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1.
针对小河沟膨胀土隧道降雨增湿塌方现象,以围岩含水率分布变化引起膨胀应力场为主要研究内容,展开增湿对隧道支护结构的影响研究。首先,利用热传导热能量平衡方程与孔隙渗流连续方程数学描述相似性,推导出热传导膨胀模拟增湿膨胀的替代方程。然后,结合室内试验和文献资料,率定膨胀土膨胀力及渗流参数。最后,在正确考虑地质构造影响的基础上运用有限差分软件FLAC3D热-力耦合模块进行建模计算,分别对不同膨胀力模型的增湿过程进行仿真模拟,得出支护结构受力变形随含水率分布及膨胀力大小的变化规律。分析得到了对隧道支护结构造成不良影响的关键含水率和膨胀力值。研究成果可以有效指导膨胀性黄土隧道支护设计和变形控制。 相似文献
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The development of a numerical procedure for the finite element analysis of anchors dynamically penetrating into saturated soils is outlined, highlighting its unique features and capabilities. The mechanical behaviour of saturated porous media is predicted using mixture theory. An algorithm is developed for frictional contact in terms of effective normal stress. The contact formulation is based on a mortar segment-to-segment scheme, which considers the interpolation functions of the contact elements to be of order N, thus overcoming a numerical deficiency of the so-called node-to-segment (NTS) contact algorithm. The nonlinear behaviour of the solid constituent is captured by the Modified Cam Clay soil model. The soil constitutive model is also adapted so as to incorporate the dependence of clay strength on strain rate. An appropriate energy-absorbing boundary is used to eliminate possible wave reflections from the artificial mesh boundaries. To illustrate the use of the proposed computational scheme, simulations of dynamically penetrating anchors are conducted. Results are presented and discussed for the installation phase followed by ‘setup’, i.e., pore pressure dissipation and soil consolidation. The results, in particular, reveal the effects of strain rate on the generation of excess pore pressure, bearing resistance and frictional forces. The setup analyses also illustrate the pattern in which pore pressures are dissipated within the soil domain after installation. Hole closure behind a dynamic projectile is also illustrated by an example. 相似文献
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Settlement evaluation of soft clay reinforced with stone columns using the equivalent secant modulus 总被引：3，自引：2，他引：1
A method is proposed to evaluate settlement of soft clay reinforced with stone columns. Finite element analyses were carried out using 15-noded triangular elements with PLAXIS. A drained analysis was carried out using Mohr?CCoulomb??s criterion for soft clay, stones, and sand. The stress due to column installation has been considered in the analysis. At the interface between the stone column and soft clay, interface elements have been used. The settlement ratio (SR) of the soil has been estimated using the equivalent secant modulus. The results are compared with those available in the literature, and the advantages of the numerical analysis were highlighted. Based on the results of this analysis, the SR decrease with compaction surrounding soft soil, but decrease of SR is mainly due to a stiffer column material in soft clay. 相似文献
5.
By applying the series expansion technique in the complex variable method established by Muskhelishvili, the plane elasticity problem for the stress and displacement field around a lined circular tunnel in conjunction with the consideration of misfit and interaction between the liner and the surrounding geomaterial is dealt with. The tunnel is assumed to be driven in a homogeneous and isotropic geomaterial. The coefficients in the Laurent series expansion of the stress functions are determined. The complex potentials in the liner and the surrounding geomaterial are explicitly derived, respectively. As an example, the case of a lined circular tunnel located in an isotropic initial stress field but subjected to uniform internal pressure is numerically considered. Numerical results indicate that the installation of tunnel liner can reduce the influences of the tunnel excavation on the in situ displacement and stress fields. However, the relative thickness and rigidity of the liner should be in an appropriate range. In addition, the effect of the tunnel excavation upon the displacement field is more significant than that upon the stress field. As far as the stress field in the surrounding geomaterial is concerned, when the ratio between the cover depth of tunnel and the tunnel radius is larger than 5, the results for the stress field in the paper are applicable. When the ratio between the tunnel depth and the tunnel radius is larger than 20, the results are applicable for the displacement field. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
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In this paper, a comparison between numerical analyses and centrifuge test results relative to the seismic performance of a circular tunnel is provided. The considered experimental data refer to two centrifuge tests performed at Cambridge University, aimed at investigating the transverse dynamic behaviour of a relatively shallow tunnel located in a sand deposit. For the same geometry, different soil relative densities characterise the two tests. The four seismic actions considered, of the pseudo-harmonic type, are characterised by increasing intensity. The 2D numerical analyses were performed adopting an advanced soil constitutive model implemented in a commercial finite element code. The comparison between numerical simulations and measurements is presented in terms of acceleration histories and Fourier spectra as well as of profiles of maximum acceleration along free-field and near-tunnel verticals. In addition, loading histories of normal stress and bending moments acting in the tunnel lining were considered. In general, very good agreement was found with reference to the ground response analyses, while a less satisfactory comparison between observed and predicted results was obtained for the transient and permanent loadings acting in the lining, as discussed in the final part of the paper. 相似文献
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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
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Impact of constitutive models on the numerical analysis of underground constructions 总被引：1，自引：0，他引：1
The constitutive model frequently used in numerical calculations of tunnel excavation is linear-elastic perfectly plastic with a Mohr–Coulomb (MC) failure criterion. Generally, this leads to shallower and wider surface settlement troughs than those observed experimentally. It is therefore necessary to use adapted constitutive models for the design of underground works. In this paper, three constitutive models are implemented in a two-dimensional simulation of an underground excavation in plane strain: a linear-elastic perfectly plastic model (the MC model), an elastoplastic model with isotropic hardening [the hardening soil (HS) model, Schanz et al., Beyond 2000 in computational geotechnics, Balkema, Rotterdam, pp. 281–290, 1999] and an extension of this model which implies an evolution of the stiffness modulus in the small-strain range according to the strain level (the HS model with small-strain stiffness “HS-Small”, Benz, Small-strain stiffness of soils and its numerical consequences. Ph.D. thesis, Universitat Stuttgart, 189 pp., 2007). The study is based on the results of drained triaxial compression tests representing an overconsolidated clay (Gasparre, Advanced laboratory characterisation of London clay. Ph.D. thesis, Imperial College London, 598 pp., 2005); and is then applied to a shallow tunnel. The impact of the constitutive model is highlighted as well as the limits of the simplest constitutive model. 相似文献
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为了能够较快速、较准确地估计出穿越活断层城市地铁隧道的抗震薄弱部位,基于拟静力弹塑性有限元方法,以北京地铁7号线工程的区间隧道作为研究对象,采用数值模拟的方法研究了在走滑断层位错作用下地铁隧道的非线性反应。通过在数值计算模型中嵌入合理的损伤塑性本构模型,利用损伤指标研究了走滑断层下衬砌结构的破坏形式,重点分析了结构损伤的开始部位、发展过程以及最终的损伤程度,并建立了能够估计结构损伤范围及破坏最严重位置的统计关系式。结果表明,在走滑断层作用下衬砌结构出现损伤的区域主要发生在活断层附近一定范围内,拱腰部位的损伤最为严重;增加基岩上覆土层厚度能够减轻衬砌结构的破坏程度,当基岩上覆土层厚度大于等于临界覆盖土层厚度时可以不考虑走滑断层断裂对于浅埋隧道的影响。衬砌结构损伤区域长度与震级的大小和土层厚度有关,损伤最严重的位置随土层厚度的变化而改变。研究成果为穿越活断层地铁隧道的抗震设计和安全性评价提供了参考依据。 相似文献
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Numerical simulation of round robin numerical test on tunnels using a simplified kinematic hardening model 总被引：1，自引：0，他引：1
The paper summarizes the numerical simulation of the round robin numerical test on tunnels performed in Aristotle University of Thessaloniki. The main issues of the numerical simulation are presented along with representative comparisons of the computed response with the recorded data. For the simulation, the finite element method is implemented, using ABAQUS. The analyses are performed on prototype-scale models under plane strain conditions. While the tunnel behavior is assumed to be elastic, the soil nonlinear behavior during shaking is modeled using a simplified kinematic hardening model combined with a von Mises failure criterion and an associated plastic flow rule. The model parameters are adequately calibrated using available laboratory test results for the specific fraction of sand. The soil–tunnel interface is also accounted and simulated adequately. The effect of the interface friction on the tunnel response is investigated for one test case, as this parameter seems to affect significantly the tunnel lining axial forces. Finally, the internal forces of the tunnel lining are also evaluated with available closed-form solutions, usually used in the preliminary stages of design and compared with the experimental data and the numerical predictions. The numerical analyses can generally reproduce reasonably well the recorded response. Any differences between the experimental data and the numerical results are mainly attributed to the simplification of the used model and to differences between the assumed and the actual mechanical properties of the soil and the tunnel during the test. 相似文献
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In geotechnical engineering, numerical analysis of pile capacity is often performed in such a way that piles are modeled using only the geometry of their final position in the ground and simply loaded to failure. In these analyses, the stress changes caused by the pile installation are neglected, irrespective of the installation method. For displacement piles, which are either pushed or hammered into the ground, such an approach is a very crude simplification. To model the entire installation process of displacement piles a number of additional nonlinear effects need to be considered. As the soil adjacent to the pile is displaced significantly, small deformation theory is no longer applicable and a large deformation finite element formulation is required. In addition, the continuously changing interface between the pile and the soil has to be considered. Recently, large deformation frictional contact has been used to model the pile installation and cone penetration processes. However, one significant limitation of the analysis was the use of linear elements, which have proven to be less accurate than higher order elements for nonlinear materials such as soils.
This paper presents a large deformation frictional contact formulation which can be coupled consistently with quadratic solid elements. The formulation uses the so-called mortar-type discretisation of the contact surfaces. The performance of this contact discretisation technique is demonstrated by accurately predicting the stress transfer between the pile and the soil surfaces. 相似文献
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采用三维有限差分软件FLAC3D对地下连续墙施工进行模拟,分析苏州地区粉土地层中地连墙施工对土体扰动及周边建筑物影响。利用UBCSAND硬化规律对外部扰动作用下土体强度逐步发挥的力学特性进行表征,模拟开挖过程中浅层土体变形,并对地连墙施工中成槽开挖、钢筋混凝土施工及混凝土硬化进行全过程模拟。计算结果表明,硬化模型较好地反映地连墙施工扰动下浅层土体力学特性;地连墙成槽阶段地层变形随深度的增加而减小,地表以下20 m范围内地层变形显著,而深部土体变形较小;钢筋混凝土浇筑施工对地层变形起到抑制作用;混凝土硬化阶段地层变形趋于稳定。在该基础上采用硬化模型对苏州某基坑地连墙施工进行数值仿真,模拟结果和现场实测吻合较好。 相似文献
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Undrained stability of a square tunnel in a soil whose strength increases linearly with depth 总被引：1，自引：0，他引：1
This paper examines the undrained stability of a shallow square tunnel in a soil whose strength increases linearly with depth. Rigorous bounds on the loads needed to resist collapse are derived using two numerical techniques which are based on finite element formulations of the classical limit theorems. Both of the numerical procedures assume a linearized perfectly plastic soil model and require the solution of large sparse linear programming problems. For the range of tunnel geometries considered, the numerical results bracket the exact collapse loads closely. The solutions are presented in the form of stability charts which can be used by practising engineers for the purposes of design. 相似文献
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The use of geosynthetic-encased stone columns as a method for soft soil treatment is extensively used to increase the bearing capacity and reduce the settlement of raft foundations and the foundation of structures like embankments. Pre-strain is an effect occurring in the encasement during stone column installation due to the compaction of the stone material. The present study uses the finite element program Plaxis to perform a numerical analysis of the soft clay bed reinforced by geosynthetic-encased stone columns. An idealization is proposed for simulation of installation of geosynthetic-encased stone columns in soft clay based on the unit-cell concept. In the analyses, initially, the validity of the analysis of the single column-reinforced soil in the unit-cell model was performed through comparison with the group columns. Then, by considering a unit-cell model, the finite element analyses were carried out to evaluate the stiffness of the reinforced ground to estimate the settlement. The results of the analyses show that the improved stiffness of the encased stone column is not only due to the confining pressure offered by the geosynthetic after loading, but the initial strain of the geosynthetic that occurred during installation also contributes to the enhancement of the stiffness of the stone column and the reduction of the settlement. 相似文献
16.
Application of a continuum numerical model for pile driving analysis and comparison with a real case
This paper presents the results of a so-called continuum numerical model for wave propagation analysis and soil-pile dynamic response during pile driving. An axisymmetric finite difference numerical model is developed having solid elements for both pile structure and the soil media surrounding and below the pile. Interface elements are used between the pile shaft and the soil to facilitate the sliding between the two media. The performance of the developed model is verified in two stages. First, a simple rod is subjected to a half sine-wave force function at the rod head and the corresponding reflections of force and velocity (multiplied by impedance) are presented for different boundary conditions at the rod tip. The model is then used for signal matching analysis of a real driven pile for which complete information of soil layering, dynamic test signals, and static load test results are available. The signal matching analysis was performed successfully and comparison between several other predicted and measured parameters proved the reasonably good performance of the developed continuum model. 相似文献
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Three-Dimensional Back-Analysis of an Instrumented Shallow Tunnel Excavated by a Conventional Method
Mohamed Nabil Houhou Fabrice Emeriault Émilie Vanoudheusden 《Geotechnical and Geological Engineering》2016,34(4):1101-1117
The excavation of a shallow tunnel induces deformations of the soil volume in the vicinity and above the tunnel and consequently on the nearby buildings. The range of these deformations depends among other on the geological conditions, the geometry of the tunnel, and the excavation method. In this context, this research focuses on the 3D numerical modeling of a shallow tunnel instrumented during its construction, located on the Toulouse (France) subway line B for which the excavation has been carried out in a conventional manner in an over consolidated molassic geological context. The objective of this analysis is to estimate the tunnel behavior in terms of vertical and horizontal movements of the surrounding soil and the deformations of the existing buildings. The explicit finite differences numerical code FLAC3D is used to model the various implementation phases of the work where the fluid–soil interaction is taken into account through an undrained coupled analysis. The results of this 3D model are compared to those of the in situ measurements in order to validate the geotechnical characteristics of the molasses. The latter are a useful basis for the back-analysis of the different monitoring sections implemented in areas where the tunnel excavation is made by TBM with pressurized front. 相似文献
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Souhir Ellouze Zeineb Bensalem Mohamed Nadhir Znaidi 《Geomechanics and Geoengineering》2017,12(2):73-85
This paper addresses the installation effects of stone columns in soft soils. Focus is made on the lateral expansion of stone material using the vibro displacement and substitution techniques by means of numerical simulations. The behaviour of reinforced soil after stone column installation is investigated to show how the properties of soft soils can be improved prior to final loading. The effect of such an improvement on the prediction of reinforced soil settlement is evaluated. The axisymmetric unit cell model (UCM) served for the comparison between numerical predictions made by the Mohr-Coulomb and hardening soil constitutive laws adopted for the soft soil. An equivalent group of end bearing columns model was investigated in the axisymmetric condition to predict the settlement of reinforced soil by adopting the Mohr-Coulomb constitutive model for soft clay. The reduction of settlements predicted by the unit cell and group of columns models, due the improvement of the Young’s modulus of soft clay, were compared. It is concluded that a significant reduction of settlement is expected when the group of columns model is considered. 相似文献
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基于Biot理论,研究了饱和土中带有衬砌的圆形隧洞在移动环形荷载作用下的动力响应。假定衬砌为弹性体,土体为饱和多孔介质,引入两类势函数来表示土体、孔隙水和衬砌的位移,使隧洞的控制方程解耦。结合边界条件及连续条件,通过傅立叶变换得到频率-波数域中衬砌和土体的应力、位移和孔隙水压力解答,最后用傅立叶积分逆变换得到时-空域中的数值解。计算并比较了3种隧洞模型（弹性土体隧洞、饱和土体隧洞和饱和土衬砌隧洞）的动力响应分析。数值分析结果说明：（1）移动荷载速度对3种隧洞动力响应均具有较大影响;（2）弹性土体隧洞和饱和土体隧洞的动力响应具有明显区别,所以在富水地区的隧洞动力响应中土体应该视为饱和土体;（3）衬砌对隧洞动力响应有较大影响,故隧洞的动力分析中不能忽略衬砌作用。 相似文献
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Soil-structure interaction in shield tunnelling in soft soil 总被引：1，自引：0，他引：1
The development and extension of large cities creates a need for multiple shallow tunnels in the soft ground of building areas. Prediction of the ground settlement caused by the tunnel excavation is a major engineering challenge. A numerical simulation using a finite element method was implemented in the aim of developing a procedure to predict the movement induced by shield tunnelling in soft soil. This study describes a two-dimensional modelling and compares two procedures. The first procedure is done in a simple way (called “deconfinement modelling”) simulating the excavation using a stress decrease vector exerted on the excavation boundary (inside the tunnel) described by a stress release scalar parameter λ (named the “deconfinement factor”). The second procedure is composed of a complete stage of modelling (called “phase modelling”) taking into account different phases which simulate the different kinds of interactions between the tunnel and the soil (deconfinement, lining installation, pore pressure applied on the lining, and weight of the lining). Using a shallow lined tunnel with homogeneous soil conditions, the two procedures are analysed and compared. Then, the second modelling procedure is applied to the case of the metro of Lyon where field data have been obtained. Observations of the results and comparison with the experimental data demonstrate that the proposed modelling is adequate for the analyses of settlement induced by tunnelling in soft soil. 相似文献