Force analysis of pile foundation in rock slope based on upper-bound theorem of limit

Based on the characteristic that the potential sliding surfaces of rock slope are commonly in the shape of either line or fold line,analysis thought of conventional pile foundation in the flat ground under complex load condition was applied and the upper-bound theorem of limit analysis was used to compute thrust of rock layers with all possible distribution shapes. The interaction of slope and pile was considered design load in terms of slope thrust,and the finite difference method was derived to calculate inner-force and displacement of bridge pile foundation in rock slope under complex load condition. The result of example shows that the distribution model of slope thrust has certain impact on displacement and inner-force of bridge pile foundation. The maximum displacement growth rate reaches 54% and the maximum moment and shear growth rates reach only 15% and 20%,respectively,but the trends of inner-force and displacement of bridge pile foundation are basically the same as those of the conventional pile foundation in the flat ground. When the piles bear the same level lateral thrust,the distribution shapes of slope thrust have different influence on inner-force of pile foundation,especially the rectangle distribution,and the triangle thrust has the smallest displacement and inner-force of pile foundation.

Combined influence of nonlinearity and dilation on slope stability evaluated by upper-bound limit analysis

The combined influence of nonlinearity and dilation on slope stability was evaluated using the upper-bound limit analysis theorem.The mechanism of slope collapse was analyzed by dividing it into arbitrary discrete soil blocks with the nonlinear Mohr–Coulomb failure criterion and nonassociated flow rule.The multipoint tangent(multi-tangent) technique was used to analyze the slope stability by linearizing the nonlinear failure criterion.A general expression for the slope safety factor was derived based on the virtual work principle and the strength reduction technique,and the global slope safety factor can be obtained by the optimization method of nonlinear sequential quadratic programming.The results show better agreement with previous research result when the nonlinear failure criterion reduces to a linear failure criterion or the non-associated flow rule reduces to an associated flow rule,which demonstrates the rationality of the presented method.Slope safety factors calculated by the multi-tangent inclined-slices technique were smaller than those obtained by the traditional single-tangent inclined-slices technique.The results show that the multi-tangent inclined-slices technique is a safe and effective method of slope stability limit analysis.The combined effect of nonlinearity and dilation on slope stability was analyzed,and the parameter analysis indicates that nonlinearity and dilation have significant influence on the result of slope stability analysis.

PLASTIC LIMIT ANALYSIS OF DISCONTINUOUS LINING UNDERGROUND PRESSURE

Discontinuous lining is a special form of support in underground excavation. Based on the method of plastic limit analysis, it is found the upper and the lower bound solution of the pressure of circular discontinuous lining and discussed support parameter of discontinuous lining and its applicable conditions , which provides theoretical basis for the design and calculation of discontinuous lining.

Upper bound analysis of slope stability with nonlinear failure criterion based on strength reduction technique

Based on the upper bound limit analysis theorem and the shear strength reduction technique,the equation for expressing critical limit-equilibrium state was employed to define the safety factor of a given slope and its corresponding critical failure mechanism by means of the kinematical approach of limit analysis theory.The nonlinear shear strength parameters were treated as variable parameters and a kinematically admissible failure mechanism was considered for calculation schemes.The iterative optimization method was adopted to obtain the safety factors.Case study and comparative analysis show that solutions presented here agree with available predictions when nonlinear criterion reduces to linear criterion,and the validity of present method could be illuminated.From the numerical results,it can also be seen that nonlinear parameter m,slope foot gradient β,height of slope H,slope top gradient α and soil bulk density γ have significant effects on the safety factor of the slope.

Stability analysis for natural slope by kinematical approach

The stability of natural slope was analyzed on the basis of limit analysis. The sliding model of a kind of natural slope was presented. A new kinematically admissible velocity field for the new sliding model was constructed. The stability factor formulation by the upper bound theorem leads to a classical nonlinear programming problem, when the external work rate and internal energy dissipation were solved, and the constraint condition of the programming problem was given. The upper bound optimization problem can be solved efficiently by applying a nonlinear SQP algorithm, and stability factor was obtained, which agrees well with previous achievements.

Characterizing model uncertainty of upper-bound limit analysis on slopes using 3D rotational failure mechanism

The slope stability assessment is a classical problem in geotechnical engineering.This topic have attracted many researcher’s attention and various theoretical models for predicting critical slope heights or safety factors in the light of the limit equilibrium(LE)method and the kinematical approach of limit analysis(LA)method.Meanwhile,a large number of experimental studies have been conducted to check the slope stability.Using centrifuge testing results,this paper aims to employ Bayesian method to characterize the model uncertainties of the classical three-dimensional rotational failure mechanism proposed by Michalowski and Drescher(2009)to predict critical slope heights in frictional soils,by incorporating the test uncertainties and parameter uncertainties.The obtained results show that the LA three-dimensional rotational failure mechanism overestimates the critical slope height compared with the LE method,and the experimental observational uncertainty has negligible influences on the posterior statistics of model uncertainty.

考虑水力效应的裂缝边坡稳定性非线性能耗分析

现有考虑水力效应的裂缝边坡稳定性分析大多基于线性破坏准则,而岩土体破坏往往呈现非线性特征,因此开展水力效应影响下的裂缝边坡稳定性非线性极限上限分析具有重要意义。基于极限分析上限定理及强度折减技术,结合“外切线法”非线性破坏准则,构建坡顶含竖直裂缝的边坡对数螺旋线破坏模式,根据虚功原理推导出裂缝边坡安全系数解析式,通过MATLAB优化计算,结合边坡工程实例探讨了典型因素对裂缝边坡稳定性、临界裂缝及滑动面位置的影响规律。研究结果表明:随着地下水位h的持续上升,边坡安全系数不断降低,临界裂缝深度逐渐增大且临界裂缝位置逐渐向坡顶缘偏移;非线性系数m明显影响边坡的稳定性,边坡安全系数随着非线性系数的增大显著减小,采用线性破坏准则会高估地下水位变化对边坡稳定性的影响;随着非线性系数的增大,临界裂缝深度随之增大,临界裂缝位置距离坡顶缘越来越远,滑坡体体积逐渐增大;裂缝与坡顶缘距离l m随着非线性系数m的增大而增大(当m增大0.2时,l m增大约1 m),且随着裂缝与坡顶缘距离的增大,边坡安全系数无明显变化,临界裂缝深度先逐渐减小后趋于稳定。

地震作用下双层土质边坡稳定性上限分析

为探究地震作用对双层土质边坡稳定性的影响,基于极限分析上限理论,建立了地震作用下双层土质边坡旋转破坏机构。采用拟静力法简化地震荷载作用,推导了双层土质边坡安全系数表达式。分析土体黏聚力比、边坡坡角以及地震作用对双层土质边坡稳定性及其滑动面参数的影响。研究结果表明:在水平地震作用下,随着黏聚力比的增大,边坡安全系数呈非线性增大且潜在滑动面变浅;当水平地震作用增强时,边坡失稳破坏范围显著加大;随着竖向地震系数及黏聚力比的增大,边坡安全系数略微降低;水平地震作用增强时,竖向地震作用对边坡稳定性的影响逐渐增大,此时需要考虑竖向地震的影响。

基于多对数螺旋曲线破坏机构的富水软岩隧道开挖面支护应力分析

为了避免对胡克-布朗准则进行任何线性化处理,将广义胡克-布朗(generalized Hoek-Brown, GHB)强度准则直接引入到开挖面稳定性分析中,基于极限分析理论构建了富水地层浅埋隧道开挖面多对数螺旋线破坏机构。在考虑孔隙水压力的作用下,推导出能量平衡方程,得到开挖面极限支护应力表达式,并且通过程序优化得到支护应力最优上限解。在此基础上,分析了GHB强度参数、孔隙水压力系数、岩土体重度以及隧道埋深比对开挖面稳定性的影响。最后通过归一化处理得到不同情况下的开挖面极限支护应力稳定性图表,通过该图表能够快速便捷地获得富水地层隧道开挖面维持稳定性所需的极限支护应力,为盾构隧道初步设计提供理论依据。

深埋矩形隧道三维塌落机制的上限分析

深埋隧道的周围为高地应力环境,还会受到地下水的影响,故深埋隧道顶部围岩易发生塌落。论文基于极限分析上限法和非线性Mohr-Coulomb准则,在考虑地下水以孔隙水压力形式作用于隧道下,构建了隧道顶部为矩形的深埋隧道的三维塌落机制,获取矩形深埋隧道塌落范围及塌落土体重力的精确解,并得出不同参数对塌落范围和塌落土体重力的影响规律。结果表明:不同参数对塌落范围和塌落土体重力的有不同程度的影响,这些参数中,孔隙水压力的影响显著。通过与既有研究对比,证明了计算方法的合理性,对于隧道支护结构的优化设计和稳定性研究有重要意义。

加筋土坡动态稳定性拟静力分析

加筋土工结构被广泛采用的原因不仅是其具有良好的静力性能,且也在于出色的动力稳定性能,现有研究较少考虑竖向地震效应对加筋土坡动态稳定性的影响。基于塑性极限分析上限理论,假定不同的破坏面,同时考虑水平和竖向地震影响并结合不同加筋模式,采用拟静力分析方法推导一定加筋强度条件下的边坡临界高度和一定边坡高度条件下的临界加筋强度计算公式,并对所导公式采用序列二次规划法进行了优化计算,数值计算与分析表明:简单静态和动态条件下,该结果与现有研究成果有较好的一致性,可以证明该方法的正确性;水平和竖向地震、岩土材料强度特性、边坡倾斜度均对加筋土坡的动态稳定性有重要影响,特别当边坡较陡,岩土填筑材料质量较差和地震影响强度较大时,忽视竖向地震影响将会导致设计偏于不安全;最后针对工程实际,提出相应的工程建议。

加锚岩质边坡稳定性评价的极限分析上限法研究

基于极限分析上限法的基本原理,考虑岩石锚杆的支护效应、地震作用力和裂隙水压力的影响,提出加锚岩质边坡稳定分析计算模型。通过该岩质边坡极限分析上限法计算模型,可以将滑体按照滑裂面和侧向结构面离散为不同的滑体单元,并可构建一个机动许可的速度场。根据相关联流动法则和位移协调条件,相邻滑体单元的移动不能导致它们重叠或分离,进而可以得到应变速度场的数学表达式。应用该计算模型,不仅可以合理计算出由滑体自重、地震力、裂隙水压力和锚固力所做的外力功率,而且可以得到产生于滑体底滑裂面和侧向结构面的内能耗散。根据滑体处于极限状态时两功率相等(虚功率方程)的条件,可以推导得到加锚岩质边坡的极限分析上限法稳定系数计算公式。通过典型算例的稳定性分析计算表明,考虑裂隙水压力和地震作用力的边坡稳定系数将会减小,而合理加锚后稳定系数将会得到提高。

层状岩体边坡动态稳定性拟静力上限分析

将强度折减技术与极限分析上限定理结合,利用安全系数Fs评定指标对层状岩体边坡进行稳定性上限分析,与已有研究成果进行了对比分析,并较为详细地分析了相关参数对层状岩体坡体安全系数和潜在破裂面的影响。分析结果表明,与同类计算方法的对比可以证明表明文中方法的正确性;边坡安全系数和破坏范围受边坡坡度、岩体重度、边坡高度、动载效应系数和岩层倾角的控制;当岩层倾角处于一定范围时,层状岩体边坡发生顺层失稳的可能性最大,工程中需特别注意。

滩海桶形基础破坏机制及极限承载力分析研究

针对饱和软黏土地基上桶形基础结构,基于弹塑性极限分析中的上限法,建立了一种竖向荷载作用下桶形基础的极限分析模型。采用有限元数值分析解验证了所提出极限分析模型的可行性和有效性,进而,据此进行了一系列变动参数比较计算,以此对大量的计算结果进行了系统的分析,所得到的数值计算结果与分析结论为工程设计提供参考依据。

基于系统仿真的施工导流不确定性分析

施工导流系统风险分析采用Monte-Carlo计算机仿真方法,改变了传统导流标准设计只考虑单一水文不确定性因素及数学模型中水力参数为定值的限制.而基于多元不确定性因素的仿真,由于水文和水力参数的不确定性,使仿真计算的堰前水位具有不确定性.为此,建立了施工导流仿真运算数学模型,采用计算机仿真方法模拟系统运行过程,求解堰前水位,应用中心极限定理确定仿真最小运行次数,通过数据统计分析,描绘出堰前水位的经验累计曲线和概率分布曲线.定义系统在设计挡水位失效的概率来描述施工导流系统的风险率,根据概率分布曲线确定现行导流标准下系统的风险率,为施工导流决策提供技术支持.

圆形浅基础地基承载力极限分析的上限解析解

针对圆形浅基础 ,根据极限分析中的上限定理 ,选择合适的机动位移速度场 ,推导出地基承载力的上限解析解。绘制上限解析解与粘聚力、内摩擦角的关系曲线。同时根据工程实例 。

非均质软土基坑抗隆起稳定性的极限分析方法

考虑到实际工程中土体非均质以及软土地区基坑开挖过程中土体稳定性的特点,将极限分析上限方法应用于非均质软土基坑抗隆起稳定分析计算中,讨论了极限分析方法的适用性问题。选用Prandtl机构建立了非均质软土地区基坑抗隆起稳定分析的运动许可速度场,根据速度场推导了极限分析上限方法的计算公式。讨论了该方法中土体强度、基坑宽度、支护墙体入土深度、基岩埋置深度等因素对坑底抗隆起稳定的影响。通过几个工程的计算与对比,验证了该方法的适用性和优越性。

土坡稳定性塑性极限分析条分法

从土塑性力学极限分析上限定理出发 ,建立了土坡条分法平移破坏机构。根据外部作用荷载和土体自重所做的外功率与塑性变形区的内部能量耗损率相等的条件 ,建立起虚功率方程 ,并由此得到了土坡稳定系数计算公式。该公式具有概念清楚、使用方便可靠等特点 ,对土坡稳定性分析具有一定实用意义。

基于失稳状态耗能最小原理的预应力锚索加固边坡稳定性上限解析

基于岩土塑性极限分析上限理论的基本原理,考虑预应力锚索的加固效应,分析了单预应力锚索加固措施条件下边坡的稳定性特性,并由此探讨了多预应力锚索共同加固边坡的稳定性能量分析方法。结合强度折减技术,采用内点迭代方法和序列二次规划优化迭代法对锚固边坡安全系数目标函数进行了能量耗散最小化意义上的优化计算。典型算例的分析计算表明:锚索加固效应可以有效地提高边坡的稳定性,预应力锚索设置位置对边坡安全系数、临界滑裂面位置和锚索长度有显著影响。综合考虑锚索设置位置对边坡安全系数和锚索长度的影响,单锚索的最优设置位置应位于边坡中下部区域。采用多排锚索加固既可以保证边坡的安全储备,也可有效避免局部稳定性问题。

洪水作用下滑坡稳定性变化

为了研究洪水作用过程中河流两岸滑坡复活,用极限分析理论建立洪水作用下曲线形滑面滑坡复活模型,研究洪水作用过程中洪水位、冲刷量、地下水位等参数对滑坡稳定性影响情况。结果发现:随着地表水升高稳定性系数升高,随着地下水位升高滑坡稳定系数降低,滑坡在地下水与土体内摩擦角折减双重作用下,在内摩擦角15°~25°范围内有一个复活破坏过程;随着冲刷深度增加稳定性系数降低,随着边坡高度增加,冲刷深度对稳定性系数影响减小;相对于其他参数,冲刷深度与内摩擦角对稳定性系数影响大。