加筋土筋土界面抗剪强度影响因素试验研究

通过室内筋土界面直剪试验,考虑筋土界面抗剪强度的影响因素,进行了不同剪切速度、筋材空隙率及土体含水率下筋土界面直剪试验,分析了不同因素对筋土界面抗剪强度的影响。试验结果表明,剪切速度主要影响筋土界面的内摩擦角,对筋土界面黏聚力几乎没有影响,随着剪切速度的增加,内摩擦角变大,导致筋土界面抗剪强度增大。筋材空隙率主要影响筋土界面黏聚力大小,空隙率越大,筋材肋条对土颗粒的约束作用越小,筋土界面抗剪强度降低。筋土界面抗剪强度受土体含水率的影响较大,随着土体含水率的增加,筋土界面黏聚力和内摩擦角都明显减小,导致筋土界面抗剪强度显著降低。     

紫茎泽兰筋材改良昔格达土物理力学试验研究

针对攀西地区特殊昔格达土质,利用广泛分布的紫茎泽兰做改良土筋材,对昔格达紫茎泽兰加筋土进行不固结、不排水的三轴压缩试验,研究不同加筋量及不同围压下加筋土的σ-ε关系曲线和抗剪强度,并分析其影响因素。试验结果表明:昔格达紫茎泽兰加筋土的抗剪强度和抵抗变形的能力较素土有显著提高;内摩擦角φ变化相对较小,相对变化率绝对值在40.13%以内,但黏聚力增长较大,最高可达17.03倍;无筋素土试样大多以剪切破坏为主,而掺入紫茎泽兰筋材后,试样的破坏主要为鼓胀破坏;抗剪强度增加量与紫茎泽兰掺入量的比例呈非线性关系,且并非掺入量越大越好。说明紫茎泽兰筋材对土体存在补强的作用,同时试验得出黏聚力c值是影响加筋土抗剪强度的主要因素。     

基于砂卵石土抗剪强度现场试验的全黏结式锚杆支护结构稳定性分析

洛阳砂卵石土现场直剪试验结果表明:对于含水率约为2%,粗粒含量P5约为78.66%的砂卵石土,黏聚力c=22~34 k Pa,内摩擦角φ=38°~40°。黏聚力和内摩擦角变化对预应力全黏结锚杆支护体系整体稳定性和锚杆轴力的影响分析表明:随着黏聚力的增加,砂卵石土层中锚杆轴力明显减小,基坑整体稳定性大幅增加。黏聚力增加约30 k Pa,基坑整体稳定性系数提高约11%~15%。     

不同筋材界面剪切试验研究

为了研究废旧轮胎、土工格室和土工格栅3种不同土工合成材料的筋-土界面抗剪特性,对试样开展了一系列大型直剪试验。对比了3种筋材的加筋效果,并研究了竖向荷载对筋-土界面抗剪强度和剪应力-剪切位移曲线特征的影响。试验结果表明:筋-土界面的剪切应力与剪切位移关系为非线性;几种不同筋材加筋效果较为显著,其中废旧轮胎的加筋效果最为明显;筋-土界面的黏聚力提高较大,内摩擦角变化相对较小,表明筋-土界面主要依靠提高黏聚力增大其抗剪强度。确定了各筋材加筋界面抗剪强度指标,并分析了3种筋材的加筋机理。     

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。     

聚丙烯纤维土在冻融循环条件下的抗剪强度分析

为研究冻融循环作用对聚丙烯纤维土抗剪强度的影响规律,采用了全组试验的方法,考虑了3个不同因素(冻结温度、含水率、冻融循环次数)对聚丙烯纤维加筋土的抗剪强度影响,并通过数据分析建立了不同影响因素对聚丙烯纤维土抗剪强度指标的拟合关系式。试验结果表明,在冻融循环作用下含水率对纤维土抗剪强度影响显著性最大,含水率越高,黏聚力和内摩擦角越小;冻融循环中冻结温度越低,内摩擦角越大,黏聚力越低;冻融次数对内摩擦角影响不显著。通过数据拟合,得到一个良好的拟合公式。     

对“钢筋(煤石干石)混凝土网格式加筋土挡土结构强度特性与试验研究”讨论的答复

雷胜友博士对笔者在《岩土工程学报》1999年第 5期上发表的“钢筋 (煤石干石 )混凝土网格式加筋土挡土结构强度特性与试验研究”一文 (以下简称原文 )的讨论 ,是有一定意义的。在原文中提出了钢筋混凝土网格式加筋土挡土结构这种非柔性筋材 ,由于不仅可以承受拉应力 ,而且可以承受剪应力 ,与一般柔性筋材加筋土只增加粘聚力Δｃ ,而视加筋与不加筋具有相同的内摩擦角 φ 不同 ,非柔性筋材加筋土与不加筋相比 ,加非柔性筋材加筋土不仅增加粘聚力Δｃ ,而且也增加了内摩擦角Δφ 。加筋土体相对于无筋土体而言 ,由于增加了Δｃ ,Δφ ,使加筋…     

纤维土的直剪试验研究

通过在黄土中加入一定比例的纤维,开展纤维加筋土的直接剪切试验研究,了解不同含水率纤维加筋黄土的粘聚力c和内摩擦角φ的变化情况,通过对黄土和纤维加筋土试验结果进行对比,可知纤维加筋土的剪切性能得到很大的改善,对施工具有指导意义。     

基于正交试验的加筋土界面摩擦影响因素分析

以河北省邢汾高速公路土工格栅加筋高填方路堤工程为背景,用正交设计表L18(37)安排了54组拉拔试验,分析了7个因素对加筋土界面摩擦特性的影响.试验结果表明,影响加筋土界面摩擦特性的因素主次顺序为上覆荷载、含水率、筋材距试验箱侧壁距离、拉拔速率、格栅类型、筋材水平埋入长度、干密度.其中,上覆荷载、含水率、筋材距试验箱侧壁距离、拉拔速率对筋-土界面摩擦特性的影响特别显著.通过分析筋-土界面拉拔摩擦系数与7个因素的关系,得到了各因素的优水平以及各因素在拉拔试验过程中的变化规律.     

钢丝网筋材的加筋作用特性试验研究

在双绞合六边形钢丝网加筋红砂岩粗粒土大三轴试验的基础上,对钢丝网筋材的加筋机理、加筋作用发挥过程和含水量、加筋间距对加筋效果的影响进行系统的研究。分析表明,加筋双绞合六边形钢丝网可以同时提高红砂岩粗粒土的黏聚力和内摩擦角,其加筋机理不宜采用“准黏聚力”理论,工程设计时也应考虑筋材对土体内摩擦角的贡献;双绞合六边形钢丝网...     

A new generation of soil-geosynthetic interaction experimentation

A new device was developed to comprehensively assess the interaction between soil and reinforcement as well as the interaction between neighboring reinforcement layers in a reinforced soil mass, under both working and ultimate interface shear stress conditions. An understanding of these two interactions is required to assess the mechanical behavior of a geosynthetic-reinforced soil mass considering varying vertical reinforcement spacings. Specifically, the new device allows direct visualization of the kinematic response of soil particles adjacent to the geosynthetic reinforcement layers, which facilitates evaluation of the soil displacement field via digital image analysis. Evaluation of the soil displacement field allows quantification of the extent of the shear influence zone around a tensioned reinforcement layer. Ultimately, the device facilitates investigating the load transfer mechanisms that occur not only at the soil-reinforcement interface, but also at distances farther from the interface, thereby providing additional insight into the effect of vertical reinforcement spacing on a reinforced soil mass. Finally, the device allows monitoring of dilatancy within the reinforced soil mass upon shear stress generation at the interface between soil and reinforcement. Overall, the device was found to provide the measurements needed to adequately predict the strains developing both in reinforcement layers tensioned by direct application of external loads as well as in reinforcement layers tensioned by the shear transfer induced by adjacent geosynthetic reinforcements. Ultimately, the proposed experimentation technique allows generation of data required to evaluate the load transfer mechanisms amongst soil and reinforcement layers in reinforced soil structures. The strain magnitude in the neighboring reinforcements was found to exceed a magnitude of 10% of the strain magnitude obtained in the active reinforcement. The zone of shear stress transfer from the soil-reinforcement interface was found to exceed 0.2 m on each side of the active reinforcement.     

新型加筋结构界面的特性试验研究

通过室内筋材拉拔模型试验,对筋材与土介质的界面摩擦特性进行了详细分析。深入分析了试验中影响界面摩擦特性的主要因素,并深入探讨了土工格栅与红砂岩粗粒土之间的筋土界面特性,为实体工程设计提供必要的数据。     

新型可视土工拉拔试验仪的研发与应用

研制了一台新型可视自动采集数据的土工拉拔试验装置,可用于多种土工材料和填料作用下的拉拔试验。该装置改进了加载系统和反力系统,实现了拉拔界面的可视与数据采集的自动化,并可量测土工材料不同嵌固长度处的位移,获取土工材料变形值,探索筋土作用过程中筋材受力机理及界面土体位移变化规律。使用新研制的试验装置开展了以砾类粗粒土为填料的格栅拉拔试验,结果表明:上覆荷载增大,土中格栅的应变变小,土体与格栅的界面摩擦和嵌固作用越显著;筋土界面处土体颗粒存在平移及转动两种运动模式,且界面处土体形成稳定的位移集中带。     

Estimation of seismic active earth pressure on reinforced retaining wall using lower bound limit analysis and modified pseudo-dynamic method

Present study estimates seismic active earth pressure on the reinforced retaining wall by combining the lower bound finite element limit analysis and the modified Pseudo-dynamic method. A series of parametric analyses are performed by varying seismic acceleration coefficient, time period of seismic loading, soil friction and dilation angles, reinforcement spacing, length of reinforcement, soil-reinforcement interface, damping ratio of soil, soil-wall interface, wall inclination, and ground inclination. Maximum active earth pressure is exerted when natural time period of reinforced soil matches with the time period of an earthquake. Reinforcement is found to be effective in terms of reducing active earth pressure significantly on the wall subjected to seismic loading. Effectiveness of reinforcement depends upon two factors, namely vertical spacing and soil-reinforcement interface friction angle. For relatively smaller reinforcement spacing, soil-reinforcement behaves like a composite block, which helps to constraint stresses within a small area behind the wall. Maximum tensile resistance is developed when fully rough interface condition is assumed between soil and reinforcement layer. Failure patterns are provided to understand the behaviour of reinforced retaining wall under different time of seismic loading.     

土工格栅加筋土地基载荷试验的数值模拟

采用FALC^3D对土工格栅加筋土地基载荷试验进行了进一步的数值模拟分析。根据计算结果,针对原型试验中难以量测的试坑变形及筋土界面摩阻力分布特征进行了讨论。利用数值模拟技术的优势,求解加筋地基的应变场,研究了加筋地基的破坏模式。结果表明:在竖向荷载作用下,试坑会发生侧向位移,通过加筋能有效减小试坑的侧向位移;筋土界面摩阻力的分布与筋土之间的相对位移直接相关;加筋地基的破坏机构因筋材的存在而发生改变,“深基础”效应以及“扩散层”效应都是加筋地基的增强机理,但地基的破坏模式随筋材的布置形式改变而有所不同。     

加筋地基土压力测试与机理分析

在素垫层内铺设土工材料加筋后,筋土的界面摩擦作用使加筋垫层的模量提高、应力扩散范围增大,有效发挥下卧土层的承载力、减小地基沉降。通过土工带加筋现场原位试验垫层底的土压力分布测试与结果分析得出：加筋薄垫层（Z/B=0.2）地基垫层底土压力分布是不均匀的,应力集中于基础的边缘,基础中心下应力较小。加筋地基强度和变形与加筋参数有关,通过引入应力扩散系数,分析不同加筋参数下加筋地基的应力扩散能力,研究筋土界面摩擦作用的应力扩散加筋机理,结合工程实际提出太原地区应力设计扩散角取值范围,为加筋地基的设计提供理论依据。     

土工合成材料大型直剪界面作用宏细观研究

利用大型直剪模型试验设备，在不同竖向压力下进行一系列的土工合成材料直剪试验，应用数码可视化跟踪技术，结合土体变形无标点量测技术来研究双向土工格栅与砂土直剪界面作用的宏细观特性，同时分析界面附近土压力分布规律，并研究界面颗粒运动变化规律和细观组构演化特征与宏观特性的关联。分析结果表明，直剪筋土界面附近竖向压力分布从前端依次向后端减少；直剪界面位移达25 mm时，形成了稳定的剪应变集中带；在筋土界面（6～8）D₅₀粒径厚度范围内，界面颗粒以旋转和平动方式同时位移，该范围外颗粒以平动方式沿剪切方向位移，且位移较小；在剪切过程中，界面颗粒发生旋转，土体发生剪胀，孔隙率增大，平均接触数减小，颗粒重新被压密，孔隙率减小，平均接触数增多，颗粒长轴排列趋于水平方向，各细观组构处于相对稳定状态。     

Geogrid-soil interaction: A new conceptual model and testing apparatus

This paper provides a more realistic representation of the soil-geogrid interface in indirectly activated geogrids. A new testing apparatus is designed using transparent soil that allows an unobstructed observation of the interface to investigate the interaction occurring along the reinforcement. In this investigation, the reinforcement is indirectly activated by the deformations of the surrounding soil. Deformations were determined by digital image correlation (DIC) using a dot pattern attached to the geogrid and a laser speckle plane within the transparent soil. The interaction is derived from relative soil-geogrid displacements, deflections of geogrid transverse members, geogrid strain and force distributions as well as shear stresses acting at the interface. Three zones were identified corresponding to the distinct modes of interaction: pushout, pullout and interlocking, whereby a micro-mechanical conceptual model was validated. The geogrid force reaches its maximum at the intersection of the critical slip plane with the reinforcement. The results indicate that the pushout, pullout and interlocking areas cover 15%, 49% and 36% of the total geogrid length respectively. In this study, a transition area between the pushout and pullout zones was observed where the mobilised interface shear stress increases to a maximum value.