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1.
The influence of the consolidation on a strutted excavation in soft soil is analysed using a computer code based on the finite element method. A base jet-grout slab is considered in order to improve stability against bottom heave failure and minimize wall displacements. The numerical model incorporates the Biot consolidation theory (coupled formulation of the flow and equilibrium equations) with soil constitutive relations simulated by the p–q–θ critical state model. Special emphasis is given to the analysis, during and after the construction period, of the pore pressures, shear stresses, stress levels and displacements in the ground, as well as strut compression loads, wall displacements and bending moments, earth pressures on the wall faces and compression loads and bending moments on the jet-grout slab. The safety factor against bottom heave is also evaluated from the finite element analysis considering formulations of the critical state soil mechanics, and also compared to values obtained with traditional methods that use limit equilibrium approach and bearing capacity fundamentals. 相似文献
2.
A new simplified Hypothesis B method for calculating the consolidation settlement of ground improved by vertical drains 
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下载免费PDF全文 Vertical drains are widely used in soft ground improvements to accelerate the consolidation process. This paper develops a new simplified Hypothesis B method for calculating the consolidation settlement of a soil layer improved by vertical drains under the instant and ramp loadings. As a comparison, the traditional Hypothesis A method is also used to calculate the settlement. Then, a fully coupled finite element consolidation analysis is utilized to examine and verify this simplified method and Hypothesis A method. For the instant loading, Carrillo‐Barron method and Zhu‐Yin method are used to obtain the average degree of consolidation for vertical drain system. Typical parameters, such as over‐consolidation ratio (OCR), smear zone, and space ratio of vertical drains, are considered. It is found that the calculation results from the new simplified method in this study agree well with finite element simulations, and relative errors are in the range of 0.1% to 12.3%. Comparatively, there are obvious differences between the calculated results from Hypothesis A method and finite element results. Carrillo‐Olson method and Zhu‐Yin method are utilized to obtain the average degree of consolidation for the vertical drain system to consider the ramp loading. Equivalent time is determined from half of the construction period to calculate the creep compression under the ramp loading. The accuracy of this simplified Hypothesis B method using both Carrillo‐Olson method and Zhu‐Yin method is acceptable with the relative errors less than 9.4%. 相似文献
3.
Embankments on Soft Soil Reinforced with Stone Columns: Numerical Analysis and Proposal of a New Design Method 总被引：5，自引：1，他引：4
José Leitão Borges Tiago Sabino Domingues António Silva Cardoso 《Geotechnical and Geological Engineering》2009,27(6):667-679
A parametric study of an embankment on soft soils reinforced with stone columns is performed using a computer program based
on the finite element method. The cylindrical unit cell formulation is used by modeling one column and its surrounding soft
soil with confined axisymmetric behaviour. The computer program incorporates the Biot consolidation theory (coupled formulation
of the flow and equilibrium equations) with constitutive relations simulated by the p–q–θ critical state model. The following parameters are analysed: the replacement area ratio, the deformability of the column
material, the thickness of the soft soil, the deformability of the fill and the friction angle of the column material. Based
on the results of this study, a new design method is proposed, relating the settlement improvement factor to the two factors
that revealed major influence: the replacement area ratio and the ratio between the deformability of the soft soil and the
deformability of the column material. 相似文献
4.
Three-dimensional analysis of embankments on soft soils incorporating vertical drains by finite element method 总被引：4，自引：0，他引：4
Jos Leito Borges 《Computers and Geotechnics》2004,31(8):665-676
Three-dimensional behaviour of an embankment on soft soils incorporating vertical drains is analysed by a numerical model based on the finite element method. The model, which incorporates the Biot’s consolidation theory (coupled formulation of the flow and equilibrium equations) and constitutive relations simulated by the p–q–θ critical state model, is applied on both the embankment with vertical drains (three-dimensional analysis) and the same problem but without vertical drains (two-dimensional analysis). Special emphasis is given to the analysis, during and after the construction period, of the excess pore pressures, settlements, horizontal displacements and stress levels. 相似文献
5.
考虑流变与固结效应的桩筏基础-地基共同作用分析 总被引：2，自引：0，他引：2
土的流变性与地基固结的综合作用,导致了上部结构与地基变形的时效性,并呈现出明显的非线性,对桩筏基础与地基共同作用的工作机理及其工作性能产生重要影响。为此,采用弹黏塑性流变模型考虑土的流变特性,通过有限元方法数值求解Biot耦合固结方程,对桩筏基础与地基共同作用的时间效应问题进行了非线性数值分析。通过算例计算,对加载后桩筏基础荷载分配和沉降特性及下覆土层中孔隙水压力的扩散和消散规律进行了探讨。研究表明,地基孔隙水压力的增长和消散不仅具有Mandel-Cryer效应,而且依赖于土的流变变形,尤其在排水条件较差时更为明显。因此,在分析桩筏基础内力变形的时效性时必须考虑土的流变性与地基的固结作用的联合效应。 相似文献
6.
电渗固结是促进低渗透性软土排水固结的有效方法。为了揭示不同电势梯度影响高岭土电渗固结的基本规律,在自制电渗试验装置上对高岭土进行电渗试验。试验过程中测量电流、排水量、沉降量以及有效电压随时间的变化,并进行单位排水能耗分析。基于电渗固结多场耦合控制方程,实现土体电渗固结全耦合分析的有限元数值方法,计算结果与解析解吻合良好,验证了程序的有效性。为预测不同电势梯度下土体沉降量随时间的变化关系,分别对0.5,1.0,1.5 V/cm 3种电势梯度电渗固结试验进行数值模拟分析,获得模型表面沉降量分布、阳极超静孔隙水压力时空发展规律、阳极位置固结度等曲线,计算结果和试验结果吻合良好,可为实际电渗试验提供理论指导。 相似文献
7.
This paper presents a finite element procedure for the analysis of consolidation of layered soils with vertical drain using general one‐dimensional (1‐D) constitutive models. In formulating the finite element procedure, a Newton–Cotes‐type integration formula is used to avoid the unsymmetry of the stiffness matrix for a Newton (Modified Newton) iteration scheme. The proposed procedure is then applied for the consolidation analysis of a number of typical problems using both linear and non‐linear soil models. Results from this simplified method are compared with those from a fully coupled consolidation analysis using a well‐known finite element package. The average degree of consolidation, excess porewater pressure and average vertical effective stress are almost the same as those from the fully coupled analysis for both the linear and non‐linear cases studied. The differences in vertical effective stresses are tolerable except for the values near the vertical drain boundaries. The consolidation behaviour of soils below a certain depth of the bottom of vertical drain is actually one‐dimensional for the partially penetrating case. Therefore, there are not much differences in whether one uses a one‐dimensional model or a three‐dimensional model in this region. The average degree of consolidation has good normalized feature with respect to the ratio of well radius to external drainage boundary for the cases of fully penetrating vertical drain using a normalized time even in the non‐linear case. Numerical results clearly demonstrate that the proposed simplified finite element procedure is efficient for the consolidation analysis of soils with vertical drain and it has better numerical stability characteristics. This simplified method can easily account for layered systems, time‐dependent loading, well‐resistance, smear effects and inelastic stress–strain behaviour. This method is also very suitable for the design of vertical drain, since it greatly reduces the unknown variables in the calculation and the 1‐D soil model parameters can be more easily determined. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
8.
Unsaturated soils are three‐phase porous media consisting of a solid skeleton, pore liquid, and pore gas. The coupled mathematical equations representing the dynamics of unsaturated soils can be derived based on the theory of mixtures. Solution of these fully coupled governing equations for unsaturated soils requires tremendous computational resources because three individual phases and interactions between them have to be taken into account. The fully coupled equations governing the dynamics of unsaturated soils are first presented and then two finite element formulations of the governing equations are presented and implemented within a finite element framework. The finite element implementation of all the terms in the governing equations results in the complete formulation and is solved for the first time in this paper. A computationally efficient reduced formulation is obtained by neglecting the relative accelerations and velocities of liquid and gas in the governing equations to investigate the effects of fluid flow in the overall behavior. These two formulations are used to simulate the behavior of an unsaturated silty soil embankment subjected to base shaking and compared with the results from another commonly used partially reduced formulation that neglects the relative accelerations, but takes into account the relative velocities. The stress–strain response of the solid skeleton is modeled as both elastic and elastoplastic in all three analyses. In the elastic analyses no permanent deformations are predicted and the displacements of the partially reduced formulation are in between those of the reduced and complete formulations. The frequency of vibration of the complete formulation in the elastic analysis is closer to the predominant frequency of the base motion and smaller than the frequencies of vibration of the other two analyses. Proper consideration of damping due to fluid flows in the complete formulation is the likely reason for this difference. Permanent deformations are predicted by all three formulations for the elastoplastic analyses. The complete formulation, however, predicts reductions in pore fluid pressures following strong shaking resulting in somewhat smaller displacements than the reduced formulation. The results from complete and reduced formulations are otherwise comparable for elastoplastic analyses. For the elastoplastic analysis, the partially reduced formulation leads to stiffer response than the other two formulations. The likely reason for this stiffer response in the elastoplastic analysis is the interpolation scheme (linear displacement and linear pore fluid pressures) used in the finite element implementation of the partially reduced formulation. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
9.
The construction of diaphragm wall panels can cause the stress change and soil movements in adjacent ground. In this paper, the construction sequence of a typical diaphragm wall panel in saturated soft clay is simulated with a 3D finite element program. The soil is assumed to behave as an isotropic linear elastic/Mohr–Coulomb plastic material with a soil–water coupled consolidation response. Influence of the pore water pressure is concerned to consider the consolidation behavior of the saturated soft clay. The analysis shows that the changes in effective horizontal stress and pore water pressure during diaphragm wall installation depend on arching mechanism and permeability. The variation in stresses and movements of ground computed by the coupled consolidation analysis and the total stress analysis are compared. Influences of the permeability coefficient on the installation effects are discussed by parametric studies. Finally, a case study of a diaphragm wall construction in Shanghai, in which the ground settlements were monitored, is presented to illustrate the prediction procedure of coupled consolidation analysis. 相似文献
10.
以准确计算预压荷载作用下软土路基的工后沉降为目的,分析了不同预压法加固软土地基时土体的应力变化。提出了用弱化应力路径变化过程的弹黏塑性模型表示软黏土的应力-应变关系。结合经典比奥固结理论,推导了预压荷载作用下土体沉降计算的有限单元法。通过具体算例,验证了所提方法。结果表明：（1）不同预压方法的加固机制和应力路径均不相同。堆载预压法加固软基是一不等向的正压固结过程,真空预压法则是在负压作用下的等向固结过程;（2）弹黏塑性模型是不受瞬时施加应力的大小及具体应力路径变化过程影响的软土流变模型,运用于预压荷载作用下的软基时具有不考虑应力路径和不划分主次固结的优越性;（3）在比奥固结理论中,用弹黏塑性模型反映软土的物理方程时,可计算软基考虑了弹黏塑变形性质的固结沉降和工后沉降;（4）弹黏塑性模型的软土体黏性参数? /V和塑性参数? /V对竖向位移都有比较明显的影响。 相似文献
11.
This paper presents a general one-dimensional (1-D) finite element (FE) procedure for a highly non-linear 1-D elastic visco-plastic (1-D EVP) model proposed by Yin and Graham for consolidation analysis of layered clay soils. In formulating the 1-D FE procedure, a trapezoidal formula is used to avoid the unsymmetry of the stiffness matrix for a Newton (modified Newton) iteration scheme. Unlike many other 1-D FE approaches in which the initial in situ stresses (or stress/strain states) are considered indirectly or even not considered, the initial in situ stress/strain states are taken into account directly in this paper. The proposed FE procedure is used for analysis of 1-D consolidation of a clay with published test results in the literature. The FE modelling results are in good agreement with the measured results. The FE model and procedure is then used to analyse the consolidation of a multi-layered clay soils with a parametric study on the effects of the variations of creep parameters in Yin and Graham's 1-D EVP model. It is found that the creep parameters ψ/V and t0 have significant influence on the compression and porewater pressure dissipation. For some boundary conditions, changes of parameters in one layer will have some effects on the consolidation behaviour of another layer due to the different consolidation rates. Finally, the importance of initial stress/strain states is illustrated and discussed. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
12.
Clayey soils in the vicinity of energy geostructures may be exposed to long-term periodic thermal cycles. The creep and consolidation behaviors of the clayey soils can be both rate-dependent and temperature-dependent, and the underlying physical mechanisms are merely investigated theoretically. In this study, based on the theory of thermodynamics, a fully coupled thermo-hydro-mechanical (THM) finite element (FE) program for saturated soils is developed for this purpose. The FE formulation accounts for the combined effect of rate and temperature through the novel concept of granular temperature. Simulations of THM coupled validation cases and a series of experimental observations on the soft Bangkok clay are carried out. The obtained numerical results exhibit good agreement with analytical solutions and laboratory measurements. It is found that three fundamental physical mechanisms contribute to the irreversible thermal contraction observed for normally consolidated and lightly overconsolidated clays under drained thermal cycles: (1) the thermal creep excited by mass exchange from adsorbed water to free water; (2) the mechanical creep induced by confining stresses; and (3) the increase in granular packing caused by the thermal expansion of soil particles. The thermal contraction generally stabilizes within a few thermal cycles, as a result of the noticeable reduction in the thermal creep rate. It is further demonstrated that the transient heat transfer and the heating rate can greatly influence the deformation of clays subjected to thermal cycles.
相似文献13.
A two-dimensional computational model is developed here in order to simulate the continuous advance of the Earth Pressure Balance (EPB) Shield during the tunneling process in cohesive soils. The model is based on the combination of the plane strain “transverse–longitudinal” sections that can incorporate the three-dimensional deformation of the soil around and ahead of the shield face. This model is capable of prediciting the soil response due to the shield tunneling before the event, especially in soft ground conditions. An elasto-plastic finite element analysis that is based on the coupled theory of mixtures for inelastic porous media for finite deformation is used in this work to describe the time-dependent deformation of the saturated cohesive soils. The results of this model are compared with the in situ field measurements of the N-2 tunnel project excavated in 1981 in San Francisco using the EPB shield tunneling machine. Reasonable agreement is found between the observed field measurements and the predicted deformations of the soil using the proposed numerical simulation. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
14.
The governing equations for one‐dimensional consolidation of layered structured soils under time‐dependent loading are established. Using simplified k‐σ′ and mv‐σ′ models, n‐layered structured soils are transformed into (n + 1) or (n + 2)‐layered soils in which the thickness of upper and lower layers are gradually changing. The approximate solutions for the governing equations are then obtained under two types of boundary conditions, and the computer program is developed. Based on the solutions and computer program, the consolidation behavior of layered structured soils with soft interlayer is studied. It is shown that the permeability and compressibility of the soft interlayer have the greatest influences on the rate of settlement and rate of the dissipation of excess pore water pressure. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
15.
A coupled elastic–plastic finite element analysis based on simplified consolidation theory for unsaturated soils is used to investigate the coupling processes of water infiltration and deformation. By introducing a reduced suction and an elastic–plastic constitutive equation for the soil skeleton, the simplified consolidation theory for unsaturated soils is incorporated into an in-house finite element code. Using the proposed numerical method, the generation of pore water pressure and development of deformation can be simulated under evaporation or rainfall infiltration conditions. Through a parametric study and comparison with the test results, the proposed method is found to describe well the characteristics during water evaporation/infiltration into unsaturated soils. Finally, an unsaturated soil slope with water infiltration is analyzed in detail to investigate the development of the displacement and generation of pore water pressure. 相似文献
16.
《Geomechanics and Geoengineering》2013,8(3):195-207
This paper presents the finite element (FE) analysis of the consolidation of the foundation of an embankment constructed over soft clay deposit which shows significant time dependent behaviour and was improved with prefabricated vertical drains. To assess the capability of a simple elastic viscoplastic (EVP) model to predict the long term performance of a geotechnical structure constructed on soft soils, a well documented (Leneghans) embankment was analyzed to predict its long term behaviour characteristics. Two fully coupled two dimensional (2D) plane strain FE analyses have been carried out. In one of these, the foundation of the embankment was modelled with a relatively simpler time dependent EVP model and in the other one, for comparison purposes, the foundation soil was modelled with elasto-plastic Modified Cam-clay (MCC) model. Details of the analyses and the results are discussed in comparison with the field performance. Predictions from the creep (EVP) model were found to be better than those from Elasto-plastic (MCC) analysis. However, the creep analysis requires an additional parameter and additional computational time and resources. 相似文献
17.
F. E. analysis of field consolidation curves obtained with the modified borehole shear device (BHSD)
A modified version of the bore hole sheat device (BHSD) was used to obtain field consolidation curves in a soft sensitive clay. The Porewater pressure dissipation was monitored at the centre of one of the shear plates. This paper describes briefly the in situ device employed and demonstrates the basic features of the linearelastic F. E. program ‘SOL’. A detailed study is made to simulate the field behaviour with the finite element approach. Comparisons are made between the field and analytical consolidation behaviour. Difficulties in predicting the value of the coefficient of consolidation of a sensitive clay using the BHSD consolidation curves are discussed. 相似文献
18.
竖井排水固结法中井阻随时空演变（即由淤堵和弯折所引起的竖井排水能力下降）的现象已引起广泛关注,且变井阻对竖井地基固结速率的影响不容忽略。但目前能同时考虑变荷载及井阻随时间和空间变化的固结解析解还鲜有报道。考虑井阻随时空演变过程,引入实际中广泛采用的单级或多级加载模式,建立了竖井地基固结模型,并应用分离变量法获得固结模型的解析解答。通过与已有的解析解、有限差分解及工程实测值进行对比分析,充分验证了该模型的正确性。通过大量的计算,分析变井阻参数对竖井地基固结性状的影响。结果表明：竖井地基固结速率随竖井最终排水能力的增大而加快,随深度井阻参数及时间井阻参数的增大而减缓,且时间井阻参数的影响更为显著。 相似文献
19.
A new simplified Hypothesis B method for calculating consolidation settlements of double soil layers exhibiting creep 下载免费PDF全文
下载免费PDF全文 This paper presents a new simplified method, based on Hypothesis B, for calculating the consolidation settlements of double soil layers exhibiting creep. In the new simplified Hypothesis B method, different stress–strain states including over‐consolidation and normal consolidation states can be considered with the help of the ‘equivalent time’ concept. Zhu and Yin method and US Navy method are adopted to calculate the average degree of consolidation for a double soil layer profile. This new simplified Hypothesis B method is then used to calculate the consolidation settlements of double soil layers, which have two different total thicknesses of soil layer (4 m and 8 m) and three different OCR values (Over‐Consolidation Ratio, OCR = 1, 1.5 and 2). The accuracy and verification of this new simplified method are examined by comparing the calculated results with simulation results from a fully coupled finite element (FE) program using a soft soil creep model. Four cases of double layer soil profiles are analyzed. Hypothesis A method with US Navy method for the average degree of consolidation has also been used to for calculating consolidation settlements of the same cases. For Case I(4m) and Case III(8m), it is found that curves of the new simplified Hypothesis B method using both Zhu and Yin method and US Navy method are very close to the results from FE simulations with the relative errors within 8.5%. For Case II(4m) and Case IV(8m), it is found that curves of the new simplified Hypothesis B method using Zhu and Yin method agree better with results from FE simulations with the relative errors within 11.7% than curves of the new simplified Hypothesis B method adopting US Navy method with the relative error up to 36.1%. Curves of Hypothesis A method adopting US Navy method have the relative error up to 55.0% among all four cases. In overall, the new simplified Hypothesis B method is suitable for calculation of consolidation settlements of double soil layers exhibiting creep, in which, Zhu and Yin method is recommended to obtain the average degree of consolidation. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
20.
为考虑基坑工程的空间效应,土体分别采用K0固结和正常固结试样固结不排水(CU)试验得到的Duncan-Chang非线性弹性模型和Mohr-Coulomb理想弹塑性模型,运用ABAQUS软件按照三维实体单元、壳单元、梁单元考虑接触相互作用的耦合有限元法,建立了福州市一典型软土基坑工程整体三维有限元分析模型,对基坑施工的各工况下整个体系的响应进行了数值模拟"目标试验",并与实测结果和二维数值模拟结果进行了比较,结果表明,采用K0固结试样CU试验参数的Duncan-Chang模型对该基坑进行的三维非线性数值模拟分析方法是较为可靠的,较之Mohr-Coulomb理想弹塑性模型和二维有限元分析,其结果的优势是明显的,是值得推崇和具有较好应用价值的方法。 相似文献