土的应力应变特性;在此基础上,分析了暴雨滑坡泥石流的形成机理和过程。 相似文献
20.
通过直剪试验和三轴试验,研究了超固结状态和正常固结状态土强度指标的差异性。抗剪强度指标在大于和小于前期固结压力的压力段明显不同,试验资料整理时应分别确定抗剪强度指标。剪切前,试样在其自重固结压力（重塑土为预固结压力）下作预处理,比较了在垂直压力或围压小于前期固结压力和大于前期固结压力两个压力段的强度指标,前者不固结不排水剪黏聚力c小于后者,内摩擦角φ大于后者;固结不排水剪黏聚力c大于后者,内摩擦角φ小于后者。重塑土强度试验模拟的应力历史很难真实反映实际工况土体的强度特性,室内试验应尽量使用原状土进行抗剪强度测试。室内试验确定土的抗剪强度指标时,应先确定地基土的前期固结压力、K0状态参数,按工程实际应力状态确定。 相似文献