加筋挡土墙长期工作性能的黏弹塑性有限元分析

随着工程上的广泛应用，作为设计中的关键技术问题之一，土工合成材料加筋挡土墙长期工作性能的合理评价日益得到重视，对此必须考虑加筋材料的非线性蠕变效应。对于加筋挡土墙，采用黏弹塑性流变模型和黏弹性本构模型分别考虑填土与土工合成材料的非线性蠕变性，合理考虑筋材与填土、填土与面板及面板之间的相互作用效应，同时在计算中反映逐层填筑过程，采用增量一初应变迭代法，对土工合成材料加筋挡土墙结构的工作性能评价发展了二维有限元数值分析方法。基于Denver黏性土试验挡土墙的试验结果确定计算参数，利用所建议的分析方法对Denver黏性土试验挡土墙进行了数值计算与分析，通过与实测结果及与常规方法的对比分析，论证了所建议的有限元数值分析方法的合理性及其可靠性。     

加筋土柔性桥台性能的FLAC数值分析

采用有限差分程序FLAC5.0来模拟加筋土柔性桥台, 计算出土工格栅加筋土桥台结构的墙面板水平位移,加筋材料的内力与变形, 讨论了应力在加筋土结构中的扩散形式,并与实测数据进行比较,提出加筋土桥台的应用方法.     

有限元强度折减法在加筋格宾陡坡支挡结构中的应用

依托我国第一座高速公路加筋格宾陡坡支挡结构--湖北大广北高速公路兰溪互通AK0+939.68～AK1+079.71,BK0+296.55～366.18陡坡加筋土工程,以岩土工程专业有限元程序Phase2 V6.0为研究平台,采用有限元强度折减法对该加筋格宾陡坡的稳定性进行评价.以经典极限平衡条分法的计算结果为基础,分析单元选型对计算结果的影响,提出采用有限元强度折减法计算筋材拉力分布,从而确定加筋土结构内部破裂面的方法,探讨填料黏聚力c、内摩擦角φ、网面拉力、地震力、填土重度、车辆荷载以及加筋间距等重要参数对安全系数的影响.相关成果可指导具体工程设计.     

加筋地基的有限元分析研究

土工合成材料加筋土技术是岩土工程中新发展起来的一个分支,该材料的设计原理和方法大多以岩土力学为基础.基于APDL语言编制的程序对加筋地基进行了非线性静力分析,采用ANSYS软件建立加筋地基的计算模型,并提取计算结果,结合现场载荷试验及室内三轴试验的结果绘制出相应于各级荷载下不同加筋层数下加筋复合地基的沉降和不同地基形式...     

土工格栅加筋砂土复合体极限承载能力分析

土工合成材料加筋土桥台可以有效减小桥梁与路基之间的差异沉降,避免“桥头跳车”现象的发生。为了计算土工合成材料加筋土复合体在设计中承受荷载的安全冗余度,对其极限承载能力进行了分析。首先讨论了评价加筋土复合体极限承载能力的计算公式,并提出了该公式是否适用于评价加筋细颗粒土复合体承载性能的问题。然后在平面应变的条件下,进行了5组土工格栅加筋砂土模型试验和1组无加筋模型试验,考虑了加筋间距和筋材强度对加筋砂土复合体极限承载能力的影响,并将试验结果与公式的计算结果进行对比,发现该公式低估了加筋砂土的承载能力。基于莫尔库仑破坏准则,并假定加筋土的破坏面符合朗肯破坏面,提出了预测加筋砂土极限承载能力的分析模型,并将模型的计算值与试验值进行对比,发现两者基本吻合。     

网状及条带式加筋拉拔特性的试验研究

在试验的基础上,分析了网状加筋与填土的相互作用机理及其抗拔力的组成,并按筋网与土体之间相对位移的大小,将抗拔过程划分为初始阶段、发展阶段和破坏阶段;得出了网状加筋抗拔力比条带式加筋抗拔力大得多的结论;提出了网状加筋抗拔力的计算公式,对条带式加筋进行抗拔力计算时,应考虑水平和垂直两个方向的“群筋效应系数”,加筋土支挡结构的抗拔力计算,宜采用拉拔似摩擦系数．     

加筋土强度的新认识

回顾了加筋土的发展历史 ,从而将加筋材料分成两类 ,文中采用 C,φ值同时提高的方法分析了非柔性加筋材料加筋土的强度特性 ,并就有关问题作了讨论 ,所得结果对工程应用具有指导意义     

基于蒙特卡罗法的加筋路堤稳定可靠性分析

软土路基上加筋路堤的稳定性可以采用圆弧滑动极限平衡法进行分析,加筋路堤的破坏可以归纳为圆弧内加筋的破坏、圆弧外加筋的破坏以及加筋路堤的整体破坏,建立了计算加筋路堤稳定系数K的3个不同的稳定系数表达式,运用蒙特卡罗法对设计参数随机变量与加筋土路堤稳定可靠指标的关系进行分析,通过数值计算发现密度越小,黏聚力、内摩擦角、筋材抗拉强度和筋土摩擦角越大,加筋土路堤稳定性越好,因此,在加筋土路堤可靠性设计中建议采用密度小、黏聚力和内摩擦角大的填料以及高强度筋材,并且重点考虑内摩擦角的变异水平。     

浅谈加筋土技术原理及在工程中的应用

通过对加筋土和加筋材料的概述,阐述了加筋土技术原理及设计计算方法,介绍了加筋土挡墙、加筋土边坡、加筋土地基等加筋技术的工程应用,以推动我国加筋土技术的发展。     

水平向加筋体抗沉陷作用机理分析及设计方法

针对高速公路修筑过程中经常遇到松散、沉陷地基的问题,分析了水平向加筋体加固沉陷区筋材–填土在路堤荷载作用下荷载传递机理。考虑了筋材张拉膜效应和路堤土拱效应在路堤荷载传递中的作用,分别采用薄板理论和Trapdoor理论分析筋材张拉膜效应和路堤土拱效应,推导出水平向加筋体加固沉陷区时最大挠度,并提出设计挠度已知情况下的设计方法。最后采用本文计算方法对工程实例进行计算分析,并综合分析了沉陷区宽度、填土高度、黏聚力、内摩擦角和筋材抗拉模量对水平向增强体设计计算的影响。随着沉陷区宽度的增加,加筋薄板层最大挠度呈非线性增加;随着填土高度的增加,加筋薄板层最大挠度逐渐增加,但增幅不大;随着筋材抗拉模量的增加,加筋薄板层最大挠度逐渐减小。     

Sliding stability and lateral displacement analysis of reinforced soil retaining walls

Field observations have demonstrated that reinforced soil retaining walls generally have superior seismic performance when compared to traditional gravity retaining walls. However, current design guidelines for reinforced soil retaining walls are typically based on pseudo-static methods of analysis, which involve simplifying assumptions. For instance, the reinforced zone is usually assumed as a rigid body in external stability calculations. As a result, the influences of reinforcement arrangement and properties on the sliding stability and displacement of the wall cannot be accounted for in their design. Additionally, the soil shear strength is assumed to be constant in conventional displacement calculations using the Newmark sliding block method. In this paper, an analysis method is proposed to determine the yield acceleration and lateral displacement of reinforced soil walls that includes soil shear strength mobilization and a two-part wedge planar failure mechanism. The proposed method is validated against the results of laboratory model tests, and influences of factors such as ground acceleration coefficients, and reinforcement and backfill properties on the stability of the wall are examined.     

加筋土挡墙筋材层间距的研究

从平面布筋率的角度得出了加筋土挡墙筋材的最大层间距。假定加筋土挡墙破裂面为H/2折线型破裂面,考虑填料的粘聚力c的作用,用极限平衡法导出了筋材的最大层间距的计算公式。通过与前人试验结果的比较,表明该公式是可行的。     

粘性填粘加筋土挡墙设计方法研究

对于粘性填料的加筋土挡墙的内部稳定分析,考虑其破裂面形状为园弧滑面,且筋带受力沿筋带埋置深度呈线性分布,导出了拉筋受力、筋带长度的计算公式。用该公式进行设计更符合粘性填料加筋土挡墙的实际情况,也可节约筋材。     

Post-construction performance of a two-tiered geogrid reinforced soil wall backfilled with soil-rock mixture

There have been very few studies on the application of soil-rock mixtures as the backfills of geogrid reinforced soil retaining walls with due concern for their long-term performance and safety. In this study, a 17-m high two-tiered reinforced soil wall backfilled with soil-rock mixture was instrumented for its performance under gravity load after construction. The instrumentation continued for 15 months. It is found that soil-rock mixtures with small rock content (<30%) have the potential to be used as the backfill materials of geogrid-reinforced retaining walls, but special attentions should be given to compaction quality, backfill–geogrid interaction, and installation damage to geogrids. Reinforcement slippage is possible because of the large particles, but it was small in this case and ceased to develop nine months after the end of construction. Compressibility difference between reinforced and unreinforced backfill might led to rotation of the upper tier. Using the estimated soil strength, the predictions of reinforcement loads by the FHWA methods were 100% higher than the estimated ones from measured strains.     

某河道护岸工程加筋土挡墙的原型观测

通过对某河道护岸工程加筋土挡墙的筋带拉力、面板土压力、基底压力、填土分层沉降、面板水平位移以及潮位变化等进行施工期间的原型观测 ,分析并研究了筋带拉力、面板土压力和基底压力随填土厚度变化的规律 ,以及填土分层沉降、面板水平位移以及潮位变化的分布规律及其影响因素     

Failure mechanisms governing reinforcement length of geogrid reinforced soil retaining walls

Current design practice of reinforced soil retaining walls is based on the limit equilibrium approach. The walls are designed for both external and internal stability criteria. Design reinforcement length should be such that minimum required safety factors are fulfilled for all failure modes. Most agencies require minimum reinforcement length equal to 70 percent of wall height. However, it is not always possible to have enough space behind a wall to accommodate these required reinforcement lengths due to an existing natural rock formation, man-made shoring system, or the presence of another reinforced soil retaining wall. This study was performed to investigate governing failure mode in determining the required minimum reinforcement length and also to investigate the possibility of shortening the specified minimum reinforcement lengths. Effect of different parameters involved in the design of reinforced soil retaining walls on the required minimum reinforcement length and the governing failure mode were studied. Parameters considered included wall height, surcharge, reinforcement vertical spacing, reinforced soil properties, backfill/retained soil properties, and foundation soil properties. Results indicated that both external and internal failure modes can be governing criteria in determining the required minimum reinforcement length depending on the parameters involved for a specific wall. In addition, it may be possible to use reinforcement lengths as low as almost 50 percent of the wall height, instead of 70 percent as required by many agencies around the world. This paper presents the results of parametric studies conducted, including the effect of different parameters on the required minimum reinforcement length and the governing failure criteria.     

Seismic analysis of geosynthetic-reinforced retaining wall in cohesive soils

Although a cohesionless backfill is recommended for geosynthetic reinforced earth retaining walls, cohesive soil have been widely used in many regions across the globe for economic reasons. This type of backfill exposes the soil to the crack formation that leads to reduce the stability of the system. In this paper, to investigate the internal seismic stability of reinforced earth retaining walls with cracks, the discretization method combined with the upper bound theorem of limit analysis are used. The potential failure mechanism is generated using the point-to-point method. Two types of cracks are considered, a pre-existing crack and a crack formation as a part of the failure mechanism. The use of the discretization method allows the consideration of the vertical spatial variability of the soil properties. A pseudo-dynamic approach is implemented which allows the account of the dynamic characteristics of the ground shaking. The presented method is validated using the conventional limit analysis results of an existing study conducted under static conditions. Once the proposed technique to consider the cracks is validated, a parametric study is conducted to highlight the key parameters effects on the lower bound of the required reinforcement strength.     

循环荷载作用下黏性土加筋挡墙有限元动力特性分析

在循环荷载作用下,对加筋土挡墙进行有限元模拟分析,研究黏性土加筋土挡墙的动力特性.重点研究挡墙回填土为黏性土条件下,不同加筋材料、动荷载峰值加速度对加筋土挡墙的影响.由计算结果认为在循环荷载作用下加筋土挡墙水平位移受动荷载峰值加速度影响较大,加筋土挡墙最大位置出现在挡墙下部,黏性回填土的加筋土挡墙变形量要小于砂土回填的加筋土挡墙.     

Seismic analysis of semi-gravity RC cantilever retaining wall with TDA backfill

The seismic behavior of Tire Derived Aggregate (TDA) used as backfill material of 6.10 m high retaining walls was investigated based on nonlinear time-history Finite Element Analysis (FEA). The retaining walls were semi-gravity reinforced concrete cantilever type. In the backfill, a 2.74 m thick conventional soil layer was placed over a 3.06 m thick TDA layer. For comparison purpose, a conventional all soil-backfill model was also developed, and the analysis results from the two models under the Northridge and Takatori earthquakes were compared. The FEA results showed that both models did not experience major damage in the backfill under the Northridge earthquake. However, under the Takatori earthquake, the TDA-backfill model developed substantially large displacement in the retaining walls and in the backfill compared with the soil-backfill model. Regions of large plastic strain were mainly formed in the TDA layer, and the soil over the TDA layer did not experience such large plastic strain, suggesting less damage than the soil-backfill model. In addition, the acceleration on the backfill surface of the TDA-backfill model decreased substantially compared with the soil-backfill model. If an acceleration sensitive structure is placed on the surface of the backfill, the TDA backfill may induce less damage to it.     

One-step analytical method for required reinforcement stiffness of vertical reinforced soil wall with given factor of safety on backfill soil

The selection of geosynthetic reinforcements in the design of geosynthetic-reinforced soil (GRS) retaining walls has been based on the requirement on the long-term strength. However, the mobilized loads in the reinforcements are related to both the reinforcement stiffness and soil deformation, and the desired factor of safety may not exist in the earth structure if they are not properly considered. Therefore, it is also important to take into account the long-term reinforcement stiffness when designing GRS retaining walls. In this study, a simplistic analytical method is proposed to determine the required reinforcement stiffness with given factor of safety on the backfill soil. The method takes into account soil-reinforcement interaction, nonlinear stress-strain behavior of soil, and soil dilatancy. The reinforcement strains predicted by the proposed method were compared to those analyzed by validated nonlinear Finite Element analyses, and close agreement was obtained.