Influences of nonassociated flow rules on seismic bearing capacity factors of strip footing on soil slope by energy dissipation method

Seismic bearing capacity factors of a strip footing placed on soil slope were determined with both associated and nonassociated flow rules. Quasi-static representation of earthquake effects using a seismic coefficient concept was adopted for seismic bearing capacity calculations. A multi-wedge translational failure mechanism was used to obtain the seismic bearing capacity factors for different seismic coefficients and various inclined angles. Employing the associated flow rule, numerical results were compared with the published solutions. For bearing capacity factors related to cohesion and equivalent surcharge load, the maximum difference approximates 0.1%. However, the difference of bearing capacity factor related to unit weight is larger. With the two flow rules, the seismic bearing capacity factors were presented in the form of design charts for practical use. The results show that seismic bearing capacity factors related to the cohesion, the equivalent surcharge load and the unit weight increase greatly as the dilatancy angle increases, and that the nonassociated flow rule has important influences on the seismic bearing capacity.     

Seismic failure mechanisms for loaded slopes with associated and nonassociated flow rules

Seismic failure mechanisms were investigated for soil slopes subjected to strip load with upper bound method of limit analysis and finite difference method of numerical simulation, considering the influence of associated and nonassociated flow rules. Quasi-static representation of soil inertia effects using a seismic coefficient concept was adopted for seismic failure analysis. Numerical study was conducted to investigate the influences of dilative angle and earthquake on the seismic failure mechanisms for the loaded slope, and the failure mechanisms for different dilation angles were compared. The results show that dilation angle has influences on the seismic failure surfaces, that seismic maximum displacement vector decreases as the dilation angle increases, and that seismic maximum shear strain rate decreases as the dilation angle increases.     

Slope stability analysis considering joined influences of nonlinearity and dilation

The soil masses of slopes were assumed to follow a nonlinear failure criterion and a nonassociated flow rule. The stability factors of slopes were calculated using vertical slice method based on limit analysis. The potential sliding mass was divided into a series of vertical slices as well as the traditional slice technique. Equating the external work rate to the internal energy dissipation, the optimum solutions to stability factors were determined by the nonlinear programming algorithm. From the numerical results, it is found that the present solutions agree well with previous results when the nonlinear criterion reduces to the linear criterion, and the nonassociated flow rule reduces to the associated flow rule. The stability factors decrease by 39.7% with nonlinear parameter varying from 1.0 to 3.0. Dilation and nonlinearity have significant effects on the slope stability factors. Foundation item: Project (200550) supported by the Foundation for the Author of National Excellent Doctoral Dissertation of China; Project (200631878557) supported by West Traffic of Science and Technology of China     

Effects of nonlinear strength parameters on stability of 3D soil slopes

Actual slope stability problems have three-dimensional(3D) characteristics and the soils of slopes have curved failure envelopes. This incorporates a power-law nonlinear failure criterion into the kinematic approach of limit analysis to conduct the evaluation of the stability of 3D slopes. A tangential technique is adopted to simplify the nonlinear failure criterion in the form of equivalent Mohr-Coulomb strength parameters. A class of 3D admissible rotational failure mechanisms is selected for soil slopes including three types of failure mechanisms: face failure, base failure, and toe failure. The upper-bound solutions and corresponding critical slip surfaces can be obtained by an efficient optimization method. The results indicate that the nonlinear parameters have significant influences on the assessment of slope stability, especially on the type of failure mechanism. The effects of nonlinear parameters appear to be pronounced for gentle slopes constrained to a narrow width. Compared with the solutions derived from plane-strain analysis, the 3D solutions are more sensitive to the values of nonlinear parameters.     

膨胀特性对软岩巷道围岩变形规律的影响研究

针对软岩巷道的特点，利用泥灰岩三轴试验结果，分析了膨胀特性对深井软岩巷道围岩稳定性的影响；利用最新的弹塑性理论研究成果。推导出了膨胀角与围岩变形的直接关系式；采用数值力学的研究方法，分析了软岩巷道周围体积膨胀与扩容现象．数值模拟结果表明：软岩巷道表面变形和巷道周边体积应变随膨胀角的变化均成非线性递增，膨胀角愈大，软岩巷道的围岩条件愈差，巷道周边围压越大，所需要的支护力就越大。这些重要结论为深井条件下软岩巷道工程提供参考．     

膨胀特性对软岩巷道围岩变形规律的影响研究

针对软岩巷道的特点,利用泥灰岩三轴试验结果,分析了膨胀特性对深井软岩巷道围岩稳定性的影响;利用最新的弹塑性理论研究成果,推导出了膨胀角与围岩变形的直接关系式;采用数值力学的研究方法,分析了软岩巷道周围体积膨胀与扩容现象.数值模拟结果表明:软岩巷道表面变形和巷道周边体积应变随膨胀角的变化均成非线性递增,膨胀角愈大,软岩巷道的围岩条件愈差,巷道周边围压越大,所需要的支护力就越大,这些重要结论为深井条件下软岩巷道工程提供参考.     

考虑岩土体变形的边坡临界高度上限解

考虑岩石和土体变形，取对数螺旋面为破坏面，利用塑性力学中的极限分析方法对边坡的临界高度进行了研究,由库仑材料相关联流动法则推得了变形破坏区的速度场．由变形破坏机构得到了边坡临界高度上限解随坡角及岩土内摩擦角的变化规律．并通过比较发现：变形破坏机构对应的上限解略小于刚体平动机构对应的上限解，略大于刚体转动机构得到的上限解．     

考虑岩土体变形的边坡临界高度上限解崔新壮

考虑岩石和土体变形，取对数螺旋面为破 坏面，利用塑性力学中的极限分析方法对边坡的临界高度进行了研究.由库仑材料相关联流动法则推得了变形破坏区的速度场.由变形破坏机 构得到了边坡临界高度上限解随坡角及岩土内摩擦角的变化规律.并通过比较发现：变形破坏机构对应的上限解略小于刚体平动机构对应的上 限解，略大于刚体转动机构得到的上限解.     

颗粒粒径对立体格栅网-砂界面剪切特性影响

立体格栅网在传统平面格栅基础上增强了横肋与土体的侧阻力作用,有助于提高加筋土结构中筋土界面相互作用。为了研究网孔尺寸和颗粒粒径对立体格栅网-石英砂界面剪切特性的影响,通过3D打印技术制作不同网孔尺寸的立体格栅网,进行一系列单调直剪试验。试验分析了颗粒粒径、竖向应力和格栅网孔开口率变化时界面的摩擦角、剪胀角以及剪切强度系数的变化规律;在试验基础上,建立了界面剪胀系数模型,定量分析了颗粒平均粒径和格栅网孔开口率对立体格栅网-砂界面剪胀特性的影响。结果表明：颗粒粒径对立体格栅网-砂界面的似黏聚力影响更明显,对摩擦角的影响较小;界面最大剪胀角随竖向应力的增加而逐渐降低;颗粒粒径较大、格栅网孔开口率较小时,界面的剪胀性更强;剪切强度系数随粒径的增大而增加,表明立体格栅网与粒径较大的填料之间具有更好的互锁作用。     

Pseudo-dynamic analysis of seismic stability of reinforced slopes considering non-associated flow rule

The required reinforcement force to prevent instability and the yield acceleration of reinforced slopes are computed under seismic loading by applying the kinematic approach of limit analysis in conjunction with the pseudo-dynamic method for a wide range of soil cohesion, friction angle, dilation angle and horizontal and vertical seismic coefficients. Each parameter threatening the stability of the slope enhances the magnitude of the required reinforcement force and vice versa. Moreover, the yield acceleration increases with the increase in soil shear strength parameters but decreases with the increase in the slope angle. The comparison of the present work with some of the available solutions in the literatures shows a reasonable agreement.     

Multi-factor sensitivity analysis of shallow unsaturated clay slope stability

An unsaturated clay slope, with various sloping angles and a thickness of 14 m, consists of backfill, slope soil and residual soil. Slide interfaces were determined by geophysical approaches and the original slope was reconstructed. Sub-slope masses were classified based on the varieties of sloping angle. A force recursive principle was proposed to calculate the stability coefficient of the sub-slope masses. The influencing factors such as sloping angle, water content, hydrostatic pressure, seismic force as well as train load were analyzed. The range and correlation of the above-mentioned factors were discussed and coupled wave equations were established to reflect the relationships between unit weight, cohesion, internal frictional angle, and water content, as well as between internal frictional angle and cohesion. The sensitivity analysis of slope stability was carried out and susceptive factors were determined when the factors were taken as independent and dependent variables respectively. The results show that sloping angle, water content and earthquake are the principal susceptive factors influencing slope stability. The impact of hydrostatic pressure on slope stability is similar to the seismic force in quantity. Train load plays a small role in slope stability and its influencing only reaches the roadbed and its neighboring slope segment. If the factors are taken as independent variables, the influencing extent of water content and cohesion on slope stability can be weakened and train load can be magnified.     

超固结土的蛋形弹塑性本构模型

为了描述超固结软土在不同应力条件下的强度变形特征,以蛋形函数为基本框架,建立并发展适用于超固结土体的弹塑性本构模型. 通过对一系列超固结土应力路径三轴压缩试验结果的分析,探讨土体在超固结状态下塑性应变的发展规律(剪胀/剪缩). 在先前提出的旋转塑性势面流动法则基础上对其进行发展与改进,引入峰值应力比,构建剪胀状态下归一化塑性势面旋转角与应力状态参数之间的近似线性关系,以满足超固结土的塑性变形特性. 结合基于等效硬化参量的广义塑性功硬化原理构建超固结软土的蛋形弹塑性本构模型. 将三轴压缩试验数据与数值预测结果进行对比以验证模型有效性,结果表明该模型可以有效反映超固结软土在不同加载条件下的应力应变特性,比如软化与剪胀.     

基于未确知测度理论的基坑边坡稳定性评价

影响基坑边坡稳定的不确定性因素较多,如基坑规模、场地岩土体性质、施工质量、环境因素等。为了探索科学合理的基坑边坡的稳定性评价方法,本文基于未确知测度理论,选取了基坑深度、支护方式、主要土层粘聚力、主要土层内摩擦角、地下水及地表水作用、邻近荷载、邻近荷载坑边距、施工质量八个因素作为评价指标,利用三标度法结合层次分析法确定各指标权重,建立基坑边坡稳定性评价模型。将此模型应用于两个基坑工程实例,对比实际监测结果,评价结果的可靠度较高。结果表明,基于未确知测度理论的基坑边坡稳定性评价模型具有可行性。     

考虑分区各向异性和渗流作用的边坡稳定性研究

土体强度各向异性和渗流作用是影响边坡稳定性的重要因素。为使稳定性计算时边坡土体强度的各向异性更切合实际,提出对成层边坡土体进行分级加载和分区考虑强度各向异性的方法：将边坡土体最大主应力方向角与成层土相交区域设置为初始分区,然后结合有限元计算结果,推导各成层土各向异性强度参数计算公式,并即时计算各分区内土体强度参数;在逐级施加荷载过程中,根据计算所得土体强度参数,进一步调整初始分区,通过初分、细分和精分3级控制,确定耦合计算分区和各分区土体强度参数。在此基础上,建立考虑土体分区各向异性、未分区各向异性和未分区各向同性3种工况的流固耦合模型,分析边坡体应力场、位移场和渗流场的变化规律和特点,并采用强度折减法计算边坡稳定性。结果表明：考虑土体分区各向异性时,坡体平均应力最大值较未分区各向异性时有所减小,但较未分区各向同性时有所增大,其渗流域和流速较其他两种工况均有所减小;考虑土体分区各向异性时,计算所得边坡稳定性系数为1.109,较其他两种工况分别下降了2.8%和21.3%。     

加筋土坡地震稳定性的拟动力分析

研究加筋土坡在地震惯性力影响下的稳定问题。采用拟动力的方法表示作用在土坡滑动体上的水平与竖直地震惯性力。由于研究对象为加筋的土坡,所以引入水平条分法来研究加筋土坡的筋材拉力,并通过公式推导,设置算例研究土坡坡角、土体内摩擦角、地震加速度系数等因素对加筋效果的影响。结果表明:加筋拉力随地震加速度系数(k_h =0.0、0.15、0.3)的增大而增大,随土坡坡角(60°~90°)增大而增大,随土体内摩擦角增大而减小。       

临河岩质边坡地震抗倾覆稳定性拟动力分析

基于拟动力法推导出不同工况条件下临河岩质边坡地震抗倾覆稳定安全系数计算公式。通过参数分析,研究不同岩体放大系数下,水平和垂直地震力、张裂缝积水深度、边坡超载、锚固效应、流水淘蚀等对岩质边坡地震抗倾覆稳定性的影响,研究表明,不同工况下,张裂缝积水深度、水平地震力、流水淘蚀不利于岩质边坡地震抗倾覆稳定,但竖向地震力、锚固力、锚固高度、坡顶超载等有利于岩质边坡地震抗倾覆稳定;随着岩体放大系数的增加,水平地震力、竖向地震力对岩质边坡抗倾覆稳定性的影响增大,坡顶超载、张裂缝积水深度、锚固应力、锚固高度、临河水位对岩质边坡抗倾覆稳定性的影响减小,而锚固倾角、坡脚淘蚀高度对边坡抗倾覆稳定性的影响基本不变。     

饱和黏性土坡的地震稳定状态研究

通过对无限边坡的拟静态平衡分析,探讨了动孔压对饱和黏性土无限边坡的地震稳定状态的影响.分析表明,地震时孔隙水压累积导致的抗剪强度衰减会导致边坡发生永久变形,甚至导致整体滑动破坏,对某些黏性土也可因液化而发生流滑破坏.引入一个黏聚力界限值来区别此类边坡的最终破坏模式,以及两个界限动孔压比值来评价抗剪强度衰减对其破坏机制的影响.最后给出了此类边坡稳定状态的判别图,并建议了分析步骤.     

Bearing capacity of foundation on slope determined by energy dissipation method and model experiments

To determine the ultimate bearing capacity of foundations on sloping ground surface in practice, energy dissipation method was used to formulate the bearing capacity as programming problem, and full-scale model experiments were investigated to analyze the performance of the soil slopes loaded by a strip footing in laboratory. The soil failure is governed by a linear Mohr-Coulomb yield criterion, and soil deformation follows an associated flow rule. Based on the energy dissipation method of plastic mechanics, a multi-wedge translational failure mechanism was employed to obtain the three bearing capacity factors related to cohesion, equivalent surcharge load and the unit gravity for various slope inclination angles. Numerical results were compared with those of the published solutions using finite element method and those of model experiments. The bearing capacity factors were presented in the form of design charts for practical use in engineering. The results show that limit analysis solutions approximate to those of model tests, and that the energy dissipation method is effective to estimate bearing capacity of soil slope.     

三维地震技术在探测陷落柱中的应用

本文从探测陷落柱的物性前提出发 ,结合阳泉一矿三维地震解释陷落柱实例 ,着重介绍了三维地震对陷落柱的解释方法。     

含锯齿状结构面的岩质边坡稳定性拟动力分析

为了研究含有锯齿状结构面的岩质边坡稳定性，结合锯齿状结构面的剪切强度经验公式，综合考虑结构面参数、锚固效应、地震作用以及地下水位深度等因素的影响，基于改进的拟动力法推导了加锚结构面边坡抗滑稳定性安全系数计算式，并分析了岩石边坡稳定性的影响因素，结果表明：锯齿状结构面的抗剪强度与起伏角呈线性关系，随着起伏角的增大而增大；随着地震系数、滑动面倾角、水位深度、边坡倾角以及土体重度的增加，边坡稳定性降低，随着内摩擦角的增大而提高；锚固力越大，岩体的抗剪强度增大，边坡抗滑稳定性提高，但是锚固角的增大对边坡的稳定性起着负面效应。