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1.
The behaviour of an artificially cemented sandy gravel 总被引：1，自引：0，他引：1
The major section of the city of Tehran, Iran has been developed on cemented coarse-grained alluvium. This deposit consists of gravely sand to sandy gravel with some cobbles and is dominantly cemented by carbonaceous materials. In order to understand the mechanical behaviour of this soil, a series of undrained triaxial compression tests and unconfined compression tests were performed on uncemented and artificially cemented samples. Portland cement type I was used as the cementation agent for preparing artificially cemented samples. Uncemented samples and lightly cemented samples (1.5% cement) tested at high confining pressure showed contractive behaviour accompanied with positive excess pore water pressure and a barrelling failure mode. However, cemented samples and uncemented samples tested at low confining pressure (25 and 50 kN/m2) showed dilative behaviour accompanied with negative excess pore water pressure. Shear zones were formed in these samples and a clear peak in excess pore water pressure and stress ratio against strain could be observed. Test results showed that the limiting stress ratio surface for cemented samples is curved and expands as the cementation and density increase. Unconfined compression strength of cemented samples increases with increases in cementation and density as well. 相似文献
2.
Jianhong Jiang Hoe I. Ling Victor N. Kaliakin Xiangyong Zeng Ching Hung 《Acta Geotechnica》2017,12(2):335-348
An anisotropic time-dependent bounding surface model for clays is developed by generalizing a previous time-independent model that adopts a flexible bounding surface. It is based on the framework for coupled elastoplasticity–viscoplasticity for clays and Perzyna’s overstress theory. Three viscoplastic parameters were introduced and explained in detail. The model was validated against undrained creep tests for both isotropically and anisotropically consolidated clays, undrained and drained stress relaxation tests on some undisturbed clays, and undrained triaxial tests with varying strain rates on natural Hong Kong marine deposit clay. The general agreement between the model simulations and test results was satisfactory. The varying effects of lower-level parameters were discussed on the undrained multistage stress relaxation response for normally consolidated soils which had been ignored in literature. The flexibility of the model in capturing the shear strengths, which is the unique feature of the current model, was shown in the simulations of time-dependent triaxial tests on Taipei silty clay. All the simulations show that the proposed model is a relatively practical model considering both anisotropy and time dependency of clays. 相似文献
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Allison J. Quiroga Zachary M. Thompson Kanthasamy K. Muraleetharan Gerald A. Miller Amy B. Cerato 《Acta Geotechnica》2017,12(5):1003-1020
The results of a series of laboratory tests on unimproved and cement-improved specimens of two clays are presented, and the ability of a bounding surface elastoplastic constitutive model to predict the observed behavior is investigated. The results of the oedometer, triaxial compression, extension, and cyclic shear tests demonstrated that the unimproved soil behavior is similar to that of soft clays. Cement-improved specimens exhibited peak/residual behavior and dilation, as well as higher strength and stiffness over unimproved samples in triaxial compression. Two methods of accounting for the artificial overconsolidation effect created by cement improvement are detailed. The apparent preconsolidation pressure method is considerably easier to use, but the fitted OCR method gave better results over varied levels of confining stresses. While the bounding surface model predicted the monotonic behavior of unimproved soil very well, the predictions made for cyclic behavior and for improved soils were only of limited success. 相似文献
6.
S. M. Haeri A. Hamidi S. M. Hosseini E. Asghari D. G. Toll 《Geotechnical and Geological Engineering》2006,24(2):335-360
The behavior of a cemented gravely sand was studied using triaxial compression tests. Gypsum, Portland cement and lime were
used as the cementing agents in sample preparation. The samples with different cement types were compared in equal cement
contents. Three cement contents of 1.5%, 3.0% and 4.5% were selected for sample preparation. Drained and undrained triaxial
compression tests were conducted in a range of confining pressures from 25 kPa to 500 kPa. Failure modes, shear strength,
stress–strain behavior, volume and pore pressure changes were considered. The gypsum cement induced the highest brittleness
in soil among three cement types while the Portland cement was found to be the most ductile cementing agent. In lower cement
contents and lower confining pressures the soil cemented with Portland cement showed the highest shear strength. However,
in the same range of cement content, the soil cemented with gypsum showed highest shear strength for highest tested confining
stress. For higher cement contents the shear strength of soil cemented with Portland cement is higher than that for the two
other cement types for the range of confining pressures tested in the present study. The samples cemented with lime had the
least peak and ultimate shear strength and the highest pore pressure generation in undrained tests. Contrary to the soil cemented
with lime, the brittleness of soil cemented with gypsum and Portland cement reduces in undrained condition. Finally it was
found that the effect of cement type on the shear strength of cemented soils is more profound in drained condition compared
to undrained state. 相似文献
7.
Jean-Herv Prvost 《国际地质力学数值与分析法杂志》1977,1(2):195-216
The proposed general analytical model describes the anisotropic, elasto-plastic, path-dependent, stress-strain-strength properties of inviscid saturated clays under undrained loading conditions. The model combines properties of isotropic and kinematic plasticity by introducing the concept of a field of plastic moduli which is defined in stress space by the relative configuration of yield surfaces. For any loading (or unloading) history, the instantaneous configuration is determined by calculating the translation and contraction (or expansion) of each yield surface. The stress-strain behaviour of clays can thus be determined for complex loading paths and in particular for cyclic loadings. The stress-strain relationships are provided for use in finite element analyses. The model parameters required to characterize the behaviour of any given clay can be derived entirely from conventional triaxial or simple shear soil test results. The model's extreme versatility is demonstrated by using it to formulate the behaviour of the Drammen clay under both monotonic and cyclic loading conditions. The parameters are determined by using solely the results from monotonic and cyclic strain-controlled simple shear experimental tests, and the model's accuracy is evaluated by applying it to predict the results of other tests such as (1) cyclic stress-controlled simple shear tests, (2) monotonic triaxial loading compression and unloading extension tests, and (3) cyclic stress- and strain-controlled triaxial tests on, this same clay. The theoretical predictions are found to agree extremely well with the experimental test results. 相似文献
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In this paper, a simple bounding surface plasticity model is used to reproduce the yielding and stress–strain behavior of the structured soft clay found at Shanghai of China. A series of undrained triaxial tests and drained stress probe tests under isotropic and anisotropic consolidation modes were performed on undisturbed samples of Shanghai soft clay to study the yielding characteristics. The degradation of the clay structure is modeled with an internal variable that allows the size of the bounding surface to decay with accumulated plastic strain. An anisotropic tensor and rotational hardening law are introduced to reflect the initial anisotropy and the evolution of anisotropy. Combined with the isotropic hardening rule, the rotational hardening rule and the degradation law are incorporated into the bounding surface formulation with an associated flow rule. Validity of the model is verified by the undrained isotropic and anisotropic triaxial test and drained stress probe test results for Shanghai soft clay. The effects of stress anisotropy and loss of structure are well captured by the model. 相似文献
9.
Cemented coarse-grained alluvium is present in a vast area of Tehran city, Iran including its suburbs. This deposit consists of gravely sand to sandy gravel with some cobbles and is dominantly cemented by carbonaceous materials. In order to understand the mechanical behaviour of this soil, a series of triaxial compression tests were performed on uncemented, artificially cemented and destructured samples. Hydrated lime was used as the cementation agent for sample preparation to model the Tehran deposit. The tests were performed on cemented samples after an appropriate time for curing. The tests on cemented samples show that a shear zone appears as the shear stress approaches the peak shear strength. During shearing these samples undergo dilation at confining stress lower than 1000kPa. However, the uncemented and destructured samples show contraction during shearing. Peak shear strength is followed by strain softening for all cemented samples. The shear strength increases with increasing cement content but the influence of the cementation decreases as the confining stress increases. With increasing cementation the stress-strain behaviour of samples tend towards the behaviour expected of high-density soils. Test results indicate that the failure envelope for cemented samples is curved and not linear. 相似文献
10.
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
11.
软黏土加载速率效应特性试验研究:进展与趋势 总被引：1，自引：0，他引：1
大量的室内和现场试验都表明,软黏土的强度与变形速率相关。为了更深入地认识软黏土的加载速率效应特性,首先分析了一维应力条件下先期固结压力和三轴应力条件下不排水抗剪强度的加载速率效应及应力-应变关系的归一化,探讨了一维和三轴条件下的5个速率方程(2个指数形式和3个对数形式)在拟合黏土先期固结压力和不排水强度加载速率效应上的适用性;使用5个速率方程估计了一维和三轴条件下的加载速率参数,以及拟合了加载速率参数与液塑限的关系,并且分析了复杂应力(十字板剪切和旁压条件)下的非理想土单元体的黏土加载速率效应特性等;讨论了黏土加载速率效应特性在一维和三维、压缩与伸长、不同超固结比(OCR)条件下的统一性;最后,从香港黏土压缩与伸长和不同OCR条件下的剪缩、剪胀特性方面更深入地探讨了软黏土加载速率效应特性,并讨论了典型的剪缩、剪胀方程在黏土的力学特性模拟中的有效性。结果表明,为更好地描述黏土的应力剪胀特性,现有典型的剪胀关系需要更一步改进。 相似文献
12.
This paper presents a new viscohypoplastic model for soft clays accounting for their typical features—strength anisotropy and rate dependency. The model is based on the hypoplastic model for clays enhanced by the anisotropic shape of the asymptotic state boundary surface. It has been shown that if the surface is skewed, the model predicts different ultimate strength in compression and in extension. Additional enhancement makes the tensor L bilinear in the strain rate, which more realistically predicts the stress paths of K0 consolidated samples. The new model has been evaluated by simulating laboratory experiments on soft marine clays (Singapore and Bangkok clays). The model can be easily calibrated using only undrained triaxial and odometer tests. The model is subsequently enhanced by the rate effects. The resulting viscohypoplastic model has been evaluated using experiments of remolded kaolin clay and St. Herblain clay. It is shown that the enhanced model can predict important features of soil viscous behavior, such as rate dependency of strength and preconsolidation pressure, relaxation, and creep. 相似文献
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This paper evaluates the performance of a generalized effective stress soil model for predicting the rate independent behaviour of freshly deposited sands, while a companion paper describes model capabilities for clays and silts. Most material parameters can be obtained from standard laboratory data, including hydrostatic or one‐dimensional compression, drained and undrained triaxial shear testing. A compilation of data on compression behaviour allows for estimation of compression parameters when this type of data is not available. Extensive comparisons of model predictions with measured data from undrained triaxial shear tests shows that the model gives excellent predictions of the transition from dilative to contractive shear response as the confining pressure and/or the initial formation void ratio increases. A parametric study of drained response shows that the model describes realistically the variation of peak friction angle and dilation rate as a function of confining pressure and density when compared with an empirical correlation valid for many sands. The proposed formulation predicts a unique critical state locus for both drained and undrained triaxial testing which is non‐linear over the entire range of stresses and is in excellent agreement with recent experimental data. Overall, the model provides excellent predictions of the stress–strain–strength relationships over a wide range of confining pressures and formation densities. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
14.
Hiroyoshi Hirai 《国际地质力学数值与分析法杂志》1987,11(5):503-520
The constitutive model of sands is proposed to describe the characteristics of plastic behaviour for cyclic loadings. A non-associated flow rule is used and both yield function and plastic potential are generalized forms of the Modified Cam clay model. The hardening parameter is represented by the plastic work related to different portions of volumetric and deviatoric changes. The boundary surface is employed to describe the plastic strain within the yield surface. The directional independency of yield condition in triaxial compression and extension tests is extended to that in general stress states. Several drained and undrained cyclic tests are predicted and the comparison is made with experimental results. The proposed model is capable of representing the monotonic and cyclic behaviours of sands with reasonable accuracy. The simulation is performed for both included and excluded membrane penetration effects and it is suggested that the membrane penetration causes the significant influences on the results of undrained cyclic tests. 相似文献
15.
基于Wheeler土体各向异性旋转硬化法则,结合边界面理论,构造一个能够反映土体初始各向异性及加载后应力诱发各向异性的边界面本构模型,并借助ABAQUS软件提供的UMAT子程序接口,采用隐式积分算法--图形返回算法实现。通过对正常固结状态下（OCR=1）高岭土试样三轴不排水剪切试验进行模拟,并将模拟结果与ABAQUS自带的修正剑桥模型模拟结果进行了比较分析,表明本模型的模拟结果能够反映土体在偏压加载过程中产生的各向异性现象。在此基础上,采用本模型对中等超固结（OCR=4）高岭土试样三轴不排水剪切试验进行模拟,并再次与ABAQUS自带的修正剑桥模型模拟结果进行比较,表明本模型能够较好地反映中等超固结土在小应变情况下的非线性特性。相比于经典弹塑性模型,如修正剑桥模型,本模型的模拟结果更符合中等超固结土的变形特性。 相似文献
16.
考虑循环载荷下饱和黏土软化的损伤边界面模型研究 总被引：1，自引：0，他引：1
研究表明,循环载荷作用下饱和黏土将发生软化,其机制主要有两个：一是孔压的积累;二是土体原有结构的不断损伤和新结构的不断重塑。针对上述机制,基于广义各向同性硬化准则建立了考虑饱和黏土循环软化的损伤单面模型。该模型在有效应力空间中引入损伤变量,表征土体结构的损伤和重塑程度,在连续的循环加载下,损伤不断累积,边界面则随着损伤的累积不断收缩,以模拟饱和黏土刚度和强度的软化;以应力反向点作为边界面的广义各向同性硬化中心和映射法则的映射中心,灵活地选择塑性模量的插值公式以模拟塑性变形和孔压的累积以及应力-应变的滞回特性。应用该模型对不排水循环三轴试验进行模拟,并且考查了循环周次、循环应力水平和固结历史对饱和黏土循环软化特性的影响,并与相关试验比较,验证了模型的有效性。 相似文献
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Tsutomu Namikawa 《国际地质力学数值与分析法杂志》2001,25(6):605-627
A delayed plastic model, based on the theory of plasticity, is proposed to represent the time‐dependent behaviour of materials. It is assumed in this model that the stress can lie outside the yield surface and the conjugate stress called static stress is defined on the yield surface. The stress–strain relation is calculated based on the plastic theory embedding the static stress. Thus, the stress–strain relation of the model practically corresponds to that of the inviscid elastoplastic model under fairly low rate deformation. The delayed plastic model is coupled with the Cam‐clay model for normally consolidated clays. The performance of the model is then examined by comparing the model predictions with reported time‐dependent behaviour of clays under undrained triaxial conditions. It is shown that the model is capable of predicting the effect of strain rate during undrained shear and the undrained creep behaviour including creep rupture. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
18.
Yannis F. Dafalias Majid T. Manzari Achilleas G. Papadimitriou 《国际地质力学数值与分析法杂志》2006,30(12):1231-1257
SANICLAY is a new simple anisotropic clay plasticity model that builds on a modification of an earlier model with an associated flow rule, in order to include simulations of softening response under undrained compression following Ko consolidation. Non‐associativity is introduced by adopting a yield surface different than the plastic potential surface. Besides, the isotropic hardening of the yield surface both surfaces evolve according to a combined distortional and rotational hardening rule, simulating the evolving anisotropy. Although built on the general premises of critical state soil mechanics, the model induces a critical state line in the void ratio–mean effective stress space, which is a function of anisotropy. To ease interpretation, the model formulation is presented firstly in the triaxial stress space and subsequently, its multiaxial generalization is developed systematically, in a form appropriate for implementation in numerical codes. The SANICLAY is shown to provide successful simulation of both undrained and drained rate‐independent behaviour of normally consolidated sensitive clays, and to a satisfactory degree of accuracy of overconsolidated clays. The new model requires merely three constants more than those of the modified Cam clay model, all of which are easily calibrated from well‐established laboratory tests following a meticulously presented procedure. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
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The discrete element method has been used to investigate the micro mechanics of cemented sand. High‐pressure drained triaxial tests are modelled in 3D using a flexible membrane that allows the correct deformation to develop. Simulations with up to 12 MPa confining pressure are presented, which are compared with laboratory experiments on a sand with a range of cement contents. Cementation is modelled using ‘parallel bonds’, and various parameters and strength distributions are investigated. Varying levels of cementation are successfully modelled, with the correct qualitative behaviour observed and the separate effects of cementation and confining pressures demonstrated. The triaxial behaviour is found to be highly influenced by the distribution of bond strengths. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献