在考虑惯性力情况下挡土墙后黏性填土主动土压力的计算

本文在已有研究成果的基础上,根据库伦土压力的计算原理,从滑动土楔处于极限平衡状态时力的平衡条件出发,考虑实际地震中对挡土墙稳定性最不利的情况,推导出了计算黏性土或无黏性土主动土压力的公式。该公式适用于均布荷载作用于挡土墙后任意位置。对地震多发区考虑水平惯性力作用下重力式挡土墙设计中土压力的计算具有一定参考价值。     

岩石场地重力式挡土墙地震土压力振动台实验研究

结合汶川震区调查资料,利用大型振动台模型试验,分析了碎石土填料的岩石场地重力式挡土墙的地震土压力及其分布规律,并以此对我国现行铁路、公路抗震规范做合理性讨论和细化。研究发现,地震作用下,挡土墙的动土压力沿墙高呈单峰曲线状分布,且60%～80%集中作用于挡墙中部;随着地震峰值加速度的增加,地震土压力分布逐渐偏离现行振震设计规范所认为的三角形线性状,而呈现非线性状;合力作用点高于1/3墙高,0.4g地震加速度作用下,接近0.4倍墙高,对岩石场地下粗粒径墙背填料的地震土压力作用点高度,建议取0.35倍墙高。对比计算表明,现行规范能基本满足工程抗震设计需要,但建议对柔性挡土墙的抗震设计作出必要规定。     

地震作用下非饱和土主动土压力极限分析半解析法

地震是诱发边坡失稳的主要因素之一,重力式挡土墙作为一种广泛采用的岩土支挡结构,有必要对其地震稳定性问题进行深入的研究.为有效评估地震作用下非饱和填土的主动土压力,基于极限分析上限原理和拟动力法,提出一种半解析水平片分法,计算具有非线性分布特征的非饱和土重力和地震惯性力所做外功率,并构建功能平衡方程,得到非饱和填土主动土压力显示半解析解.通过与解析解对比,验证该方法的合理性,并通过算例分析,揭示吸力效应的强化机制和非饱和填土主动土压力的地震响应规律.结果表明:忽略吸力效应会高估填土的主动土压力,吸力的强化作用不仅取决于填土类型,还与地震动特性密切相关;水平和竖向地震动对土压力有较大影响, 土压力系数峰值随土剪切模量的增加略有增加并向负方向移动,随地震周期的增加略有增加并向正方向移动;填土倾角较大时,坡顶附加荷载的影响更加显著;对于倾角大于100°的填土,墙G土界面摩擦角较大时,土压力相对较高.     

饱和粉土液化特性的大型振动台模型试验研究

京沪高速铁路徐沪段路基的粉土粘粒含量少于1.5%、粉粒含量约为80%,在强烈地震作用下存在着液化可能性.为充分研究这一饱和粉土地层的液化特性,本文作者利用大型地震模拟振动台,进行了模拟自由场地饱和粉土的地震液化模型试验,试验结果再现了自然地震触发的粉土液化的各种宏观震害现象,揭示了饱和粉土的地震液化规律和特征。试验结果为京沪高速铁路徐沪段路基的抗震设计提供了参考依据。     

地震作用下重力式挡土墙土压力特性数值模拟研究

重力式挡土墙在地震作用下的土压力特性一直是挡土墙设计的重要内容。本文通过数值模拟,在挡土墙墙背轴线上设置一系列监测点,得到地震过程中监测点的加速度、土压力强度时程曲线;然后根据时程曲线分析墙后土压力强度分布特征、根据土压力强度分布求出总土压力、根据总土压力求出其对墙趾的力矩;最后分别将土压力强度分布、总土压力、总土压力对墙趾的力矩与现有的研究方法及规范对比。结果表明:地震作用下墙背各点加速度峰值在同时刻发生,但土压力峰值不在同时刻发生;现有的一些研究方法未考虑土压力强度峰值时程变化,其结果比实际偏大;在低地震烈度条件下,规范计算的总土压力及倾覆力矩偏于保守,而在高烈度条件下则偏于危险。     

一种计算地下结构地震主动土压力的新方法

针对目前地下结构地震土压力设计方法的研究现状,介绍了计算挡土墙地震主动土压力的物部·冈部公式及浅埋隧道谢家然围岩压力理论。并结合物部·冈部公式、谢家然理论提出了一种适用于计算地下结构地震土压力的新方法。该方法基于极限平衡理论,根据谢家然理论提供的滑裂面参数构造了滑动土体,采用物部·冈部公式计算了滑动土体作用在地下结构边墙上的地震土压力。最后结合工程实例,将本文方法与其它计算方法进行了比较,评价了该计算方法的优缺点。     

土质场地重力式挡土墙地震土压力振动台实验研究

汶川震区路基挡土墙震害表明,地震动荷载作用下重力式挡墙的位移、破坏与基础场地形式有关,除岩质场地和土质场地挡墙所共有的外倾形式,土质地基挡土墙还表现有整体推移及下部向外推移的倾转变形等复杂模式,因此地震土压力大小及分布也将受到这种复杂土-结相互作用的影响。基于碎石土及风化花岗岩填料的土质场地重力式挡土墙大型振动台模型实验,对挡土墙地震土压力及变形模式开展了对比研究,发现在强震作用下,土质地基挡墙因基础约束较弱而产生位移,并伴随明显的墙—土分离现象,致使实测地震土压力较之抗震设计规范计算值偏小（0.4g峰值加速度下约小6%～15%）,但作用点高度变化不大。由实验结果与现行抗震规范计算值的安全系数对比,认为对土质场地挡墙的地震土压力计算,按现行国内抗震设计规范基本能满足实际工程抗震设计需要;对于地震区挡墙设计,在允许挡墙发生少量容许位移的前提下可采用内摩擦角较大、自稳能力更好的墙背填料以减少地震土压力。     

倾斜挡土墙后粘性土的地震主动土压力分析

文中考虑水平地震加速度、竖向地震加速度、卓越周期和墙面倾角的因素,运用拟动力学的分析方法,得到了考虑时间和相位变化的粘性土地震主动土压力系数、土压力合力和土压力分布强度的理论公式。在此基础上,分析了水平和竖向地震加速度系数、内摩擦角、墙面摩擦角对最不利工况下滑动面倾角、主动土压力系数、主动土压力分布的影响。研究表明:地震主动土压力分布为非线性;地震加速度导致粘性土的主动土压力大幅增加,增加的程度随着地震水平加速度系数的增大而增加。     

微型土压力传感器标定方法研究

离心模型试验常用微型土压力传感器测量地基或土与结构接触边界上的土压力。传感器使用之前应进行标定。传统的液标或气标方法不能准确反映传感器埋置过程对土体的扰动或传感器周围人为土拱边界条件形成,导致测试结果不甚理想。故针对试验条件,设计制作一套标定微型土压力传感器的方法和装置,以水、粉质黏土和福建标准砂为标定介质,考虑有无刚性靠背两种工作状态对多个传感器进行室内标定,得到标定系数。结果表明:水标未出现卸载滞后,砂标和土标均出现卸载滞后,且表现为非线性;引入滞后比R评价微型土压力传感器的滞后性,认为标定介质和传感器类型是影响滞后比的两个主要因素;传感器自身材料特性和几何特性、地基土的制备和传感器放置、加载预压和加卸载循环等对土体密实度、土体强度等的改变、工作介质和状态等对标定结果有影响。建议尽量模拟试验工作介质和工作状态,逐个标定传感器,以得到更准确的土压力测量值。     

挡土墙地震主动土压力及其分布形式研究

物部理论认为地震主动土压力呈线性分布,而且作用点位于墙底以上1/3高度处,与实测结果相差较大。基于库仑土压力理论的平面滑裂面假定,根据挡土墙后滑裂土体的力矩平衡,引入了土体对地震的放大效应,提出了地震主动土压力作用点位置的确定方法,给出了地震主动土压力强度的理论公式,并分析了地震放大系数对地震主动土压力及其分布的影响。结果表明,如果不考虑地震放大系数,地震主动土压力值与物部理论的计算结果基本相同,可见物部理论是本文方法的一种特例;地震主动土压力作用点都位于墙底以上0.40~0.50倍高度处,与试验结果比较吻合,说明物部理论有待进一步完善;地震主动土压力强度是一种作用等价的非线性分布,沿墙高的分布形式接近于抛物线,最大值也不再恒定于墙底,在挡土墙的稳定性设计时应予以重视。     

Seismic active pressure distribution history behind rigid retaining walls

Evaluating the seismic active earth pressure on retaining walls is currently based on pseudo-static method in practices. In this method, however, it is not simple, choosing an appropriate value for earthquake coefficient, which should fully reflect the dynamic characteristics of both soil and loading is an important problem. On the other hand, by using only two extra dynamic parameters that are shear wave velocity of soil and predominant frequency of probable earthquake, one can benefit from another more accurate tool called pseudo-dynamic method to solve the problem of earth pressure.In this study in the framework of limit equilibrium analysis, pseudo-dynamic method has been applied into horizontal slice method of analysis to account for the effect of earthquake on lateral earth pressure history behind rigid retaining walls. The pressure history resulted from a number of analyses shows that before and after reaching the peak resultant force, different pressure distributions occur behind a wall that put more local pressure than the same at peak. This method would be a tool to control this phenomenon in wall design.     

Evaluation of pseudostatic active earth pressure coefficient of cantilever retaining walls

A stress plasticity solution is proposed for evaluating the gravitational and dynamic active earth pressures on cantilever retaining walls with long heel. The solution takes into account the friction angle of the soil, wall roughness, backfill inclination and horizontal and vertical seismic accelerations. It is validated by means of the comparison with both traditional limit equilibrium methods (e.g. Mononobe–Okabe equations) and static and pseudostatic numerical FLAC analyses. For numerical analyses the soil is modelled as an elasto-plastic non-dilatant medium obeying the Mohr–Coulomb yield criterion, while the wall is elastic. The solutions for the horizontal and vertical seismic coefficients are proposed, which allow one to determine the intensity of the active thrust and its inclination δ with respect to the horizontal. It is demonstrated that the latter also depends on the soil friction angle φ. The inclination in seismic conditions δ_E is greater than the one in static conditions, δ_S, usually adopted in both cases. As a matter of fact, since wall stability conditions improve with the increase of inclination δ, the present method gives solutions that are less onerous than traditional ones, producing less conservative wall designs. Finally pseudostatic results are compared with proper dynamic analyses (by FLAC code) performed utilising four Italian accelerometric time-histories as input ground motion.     

Seismic earth pressures on rigid and flexible retaining walls

While limiting-equilibrium Mononobe–Okabe type solutions are still widely used in designing rigid gravity and flexible cantilever retaining walls against earthquakes, elasticity-based solutions have been given a new impetus following the analytical work of Veletsos and Younan [23]. The present paper develops a more general finite-element method of solution, the results of which are shown to be in agreement with the available analytical results for the distribution of dynamic earth pressures on rigid and flexible walls. The method is then employed to further investigate parametrically the effects of flexural wall rigidity and the rocking base compliance. Both homogeneous and inhomogeneous retained soil is considered, while a second soil layer is introduced as the foundation of the retaining system. The results confirm the approximate convergence between Mononobe–Okabe and elasticity-based solutions for structurally or rotationally flexible walls. At the same time they show the beneficial effect of soil inhomogeneity and that wave propagation in the underlying foundation layer may have an effect that cannot be simply accounted for with an appropriate rocking spring at the base.     

Dynamic pressures on a pair of rigid walls retaining poroelastic soil

This work deals with the evaluation of the dynamic pressures and the associated forces on a pair of rigid vertical cantilever walls retaining a uniform, fully saturated poroelastic layer of soil. Hysteretic damping in the soil skeleton may also be present. Wall pressures and forces are induced by horizontal ground shaking harmonically varying with time and spatially invariant. The problem is solved analytically under conditions of plane strain. The governing partial differential equations of motion, after separation of variables and the simplifying assumptions of zero vertical normal stresses and zero horizontal variation of vertical displacements, reduce to a system of two ordinary differential equations for the amplitudes of the solid skeleton horizontal displacement and the pore water pressure, which are easily solved. The parameters examined include the ratio of the distance between walls to the height of the retained soil material and the soil material properties such as porosity, permeability and damping. The comprehensive numerical data presented indicate that the displacements, wall pressures and resultant forces are highly dependent on the distance between the walls for any values of porosity and permeability.     

Dynamic earth pressure on rigid retaining walls induced by a neighboring machine foundation,by the meshless local Petrov-Galerkin method

Dynamic earth pressure induced by machine foundations on a neighboring retaining wall is analyzed with emphasis on factors which control the intensity and location of the design forces. The meshless local Petrov-Galerkin(MLPG) method is used to analyze the problem for a variety of retaining wall and machine foundation geometries. The soil medium is assumed to be homogeneous and visco-elastic. The machine foundation is idealized as a harmonic sinusoidal dynamic force often encountered in practice. A number of analyses have been made to reveal the effect of the loading frequency, the location and size of the foundation and the soil shear wave velocity on the distribution and magnitude of the dynamic earth pressure. Results indicate that there is a critical frequency and a critical location for which the passive pressure takes the maxima in the entire duration of the dynamic load.     

Seismic active earth pressure of cohesive-frictional soil on retaining wall based on a slice analysis method

The M–O (Mononobe–Okabe) theory is used as a standard method to determine the seismic earth pressure. However, the M–O theory does not consider the influence of soil cohesion, and it cannot determine the nonlinear distribution of the seismic earth pressure. This paper presents a general solution for the nonlinear distribution of the seismic active earth pressure of cohesive-frictional soil using the slice analysis method. A new method is proposed to determine the critical failure angle of the backfill wedge under complex conditions, and an iterative calculation method is presented to determine the tension crack depth of the seismic active earth pressure. The considered parameters in the proposed method include the horizontal and vertical seismic coefficients, wall inclination angle, backfill inclination angle, soil friction angle, wall friction angle, soil cohesion, wall adhesion and uniform surcharge. The classical methods of the M–O and Rankine theories can be regarded as special cases of the proposed method. Furthermore, the proposed method is compared with the test results and previously existing solutions to validate the correctness of the results. Additionally, the parameters׳ effect on the critical failure angle, the resultant force, the application-point position, the tension crack depth and the nonlinear distribution of seismic active earth pressure are studied in graphical form.     

Pseudo-dynamic active force and pressure behind battered retaining wall supporting inclined backfill

Knowledge of seismic active earth pressure behind rigid retaining wall is very important. Commonly used Mononobe–Okabe method considers pseudo-static approach, which gives the linear distribution of seismic earth force. In this paper, the pseudo-dynamic approach, which considers the effect of primary and shear wave propagations, is adopted to calculate the seismic active force. Considering the planar rupture surface, the effect of wide range of parameters like inclination of retaining wall, inclination of backfill surface, wall friction and soil friction angle, shear wave and primary wave velocity, horizontal and vertical seismic coefficients are taken into account to evaluate the seismic active force. Results are presented in terms of seismic coefficients in tabular form and variation of pressure along the depth.     

Seismic pressures on rigid cantilever walls retaining elastic continuously non-homogeneous soil: An exact solution

The dynamic response of an elastic continuously nonhomogeneous soil layer over bedrock retained by a pair of rigid cantilever walls to a horizontal seismic motion and the associated seismic pressure acting on these walls are determined analytically–numerically. The soil non-homogeneity is described by a shear modulus increasing nonlinearly with depth. The problem is solved in the frequency domain under conditions of plane strain and its exact solution is obtained analytically. This is accomplished with the aid of Fourier series along the horizontal direction and solution of the resulting system of two ordinary differential equations with variable coefficients by the method of Frobenius in power series. Due to the complexity of the various analytical expressions, the final results are determined numerically. These results include seismic pressures, resultant horizontal forces and bending moments acting on the walls. The solution of the problem involving a single retaining wall can be obtained as a special case by assuming the distance between the two walls to be very large. Results are presented in terms of numerical values and graphs using suitable dimensionless quantities. The effect of soil non-homogeneity on the system response is assessed through comparisons for typical sets of the parameters involved.     

Seismic response of multi-tiered reinforced soil retaining walls

In this study, a validated Finite Element procedure was used to investigate the similarities and differences of seismic performances between single- and multi-tiered reinforced soil walls. Three-tiered walls at a total height of 9 m were analyzed together with vertical walls at the same height. It was found from the Finite Element analyses that the resonant frequency of reinforced soil walls might increase with an increase in the tier-offset. The multi-tiered configuration could considerably reduce the residual lateral facing displacement and the average reinforcement load, and the reinforcement load distribution with height was different from that in vertical walls. With the same reinforcement length and spacing, the multi-tiered walls resulted in smaller reinforcement connection loads with the facing blocks. The study filled the gap of seismic behavior of multi-tiered reinforced soil retaining walls and revealed a few unique dynamic properties of this type of earth structures.