土工织物加固堤基的离心模型试验

<正> 一、前言具有一定抗拉强度的土工织物,在国内外已被广泛用作挡土结构物、堤坝边坡和堤基的加筋材料。工程实践表明,土工织物加固地基具有其独特的优点。在土体拉伸变形方向设置一定强度的土工织物形成的复合体(加筋土),其力学性能不仅与土体、土工织物的性能有关,同时还取决于土和土工织物的界面特性。由于土工织物侧限     

土工织物与砂土界面特性数值模拟研究

文章采用有限元法模拟土工织物加筋土的剪切试验,研究不同上覆土压力、土体强度、加筋体长度、加筋体间距和接触面对直剪试验剪切力-位移即筋土界面本构关系的影响。计算结果表明,土工织物与砂土的界面特性受多种因素的影响。在一定程度上增大上覆土压,提高土体密实度和强度,加大土工织物长度,加密土工织物间距和选择粗糙的土工织物均能提高加筋效果。     

用土工织物垫层处理气柜工程软土地基

<正> 近年来,把土工织物作为加筋土的筋材应用于加固挡墙、公路和铁道路基逐年增多,并且已取得了良好的技术效果和经济效益。但是,把土工织物应用于处理建筑物软基尚不普遍,因为人们对土工织物的加固机理和变形特性尚未明了,对其加固效果尚存在不同的看法,另外还有土工织物的耐久性等问题,所以土工织物在处理建筑物软基中的应用尚处于探索阶段。本文通过在气柜工程软     

土工织物加固软土路基的非线性有限元分析

采用非线性有限元方法对土工织物加固软土路堤的效果和机理进行了探讨.通过对比计算表明: 土工织物对软土路堤的加固有明显的效果,可以使路堤的竖向沉降减小10%~20%, 侧向位移减小15%~25%; 土工织物弱化了路堤与地基之间塑性区的贯通, 并使塑性应变的数值及塑性分布区域均有所减小, 从而增加了路堤的稳定性; 加设多层土工织物时, 其对路堤体内的竖向沉降和侧向位移基本上没有影响, 但可以进一步提高路堤的安全性; 为了更好地发挥土工织物的加固效果, 土工织物应尽量布置在高应力区域.分析还表明: 传统的极限平衡分析方法很难合理地反映土工织物与土之间的变形协调关系, 较难正确地反映土工织物的受力状态及作用机理.     

土工织物加筋堤坝软基的非线性分析

通过非线性有限单元法分析了堤坝下软基土工织物的加筋效果,土与土工织物的界面强度对加筋效果的影响,多层土工织物的加筋效果等问题,得出了最优加筋层数、加筋垫层应力扩散效果等一系列对工程设计有用的结论     

土工织物分类及其垂直渗透系数和等效孔径特性分析研究

根据土工织物制造方法和物理特性将其分成短纤针刺无纺土工布、长丝纺粘针刺非织造土工布、长丝机织土工布、裂膜丝机织土工布及塑料扁丝编织土工布。通过对500份土工织物样本的垂直渗透系数和等效孔径特性进行分析研究,找出不同种类土工织物垂直渗透系数和等效孔径特性的规律,有助于设计人员根据不同工程生产实际选择不同种类的土工织物。     

土工织物在软土地基中的应用

指出土工织物是岩土工程领域中一种新型建筑材料,在道路工程中被广泛地应用于软土处理,对土工织物的特性、应用、设计计算及工程应用概况进行了较详细的阐述,工程实例证明土工织物在软土地基处理中的可行性。     

土工织物对软土地基的加筋作用分析

土工布、土工格栅等土工织物广泛应用于建设工程中,论文分析了土工织物的加筋作用原理,通过工程实例,在极限填土高度、沉降、侧向位移及土压力等工程关键指标上,通过实测数据对比分析论证了土工织物的加筋作用。     

采用有纺土工织物与插筋补强混合的基坑支护作法

土工织物分有纺和无纺两种。有纺土工织物具有突出的高抗拉强度、高抗腐蚀性、良好的整体性、连续性、抗微生物侵蚀性强、质地柔韧、能与土很好结合、耐久性好和具有良好的水理性等性能。有纺土工织物能用于深基坑支护最重要的是具有高强度、高模量、低延伸率和界面粗糙等工程特性。而无纺土工织物是高延伸率、低强度。１采用有纺土工织物与插筋补强混合支护的原理有纺土工织物用于深基坑支护是利用其有纺土工织物高抗拉强度、高模量、低延伸率及界面粗糙等特性。插筋补强边坡在荷载作用下侧向变形与应力状态可分为四个阶段 ,即弹性变形阶段…     

土工织物在边坡支护中的应用

土工织物是一种多功能材料 ,可广泛应用于诸多领域。介绍了土工织物的主要功能 ,分析了有纺土工织物在边坡支护应用中的相关原理、施工技术及注意事项。     

Geotextile filtration opening size under tension and confinement

Nonwoven geotextiles have been used as filters in geotechnical and geoenvironmental works for half a century. They are easy to install and can be specified to meet the requirements for proper filter performance. There are situations where a geotextile filter may be subjected to tensile loads, which may alter relevant filter properties, such as its filtration opening size. Examples of such situations are silty fence applications, geotextile separators, geotextile tubes and geotextiles under embankments on soft soils. This paper investigates the effects of tensile strains on geotextile pore dimensions. A special equipment and testing technique allowed tests to be carried out on geotextile specimens subjected to tension and confinement. The results obtained showed that the variation in filtration opening size depends on the type of strain state the geotextile is subjected, under which the geotextile pore diameter may remain rather constant or increase significantly. However, confinement reduces the geotextile filtration opening size independent on the strain mobilised. An upper bound for the filtration opening size of strained nonwoven geotextiles is introduced and was satisfactory for the geotextile products tested.     

Influence of particle shape on the shear strength and dilation of sand-woven geotextile interfaces

The influence of particle shape on the mechanical behavior of sand-woven geotextile interfaces over a wide domain of soil density and normal stress is studied. A uniformly graded angular fine sand, and a blend of well rounded glass beads with identical particle size distributions, were selected as granular material. Experiments revealed the impact of particle shape on peak and residual friction angles as well as the maximum dilation angle of interfaces between both granular media and woven geotextile. It was observed that the residual friction angles of interfaces between angular sand/glass-beads and woven geotextile are very similar to the residual friction angles of angular sand and glass-beads in soil–soil direct shear test. It is understood that the peak friction angle and maximum dilation angle of angular sand-woven geotextile were slightly lower than corresponding values for angular sand in soil–soil direct shear test. While the peak friction angle and maximum dilation angle of angular sand-woven geotextile interface decrease with the increase in normal stress, experiments showed that these factors are insensitive to normal stress for glass beads-woven geotextile interfaces, at least for the range studied herein. All interfaces with woven geotextile as the contact surface exhibit an abrupt loss of shear strength in the post-peak regime of behavior. Finally, a unified stress-dilation law for the angular sand-woven geotextile, glass beads-woven geotextile, and angular sand-roughened steel interfaces is obtained.     

Improved design criteria for nonwoven geotextile filters with internally stable and unstable soils

In geotextile filtration, the soil fines are either accumulated near the interface, clogged, or washed out, which primarily depends on the grain size distribution (GSD) of soil and the constriction size distribution (CSD) of geotextile. Also, the movement of fines significantly affects the flow capacity of geotextile. Currently, the retention requirement is satisfied based on representative grain and opening sizes, whereas the hydraulic conductivity and clogging requirements are satisfied considering the properties of virgin geotextile. This paper presents a probabilistic retention criterion considering the grain and constriction sizes as random variables. The influence of geotextile thickness is incorporated into the criterion by considering the number of geotextile constrictions in a filtration path. A theoretical approach to predict CSD is presented if the measured data is unavailable. For hydraulic conductivity and clogging requirements, a criterion is presented considering the expected partial clogging of geotextile, which is predicted based on the semi-analytical approach. The limit states for the developed criteria are evaluated based on the wide range of experimental data from the current study and published literature. The developed design criteria are applicable to internally stable and unstable soils, which offers an improvement in design compared to the existing criteria in practice.     

Laboratory evaluation of governing mechanism of frictionally connected MSEW face and implications on design

This paper presents a laboratory evaluation of purely frictionally connected geotextile and concrete facing block of Mechanically Stabilized Earth Wall (MSEW) systems. The study focuses on investigating the governing failure mechanism along the wall face, as determined from the pullout of reinforcement in between the facing blocks (herein referred as pullout mechanism) and sliding of the blocks over the geotextile, where the reinforcement stays stationery (herein referred as direct shear mechanism). A total of seventy-two tests were performed to investigate the effect of laboratory specimen size, difference in geotextile reinforcement, and repeatability of the test results. Overall, the results showed that at lower normal loads, sliding of the blocks over the geotextile reinforcement along the wall face is more likely to occur before the pullout of the geotextile in between the blocks. At higher normal loads, this order is reversed and pullout of the geotextile appears to occur first. The test results also indicated that the size of the specimen tested in the laboratory frictional connection evaluation has an effect on the measured connection strength.     

Evaluation of moisture reduction in aggregate base by wicking geotextile using soil column tests

This study investigated the distance effect on water reduction by the wicking geotextile in a base course experimentally using three sets of soil column tests. In each set of tests, two soil columns were constructed by compacting well-graded aggregate over a non-wicking woven geotextile and a wicking geotextile. A portion of the geotextile specimen was extended outside of the soil column for evaporation. The changes of the water contents in the soil column were monitored by volumetric water content sensors installed at various depths. The experimental results indicate the capillary drainage by the wicking geotextile effectively reduced water content within the soil column up to a distance from the wicking geotextile (i.e., approximately 200 mm for this specific aggregate with 10% fines). The test results also show that the wicking geotextile could reduce more water content of the aggregate below its optimum water content at a faster rate than the non-wicking geotextile.     

Investigation of geotextile–soil interaction under a cyclic vertical load using the discrete element method

Geotextiles are often used in roadway construction as separation, filtration, and reinforcement. Their performance as reinforcement in geotextile-reinforced bases depends on geotextile–soil interaction. This paper investigates the geotextile–soil interaction under a cyclic wheel load using the Discrete Element Method (DEM). In this study, soil was modeled as unbonded particles using the linear contact stiffness model, and the geotextile was modeled as bonded particles. The micro-parameters of the soil and the geotextile were determined using biaxial tests and a tensile test, respectively. The influence of the placement depth and the stiffness of the geotextile on the performance of the reinforced base was investigated. The DEM results show that the depth of the geotextile significantly affected the degree of interaction between the geotextile and the soil. Under the applied cyclic vertical load, the geotextile developed a low tensile strain. The effect of the stiffness of the geotextile on the deformation was more significant when the geotextile was placed at a shallower location than when placed at a deeper location.     

非水反应高聚物与土工材料的界面剪切特性

基于单调直剪试验,研究了竖向应力、剪切速率对非水反应类高聚物-土工布界面及高聚物-砂土界面的剪切应力、剪切位移、抗剪强度和剪切模量等剪切特性的影响.结果表明:在给定竖向应力和剪切速率下,随着剪切位移的增加,高聚物-土工布界面、高聚物-砂土界面均表现出剪切软化的特性;竖向应力对高聚物-土工布界面抗剪强度及剪切模量的影响显...     

Field monitoring of wicking geotextile to reduce soil moisture under a concrete pavement subjected to precipitations and temperature variations

Wicking geotextile can reduce water contents in pavement layers under unsaturated conditions due to capillary action through grooves of wicking fibers. Reduction of soil water content under the pavement can minimize pavement distresses. So far, there have been limited use and verification of the wicking geotextile in reducing water content of soil under concrete pavements in the field. In this field study, moisture sensors were installed in three test sections under a newly-built concrete pavement during its re-construction. The base course in one test section had a higher percentage of small particles than those in other two sections. The wicking geotextile was used between the base course and the subgrade in two test sections while a nonwoven geotextile was used in one test section. All test sections were subjected to precipitations and temperature variations. Field monitoring data showed that the wicking geotextile reduced the volumetric water content (VWC) of an aggregate base more than the nonwoven geotextile and its wicking ability decreased as the content of small particles increased. In addition, the wicking ability of the wicking geotextile decreased as the temperature decreased due to the reduction in the evaporation rate and the increase in the water retention capacity of the soil at low temperatures.     

土工布加固软土地基的机理试验研究

土工布与土体的界面摩擦力是衡量其对土体加固效果的关键因素,本文首先根据土工布与土体拉拔摩擦试验的机理,设计并制作了界面剪切测试仪,该试验测试仪具有试验精度高、应用广泛和操作步骤简单的特征,然后采用此测试仪对土工布与砂土的界面摩擦力进行了试验研究,试验参数包括不同的竖向压力、土工布层数和砂土含水率。试验结果表明:增加竖向压力能够显著提高土工布与土体的界面摩擦力;相同竖向压力作用下,土工布层数超过2层时,对其界面摩擦力提高并不显著;相同条件下,当砂土含水率超过5%时,提高砂土含水率能够显著降低土工布与土体界面摩擦力。这些研究结果可为土工布加固土体的设计和施工提供依据。     

Numerical parametric investigation of infiltration in one-dimensional sand–geotextile columns

Geotextiles are routinely used in separation and filtration applications. Design of these systems is currently based on saturated properties of the geotextiles and the surrounding soils. However, in the field, soil and geotextile can be in an unsaturated state for much of their design life during which they are essentially hydraulically non-conductive. Periodic wetting and drying cycles can result in rapid and large changes in hydraulic performance of soil–geotextile systems. The writers have reported the results from physical water infiltration tests on sand columns with and without a geotextile inclusion. The geotextile inclusions were installed in new and modified states to simulate the influence of clogging due to fines and to broaden the range of hydraulic properties of the geotextiles in the physical tests. This paper reports the results of numerical simulations that were undertaken to reproduce the physical tests and strategies adopted to adjust soil and geotextile properties from independent laboratory tests to improve the agreement between numerical and physical test results. For example the paper shows that the hydraulic conductivity function of the geotextile must be reduced by up to two orders of magnitude to give acceptable agreement. The lower hydraulic conductivity is believed to be due to soil intrusion that is not captured in conventional laboratory permeability tests. The calibrated numerical model is used to investigate the influence of geotextile and soil hydraulic conductivity and thickness as well as height of ponded water at the surface on wetting front advance below the geotextile and potential ponding of water above the geotextile due to a capillary break mechanism. A simple analytical model is also developed that predicts the maximum ponding height of water above the geotextile based on two-layer saturated media and 1-D steady state flow assumptions. The analytical model is used to generate a design chart to select geotextiles to minimize potential ponding of water above the geotextile. Ponding can lead to lateral flow of water along the geotextile in reinforced wall, slope, embankment and road base applications.