核安全相关边坡与一般边坡挡土墙抗震稳定性验算对比分析

在挡土墙稳定性计算基本原理基础上, 引入《核电厂抗震设计规范》(GB 50267-97) 关于地震系数的规定, 重新建立了安全相关边坡挡土墙土压力和地震角计算公式, 并应用到实际工程中。对比分析显示, 挡土墙按核安全边坡和一般边坡进行抗震验算时, 地震系数、地震角的取值相差较大; 由于按核安全边坡计算时地震力远大于一般边坡, 因此稳定系数远小于一般边坡。      

基于灰色关联与模糊数学的重力式挡土墙震害评估

龙门山地区强震荷载导致大量已建边坡支挡结构严重受损,如何对震区受损挡土墙进行震害评估成为亟待解决的技术难点。本文首先通过对研究区挡土墙的震害分析,总结出其主要破坏模式包括滑移破坏、沉降破坏、倾覆破坏、墙身破坏以及越顶破坏5类。然后根据全面性、重要性以及科学性原则对影响震害评价的因子进行定性分析和分类,并结合挡墙的破坏模式,综合分析得到挡土墙安全评估的敏感性因子和一般因子。将震害范围60%作为挡墙评价的敏感性因子,而一般因子分为两级共10个指标,包括:滑移距离,沉降深度,倾斜角度,裂缝数量,裂缝长度比,开裂深度比,开裂宽度,错动距离,垮塌范围,覆盖范围。最后,采用灰色关联分析与模糊数学理论相结合的方法构建挡土墙震害评估体系,从而变事后处理为事先预防,为灾后恢复重建服务。     

Seismic Retrofit of Gravity Retaining Walls for Residential Fills Using Ground Anchors

Failure of several gravity retaining walls in residential areas built on reclaimed land, during the October 23, 2004 Chuetsu earthquake in Niigata Prefecture, Japan, determined the authorities to consider the seismic retrofit of the walls in order to mitigate future similar disasters in the urban environment. This study addresses the effectiveness of ground anchors in improving the seismic performance of such retaining structures through a sliding block analysis of the seismic response of an anchored gravity retaining wall supporting a dry homogeneous fill slope subject to horizontal ground shaking. Sliding failure along the base of the wall and translational failure along a planar slip surface of the active wedge within the fill material behind the wall were considered in the formulation, whereas the anchor load was taken as a line load acting on the face of the gravity retaining wall. The effects of magnitude and orientation of anchor load on the yield acceleration of the wall-backfill system and seismically induced wall displacements were examined. It was found that for the same anchor orientation, the yield acceleration increases in a quasi-linear manner with increasing the anchor load, whereas an anchor load of a given magnitude acting at various orientations produces essentially identical yield accelerations. On the other hand, the computed earthquake-induced permanent displacements of the anchored gravity retaining wall decrease exponentially with increasing magnitude of anchor load. Additionally, the influence of backfill strength properties (e.g., internal friction angle) on the seismic wall displacement appears to diminish considerably for the anchored gravity retaining wall. A dynamic displacement analysis conducted for the anchored gravity retaining wall subjected to various seismic waveforms scaled to the same peak earthquake acceleration revealed a good correlation between the calculated permanent wall displacements and the Arias intensity parameter characterizing the input accelerogram.     

New Method to Compute Seismic Active Earth Pressure on Retaining Wall Considering Seismic Waves

In earthquake prone areas, calculation of seismic active earth pressure on retaining wall is very important. Analytical methods till date for computation of seismic active earth pressure do not consider the effect of Rayleigh wave though it constitutes about 67 % of the total seismic energy. In this paper a new dynamic approach is proposed by considering all possible seismic waves viz. primary, shear and Rayleigh waves for estimation of seismic active earth pressure on rigid retaining wall by satisfying all the boundary conditions. Limit equilibrium method is used for estimation of optimised seismic active earth pressure for a rigid retaining wall supporting cohesionless backfill with critical combinations of seismic accelerations. The seismic influence zone obtained in this study is about 22 and 17 % larger when compared with available pseudo-static and pseudo-dynamic methods respectively, which indicates the significant effect of Rayleigh wave. Also, there is an increase of about 14 and 6 % in seismic active earth pressure coefficient when the present results are typically compared with pseudo-static and pseudo-dynamic methods respectively. Moreover present results compare well with the available experimental results. Present results are more critical for the design estimation of seismic active earth pressure by considering all major seismic waves as proposed in the new dynamic approach.     

Pseudo-dynamic approach of seismic active earth pressure behind retaining wall

Knowledge of seismic active earth pressure behind rigid retaining wall is very important in the design of retaining wall in earthquake prone region. Commonly used Mononobe-Okabe method considers pseudo-static approach, which gives the linear distribution of seismic earth pressure in an approximate way. In this paper, the pseudo-dynamic method is used to compute the distribution of seismic active earth pressure on a rigid retaining wall supporting cohesionless backfill in more realistic manner by considering time and phase difference within the backfill. Planar rupture surface is considered in the analysis. Effects of a wide range of parameters like wall friction angle, soil friction angle, shear wave velocity, primary wave velocity and horizontal and vertical seismic accelerations on seismic active earth pressure have been studied. Results are provided in tabular and graphical non-dimensional form with a comparison to pseudo-static method to highlight the realistic non-linearity of seismic active earth pressures distribution.     

Seismic damage of earth structures of road engineering in the 2008 Wenchuan earthquake

To understand the mechanism of the earth structure damage, a wide range of investigations along roads in seismic hazard areas have been carried out after the 2008 Wenchuan earthquake. In this paper, the results from 41 roads investigated are presented, and the 41 roads are located in 7–11 intensity zones and consist of rural/county roads, province roads and state roads in Sichuan province. According to the investigation, the types of damaged slopes and retaining walls are classified and statistical analyses are performed. In the statistical analyses, various impact factors to seismic slope and retaining wall damage were studied, such as slope inclination, height of slope and retaining wall, site conditions, and seismic intensity. In addition, some relationships were developed, including the quantity of damaged slopes with slope inclination and height, the angle between route and fault rupture directions, and site conditions. Finally, some reasonable suggestions are put forward on the designs and constructions of slopes and retaining walls when they are subject to seismic activity.     

地下结构地震破坏静-动力耦合模拟研究

地下结构地震破坏过程模拟是研究地下结构抗震性能的有效手段,通过人工边界条件设置将围岩土体的自重应力作为动力响应模拟的初始状态,实现了地下结构地震响应静-动力耦合数值模拟。基于有限元分析软件ABAQUS,将极限剪应变作为破坏标准,采用生死单元法模拟了地下结构的地震破坏过程,通过结构埋深考虑了初始地应力对地下结构抗震性能的影响。模拟结果表明,地下结构的抗震性能存在一个最不利埋深,即最容易地震破坏的埋深,当结构的埋深超过最不利埋深时,结构的极限抗震能力增强,若结构产生地震破坏,则结构埋深越深即初始地应力越高其破坏程度也越强。     

Experimental study on seismic performances of geogrid striped-reinforced waste tire-faced retaining wallsEI北大核心

废旧轮胎胎面挡土墙是一种有效利用废旧轮胎的理想途径,但直立的模块式废旧轮胎胎面挡土墙不能承受高强度的地震作用,因而提出格栅条带式加筋的方法提高其抗震性能。根据土-结构动力相似体系,设计格栅条带式加筋废旧轮胎胎面挡土墙振动台试验模型,考虑地震强度、地震波、格栅加筋长度、格栅加筋间距以及墙面坡度的影响,分析胎面墙体与回填料加速度、墙体侧向位移、墙顶表面回填料沉降以及墙背动土压力等地震响应特征,并与无加筋的废旧轮胎胎面挡土墙的振动台模型试验进行对比。研究结果表明:格栅条带式加筋胎面挡土墙的方式显著改善了无加筋状态的胎面挡土墙的地震响应特征,提高了胎面挡土墙的抗震性能,格栅条带式加筋直立式废旧轮胎胎面挡土墙可以作为理想的墙体进行工程推广应用。     

地震条件下黏性土挡土墙土压力分析

Mononobe-Okabe理论是现阶段计算地震土压力的常用方法,但Mononobe-Okabe理论的诸多假设使其具有一定的局限性。针对Mononobe-Okabe理论的不足,考虑到地震作用下挡土墙偏转对土压力的影响,采用斜向条分法推导了复杂条件下黏性土地震土压力强度分布、土压力合力及其作用点位置公式,并利用图解法给出了临界破裂角的解析解。研究表明：填土黏聚力和地震系数对土压力影响显著;忽略黏性填土表面开裂与地震作用对均布超载及开裂填土等效超载的影响将使主动土压力计算结果偏小,其误差随着填土黏聚力和均布超载的增大而增大;在不同水平地震系数下土压力沿墙高呈非线性分布;所提公式适用范围更广,有效完善了Mononobe-Okabe理论。     

俯斜式混凝土重力挡土墙强震反应数值模拟

首先,介绍了基于OpenSees独立开发的一套用于挡土墙-土地震反应相互作用有限元分析计算软件RW_2DPS.据此建立了俯斜式混凝土重力挡土墙-土强震相互作用有限元模型.模型中,引入非线性有限元计算方法,选用多屈服面弹塑性本构模型模拟砂土的动力属性,应用零长度接触单元模拟墙与土体之间的接触特性,且采用一致耗能阻尼边界与速度边界条件.最后,输入随机地震动,进行挡土墙-土强震反应分析,并重点探讨墙背地震土压力和水平地震惯性力沿挡土墙高度分布规律.结果表明,墙背动土压力峰值出现在距挡土墙底约1/3墙高处;挡土墙背加速度具有放大效应,加速度峰值出现在挡土墙顶部;不同地震动作用下,加速度放大系数沿墙高分布规律不同,动土压力沿墙高变化规律基本一致.     

RT模式下地震非极限主动土压力的拟动力分析

为考虑挡墙位移效应对地震土压力的影响,依据前人试验研究的结论,将摩擦角表示为与挡墙位移量和位置高度相关的函数,然后基于拟动力法和水平层分析法,推导得出RT位移模式下的地震非极限主动土压力和合力作用点的计算表达式。计算模型可描述摩擦角沿着墙高逐渐发展的不同非极限位移状态工况,并建立了挡墙位移、地震动荷载和土压力之间的相互联系。参数分析讨论了振动时间、挡土墙位移状态、地震加速度参数和土体摩擦角对地震主动土压力分布、合力大小以及合力作用点高度的影响。相比于传统的极限状态地震土压力理论,所提方法更合理地描述了地震土压力随挡墙位移的发展过程,对发展非极限土压力理论和改进边坡工程中的抗震计算方法具有一定的参考意义。     

格宾挡墙发展综述

格宾挡墙是一种新型柔性支挡技术,且优于以往传统方法,具有柔性、透水性、耐用性、抗震性以及利于植被生长等优点。近年来逐渐在我国水利、航道、公路、铁路、矿业、地灾、机场等工程建设中广泛应用。回顾了格宾挡墙发展历程,分析了现阶段格宾挡墙的双绞合六边形钢丝网和多种不同填料的界面摩擦特性、格宾挡墙的破裂面形式、加筋格宾挡墙的加筋机理、加筋格宾挡墙最佳布筋方式等研究热点。最后,探讨了格宾挡墙研究理论滞后、设计规范缺失等问题,并提出了对策。     

Seismic response of flexible cantilever retaining walls with dry backfill

Failure of retaining walls during earthquakes has occurred many times in the past. Although significant progress has been made in analysing the seismic response of rigid gravity type retaining walls, considerable difficulties still exist in the seismic-resistant design of the flexible cantilever type of retaining walls because of the complex nature of the dynamic soil–structure interaction. In this paper the seismic response of cantilever retaining walls with dry backfill is simulated using centrifuge modelling and numerical modelling. It is found that bending moments on the wall increased significantly during an earthquake. After the end of base shaking, the residual moment on the wall was significantly higher than the moment under static loading. The numerical simulation is able to model quite accurately the main characteristics of acceleration, bending moment, and displacement recorded in the centrifuge test.     

穿越黏滑断层分段接头隧道模型试验研究

数次大地震震害调查表明,隧道穿越断层处是受地震破坏较为严重的区域。为此,基于地震动能量的传播与释放特征,建立了一种穿越断层隧道结构抗减震的设计理念,并提出了一种穿越断层隧道节段接头形式。以跨断层龙溪隧道为依托,采用振动台模型试验研究了单一错动方式与断层错动-震动综合加载方式下带有接头的衬砌结构响应。研究结果证明：强震作用下,地震波对穿越断层隧道的影响是不可忽略的,断层错动-震动综合加载方式是合理的;新型接头能够自身适应性变形协调减轻隧道结构震害,节段间接头的设置改变了隧道的变形形态,提高隧道整体抗震能力;同时减小了衬砌的环向破坏,消弱了节段间地震力的传递,实现了衬砌震害的局部化。由于接头的设置,上盘隧道结构震害集中在距断层1.8倍洞径的范围内,下盘处隧道衬砌震害集中在距断层1.2倍洞径范围内;上盘的衬砌震害主要是由错动-震动联合作用造成的,而下盘衬砌震害主要受地震动的影响。     

地震作用下挡土墙主动土压力及转动位移分析

分析地震引起的挡土墙位移及墙后土压力,对于评估挡土墙可靠性具有重要意义。基于拟动力法,考虑时效、地震波传播的相位差、超载、墙背摩擦角、填土黏聚力以及填土开裂等影响,建立地震作用下挡土墙主动土压力计算模型,获得挡土墙绕墙趾转动模式下主动土压力大小、分布形式及作用点高度。同时,考虑挡土墙本身受地震荷载作用的影响,求出挡土墙绕墙趾的转动位移。通过与Mononobe-Okabe法对比可知,文中获得的主动土压力值与Mononobe-Okabe法接近,但Mononobe-Okabe法低估了主动土压力作用点高度,表明采用Mononobe-Okabe法设计存在风险。通过算例分析了地震系数、墙背摩擦系数、超载大小、时间、填土黏聚力和内摩擦角对挡土墙转动位移的影响。     

Pseudo-dynamic methods for seismic passive earth pressure behind a cantilever retaining wall with inclined backfill

The designing of retaining walls requires the complete knowledge of earth pressure distribution. Under earthquake conditions the design needs special attention to reduce the devastating effect, but under seismic conditions, the available literature mostly uses the pseudo-static analytical solution as an approximate to the real dynamic nature of the complex problem. This paper shows a detailed study on the seismic passive earth thrust behind a cantilever retaining wall with inclined backfill surface by pseudo-dynamic analysis. A planar failure surface has been considered. The effect of variation of parameters such as soil friction angle, wall friction angle and back fill inclination have been explored. A complete analysis shows that the time dependent non-linear behaviour of the pressure distribution obtained in the present method results in more realistic design values of earth pressures under earthquake conditions. Results are provided in tabular and graphical non-dimensional form and compared thoroughly with the existing values in the literature.     

多级支挡结构地震主动土压力的极限分析

多级组合支挡结构形式在高边坡防护工程中得到了广泛采用,但现有研究却较少涉及这种支挡结构形式的地震土压力计算问题。应用拟静力法和塑性极限分析上限定理,并且基于强度折减技术,推导了重力式挡墙与两级锚杆挡墙组合支挡结构形式的地震主动土压力及其系数的上限解。该上限解考虑了水平和竖向地震系数、墙背倾角、坡面形式及多级支护方式、土体黏聚力、土体与墙背的黏附力等诸多因素。二级锚杆挡墙实例分析表明：静力条件下主动土压力计算值与现有相关方法的计算结果一致,土的抗剪强度折减系数、上挡墙锚杆轴力等参数,对下挡墙地震主动土压力影响显著。二级组合支挡结构地震主动土压力影响参数敏感性分析表明：水平地震系数以及重力式挡墙墙高和倾角的敏感性较大,上挡墙锚杆的轴力和倾角等参数的敏感性相对较小     

高烈度地震区隧道减震模型的建立及其减震效果模型试验研究

现场调查表明：5.12汶川大地震共造成21条高速公路和16条国道、省道干线上总延长达20 417 m的24座隧道结构受损,严重影响了灾区救援和灾后重建。可见,传统的隧道抗震技术已不能保证高烈度地震区隧道结构的安全。为此,在分析隧道震害特点及原因的基础上,建立了隧道支护体系内设置减震层的减震模型,根据这一减震模型,研究了减震层刚度、地震波输入频率和减震层阻尼等参数对隧道减震效果的影响。通过三维数值模拟和室内模型试验,验证了该减震模型的减震效果。研究成果可为高烈度地震区隧道结构减震设计提供参考。     

地震作用下返包式加筋土挡墙数值模拟

返包式加筋土挡墙是一种柔性面板挡墙,因其良好的地基适应性及地震安全性广泛应用于交通、市政和水利等诸多领域中。本文使用FLAC^3D数值模拟程序对返包式加筋土挡墙墙面坡度、土工袋填料及筋材强度进行了抗震性能研究。研究结果表明：当墙面坡度<1∶0.30时,墙后侧向土压力分布均匀且数值较小,近似于一条竖向直线;当墙面坡度≥1∶0.30时,墙后侧向土压力分布规律一致且符合朗肯土压力理论。因此,当墙面坡度<1∶0.30时,加筋土结构应按加筋土边坡进行设计;当墙面坡度≥1∶0.30时,加筋土结构应按加筋土挡墙进行设计。土工袋填料种类对返包式加筋土挡墙地震动力响应几乎没有影响,在抗震设计时可不考虑其对挡墙的影响。筋材强度越高,返包式加筋土挡墙抗震性能越好,但筋材强度与挡墙的抗震性能不成正比例,由于加筋土结构的"加筋作用饱和"现象,大幅度提升筋材强度并不会使挡墙的抗震性能得到大幅度提升;因此,工程中在保证筋材强度达标的前提下需注意经济性。     

重力式挡土墙地震旋转位移下的屈服加速度

旋转位移假设下,将挡土墙和填土看成一个系统,建立挡土墙在地震作用下的旋转破坏模式,应用极限分析上限法推导了系统外力功率和耗散功率,得到了水平屈服加速度系数的理论计算公式,并采用MATLAB语言进行数值求解,获得了破裂角和水平屈服加速度系数的数值解。计算公式考虑了填土与墙体接触面上的黏聚力、墙和填土的摩擦角、竖向地震加速度系数、填土黏聚力、填土内摩擦角等对水平屈服加速度系数的影响。研究结果表明：填土与墙体接触面上的黏聚力、墙和填土的摩擦角和竖向地震作用对水平屈服加速度系数的影响显著,在实际工程设计中需合理取值以达到安全经济的目的。