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1.
A large strain analysis of undrained expansion of a spherical/cylindrical cavity in a soil modelled as non‐linear elastic modified Cam clay material is presented. The stress–strain response of the soil is assumed to obey non‐linear elasticity until yielding. A power‐law characteristic or a hyperbolic stress–strain curve is used to describe the gradual reduction of soil stiffness with shear strain. It is assumed that, after yielding, the elasto‐plastic behaviour of the soil can be described by the modified Cam clay model. Based on a closed‐form stress–strain response in undrained condition, a numerical solution is obtained with the aid of simple numerical integration technique. The results show that the stresses and the pore pressure in the soil around an expanded cavity are significantly affected by the non‐linear elasticity, especially if the soil is overconsolidated. The difference between large strain and small strain solutions in the elastic zone is not significant. The stresses and the pore pressure at the cavity wall can be expressed as an approximate closed‐form solution. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
2.
This paper presents a novel, exact, semi-analytical solution for the quasi-static undrained expansion of a cylindrical cavity in soft soils with fabric anisotropy. This is the first theoretical solution of the undrained expansion of a cylindrical cavity under plane strain conditions for soft soils with anisotropic behaviour of plastic nature. The solution is rigorously developed in detail, introducing a new stress invariant to deal with the soil fabric. The semi-analytical solution requires numerical evaluation of a system of six first-order ordinary differential equations. The results agree with finite element analyses and show the influence of anisotropic plastic behaviour. The effective stresses at critical state are constant, and they may be analytically related to the undrained shear strength. The initial vertical cross-anisotropy caused by soil deposition changes towards a radial cross-anisotropy after cavity expansion. The analysis of the stress paths shows that proper modelling of anisotropic plastic behaviour involves modelling not only the initial fabric anisotropy but also its evolution with plastic straining. 相似文献
3.
The action of tunnel excavation reduces the in-situ stresses along the excavated circumference and can therefore be simulated by unloading of cavities from the in-situ stress state. Increasing evidence suggests that soil behavior in the plane perpendicular to the tunnel axis can be modelled reasonably by a contracting cylindrical cavity, while movements ahead of an advancing tunnel heading can be better predicted by spherical cavity contraction theory. In the past, solutions for unloading of cavities from in-situ stresses in cohesive-frictional soils have mainly concentrated on the small strain, cylindrical cavity model. Large strain spherical cavity contraction solutions with a non-associated Mohr–Coulomb model do not seem to be widely available for tunnel applications. Also, cavity unloading solutions in undrained clays have been developed only in terms of total stresses with a linear elastic-perfectly plastic soil model. The total stress analyses do not account for the effects of strain hardening/softening, variable soil stiffness, and soil stress history (OCR). The effect of these simplifying assumptions on the predicted soil behavior around tunnels is not known. In this paper, analytical and semi-analytical solutions are presented for unloading of both cylindrical and spherical cavities from in-situ state of stresses under both drained and undrained conditions. The non-associated Mohr-Coulomb model and various critical state theories are used respectively to describe the drained and undrained stress-strain behaviors of the soils. The analytical solutions presented in this paper are developed in terms of large strain formulations. These solutions can be used to serve two main purposes: (1) to provide models for predicting soil behavior around tunnels; (2) to provide valuable benchmark solutions for verifying various numerical methods involving both Mohr–Coulomb and critical state plasticity models. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
4.
A hypoplastic constitutive model for clays 总被引：3，自引：0，他引：3
D. Ma&#x;ín 《国际地质力学数值与分析法杂志》2005,29(4):311-336
This paper presents a new constitutive model for clays. The model is developed on the basis of generalized hypoplasticity principles, which are combined with traditional critical state soil mechanics. The positions of the isotropic normal compression line and the critical state line correspond to the Modified Cam clay model, the Matsuoka–Nakai failure surface is taken as the limit stress criterion and the non‐linear behaviour of soils with different overconsolidation ratios is governed by the generalized hypoplastic formulation. The model requires five constitutive parameters, which correspond to the parameters of the Modified Cam clay model and are simple to calibrate on the basis of standard laboratory experiments. This makes the model particularly suitable for practical applications. The basic model may be simply enhanced by the intergranular strain concept, which allows reproducing the behaviour at very small strains. The model is evaluated on the basis of high quality laboratory experiments on reconstituted London clay. Contrary to a reference hypoplastic relation, the proposed model may be applied to highly overconsolidated clays. Improvement of predictions in the small strain range at different stress levels is also demonstrated. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
5.
在实际工程中,土体往往因卸载、再加载等复杂应力路径而处于超固结状态,而现有的圆孔扩张问题的计算模型往往不能反映超固结土中剪胀、软化等一些特殊性质。为了解决这一问题,基于相似性原理和统一硬化（UH）模型,结合相关联的流动法则和大变形理论,采用相似求解技术求解了超固结土不排水扩张问题的半解析解答。通过理想化算例分析了圆孔扩张挤土产生的应力和孔压响应,并通过分析不同超固结比OCR的土体应力路径的变化规律,讨论了UH模型的适用性。结果表明：对于轻超固结土,空腔周围土体孔压在塑性区沿径向单调递减,随着OCR增大,塑性区内孔压分布呈现出“S”形的趋势,孔壁附近的孔压逐渐减小,孔壁周围甚至出现负孔压。随着OCR增大,压力?扩张曲线收敛变慢。在扩孔过程中正常固结土一直处于剪缩硬化阶段。而对于超固结土,土体则经历了临界状态→剪胀硬化阶段→临界（特征）状态→剪缩硬化阶段。该研究成果不仅丰富了相似求解技术的应用,而且为超固结土中桩基承载力、隧道围岩变形预测和原位测试参数等岩土工程问题的计算提供了理论依据。 相似文献
6.
由于黏性土表面带有丰富的负电荷,孔隙水溶液化学状态的变化对黏性土的物理力学特性存在明显影响。随着化学-力学耦合的相关岩土工程问题日益突出,进行有效的化学-力学耦合行为的数值分析评价显得尤为重要。因此,建立一个简单有效的考虑化学-力学耦合的本构模型是非常关键的。基于传统的修正剑桥模型,提出了一个简单的化学-力学耦合模型。该模型采用渗透吸力π描述孔隙水的化学状态,建立了前期屈服应力,临界状态线斜率M和弹性刚度与渗透吸力π之间的关系式,从而实现了模型对盐溶液饱和黏性土的变形和强度特性的有效模拟。通过与试验数据的对比和分析,说明该模型能有效地模拟孔隙盐溶液饱和黏性土的等向压缩行为、 状态下压缩行为以及 状态下化学-力学循环加载行为。此外,通过对黏性土三轴压缩试验的模拟,说明该模型能反映黏性土三轴应力状态下的基本力学特征。 相似文献
7.
An analytical solution of cavity expansion in two different concentric regions of soil is developed and investigated in this paper. The cavity is embedded within a soil with finite radial dimension and surrounded by a second soil, which extends to infinity. Large‐strain quasi‐static expansion of both spherical and cylindrical cavities in elastic‐plastic soils is considered. A non‐associated Mohr–Coulomb yield criterion is used for both soils. Closed‐form solutions are derived, which provide the stress and strain fields during the expansion of the cavity from an initial to a final radius. The analytical solution is validated against finite element simulations, and the effect of varying geometric and material parameters is studied. The influence of the two different soils during cavity expansion is discussed by using pressure–expansion curves and by studying the development of plastic regions within the soils. The analytical method may be applied to various geotechnical problems, which involve aspects of soil layering, such as cone penetration test interpretation, ground‐freezing around shafts, tunnelling, and mining. © 2014 The Authors. International Journal for Numerical and Analytical Methods in Geomechanics published by John Wiley & Sons Ltd. 相似文献
8.
9.
This paper presents an analytical solution for cavity expansion in thermoplastic soil considering non‐isothermal conditions. The constitutive relationship of thermoplasticity is described by Laloui's advanced and unified constitutive model for environmental geomechanical thermal effect (ACMEG‐T), which is based on multi‐mechanism plasticity and bounding surface theory. The problem is formulated by incorporating ACMEG‐T into the theoretical framework of cavity expansion, yielding a series of partial differential equations (PDEs). Subsequently, the PDEs are transformed into a system of first‐order ordinary differential equations (ODEs) using a similarity solution technique. Solutions to the response parameters of cavity expansion (stress, excess pore pressure, and displacement) can then be obtained by solving the ODEs numerically using mathematical software. The results suggest that soil temperature has a significant influence on the pressure‐expansion relationships and distributions of stress and excess pore pressure around the cavity wall. The proposed solution quantifies the influence of temperature on cavity expansion for the first time and provides a theoretical framework for predicting thermoplastic soil behavior around the cavity wall. The solution found in this paper can be used as a theoretical tool that can potentially be employed in geotechnical engineering problems, such as thermal cone penetration tests, and nuclear waste disposal problems. 相似文献
10.
In order to capture the influence of the cavity expansion velocity, this paper presents a semianalytical solution for dynamic spherical cavity expansion in modified Cam Clay (MCC) soil. The key problem is solving the six coupled partial differential equations (PDEs) of cavity expansion, in which the dynamic term is considered in the stress equilibrium equation. The similarity transformation technique is used to transform the PDEs into ordinary differential equations (ODEs). Subsequently, the numerical method using the function “ODE45” in MATLAB is selected to solve the ODEs, which allows the stress and excess pore pressure around the expanding spherical cavity wall to be obtained. The proposed semianalytical solution for dynamic spherical cavity expansion was validated by comparting the degenerate solution with the published quasistatic solution for the MCC model. Parametric study was then conducted to capture the influence of the cavity wall velocity on the cavity expansion response. The proposed solution has potential application to geotechnical problems such as dynamic pile driving, the dynamic cone penetration test, and so forth. 相似文献
11.
Constitutive models for unsaturated soils are most commonly based on conventional critical state type models for saturated soils. The ellipse of the modified Cam-clay model is usually adopted for the formulation of the yield and the plastic potential surfaces in the mean stress – deviatoric stress plane. Despite the wide use of this ellipse it has long been shown that the peak deviatoric stress observed for highly overconsolidated states may be largely overestimated. For fully saturated conditions, a planar surface, termed the Hvorslev surface, has been employed in the literature in order to overcome this shortcoming on the dry side of the critical state. In addition, by employing a no-tension cut-off, stress states are restricted within the compressive region. In unsaturated conditions and due to the effect of suction the soil may be subjected to tensile total stresses which should not, however, exceed a model dependent limit. Nonetheless, adopting a planar surface and in the absence of any provision, illegal tensile stresses may be obtainable. For this reason, a new expression for the Hvorslev surface, which restricts the stress state within acceptable boundaries, is proposed, based on a small number of model parameters. The new surface is curved rather than planar and can also be used in combination with critical state type constitutive models developed for saturated conditions. The new surface is calibrated based on fully saturated undrained triaxial compression and extension tests and on unsaturated drained triaxial tests. The superiority of the new surface in comparison with commonly adopted shapes for the yield and the plastic potential functions – such as the ellipse and the bullet shape of the modified and the original Cam clay models – is demonstrated through numerical analyses of the unsaturated drained triaxial laboratory tests. 相似文献
12.
The modified Cam clay (MCC) model is used to study the response of virgin‐compressed clay subjected to undrained triaxial compression. The MCC constitutive relationship is obtained in a closed form. Both elastic and plastic deviatoric strains are considered in the analysis. The solution allows to obtain total and effective stress paths followed by the clay in undrained spherical expansion. Pore water pressures are determined from the difference between total and effective mean stresses. For illustration purposes, the analysis is also applied to the well‐known reconstituted normally consolidated London clay and the results are compared with the recently published data obtained by a numerical approach. In addition, the Almansi large strains are used in the analysis, as these allow to obtain limit expansion and pore pressures, whereas both small‐strain and logarithmic‐strain approaches do not permit to determine them. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
13.
The paper presents numerical simulations investigating the settlement reduction caused by stone columns in a natural soft clay. The focus is on the influence of the soft soil alteration caused by column installation. A uniform mesh of end-bearing columns under a distributed load was considered. Therefore, the columns were modelled using the “unit cell” concept, i.e. only one column and the corresponding surrounding soil in axial symmetry. The properties of the soft clay correspond to Bothkennar clay, which is modelled using S-CLAY1 and S-CLAY1S, which are Cam clay type models that account for anisotropy and destructuration. The Modified Cam clay model is also used for comparison. Column installation was modelled independently to avoid mesh distortions, and soft soil alteration was directly considered in the initial input values. The results show that the changes in the stress field, such as the increase of radial stresses and mean stresses and the loss of overconsolidation, are beneficial for high loads and closely spaced columns but, on the contrary, may be negative for low loads, widely spaced columns and overconsolidated soils. Moreover, whilst the rotation of the soil fabric reduces the settlement, in contrast the soil destructuration during column installation reduces the improvement. 相似文献
14.
The problem of the symmetric quasi‐static large‐strain expansion of a cavity in an infinite granular body is studied. The body is assumed to be dry or fully drained so that the presence of the pore water can be disregarded. Both spherical and cylindrical cavities are considered. Numerical solutions to the boundary value problem are obtained with the use of the hypoplastic constitutive relation calibrated for a series of granular soils. As the radius of the cavity increases, the stresses and the density on the cavity surface asymptotically approach limit values corresponding to a so‐called critical state. For a given soil, the limit values depend on the initial stresses and the initial density. A comparison is made between the solutions for different initial states and different soils. Applications to geotechnical problems such as cone penetration test and pressuremeter test are discussed. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
15.
A cavity expansion–based solution is proposed in this paper for the interpretation of CPTu data under a partially drained condition. Variations of the normalized cone tip resistance, cone factor, and undrained-drained resistance ratio are examined with different initial specific volume and overconsolidation ratio, based on the exact solutions of both undrained and drained cavity expansion in CASM, which is a unified state parameter model for clay and sand. A drainage index is proposed to represent the partially drained condition, and the critical state after expansion and stress paths of cavity expansion are therefore predicted by estimating a virtual plastic region and assuming a drainage-index–based mapping technique. The stress paths and distributions of stresses and specific volume are investigated for different values of drainage index, which are also related to the penetration velocity with comparisons of experimental data and numerical results. The subsequent consolidation after penetration is thus predicted with the assumption of constant deviatoric stress during dissipation of the excess pore pressure. Both spherical and cylindrical consolidations are compared for dissipation around the cone tip and the probe shaft, respectively. The effects of overconsolidation ratio on the stress paths and the distributions of excess pore pressure and specific volume are then thoroughly investigated. The proposed solution and the findings would contribute to the interpretation of CPTu tests under a random drained condition, as well as the analysis of pile installation and the subsequent consolidation. 相似文献
16.
SBPT测定饱和黏土不排水强度的数值分析 总被引：1，自引：0，他引：1
自钻式旁压试验（SBPT）因其扰动小、测试深度大、可以获得应力-应变、超孔隙水压力-时间等数据,在确定地基土性参数和地基承载力上有广阔的应用前景。然而由于用以解释SBPT的柱孔扩张理论（Gibson解）所采用的平面应变假设与实际旁压腔几何特征存在差异,导致试验所确定的黏土不排水剪切强度su与其他原位试验或室内试验结果存在差别。针对旁压腔几何尺寸及应变区间的选择对确定su的影响,基于修正剑桥模型,采用低渗透系数控制加载过程中不排水条件,利用有限元法模拟SBPT,建议了不同应力历史下确定su的应变区间,并给出考虑几何尺寸影响时相应应变区间上su的修正系数。 相似文献
17.
初始应力各向异性土的弹塑性模型 总被引：17，自引：8，他引：9
剑桥模型沿球应力轴(p 轴)等向塑性体变硬化; 在日本广泛采用的关口 — 太田模型沿初始固结线( K0 线)不等向塑性体变硬化。三轴试验数据表明: 自 K0 状态向伸长方向剪切时, 前者方法计算的体积应变偏小, 而后者方法计算的体积应变偏大。 作者提出一种介于上述两者之间 、考虑初始应力各向异性(如 K0 固结)的不等向塑性体变硬化弹塑性模型。 为了使模型在三维应力下较好地反映土的强度和变形特性, 模型的剪切屈服准则使用 SMP 准则。模型的土性参数与剑桥模型一样, 其预测值与粘土实测值的比较表明, 提出的模型是简单合理的, 可望在实际工程计算中得到使用。 相似文献
18.
基于天然饱和黏土地基中静压沉桩扩孔问题的弹塑性解,以沉桩结束后桩周土体的应力状态为初始条件,推导了桩周孔压消散的解析解。在此基础上,考虑桩周土体再固结过程中的土体松弛效应,提出了采用有效应力计算天然饱和黏土中静压桩时变承载力的理论方法。通过已有离心模型试验和现场试验结果对该方法进行了验证,研究了沉桩结束后静压桩承载力随固结时间的变化规律。结果表明,提出的理论方法合理考虑了土体的原位力学特性、沉桩效应及沉桩结束后土体有效应力的变化,因而可以较好地预测静压桩的时变承载力。该研究成果为合理确定黏土中静压桩承载力提供了理论依据,具有一定的理论和工程意义。 相似文献
19.
A new constitutive model for soft structured clays is developed based on an existing model called S‐CLAY1S, which is a Cam clay type model that accounts for anisotropy and destructuration. The new model (E‐SCLAY1S) uses the framework of logarithmic contractancy to introduce a new parameter that controls the shape of the yield surface as well as the plastic potential (as an assumed associated flow rule is applied). This new parameter can be used to fit the coefficient of earth pressure at rest, the undrained shear strength or the stiffness under shearing stress paths predicted by the model. The improvement to previous constitutive models that account for soil fabric and bonding is formulated within the contractancy framework such that the model predicts the uniqueness of the critical state line and its slope is independent of the contractancy parameter. Good agreement has been found between the model predictions and published laboratory results for triaxial compression tests. An important finding is that the contractancy parameter, and consequently the shape of the yield surface, seems to change with the degree of anisotropy; however, further study is required to investigate this response. From published data, the yield surface for isotropically consolidated clays seems ‘bullet’ or ‘almond’ shaped, similar to that of the Cam clay model; while for anisotropically consolidated clays, the yield surface is more elliptical, like a rotated and distorted modified Cam clay yield surface. © 2015 The Authors. International Journal for Numerical and Analytical Methods in Geomechanics published by John Wiley & Sons Ltd. 相似文献
20.
The objective of this study is to derive an effective stress‐based constitutive law capable of predicting rate‐dependent stress–strain, stress path and undrained shear strength and creep behavior. The flow rule used in the MIT‐E3 model and viscoplasticity theory is employed in the derivation. The model adopts the yield surface capable of representing the yield behavior of the Taipei silty clay and assumes that it is initially symmetric about the K0‐line. A method is then developed to compute the gyration and expansion of the loading surface to simulate the anisotropic behavior due to the principal stress rotation after shear. There are 11 parameters required for the model to describe the soil behavior and six of them are exactly the same as those used in the Modified Cam‐clay model. The five additional parameters can be obtained by parametric studies or conventional soil tests, such as consolidation tests, triaxial compression and extension tests. Finally, verification of the model for the anisotropic behavior, creep behavior and the rate‐dependent undrained stress–strain and shear strength of the Taipei silty clay is conducted. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献