土工合成材料加筋的试验研究

以 6种不同种类的国产土工合成材料为加筋材料 ,即针刺无纺土工织物、涤纶纤维经编土工格栅、玻璃纤维土工格栅、单向塑料拉伸土工格栅、双向塑料拉伸土工格栅和土工网 ,进行三轴试验比较各种土工合成材料对砂的加筋效果 ;进行直剪试验和拉拔试验比较各种土工合成材料与填料 (砂和石灰粉煤灰 )的界面作用特性 ,得到一些有益的结论 ,可指导土工合成材料的优选和研究土工合成材料的加筋机理。     

土工合成材料与细粒尾矿界面作用特性的试验研究

以有色金属铜矿的细粒尾矿为加筋填料土，利用拉拔试验，研究土工合成材料(加筋带和土工格栅)在填料土不同密实度、含水量及垂直荷载作用下，土工合成材料与填料土的界面作用特性，以及细粒尾矿加筋的作用机理。     

垃圾填埋场土工合成材料界面摩擦特性的拉拔试验研究

土工合成材料与填料的界面特性是决定垃圾填埋场中衬垫系统与土工合成材料受力特性的重要因素。选择3种不同种类的土工合成材料,用砂土和黏土为填料,通过拉拔试验研究土工合成材料的界面特性。试验结果表明:界面的峰值剪切强度与峰值位移随着法向应力的增加而增加;土工合成材料与黏土之间的摩擦角较大;填料为砂土时,无纺布与填料间的摩擦角最大,EPDM次之,HDPE最小;当HDPE上下都铺无纺布时,界面的摩擦系数最小。     

土与土工合成材料界面特性试验方法分析

土与土工合成材料接触面摩擦特性的试验研究有利于弄清土与土工合成材料之间相互作用机理，同时为土工合成材料工程应用提供设计参数。本文分析总结了近几年来关于土与土工合成材料界面特性研究中的四种试验方法(直剪试验、拉拔试验、斜板试验和扭剪试验)的试验设备、试验原理以及各种试验方法的特点，并简述了研究中的一些热点问题。在本文最后对进一步的研究提出了建议。     

土工合成材料加筋非饱和土界面作用特性研究

通过室内拉拔、摩擦试验研究绵阳非饱和土与不同土工合成材料间的界面相互作用特性及加筋效果试验,得出了三种土工合成材料在各级荷载作用下的应力-应变关系曲线;分析了曲线特征及土工合成材料与土体界面的相互作用特性,其结论为今后土工合成材料在绵阳地区的工程应用提供了理论参考依据。     

垃圾填埋场土工合成材料的界面特性试验方法研究

拉拔、直剪、单剪试验常用于材料间界面特性研究,通过对垃圾填埋场中组成复合衬垫的土工膜、土工布和砂土、黏土界面分别进行了土工膜与砂土、土工膜与黏土、土工布与砂土、土工布与黏土的拉拔试验,土工布与砂土、土工膜与黏土的直剪试验及土工网–土工膜–黏土组合界面的单剪试验。研究结果表明:土工合成材料与土界面特性主要取决于土工合成材料的表面性质,直剪和单剪试验得到应力–位移曲线的初始斜率高于拉拔试验;法向应力由低向高变化时控制滑动面也发生了变化,界面特性受到防渗结构层中相邻材料的影响;在3种试验中拉拔试验得到的界面强度包线最高,单剪次之,直剪最低;单剪试验能较合理地模拟垃圾填埋场复合防渗结构的工作条件,建议利用单剪试验技术确定界面的强度参数,直剪试验也是可选择的试验方法。     

土工合成材料与风积砂的摩擦特性研究

以拉拔试验测定土工合成材料与风积砂的界面摩擦特性。根据试验结果分析风积砂与土工合成材料在接触面上粘聚力和内摩擦角的变化，得出不同种类的土工合成材料对填料产生的影响。     

不同土工格栅的筋土界面摩擦特性研究

土工格栅与土的界面作用特征直接影响加筋高填方路堤的安全与稳定性。以河北省邢汾高速公路加筋高填方路堤工程为背景．通过室内直剪试验．分析不同类型的土工格栅在砂土中的界面摩擦特性作用。试验表明随着上覆荷栽的增加,土工格栅与砂土的摩擦特性加强。双向土工格栅与砂土之间的界面凝聚力要高于单向土工格栅．而其界面摩擦系数相差不大。通过对格栅界面特性的研究．给土工合成材料的生产建设性的意见并为实际工程选用格栅材料提供参考。     

不同土工合成材料下新型加筋土界面特性

土工合成材料对加筋土结构的界面直剪特性具有重要的影响。通过一系列大型直剪试验对不同筋材下的Sandwich型加筋土筋土界面的直剪特性进行研究,研究不同竖向应力下不同种类加筋材料对Sandwich型加筋土界面直剪特性的影响。试验结果表明:土工格栅的加筋效果最佳,两种格栅的加筋界面抗剪强度明显高于土工织物;随着竖向应力的增加,筋土界面抗剪强度提高。结合理论分析,对不同的土工格栅进行直剪试验,得出土工格栅横、纵肋对界面剪切强度的提高值分别为15.3%和4.1%。     

土工合成材料界面作用特征的拉拔试验研究

针对不同的填充材料和不同的土工合成材料在应用的过程中存在不同的拉拔系数的现象,本文通过拉拔试验分析土工工程当中合成材料的界面作用。探索了我国国产的五种土工合成材料在实践工作过程当中实现加筋的影响。结果表明,加筋工作需要通过具体的试验工作内容进行拉拔系数的确认。     

A numerical modelling technique for geosynthetics validated on a cavity model test

Numerical modelling approaches can aid in designing geotechnical constructions involving geosynthetics. However, the reliability of numerical results depends on how the model is developed, the constitutive model, and the set of parameters used. By comparing the numerical results with experiment, the present work verifies a numerical modelling technique developed to model multilayered geosynthetic lining systems for landfills. The numerical modelling technique involves strain softening at interfaces and allows the axial stiffness of the geosynthetics to evolve as a function of strain. This work focuses on a two-dimensional finite-difference model, which is used to simulate three types of experimental tests: conventional uniaxial tensile tests, direct shear tests, and a large-scale test that was used to assess the overall mechanical behaviour of a reinforced geosynthetic system that spanned over a cavity. This reinforced geosynthetic system consisted of a 50 kN/m polyvinyl alcohol geogrid reinforcement embedded in a layer of sand, a geosynthetic clay liner, a high-density polyethylene geomembrane, and a non-woven needle-punched geotextile. The uniaxial tensile tests, direct shear tests, and the large-scale test were numerically modelled and the numerical results were compared with experimental results. The results of the numerical modelling technique presented very closely match the results of the three experimental tests, which indicates that the numerical model correctly predicted the measured data.     

Novel experimental techniques to assess the time-dependent deformations of geosynthetics under soil confinement

A new experimental approach to assess the impact of soil confinement on the long-term behavior of geosynthetics is presented in this paper.The experimental technique described herein includes a novel laboratory apparatus and the use of different types of tests that allow generation of experimental data suitable for evaluation of the time-dependent behavior of geosynthetics under soil confinement.The soil-geosynthetic interaction equipment involves a rigid box capable of accommodating a cubic soil mass under plane strain conditions.A geosynthetic specimen placed horizontally at the mid-height of the soil mass is subjected to sustained vertical pressures that,in turn,induce reinforcement axial loads applied from the soil to the geosynthetic.Unlike previously reported studies on geosynthetic behavior under soil confinement,the equipment was found to be particularly versatile.With minor setup modifications,not only interaction tests but also in-isolation geosynthetic stress relaxation tests and soil-only tests under a constant strain rate can be conducted using the same device.Also,the time histories of the reinforcement loads and corresponding strains are generated throughout the test.Results from typical tests conducted using sand and a polypropylene woven geotextile are presented to illustrate the proposed experimental approach.The testing procedure was found to provide adequate measurements during tests,including good repeatability of test results.The soilegeosynthetic interaction tests were found to lead to increasing geotextile strains with time and decreasing reinforcement tension with time.The test results highlighted the importance of measuring not only the time history of displacements but also that of reinforcement loads during testing.The approach of using different types of tests to analyze the soilegeosynthetic interaction behavior is an innovation that provides relevant insight into the impact of soil confinement on the time-dependent deformations of geosynthetics.     

Electrically conductive geosynthetics for consolidation and reinforced soil

The concept of electrically conductive geosynthetics (EKG) materials has recently been introduced. These materials extend the traditional functions of geosynthetic materials by incorporating electro-kinetic phenomena. Electro-kinetic geosynthetics offer technical benefits over conventional electrodes in that they can be formed as strips, sheets, blankets or three-dimensional structures. They are light and easy to install and can be structured so as not to be susceptible to electro-chemical corrosion, whilst continuing to provide conventional functions of filtration, drainage, separation, reinforcement or to act as impervious membranes. This paper describes initial laboratory tests on different types of EKG materials which can be used as combined electrodes/drains in electro-osmotic consolidation and as conductive geosynthetic reinforcement used to improve and reinforced weak cohesive soil. Results of the consolidation tests showed that the EKG electrodes were as efficient as a copper electrode and that the filtration and drainage characteristics did not deteriorate under electro-osmotic conditions. Results of the reinforced soil tests showed that EKG reinforcement can be used to increase the undrained shear strength of cohesive fill and that reinforcement/soil bond increases in proportion to the increase in shear strength.     

Evaluation of disturbance function for geosynthetic–soil interface considering chemical reactions based on cyclic direct shear tests

Various geosynthetics for reinforcement, protection and encapsulation are widely applied to civil structures and waste landfill sites. The use of geosynthetics inevitably involves the coupled behaviors of different materials which include large displacement and strain-softening behaviors, etc. Current research indicates that the behavior of geosynthetic–soil systems depend on the shear strength of the interface governed by several intrinsic and environmental factors, such as moisture, normal stress, chemical conditions, and thermal components, etc.In this study, the effects of acidity and basicity from leachate and waste are intensively considered in order to build up the chemical reaction mechanism of the shear strength of the interface under cyclic loading based on an experimental inspection. The Multi-Purpose Interface Apparatus (M-PIA) has been newly manufactured, and cyclic direct shear tests for submerged geosynthetic–soil specimens under different chemical conditions have been performed. A Focused Ion Beam (FIB) analysis has also been performed to induce the reason for the variation in the disturbance function and to verify the hypothesis on the decay-proof ability of geosynthetics.Consequently, a new approach to reflect the chemical effect of geosynthetics has been applied by suggesting the use of new disturbance function parameters in the Disturbed State Concept. The basic schematic of the Disturbed State Concept (DSC) constitutive model is employed; then, new disturbance function parameters are proposed to describe the chemical degradation of the geosynthetic–soil interface under dynamic conditions. Furthermore, based on the FIB results, it is be deduced that the variation in the disturbance function mainly results from the different types of decay in the soil minerals.     

Soil–geosynthetic interaction: Modelling and analysis

Interaction between soils and geosynthetics is of utmost importance in applications of these materials as reinforcement in geotechnical engineering. That is also the case for some applications of geosynthetics in environmental protection works. The mechanisms of soil–geosynthetic interaction can be very complex, depending on the type and properties of the geosynthetic and the soil. This paper presents and discusses some experimental, theoretical and numerical methods for the study and evaluation of interaction between soils and geosynthetics, with particular reference to the applications of these materials in soil reinforcement. The main advantages and limitations of some traditional experimental and theoretical methods for the study of soil–geosynthetics interaction are presented and new applications of these methods are addressed. The need for improvements in experimental and theoretical techniques for a better understanding of soil–geosynthetic interaction is highlighted.     

Shear strength characteristics of geosynthetic reinforced rubber-sand mixtures

Shear strength characteristics of the geosynthetic-reinforced rubber-sand mixture (RSM) has been investigated by conducting Unconsolidated Undrained (UU) triaxial test. In the first part, a series of UU triaxial tests have been carried out to know the size effect of granulated rubber/tyre chips from seven different rubber sizes. RSM sample that provides higher strength, energy absorption capacity and stiffness is considered as the optimal size and has been used in the investigation on geosynthetic-reinforced RSM. In the second part, shear strength characteristics of geosynthetic-reinforced RSM has been investigated by varying proportions of rubber content (50% and 75% rubber by volume), type of geosynthetic (geotextile, geogrid and geonets), number of geosynthetics (1–4) layers, geosynthetic arrangement and confining pressure. The results demonstrate that RSM reinforced with geosynthetic has enhanced peak strength, failure strength and corresponding axial strain at failure. Fifty percent RSM reinforced by geotextile and 75% RSM reinforced by geonets with 4 layers of reinforcement, led to a maximum increase in shear strength. The strength and energy absorption capacity are doubled for the reinforced RSM's, and reduced the brittleness index values as close to zero, which depends on the type, number of layers and arrangement of geosynthetic.     

筋箍碎石桩桩–土界面摩擦特性试验研究及离散元模拟

筋箍碎石桩复合地基桩–土界面摩擦特性对其荷载传递机理极为重要。首先通过室内大型直剪试验,研究了法向应力、软土含水率、碎石料相对密实度、筋材设置等因素对筋箍碎石桩桩–土界面摩擦特性的影响。在此基础上,采用离散元方法分析了筋材设置、筋材开孔率、筋材抗拉刚度等因素对界面摩擦特性的影响。室内试验及数值分析结果表明:桩土界面抗剪强度随法向应力、碎石料相对密实度、筋材开孔率、筋材抗拉刚度的增大而增大,随软土含水率的增加而降低;界面摩擦系数则随法向应力、软土含水率的增大而减小,随碎石料相对密实度、筋材开孔率的增大而提高,筋材抗拉刚度对其影响较小。     

Shear strength behavior of geotextile/geomembrane interfaces

This paper aims to study the shear interaction mechanism of one of the critical geosynthetic interfaces,the geotextile/geomembrane,typically used for lined containment facilities such as landfills.A large direct shear machine is used to carry out 90 geosynthetic interface tests.The test results show a strain softening behavior with a very small dilatancy(0.5 mm) and nonlinear failure envelopes at a normal stress range of 25-450 kPa.The influences of the micro-level structure of these geosynthetics on the macro-level interface shear behavior are discussed in detail.This study has generated several practical recommendations to help professionals to choose what materials are more adequate.From the three geotextiles tested,the thermally bonded monofilament exhibits the best interface shear strength under high normal stress.For low normal stress,however,needle-punched monofilaments are recommended.For the regular textured geomembranes tested,the space between the asperities is an important factor.The closer these asperities are,the better the result achieves.For the irregular textured geomembranes tested,the nonwoven geotextiles made of monofilaments produce the largest interface shear strength.