遗传算法在斜条分上限法中的应用探讨

 应用斜条分上限解法求解边坡稳定、地基极限承载力等问题时,需要借助优化手段寻求最优的上限解。由于斜条分法中增加了条间倾角作为优化自变量,导致优化变自量增加,传统的数值优化算法经常陷入局部极值的陷阱。本文以无重力地基承载力问题为例,通过基于非均匀变异的微型遗传算法求解其临界滑移模式。发现改进后的遗传算法具有较好的全局搜索能力和局部收敛能力,能使问题较好地收敛到闭合解;采用改进遗传算法与单纯形法结合或滑裂面坐标和条块界面角分开优化的方式可以得到更为精确的解答。最后用该数值方法对地基承载力公式中考虑地基土重力的经验系数进行了对比验证。     

地基承载力的数值分析方法

介绍了边坡稳定的塑性力学上限解在计算地基承载力方面的推广。简要回顾了由Ｄｏｎａｌｄ和Ｃｈｅｎ提出的能量法的基本原理，说明该法可以得出与闭合解一样精确的解答，使用此数值方法来复核地基容重不为零时承载力计算的各种经验方法，发现这些经验方法在大多数情况下均低估了地基的承载力。计算基础有埋深和荷载偏心的经验公式也低估了地基承载力约５％～１０％。     

传递最大推力的不平衡推力法

不平衡推力法因其计算模型简便,计算过程可以显式完成,并且可以计算边坡整体的滑坡推力,在边坡分析与设计领域应用较广.条分法力学模型是一静不定模型,经各种简化而产生现有的各种条分方法,其中包括不平衡推力法.而作为静不定模型,条分法理论上有无数个满足平衡条件的解.而从这无数解中,应有更加合理和更有代表性的解存在,如具有较小安...     

考虑渗流的基坑边坡稳定分析

系统地总结了,目前基坑边坡稳定验算中常用的几种考虑渗流力的方法.在深入探讨地下水渗流对基坑边坡稳定作用机理的基础上,提出有限元法与条分法相结合的新方法.该方法采用条分法进行基坑边坡的稳定性分析;采用有限元法计算基坑周围的渗流场,求出作用于各土条上的渗流力并将其参与到稳定验算中.通过对以上几种计算方法的比较,阐明了各种方法的优劣及其适用条件.     

条形基础下临坡地基极限承载力影响因素数值模拟分析

按平面应变问题建立有限元数值模型,通过比较有限元解与极限平衡解,检验该数值模拟的计算精度。基于数值模拟计算结果,分析了地基土强度、边坡角、坡顶距、基底接触条件等因素对临坡地基极限承载力的影响。针对纯黏土,提出临界强度、过渡点的概念,建立了临坡地基土体强度与地基破坏模式的定量对应关系。得出边坡角越小,地基土内摩擦角对于临坡地基极限承载力的影响越明显;边坡角越大,临坡地基极限承载力随坡顶距的增长速度越快;纯黏土的qu/(γB)-c/(γB)曲线由曲线段及直线段构成,分别对应地基整体失稳和局部失稳破坏。     

临近基坑条形浅基础地基承载力减损的下限估算

利用极限分析有限元方法和下限定理,分析计算了考虑土体自重的临近基坑(边坡)条形浅基础c-?土地基极限承载力下限解。作为一种简化手段,分别按土的粘聚力、基础埋深(超载)和土的自重这3项承载力影响系数表达临近基坑地基极限承载力,获得了基础位置、基坑开挖的边坡角度以及土的内摩擦角取不同值时,相应的地基承载力系数下限解答,并对计算结果进行了讨论。最后将计算结果与已有文献资料以及利用多滑块Prandtl破坏模式得到的极限分析上限解答进行了分析对比,从上、下限给出了临近基坑既有建筑物地基承载力系数取值范围及其承载力上、下限平均值时的减损因数,分析了影响计算结果的因素。     

土质边坡极限分析径向条分法研究

以极限分析上限定理为基础,根据滑移线场的理论和斜分条法,提出了土质边坡极限分析径向条分法破坏机制,并建立了径向条分法计算模型。按照外荷载所做的外功率与速度间断面上产生的内能耗损相等的原理——虚功率原理,建立了计算土质边坡稳定系数的极限分析虚功率方程。采用材料储备强度的定义,根据极限方程,可以推导出土质边坡径向条分法稳定系数计算公式。通过一个典型土质边坡剖面,采用本文的方法进行了计算,并与瑞典圆弧法计算结果做了比较,验证了本文方法的正确性。     

边坡地基承载力验算和支护结构荷载计算

对成为建（构）筑物地基的边坡,目前采取的防止地基失稳的做法是：增加一项边坡稳定性计算的工作;当需要支护时,边坡支护结构荷载取按土压力理论计算出的某类岩土压力或其与修正系数的乘积。本文对这种做法存在的问题进行了探讨,提出了与地基承载力验算等效的边坡地基稳定性计算方法和刚好满足地基承载力要求的边坡地基支护结构荷载计算方法,这些方法能弥补现有方法的不足。     

瑞典条分法剖析引发的有效应力和渗流力概念问题

瑞典条分法在土力学教学和边坡工程设计中有着广泛的影响。针对其两种有效应力分析表达式,通过剖析土条底面法向有效应力的推求过程及对比分析计算结果发现：在理论上,两种表达式都不适用于一般渗流条件下的边坡稳定分析;实用上,也存在明显离散的计算误差。其原因分别在于：以土体为研究对象时,忽略了土条侧面的水压力;以土骨架为研究对象时,忽略了渗流力的作用。进一步分析微单元体平衡微分方程的结果表明, Taylor 提出的分析渗流对土骨架有效应力影响的两种等效处理方式,即以土体为研究对象,考虑饱和重力与周界上水压力的方式;或以土骨架为研究对象,考虑有效重力与渗流力的方式, 可以在刚体极限平衡分析方法中运用,例如条分法。 但是, 在涉及渗流 - 变形耦合分析的诸如边坡渗流稳定和固结问题的解析和数值方法中,只能以土体为研究对象,而不能以土骨架为研究对象、运用渗流力的概念进行分析。究其原因在于：在 渗流条件下,物理上,有效应力不是应力变量;有效应力和确定渗流力的孔隙水压力分别是决定土骨架的变形和强度以及流场的相互依赖的、非独立的应力状态变量。     

基于安全系数比的非饱和土边坡极限平衡法

 初步建立非饱和土边坡计算结果和工程安全的关系,提出对于一个给定的非饱和土边坡滑裂面,滑裂面安全的条件是最危险状态时对应的最小安全系数不小于允许安全系数。通过引入安全系数比,推导基于安全系数比的非饱和土边坡普遍条分法、非饱和土瑞典条分法和Bishop条分法,建立不同状态下的各部分计算参数和最小安全系数的关系。给出孔隙气压力等于0、饱和状态等特殊形式,在一定情况下可简化边坡安全系数的计算方式。通过具体算例,对安全系数比和重度对最小安全系数的影响进行分析。安全系数比对最小安全系数有着较大影响,随着安全系数比的增大,非饱和土的最小安全系数减少,重度对非饱和土最小安全系数影响不大。     

斜交预应力梁钢绞线形状特性及其影响

文章介绍斜交箱梁板钢绞线长度及弯起转角度的计算方法。箱梁位于腹板的钢绞线是三维曲线,若简化为平面曲线进行计算,将使下料长度和竖向弯起角与实际有不可忽视的误差,并影响张拉伸长量的计算结果。     

Analytical design method for a truss-bolt system for reinforcement of fractured coal mine roofs—illustrated with a case study

This paper presents an analytical design method for the truss-bolt system in reinforcing underground fractured rock roofs in coal mines. The analytical design method is based on the mechanical analysis of the fractured rock roof with reinforcement by inclined roof bolts and a horizontal tie-rod. The mechanical analysis for the system includes a non-linear bending model for the laterally inclined roof bolts and three upper and lower bounds. The lateral resistance of the inclined roof bolts in a truss-bolt-supported roadway is examined using classical theory of a non-linear beam in bending. The paper analyses the arching action by lateral behavior of the inclined roof bolts in reinforcing the fractured roof. Based on mechanical models, the design formula concerning the lateral bolt forces, tensions in the tie-rod in the truss system, as well as the reinforcement behavior have been derived. In order to ensure that the roof truss-bolt system reinforces the coal roof effectively, a lower bound of pre-tightening forces must be applied on the tie-rod for stabilizing the fractured roof by arching action. The pre-tightening forces exerted via the tie-rod also cannot be greater than its upper bound, since the excessive tightening force will cause localized failure in the rock near the bolt tail at the abutment of the fractured roof beam. The analytical formulas for both lower and upper bounds for truss pre-tightening forces are put forward in this paper. Furthermore, the paper also presents analytical equations for designing the axial forces and dimensions for bolts in this kind of system. Parametric studies and optimization analysis are also carried out on the basis of the proposed approach. A flow chart and procedures are presented to show the analytical design method for this truss-bolt system. Case studies are presented to show how the method can be used in actual coal mining tunnels. The predicted results compare well with those measured in the actual case studies.     

岩质边坡稳定塑性极限分析方法——斜分条法

基于塑性极限分析上限定理,依据岩质边坡沿某一滑裂面滑动破坏时,在其内部产生沿陡倾角结构面(断层、节理和层面)的剪切破坏现象,建立了岩质边坡极限分析斜分条法破坏模式。进一步根据滑体处于极限状态时的虚功率方程,推导得出了斜分条后岩质边坡的塑性极限分析稳定系数计算公式。采用超载系数的方法,将稳定系数表示在块体所受的极限荷载,避免了隐式出现,有效地简化了公式推导。以锦屏一级水电站右岸边坡为例进行了稳定性分析。计算表明,结论较为合理,对于具有倾斜界面的岩质边坡稳定性评价具有重要意义。     

Simulation of the mechanical behavior of inclined jointed rock masses during tunnel construction using Discontinuous Deformation Analysis (DDA)

In this paper, the mechanical behavior of inclined jointed rock masses during tunneling is considered. Such rock masses can be considered as an assembly of discrete blocks with the discontinuities having a significant influence on the mechanical behavior. To simulate this situation, a discrete numerical analysis method, Discontinuous Deformation Analysis (DDA), is applied. The DDA results show the existence of stress arching in the rock masses during tunneling. This stress arching is the primary influence on the stress distribution and surface subsidence. In addition, the stress arching is affected by the dip angle of the jointed rock masses. Moreover, the DDA results are in good agreement with experiments, explaining the reason for the asymmetrical vertical stress and surface subsidence obtained in laboratory tests. These results suggest that DDA can be applied to model the tunneling behavior of complicated discontinuous rock masses.     

A three-dimensional slope stability analysis method using the upper bound theorem : Part I: theory and methods

A three-dimensional (3D) slope stability analysis method, based on its two-dimensional approaches proposed by Donald and Chen (Can. Geotech. J. 34 (1997) 853.) is presented in this paper. It starts from establishing a compatible velocity field and obtains the factor of safety by the energy and work balance equation. Optimisation is followed to approach the critical failure mode that offers the minimum factor of safety. The method is demonstrated to be identical to Sarma's limit equilibrium method (1979) that employs inclined slices, if it is extended to the 3D area. However, it has been established on a sound theoretical background supported by the upper bound theorem of plasticity. Test problems have demonstrated its feasibility. A feature of the method is its very simple way to obtain the factor of safety without complicated 3D force equilibrium evaluations. Limited assumptions are involved in this method and their applicability has been justified.     

地震波斜入射时水平层状场地的非线性地震反应

利用土层和半空间的精确动力刚度矩阵,可求解地震波斜入射,水平层状场地的动力响应,并可得到各土层的位移、应力及应变结果。结合等效线性化算法,可分析斜入射地震波(SH,SV,P)时场地的非线性地震反应。研究表明:入射角对地表的加速度峰值有重要影响,未必在波垂直入射时最大,可能有多个峰值;实际地震波入射角平均在60°左右,与斜入射SV波时峰值放大倍数最大值出现的角度基本一致,按垂直入射计算得到的结果可能不安全,表明了在场地非线性地震反应中研究斜入射的必要性。     

Influence of hanger system on structural behaviour of suspension footbridges under pedestrian dynamic loads

For structural safety of footbridges and for the comfort of their users, it is essential to consider the effect of human induced vibrations. In suspension footbridges, hanger systems can affect dynamic performances. In order to improve the aerodynamic stability of the footbridges, inclined hangers can be used instead of vertical ones, but inclined hangers are more liable to undergo fatigue and slackness. In this paper, a suspension footbridge with inclined hangers has been examined as a case study. To reduce internal forces, fatigue and slackness in hangers, horizontal cables have been attached to inclined hangers. These added cables may also increase the stiffness and dynamic performance of the footbridge. In this study, the dynamic characteristics of footbridges with inclined and modified hangers such as natural modes (vertical, lateral, and torsional) and frequencies, as well as the vertical and lateral accelerations of the deck have been investigated. Also, hanger parameters such as the force, slackness, overstress, and the fatigue of inclined and modified hangers have been compared. Results showed that the modified bridge demonstrates superior performance when compared with conventional ones.     

加筋土坡的可能滑移模式和基于库仑理论的稳定分析方法

加筋土坡因其填方量少、工期短、经济安全等优势在国内外已得到广泛应用,故其稳定性分析也显得尤为重要。目前,已有多位学者将极限分析上 限定理运用于加筋土坡的稳定性分析中,并假定水平条块速度间断面。然而在其分析过程中,构造的速度场并不符合位移协调条件。提出了由于筋材的隔断 作用形成的斜向界面破坏模式,并计算相应速度场式,分别提出主动、库仑、被动三种滑移模式。通过计算比较发现,在加筋间距较密时,库仑模式总是相 应安全系数最小的控制工况。实际工作中,可以只使用这一概念清晰、计算简便的方法分析加筋土坡的稳定性。为方便工程设计快速获取安全系数或筋材间 距,将土坡各参数进行无量纲化,绘制了安全系数图,并与Michalowski设计图表进行对比,验证了该算法的有效性。且针对多个实际工程算例进行验算, 验证了库仑模式上限法的可行性。     

Centrifuge model test on dynamic behavior of group-pile foundation With inclined piles and its numerical simulation

In this paper, dynamic behavior of a grouppile foundation with inclined piles in loose sand has been investigated with centrifuge model tests. The test results are also simulated with elastoplastic dynamic finite element method, in which, not only sectional force of piles, stress of ground, but also deformation of piles are calculated using a three-dimensional elastoplastic dynamic finite element analysis (Code name: DGPILE-3D). The numerical analyses are conducted with a full system in which a superstructure, a pile foundation and surrounding ground are considered together so that interaction between pile foundation and soils can be properly simulated because the nonlinearities of both the pile and the ground are described with suitable constitutive models. Different types of piles, vertical pile or inclined pile, are considered in order to verify the different characteristics of a group pile foundation with inclined piles. The validity of the calculation is verified by the model tests.