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。     

刚性挡土墙后轻量土主动土压力特性模型试验研究

为了研究轻量土的主动土压力特性,通过开展大比尺刚性挡土墙模型试验,采用人工控制挡土墙位移的方式,分析轻量土作为墙后填土时的主动土压力分布规律。结果表明：轻量土的侧向土压力随着挡墙位移量的增加先降低后逐渐趋于稳定,侧向土压力在挡墙位移量为3 mm时初步达到稳定状态,对比发现轻量土的主动土压力显著小于重塑黄土,这表明轻量土可以有效降低墙背主动土压力。轻量土的主动土压力系数处于0～0.16之间,沿着挡墙分布较为稳定,而重塑黄土主动土压力系数介于0～0.57之间,显著大于轻量土的主动土压力系数。经朗肯理论值与模型试验值对比分析,发现轻量土的朗肯主动土压力小于试验值,理论值与试验值之间的绝对误差处于0～6.32 kPa之间,其在实际工程中可以忽略不计。鉴于模型试验中墙背与填土之间存在一定的摩擦,朗肯理论在计算轻量土的主动土压力时仍较为准确。通过模型试验研究和传统理论分析,揭示了轻量土的主动土压力特性,对于完善轻量土土压力理论具有重要意义。     

地震作用下高填减载明洞土压力研究

针对西北黄土高原地区高填方减载明洞工程,明洞顶部铺设EPS板可以有效减小明洞周围土压力,保证结构安全。然而,由于填土的动力高敏感性,地震作用将会对已经稳定的回填土体产生扰动,导致明洞结构周围土压力发生较大变动,对明洞结构造成不利影响。因此,采用数值模拟方式,对地震作用下的高填减载明洞周围土压力变化特性及土拱效应进行研究。研究结果表明:地震作用下,由于减载作用产生的土拱效应始终存在,使得土拱高度降低和效应减弱;明洞顶部竖向动土压力时程曲线在距明洞中央0~5 m范围内变化趋势一致,在距中央5~7 m范围内变化趋势相反,当明洞顶竖向动土压力达到峰值时,平均竖向动土压力为平均竖向静土压力的1.14倍;明洞两侧水平动土压力时程曲线变化趋势呈“此消彼长”状态,当水平动土压力达到峰值时,平均水平动土压力为平均水平静土压力的2.89倍。     

挡土墙地震被动土压力的拟动力分析

对地震土压力的研究是地震区挡土墙安全设计的一项重要课题。地震条件下,目前的研究主要是给出了土压力的近似拟静力解析解。本文采用可考虑动力荷载下的周期和纵波及横波效应的拟动力方法,对挡土墙后的地震被动土压力进行分析。在挡土墙后平面滑裂面假设的基础上,考虑了水平和垂直向地震加速度、纵波速度、横波速度、挡土墙摩擦角、填土内摩擦角、填土坡角对地震被动土压力的影响。与Mononobe-Okabe理论的拟静力法不同的是,用本方法得出了沿墙身地震被动土压力是非线性变化的结果,这更符合地震条件下土压力的变化规律。     

考虑填土侧向变形的地震土压力计算方法

地震土压力评价是挡土墙抗震设计的关键问题之一.以往的研究结果表明,挡墙上地震土压力的大小及分布与墙体的侧向位移或者墙后填土的侧向变形密切相关.经典的物部-冈部地震土压力公式可计算填土处于主动与被动状态的极限平衡条件下的土压力,未考虑挡墙侧向位移或填土侧向变形对土压力的影响.在研究土压力系数随应变增量比变化规律的基础上,本文指出土压力系数与挡土墙位移量之间不存在唯一性关系,发现正常固结填土的土压力系数与以应变增量比表述的填土侧向应变约束条件之间具有良好的唯一性,揭示了压剪耦合效应是土压力形成的物理本质;基于上述的唯一性关系和中间土楔等概念,提出了可考虑填土侧向变形的地震土压力实用计算方法,并通过土压力模型试验结果初步验证了该方法的合理性.     

复杂结构-桩-土振动台模型试验数据分析

本文从分析复杂结构-桩-土振动台模型试验数据入手,用加速度动力系数、最大位移、最大正应变、最大动土压力等指标对结构的地震响应全面分析,并对比桩、地下结构、地上结构的不同响应,研究发现:结构不同部分最大地震响应发生的频率不尽相同,且受地震动频谱特性及自身频率影响,天津波加载时结构的地震响应较大;地表以下,当震级较小时,土-结构对地震动起放大作用,随着震级的增加,对地震动放大作用减缓甚至减小;最大位移随结构高度增加逐渐增大,在桩与地下结构交界处和地表处,位移改变较大;地下结构柱、桩最大正应变呈中间大、两头小分布;最大动土压力随着深度增加呈两头大、中间小分布,且地表处最大;总的土压力受最大动土压力影响较大,随深度增加有先降低、后增大的趋势.     

卵石土场地地震反应特征振动台试验研究

为研究卵石土场地地震反应特征,基于四川成都典型卵石土场地,通过振动台模型试验研究卵石土场地在不同地震波、不同地震强度激励下的加速度峰值放大系数、加速度频谱反应及动土压力反应,并且对其场地地震反应非线性效应及土体动剪应力-动剪应变关系进行分析。结果表明：卵石土场地表层土层对地震波具有明显的放大效应,加速度峰值放大系数介于1～1.4之间,下部土层放大效应较小,加速度峰值放大系数介于0.9～1.2之间。卵石土场地对地震波具有低频放大,高频滤波的作用,滤波频率上、下限随激励强度的增大逐渐向低频方向移动。激励强度较小时,土体尚未破坏,动土压力在地震过程中逐渐增大;随着激励强度的增大,动土压力反应明显增大,表现出骤减后逐渐增大的现象。在激励强度较小时(SN1),中部土体最先进入非线性反应阶段,地震波在中部土层能量损耗最大;激励强度较大时(EL3),土体均发生了较大变形,土体最大动剪应变达到1.7%,此时卵石土场地对地震波的放大作用明显减弱。     

平面应变条件下基于弹性理论的土压力计算及适用性研究

针对工程中大量存在的平面应变问题,依据平面应变条件和广义胡克定律,基于SMP、Lade-Duncan、AC-SMP和广义Mises强度准则,推导出考虑中主应力及泊松比影响的无黏性土主、被动土压力计算公式,并将其扩展至黏性土,讨论基于各强度准则土压力计算公式的适用范围。结果表明：考虑中主应力对土强度的贡献后,基于各强度准则所计算的主动土压力均小于朗肯主动土压力,被动土压力均大于朗肯被动土压力;主动土压力P_a随着泊松比的增大而减小,被动土压力P_P随着泊松比的增大而增大,且泊松比越大,与实测数据更为接近;基于同一强度准则下得到的主、被动土压力适用的内摩擦角范围随着泊松比的增大而增大;基于各强度准则的土压力计算公式均能较好的描述挡土结构上土压力的大小,其中广义Mises强度准则计算结果与实际工程更为吻合,研究成果可为挡土结构上土压力的计算提供一定理论参考。     

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。     

土-大型地铁地下车站结构动力接触效应研究

以苏州地铁一号线的星海站为工程背景,考虑土与地铁车站结构非线性动力相互作用效应,分析了土与地下结构接触面的动力分离与滑移效应、土与地下结构接触面上动土压力和动摩擦力的分布规律与反应幅值,以及动力接触效应对地铁车站结构动力反应的影响规律。研究结果表明：强地震发生时,在地铁地下车站结构侧墙顶端,出现了土与结构接触分离现象,在车站结构顶底板处,土与结构产生了相对滑移现象;考虑动力接触效应时,地下结构总体动力反应是变小的。给出了车站结构侧墙上动土压力分布规律及其动土压力系数,以及车站结构顶底板上的动土压力分布规律及其反应幅值。研究结果对进一步了解土与地下结构的动力接触效应及其对地下结构动力反应的影响,具有一定的参考价值和指导意义。     

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.     

Static and seismic limit equilibrium analysis of sliding retaining walls under different surcharge conditions

The static and seismic sliding limit equilibrium condition of retaining walls is investigated, and analytical solutions for the angle of the active slip surface, the critical acceleration coefficient and the coefficient of active earth pressure are provided for different surcharge conditions. In particular, walls retaining a horizontal backfill without surcharge, walls supporting an extended uniform surcharge applied at different distances from the wall and walls supporting a limited uniform surcharge or linear uniform surcharge parallel to the wall are considered in the analysis.The solutions have been derived in the framework of the limit equilibrium approach, considering the effect of the wall through its weight, and accounting for the shear resistance at the base of the wall and the inertia force arising in the wall under seismic conditions.For the wall without surcharge the effect of the vertical component of the seismic acceleration as well as the effects of the inclination of the wall internal face and of the soil–wall friction were also investigated.The angle of the slip plane, the critical seismic acceleration coefficient and the coefficient of active earth pressure are given as functions of dimensionless parameters and the boundary conditions for the applicability of each solution are specified. The influence of soil weight, surcharge conditions and inertia forces on the active earth pressure coefficient is analysed.     

Seismic passive earth resistance using modified pseudo-dynamic method

In earthquake prone areas, understanding of the seismic passive earth resistance is very important for the design of different geotechnical earth retaining structures. In this study, the limit equilibrium method is used for estimation of critical seismic passive earth resistance for an inclined wall supporting horizontal cohesionless backfill. A composite failure surface is considered in the present analysis. Seismic forces are computed assuming the backfill soil as a viscoelastic material overlying a rigid stratum and the rigid stratum is subjected to a harmonic shaking. The present method satisfies the boundary conditions. The amplification of acceleration depends on the properties of the backfill soil and on the characteristics of the input motion. The acceleration distribution along the depth of the backfill is found to be nonlinear in nature. The present study shows that the horizontal and vertical acceleration distribution in the backfill soil is not always in-phase for the critical value of the seismic passive earth pressure coefficient. The effect of different parameters on the seismic passive earth pressure is studied in detail. A comparison of the present method with other theories is also presented, which shows the merits of the present study.     

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.     

地震中整体面板式土工格栅加筋土挡墙动土压力研究

土工格栅加筋挡土墙是一种柔性挡土结构,目前尚未建立较严密的设计方法,作用在土工格栅加筋墙壁上的地震动土压力研究是抗震设计的重要内容之一。应用基于拉格朗日法的完全非线性动有限差分法研究整体面板式土工格栅加筋土挡壁在地震作用下各设计参数对挡壁动土压力的影响。采用弹塑性模型模拟填土,采用耦合弹性参数描述格栅与土接触界面特性,参数包括加筋间距、长度、刚度、地震强度和填土性质等,分析墙壁的动土压力沿墙身的分布特征,得出了影响地震动土压力的显著参数,证明了土工格栅加筋墙体的优异吸震能力,研究结果为整体面板式土工格栅加筋土挡墙抗震设计中的动土压力研究提供参考。     

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。     

土动力学研究综述及思考

随着国家重大构筑物的不断建设实施,考虑土体具有较高的动力易损性和致灾特性,工程构筑物的工程地质灾害和岩土工程动力致灾特性研究需要愈显迫切。通过对当前土动力学与岩土地震工程方面研究进展进行归纳总结,着重从土的动力强度、土的动本构关系、砂土的振动液化、铁路路基中的动应力、边坡地震永久变形和稳定性、挡土墙上的地震土压力等六个方面进行叙述,对其中涉及的各种研究方法进行比较和论述,最后提出了土动力学有待进一步深入研究的若干问题和未来发展方向,以期基于土动力学的发展而提升构筑物的抗震设防水平。     

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.     

Earthquake-induced displacements of gravity retaining walls and anchor-reinforced slopes

This paper examines in terms of seismic performance, the effectiveness of anchor reinforcement against gravity retaining walls used to stabilize a dry homogenous fill slope in earthquake-prone environment. Both analyzed stabilizing measures have the same design yield acceleration estimated from a limit equilibrium approach. The earthquake-induced displacements are calculated using a sliding block formulation of the equation of motion. Sliding failure along the base of the gravity retaining wall and rotational failure of the soil active wedge behind the wall, as well as rotational failure of the slide mass of the anchor-reinforced slope were considered in the present formulation. For the specific characteristics of the analyzed fill slope and input horizontal ground motion, the slope reinforced with anchors appears to experience vertical and horizontal seismic displacements at slope crest smaller by 12% and respectively, 32% than the vertical and horizontal earthquake-induced deformations estimated at the top of the active wedge behind the gravity retaining wall.     

Seismic passive resistance with vertical seepage and surcharge

Present paper focuses on the computation of the seismic passive earth pressure acting on a vertical rigid retaining wall by a soil mass subjected to vertical steady-state seepage and a uniform surcharge load. Based on the basic assumptions of Coulomb's theory and a pseudo-static method of analysis, a general solution for the passive earth pressure containing two coefficients is presented. In the solution, many parameters, such as unit weight of saturated soil, soil effective internal friction angle, soil/wall friction angle, water/soil unit weight ratio, surcharge intensity coefficient, horizontal and vertical seismic acceleration coefficients, Poisson's ratio of soil mass, hydraulic gradient, and coefficients of pore water pressure, are considered. The effects of hydraulic gradient and seismic forces on passive earth pressure coefficient and passive earth pressure distribution are investigated. The results indicate that passive earth pressure increases with increasing hydraulic gradient for downward water flow case, but decreases for upward water flow case, and that the presence of seismic forces induces a reduction in passive earth pressure.