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1.
Stress‐driven integration strategies and m‐AGC tangent operator for Perzyna viscoplasticity and viscoplastic relaxation: application to geomechanical interfaces 
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下载免费PDF全文 The paper proposes a stress‐driven integration strategy for Perzyna‐type viscoplastic constitutive models, which leads also to a convenient algorithm for viscoplastic relaxation schemes. A generalized trapezoidal rule for the strain increment, combined with a linearized form of the yield function and flow rules, leads to a plasticity‐like compliance operator that can be explicitly inverted to give an algorithmic tangent stiffness tensor also denoted as the m‐AGC tangent operator. This operator is combined with the stress‐prescribed integration scheme, to obtain a natural error indicator that can be used as a convergence criterion of the intra‐step iterations (in physical viscoplasticity), or to a variable time‐step size in viscoplastic relaxation schemes based on a single linear calculation per time step. The proposed schemes have been implemented for an existing zero‐thickness interface constitutive model. Some numerical application examples are presented to illustrate the advantages of the new schemes proposed. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
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A series of finite element analyses have been undertaken to investigate the effects of interface properties on the behaviour of a vertical retaining wall and the deformation of the ground around it. The boundary between a rigid embedded wall and the soil is modelled with zero thickness interface elements. Uniform translation of the wall has been studied. The analyses show the predicted limiting active and passive pressure on the wall are dependent on the maximum wall friction angle and are in reasonable agreement with accepted approximate analytical solutions. The limiting pressure is independent of the stiffness and dilation properties of the interface elements. The dilation properties of the interface have a significant effect on the ground surface deformation around the wall. © 1998 John Wiley & Sons, Ltd. 相似文献
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Tapered piles represent a more equitable distribution of the pile material in several respects. In order to study their efficiency over piles of uniform section with the same material input, a three-dimensional finite element analysis is developed. The numerical procedure accounts for the non-linear elastic behaviour of both the soil and the pile-soil interface. In order to include the latter, which involves relative slip and debonding, zero/non-zero thickness interface elements are used. Three shapes of cross-section, viz. circular, square and triangular, have been attempted for the piles. The load-settlement behaviour under axial load predicted by the analysis is compared with laboratory test results obtained on instrumented model piles, installed as ‘replacement’ piles, and the fit obtained is found to be reasonably good. Also examined are interface shear and axial force in the pile, displacement and stress fields in the medium and the progression of failure in the latter. 相似文献
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There could be some discontinuities in a soil media such as layers, earth structures, cracks, and fissures so that estimation
of stresses and deformations in these types of soil masses are somewhat different from continuous masses. The discontinuities
in a soil mass could be considered as a special link between two blocks. Transmitted swelling pressures affected by the soil
properties of the backfill especially at the interface between the backfill and retaining wall. In order to estimate the transmitted
swelling pressure distribution behind a retaining wall, using with interface element, a new finite element model and a code
(SWELPRES) have been developed. To evaluate the effect of backfill characteristics and interface element from the transmitted
lateral swelling pressures, four cases of thickness of backfills with or without interface elements are investigated. 相似文献
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DongBichang WangJingtao ChengTao 《中国地质大学学报(英文版)》2005,16(1):89-94
INTRODUCTIONCurrently, the contact element is a problematicpoint problem in the mechanics of rock and soil engi neering. In the tenth international conference onComputer Methods and Advances in Geomechanics,held in America in January, 2001, the … 相似文献
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《Geomechanics and Geoengineering》2013,8(1):71-77
Rock bolt is a major reinforcement technique for roadways in coal mines in China. Generally, separation of the bonding interface between the rock mass and the bolt may lead to collapse of the bolted rock mass due to stress concentration. In order to establish the stress concentration mechanism on the bonding interface, the distribution functions for shear stress and longitudinal force on the interface are derived using Mindlin's model, and a failure criterion for the interface is proposed. In addition, influencing factors for the stress distribution mode are identified. Both analytical study and numerical simulations by ANSYS have shown that, as the elastic modulus of rock increases, both shear stress and the longitudinal force-concentrating zone move towards the outer end of bolt and decrease gradually from the free surface to the rock mass body. Also, there is an optimizing cement thickness which results in relatively uniform distributions of shear stress and longitudinal force on the interface. It is valuable to investigate the bolt invalidity mechanism as well as reinforcement safety estimation in underground rock engineering design. 相似文献
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将极限分析下限法理论、混合数值离散思想和线性规划结合起来研究砌石挡土墙边坡的极限承载力。采用三角形有限单元离散土体来模拟土体的连续介质力学特性,构建土体静力许可应力场的约束条件,采用块体单元离散砌石体来模拟砌石体的非连续介质力学特性,构建砌石挡土墙的静力许可应力场的约束条件;同时建立有限元单元和块体单元交界面的约束条件;然后以超载系数为目标函数建立求解砌石挡土墙极限承载力的下限法线性规划模型,并使用内点算法进行最优化求解,获得边坡的极限荷载（或安全系数）和对应的应力场。通过3个算例的分析验证了所提方法的正确性。所提方法是将混合数值离散思想引入极限分析领域的一次尝试。 相似文献
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In a companion Part I of this paper (Int. J. Numer. Anal. Meth. Geomech. 2008; DOI: 10.1002/nag.735 ), a coupled hydro‐mechanical (HM) formulation for geomaterials with discontinuities based on the finite element method (FEM) with double‐node, zero‐thickness interface elements was developed and presented. This Part II paper includes the numerical solution of basic practical problems using both the staggered and the fully coupled approaches. A first group of simulations, based on the classical consolidation problem with an added vertical discontinuity, is used to compare both the approaches in terms of accuracy and convergence. The monolithic or fully coupled scheme is also used in an application example studying the influence of a horizontal joint in the performance of a reservoir subject to fluid extraction. Results include a comparison with other numerical solutions from the literature and a sensitivity analysis of the mechanical parameters of the discontinuity. Some simulations are also run using both a full non‐symmetric and a simplified symmetric Jacobian matrix. On top of verifying the model developed and its capability to reflect the conductivity changes of the interface with aperture changes, the results presented also lead to interesting observations of the numerical performance of the methods implemented. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
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已有的刚性挡土墙上三维被动土压力的研究主要基于挡土墙平移模式(T位移模式)下开展的，而对挡土墙绕顶转动模式(RT位移模式)下三维被动土压力的研究尚不充分。因此，该文采用数值方法系统地研究了RT位移模式下三维被动土压力及三维空间滑裂面性状。针对无黏性土体，得到了挡土墙宽度与深度比值、土体摩擦角大小和墙土接触面摩擦角比值对三维被动土压力系数及墙后土体滑裂面的影响，并与T位移模式下的三维被动土压力系数和墙后土体的空间滑裂面形态进行了定量的比较。研究结果表明:RT位移模式下的三维被动土压力系数和空间滑裂面形态均受土体内摩擦角及墙土接触面摩擦角比值的影响，且两者之间存在相互联系。RT位移模式下的三维被动土压力系数和空间滑裂面形态与T位移模式下有显著的区别；RT位移模式下的三维被动土压力系数及空间滑裂面相比于T位移模式下较小。研究成果可为RT位移模式下三维被动土压力的进一步研究和相关工程设计提供参考。 相似文献
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Interface and embedded joint methods for modeling dynamic fracture opening by explosive products 下载免费PDF全文
下载免费PDF全文 Two computational approaches are proposed in the paper to model dynamic fracture opening by explosive products. The first method assumes that the fractures may be modeled using flow elements embedded along the mesh lines. This method models crack opening in a straightforward way by splitting the nodes of the computational grid. It can account for crack branching; however, the crack directions are constrained by existing mesh faces, which may lead to mesh dependence. Also, the stress in flow elements is calculated explicitly separate from the surrounding solid elements that can impose additional limits on the time step stability condition for explicit integration. The second approach uses embedded flow elements to model the cracks. Typical thickness of the cracks is much smaller than the element size. Therefore, gas pressure in the cracks is assumed to be in stress equilibrium with the element stress. To achieve this, the crack thickness and the state of the gas is updated simultaneously with the state of the solid element which contains the crack. Therefore, the time step is controlled by the explicit solver applied for the solid and does not depend on the thickness of the crack. The main disadvantage of the second approach is due to the complexity of modeling multiple intersecting cracks, which go through the same element. We discuss the areas of possible applications of these 2 methods and the ways to improve and enhance them for future practical applications. 相似文献
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Eleftherios-Stamatios Telis George Besseris Constantinos Stergiou Mukesh Limbachiya 《Geotechnical and Geological Engineering》2013,31(4):1275-1289
The aim of this paper is to present a method for simultaneous optimization of the design characteristics of an earth retaining structure design using quality tools. The design characteristics examined in this paper are safety factor, total displacements and cost. The methodology for the multi-response optimization used is the desirability analysis which gives the appropriate combinations for the design variables. Through standard experimental runs, we process the results for this optimization. The experimental measurements are calculated via finite elements analysis. The designs used are taken from two real-life case studies. This methodology is intended as a guide tool for civil and geotechnical engineers to predict the values of the design variables as long as they can be named and take discrete values. The uniqueness in this study is that approved experimental methodology can simultaneously optimize the design characteristics of an earth retaining structural design, which were until now calculated empirically. 相似文献
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Many interpretations of small-strain experiments indicate a non-linear dependence of soil stiffness on pressure. This shows that small-strain stiffness can be expressed as a power function of the mean effective stress rather than as a linear function of stress. Many cases in the field show the importance of these behaviours to load–deformation prediction in a soil-structure interaction problem. This paper presents a numerical implementation and validation of non-linear pressure-dependent stiffness in a hyperplasticity model using a strain-driven forward-Euler integration scheme. The kinematic hardening function was incorporated into a finite number of multiple-yield surfaces of Modified Cam Clay to characterise small-strain stiffness and accommodate smooth transition of stiffness corresponding to different loading conditions and stress histories. Experimental results of current state and loading history dependence in overconsolidated clay are compared to the model prediction. 相似文献
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Markov chains and embedded Markov chains in geology 总被引：2，自引：0，他引：2
Geological data are structured as first-order, discrete-state discrete-time Markov chains in two main ways. In one, observations are spaced equally in time or space to yield transition probability matrices with nonzero elements in the main diagonal; in the other, only state transitions are recorded, to yield matrices with diagonal elements exactly equal to zero. The mathematical differences in these two approaches are reviewed here, using stratigraphic data as an example. Simulations from chains with diagonal elements greater than zero always yield geometric distributions of lithologic unit thickness, and their use is recommended only if the input data have the same distribution. For thickness distributions lognormally or otherwise distributed, the embedded chain is preferable. The mathematical portions of this paper are well known, but are not readily available in publications normally used by geologists. One purpose of this paper is to provide an explicit treatment of the mathematical foundations on which applications of Markov processes in geology depend. 相似文献
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Westergaards equations are widely used in the design of rigid concrete highway and aircraft pavements. The equations assume that the pavements are either infinite or semi-infinite in extent. Recently, a numerical design procedure using finite elements has been introduced for finite sized precast concrete pavement units [raft units]. The present paper compares the computed stress results from the two methods for the interior loading on a two metre square raft unit. The results show that there is no simple “slab-size correction factor” to correlate the stress output from the two design methods as suggested by other authors. Westergaards analysis should not be used to design finite sized raft units; the numerical design procedure is recommended. 相似文献
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Estimation of the depth to the fresh-water/salt-water interface from vertical head gradients in wells in coastal and island aquifers 总被引：3，自引：2，他引：1
An accurate estimate of the depth to the theoretical interface between fresh, water and salt water is critical to estimates
of well yields in coastal and island aquifers. The Ghyben–Herzberg relation, which is commonly used to estimate interface
depth, can greatly underestimate or overestimate the fresh-water thickness, because it assumes no vertical head gradients
and no vertical flow. Estimation of the interface depth needs to consider the vertical head gradients and aquifer anisotropy
that may be present. This paper presents a method to calculate vertical head gradients using water-level measurements made
during drilling of a partially penetrating well; the gradient is then used to estimate interface depth. Application of the
method to a numerically simulated fresh-water/salt-water system shows that the method is most accurate when the gradient is
measured in a deeply penetrating well. Even using a shallow well, the method more accurately estimates the interface position
than does the Ghyben–Herzberg relation where substantial vertical head gradients exist. Application of the method to field
data shows that drilling, collection methods of water-level data, and aquifer inhomogeneities can cause difficulties, but
the effects of these difficulties can be minimized.
Received, April 1997 · Revised, January 1998 · Accepted, January 1998 相似文献
18.
露天地下开采隔离层稳定性研究 总被引：2，自引：0，他引：2
露天地下开采隔离层稳定性分析是矿山中经常遇到的问题。以大宝山矿露天地下开采的工程实例,采用数值分析方法,对隔离层稳定性进行分析计算,发现空区顶板的拉应力是关系隔离层稳定性的关键因素。通过对隔离层的安全厚度数值计算,与5种理论计算方法结果进行了比较,综合求和归一法数据处理和多项式数值逼近得到了不同空区跨度与隔离层安全厚度关系。结果为露天地下开采隔离层稳定性分析的方法进行了验证和补充,也为矿山设计隔离层厚度提供了参考,对指导露天地下开采安全生产施工具有重要意义。 相似文献
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The finite element method (FEM) and the boundary element method (BEM) are two well established numerical methods used for the analysis of underground openings. The advantages of both the methods are utilized by adopting FEBEM in which finite elements are coupled with boundary elements. A coupling procedure is presented in this paper. In using FEBEM, the effect of the location of interface boundary between finite element and boundary element regions, effect of Poisson's ratio and effect of stress ratio are discussed. It is shown that Poisson's ratio and stress ratio have significant effect on the accuracy of the results. Different discretization schemes are discussed to study their effect on accuracy and computation time. The use of different material properties in the FE region is presented. A comparative study is made with FEM for all the cases. It is shown that use of FEBEM is more advantageous than FEM. 相似文献
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Piles may be subjected to lateral soil pressures as a result of lateral soil movements from nearby construction‐related activities such as embankment construction or excavation operations. Three‐dimensional finite element analyses have been carried out to investigate the response of a single pile when subjected to lateral soil movements. The pile and the soil were modelled using 20‐node quadrilateral brick elements with reduced integration. For compatibility between the soil–pile interface elements, 27‐node quadrilateral brick elements with reduced integration were used to model the soil around the pile adjacent to the soil–pile interface. A Mohr–Coulomb elastic–plastic constitutive model with large‐strain mode was assumed for the soil. The analyses indicate that the behaviour of the pile was significantly influenced by the pile flexibility, the magnitude of soil movement, the pile head boundary conditions, the shape of the soil movement profile and the thickness of the moving soil mass. Reasonable agreement is found between some existing published solutions and those developed herein. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献