轮胎条加筋土工程特性

轮胎条具有的特殊工程特性有益于土木工程应用。以废旧轮胎为加筋材料与砂土混合形成新型轮胎条加筋土，因轮胎条的低密度，高摩擦性，高弹性及高绝热性而大大改善了砂土的工程特性。这种新型土工复合材料，不仅为处理废旧轮胎开避了新途径，又为路堤、边坡及挡墙回填工程等提供了新思路和新材料。本文综述了轮胎条加筋土的密度特性、强度特性和压缩特性，分析了轮胎条加筋土工程特性改善的机理，给出了典型轮胎条加筋土的工程应用实例，期望推进这项环境岩土工程技术在中国的发展。     

Examination of earth pressure reduction mechanism using tire-chip inclusion in sandy backfill via numerical simulation

Tire chips have special features as geomaterials, as they are lighter than soil particles, highly compressible, and softer than sand. In this study, the effect of tire chips used as a compressible inclusion in backfill on the load reduction against retaining walls is numerically investigated. It is known that a reduction in earth pressure in backfill is realized by achieving a quasi-active or intermediate active state; and thus, a field test of this behavior is herein numerically simulated. The influence of the Poisson’s ratio and elastic modulus of tire chips on the reduction in earth pressure against retaining walls is examined by assuming that tire chips can be modeled as an elastic body. The numerical simulation reveals that the attainment of the active state in sandy backfill is primarily due to the light-weight nature of tire chips, along with their low Young’s modulus and Poisson’s ratio. Furthermore, the influence of friction at the bottom of the backfill mass is also considered, and the earth pressure reduction mechanism incorporating this factor is also numerically investigated.     

Effect of spatial variability of block-type cement-treated ground on the bearing capacity of foundation under inclined load

Deep mixing methods are widely used for stabilizing soft clayey soils and improving their bearing capacity. However, spatial variability in the shear strength of the cement-treated ground introduces uncertainties in estimating the bearing capacity for design. This paper evaluates the reliability of, block-type, cement-treated foundation under inclined load conditions using random field numerical limit analyses. The undrained shear strength is modelled as a random field which is characterized by a log-normal distribution and a spatial correlation length. Monte Carlo simulations are then used to interpret the stochastic bearing capacity factor and failure mechanisms for inclined concentric loading conditions at selected ratios of the shear strength ratio of cement-treated ground to original clay, the coefficient of variation in undrained shear strength and correlation length of the cement-treated zone. Variability of the undrained shear strength can reduce the expected bearing capacity of the cement-treated ground by 50–70% compared to homogeneously mixed clay.     

土工合成材料在城市固体垃圾填埋场中的应用

对一系列新型化工产品———土工合成材料在城市固体垃圾填埋场中的应用 ,特别对其中土工织物 (GT)、土工膜 (GM)、土工合成材料粘土垫 (GCL)、土工网 (GN)、土工复合材料 (GC)以及土工泡沫 (GF)等在填埋场衬垫、封盖系统中的应用作了全面的总结 ,详尽地分析了各种材料的主要用途     

竖向土工加筋体对碎石桩承载变形影响的模型试验研究

在碎石桩桩顶一定深度内包裹竖向土工加筋体形成筋箍碎石桩,能有效提高碎石桩的承载能力,控制复合地基沉降量。采用分级加载方式,设计并完成了两组较大比例室内模型试验,对比分析了筋箍碎石桩和传统碎石桩的承载变形特性,进而探讨了筋箍碎石桩的加筋机理和鼓胀变形模式,重点分析了竖向土工加筋体的应力应变特征。分析结果表明：竖向土工加筋体能有效约束碎石桩的侧向鼓胀,在微小侧向变形内提供足够的径向约束应力;筋箍碎石桩的最大鼓胀变形多发生于加筋体以下区域,其破坏模式与筋体材料、桩体、桩周土体及其相互作用和协调变形密切相关;筋箍碎石桩的桩顶和桩底桩土应力比均明显大于传统碎石桩,上部土工加筋体在提高桩体刚度的同时,可有效地将上部荷载传递至桩底较好土层。     

废弃橡胶轮胎环箍的散体材料特性研究

为了提高废弃轮胎路基使用性能和效果,研究了废弃轮胎环箍下的散体材料压实度和承载力。由于轮胎的侧限作用,轮胎内粉质黏土的最佳含水量比标准实验测定的最优含水量大,细砂的小于最优含水量。轮胎内散体材料的压实度一定范围内随着压实功的增加而增加,级配均匀的砂土在相同压实功的条件下干密度最高,取得最优的压实效果。轮胎的半径越大承载力越低;粗骨料填充的轮胎比细骨料填充的轮胎承载力高,但变形大。轮胎新旧对其内填散体材料的压实度和承载能力没有影响。由于散体材料的横向变形受到轮胎的约束,处于三向受压状态,因此提高了竖向载荷能力。     

High-Strengthening of Cement-Treated Clay by Mechanical Dehydration

A technique called the cement-mixing and mechanical dehydration method (CMD) as one of recycling techniques for soft clay slurry is developed. In order to evaluate the effectiveness of the CMD for increasing the strength of soft clay, a series of unconfined compression tests and several durability tests were performed together with the literature review of unconfined compressive strength in cement-treated soils. Moreover, a series of constant strain rate consolidation tests were also performed to evaluate the effects of cement content and dehydration speed on the permeability of cement-treated clay. The following conclusions are obtained: 1) Literature review and theoretical considerations on the shear strength of cement-treated soils show that an additional treatment for the purpose of increasing the density of cement-treated specimen is effective for increasing the shear strength of cement-treated soil. 2) The mechanical dehydration of soft clay with high pressure is accelerated by cement mixing, where the coefficient of consolidation of cement-treated clay increases as the cement content increases. 3) The high-strength specimen having the unconfined compressive strength of more than 20 MPa can be created from soft clay treated by the CMD with the cement content of over 20% and the dehydration pressure of 20 MPa.     

Essai au bleu et nocivité des montmorillonites dans les matériaux composites

The behaviour in wet conditions of materials (aggregates, soils, rocks...) containing clay particles depends on both the latter content and its mineralogical nature. According to the technique involved (cement-treated soils, bituminous mixes, concrete...), only external surface area or both external and internal surface areas of the clays are dominantly relevant. In this paper, we describe two simple ways of using the Methylen Blue test which allow the swelling nature of the clays, through the ratio of the external to the internal surface areas as well as their amount to assessed for The operating procedures are given; potential applications are also discussed.     

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.     

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。     

Electrokinetic geosynthetics in hydraulic applications

In use most geosynthetics play a passive role. New applications for geosynthetics have been identified if they can provide an active role, initiating biological, chemical or physical change to the matrix in which it is installed as well as providing the established functions. This can be achieved by combining the electrokinetic phenomena of electro-osmosis, electrophoresis and associated electrokinetic functions such as electrolysis with the traditional functions of geosynthetics of drainage, filtration, containment and reinforcement to form electokinetic geosynthetics (EKG). Electrokinetic geosynthetics can be made singly or from combinations of woven, non-woven, needle punched knitted, extruded or laminated materials and can be formed in any 2D or 3D shape.The majority of the uses of EKG are in hydraulic applications or applications with a significant hydraulic component. These can be grouped in separate engineering categories such as civil, mining, and water engineering. The concept of electrokinetic geosynthetics is described and details of applications and case studies are provided in the paper.     

Attempt to reproduce the mechanical behavior of cement-treated soil using elasto-plastic model considering soil skeleton structure

The improvement of sand and clay using lime or cement to control solidification is common practice. Among the many constitutive models for solidification proposed for clay and sand, few can reproduce the combined behavior of cement-treated clay and cement-treated sand. Here, four typical experimental results for cement-treated soil have been chosen from the literature to consider the shear and consolidation behavior for clay and sand, especially for a low cement mixing ratio. The elasto-plastic constitutive model was used to simulate this behavior considering the soil skeleton structure.The simulation results obtained using the model agreed with the experimental test results both for the cement-treated clay and the cement-treated sand. In the case of the clays, the experimental results were reproduceable using material constants for elasto-plastic and evolution parameters and only required changes in the initial state values, regardless of whether the soil was treated or untreated. In the case of the sands, the structure decay index of the treated sand became smaller than that of the untreated sand. Moreover, the cement-treated loose sand did not exhibit softening behavior. This was attributed to the slow rate of decay of the highly structured cement-treated loose sand due to the solidification of the cement. The degree of structure and the overconsolidation ratio both increased with higher amounts of admixed cement. The model developed in this study was capable of describing the mechanical behavior of both cement-treated clay and cement-treated sand.     

格栅条带式加筋胎面挡土墙变形性能数值计算

采用土工格栅加筋的方法提高废旧轮胎挡墙的承载性能,促进废旧轮胎挡墙的推广应用,通过数值计算方法分析了不同墙顶荷载下有无土工格栅加筋的废旧轮胎挡墙的水平变形与竖向沉降反应特征,得出铺设土工格栅加筋的方法可显著减小墙体的水平变形和竖向沉降,提高废旧轮胎挡墙结构的承载能力,随着外荷载的增加,墙体变形模式依次呈凹凸微小变化型、“弯弓”型、“似弯弓”型和“鼓腮”型和直线型。考虑土工格栅的加筋长度、竖向加筋间距以及格栅加筋刚度3种因素对废旧轮胎+土工格栅加筋土挡墙的水平变形的影响,得出在废旧轮胎加筋土挡墙设计中,建议土工格栅的加筋长度选取范围为0.5H～0.7H,土工格栅竖向间距的选取范围为0.4 m~0.7 m,格栅刚度不宜大于5 000 kN/m。     

加筋土结构中加筋与土之间的摩擦性质研究

利用拉拔试验,对不同加筋材料,不同填料的加筋土的摩擦特性、抗拔位移的变化规律进行了研究,为今后的筋材拉拔试验及工程应用提供了参考.     

The use of recycled tire chips to minimize dynamic earth pressure during compaction of backfill

The backfill areas of concrete culverts constructed in roads have been subjected to differential settlement due to poorly compacted soils. Dynamic compaction rollers cannot be fully utilized to compact the backfill soils near the culverts because the high earth pressure induced by dynamic loading frequently results in cracks in the culvert walls. In this study, two cushion materials, recycled tire chips and expanded polystyrene (EPS) boards are applied on the culvert walls in backfill areas to reduce the dynamic earth pressure induced by the compaction loading as well as to improve the characteristics of compacted soils. A numerical analysis is carried out to study the effects of the cushion materials on the stress variation with soil depth in the backfill areas. The numerical analysis shows that a cushion material with low elastic modulus and high damping ratio can effectively reduce the dynamic earth pressure. Field tests are also performed to study the performance of the two cushion materials. It is found from the field tests that the both cushion materials reduce the dynamic earth pressure acting on the culvert wall. However, the recycled tire chips are more efficient in reducing the dynamic earth pressure because of its relatively high damping ratio and low stiffness values compared to the EPS.     

Experimental evaluation of geosynthetics as reinforcement for shotcrete

One of the commonly used stabilization systems for rock tunnels is shotcrete. This fine aggregate mortar is usually reinforced for improving its tensile and shear strength. In deep tunnels, its capacity to absorb energy has been recently considered for design purposes, as large displacements of the wall are expected. Two of the most used materials of reinforcement are steel welded-wire mesh and fibers (steel or polypropylene) in the shotcrete mix. This study presents the results and discussion of an experimental test program conducted to obtain the load-deformation curves of reinforced shotcrete, according to ASTM C 1550, using geosynthetics grids and geotextiles as alternative reinforcement materials. In addition, plain shotcrete and steel welded-wire mesh reinforced shotcrete specimens are also considered in the experimental program as benchmark cases. The experimental results are analyzed in terms of maximum strength and toughness. Results show that the use of geosynthetics as a reinforcement material is a promising alternative to obtain shotcrete with energy absorption capacity comparable with the most common reinforcement materials used.     

Experimental investigation of bearing capacity of sand reinforced with randomly distributed tire shreds

A series of laboratory model tests has been carried out to investigate the using of shredded waste tires as reinforcement to increase the bearing capacity of soil. Shred content and shreds aspect ratio are the main parameters that affect the bearing capacity. Tire shreds with rectangular shape and widths of 2 and 3 cm with aspect ratios 2, 3, 4 and 5 are mixed with sand. Five shred contents of 10%, 20%, 30%, 40% and 50% by volume were selected. Addition of tire shreds to sand increases BCR (bearing capacity ratio) from 1.17 to 3.9 with respect to shred content and shreds aspect ratio. The maximum BCR is attained at shred content of 40% and dimensions of 3 × 12 cm. It is shown that increasing of shred content increases the BCR. However, an optimum value for shred content is observed after that increasing shreds led to decrease in BCR. For a given shred width, shred content and soil density it seems that aspect ratio of 4 gives maximum BCR.     

土工合成材料双向拉伸多功能试验机的研制及初步应用

为揭示土工合成材料双向拉伸状态下的力学特性,自主研制了一台双向拉伸多功能试验机,能够进行瞬时和长期蠕变双向拉伸试验。瞬时拉伸采用电机控制,可以实现两个方向任意比例下应力和应变加载;蠕变拉伸采用法码加载,可同时进行3组大变形蠕变拉伸试验。经初步应用表明,该试验机能够进行复杂应力、应变路径下土工合成材料双向拉伸试验,为土工合成材料双向拉伸力学特性的研究提供了一种科学有效手段。     

Microstructure and Chemical Properties of Cement Treated Soft Bangladesh Clays

This paper examines the relationship between the microstructure and chemical properties of soft Bangladesh clays due to cementation. The microstructure was investigated using X-ray diffraction, scanning electron microscopy, pH measurement, specific surface area and soil chemical tests. The results indicate that a multitude of changes occurred in the properties and behavior of cement-treated clays that can be explained by the interaction between four underlying microstructural mechanisms. That is, it is suggested that the hydrated lime is formed by hydration, which causes the flocculation of the little clay particles, by the preferential attack of the calcium ions on kaolinite rather than on illite and monmorillinite in the pozzolanic reaction, by surface deposition and shallow infilling by cementitious products such as calcium silicate hydrate and calcium alumino silicate hydrate (CSH and CASH) on clay clusters, and finally, by the presence of water trapped within the clay clusters. The chemical properties of the cement-treated clays were found to depend on the plasticity of soil.