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.     

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.     

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.     

垃圾填埋场终场腾发覆盖系统的研究进展

垃圾填埋场的传统覆盖形式为压实黏土、土工合成材料、土工膜或由这些材料组合而成的屏障型覆盖系统,由于垃圾降解和固结沉陷等原因,几乎所有屏障型覆盖系统在长期使用过程中都可能破坏失效。近年来,腾发覆盖作为一种替代覆盖技术在美国的垃圾填埋场得到广泛应用。腾发覆盖由一层植被土构成,它利用非压实土层储蓄渗入的降水、依靠植物的蒸腾和土壤蒸发消耗土壤水,从而实现渗沥污染控制。腾发覆盖的植被宜采用灌木和草皮混合形式,覆盖土层宜采用壤土或黏壤土,土体密度宜为1.1～1.5g/cm3,土层厚度取决于植被和当地气候。腾发覆盖是一种经济、实用、易于建造和维护的生态覆盖技术,但不宜用于蒸发量∶降水量〈1.2的沿海地区。     

土工合成材料力学耐久性规律研究

土工合成材料耐久性,即使用寿命一直是人们选择和应用土工合成材料所考虑的首要问题。用力学性能衰减规律评价其耐久性是最可靠的方法之一。通过室内外试验,尤其是对跟踪工程实例长达14 a 的试验结果以及国内外相关试验数据的分析,提出了土工合成材料力学耐久性的理论模型,并推算出土工合成材料在有40 cm 厚以上岩土严密保护的条件下,初始强度大于500N/5cm,使用年限至少可达50 a,大多数情况可超过100 a。并得出自然环境温度与土工合成材料耐久性密切相关的结论。     

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.     

Parametric analyses of evapotranspiration landfill covers in humid regions

Natural soils are more durable than almost all man-made materials. Evapotranspiration （ET） covers use vegetated soil layers to store water until it is either evaporated from the soil surface or transpired through vegetation. ETcovers rely on the water storage capacity of soil layer, rather than low permeability materials, to minimize percolation. While the use of ET covers in landfills increased over the last decade, they were mainly used in arid or semi-arid regions. At present, the use of ET covers has not been thoroughly investigated in humid areas. The purpose of this paper is to investigate the use of ETcovers in humid areas where there is an annual precipitation of more than 800 mm. Numerical analyses were carried out to investigate the influences of cover thickness, soil type, vegetation level and distribution of precipitation on performance of ET covers. Performance and applicability of capillary barriers and a new-type cover were analyzed. The results show that percolation decreases with an increasing cover thickness and an increasing vegetation level, but the increasing trend becomes unclear when certain thickness or LAI （leaf area index） is reached. Cover soil with a large capability of water storage is recommended to minimize percolation. ET covers are significantly influenced by distribution of precipitation and are more effective in areas where rainy season coincides with hot season. Capillary barriers are more efficient than monolithic covers. The new cover is better than the monolithic cover in performance and the final percolation is only 0.5% of the annual precipitation.     

Landfill side slope lining system performance: A comparison of field measurements and numerical modelling analyses

Low permeability engineered landfill barriers often consist of a combination of geosynthetics and mineral layers. Even though numerical modelling software is applied during the landfill design process, a lack of data about mechanical performance of landfill barriers is available to validate and calibrate those models. Instrumentation has been installed on a landfill site to monitor multilayer landfill lining system physical performance. The lining system comprises of a compacted clay layer overlaid by high density polyethylene geomembrane, geotextile and sand. Data recorded on the site includes: geosynthetic displacements (extensometers), strains (fibre optics, Demec strain gauges, extensometers) and stresses imposed on the liner (pressure cells). In addition, temperature readings were collected by a logger installed at the surface of the geomembrane, at the clay surface using pressure cell thermistors and air temperature using a thermometer. This paper presents readings collected throughout a period of three years and compares this measured performance with the corresponding numerical modelling of the lining system for stages during construction. Numerical modelling predictions of lining system behaviour during construction are comparable with the measurements when the geosynthetics are covered soon after placement, however, where the geosynthetics are left exposed to the sun for an extended period of time, in situ behaviour of the geosynthetics cannot be replicated by the numerical analysis. This study highlights the significant influence of the effect of temperature on geosynthetics displacements. A simple thermal analysis of the exposed geosynthetics is used to support the explanation for observed behaviour.     

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.     

Interface friction: An owner''s perspective

The introduction of geosynthetics to landfill applications has generally resulted in significant environmental protection improvements. Most significant applications have been the use of geomembranes in landfill liners and final covers. Other geosynthetics that are commonly utilized, often in conjunction with and adjacent to geomembranes, include geotextiles and geonets. However, when geosynthetics are used, especially when they are placed adjacent to each other in a liner or final cover configuration, the frictional characteristics of the resulting interfaces can become a very important factor affecting the design, construction and operation of a landfill. The impact of the frictional characteristics of such interfaces and the related potential stability issues on the design, construction and operation of landfills, from a landfill owner's perspective, is the subject of this paper.     

Effect of reinforcement form on the behaviour of coir geotextile reinforced sand beds

Coir geotextile, a natural geotextile manufactured out of coir fibres, has been recognized as a feasible alternative to geosynthetics for reinforcement applications, due to its longevity and excellent engineering properties. It is best suited for low-cost applications in developing countries due to its availability at low prices compared to its synthetic counterparts. This paper presents the results of plate load test on square model footing resting on sand beds reinforced with coir geotextile in geocell and planar forms. Keeping the characteristics and amount of geotextile the same, the performance of the geocell and planar forms were compared. The results indicate that bearing characteristics clearly depend on the form in which reinforcements are applied. For the same amount of material, coir geocell reinforcement provides better performance compared to planar forms. For a settlement of 15% of foundation width, the maximum improvement in bearing capacity for coir geocell was found to be 7.92 compared to 5.83 in the case of planar forms.     

CERCLA landfill closures: Construction considerations

A properly functioning cover over an uncontrolled landfill which is regulated under the Comprehensive Environmental Response Compensation and Liability Act (CERCLA) depends on both a well-engineered cover design and prudent construction practices.

This paper focuses on several geosynthetic construction issues which ultimately impact the performance of the final constructed cover. Preparation and placement issues related to subgrade preparation, geosynthetic placement, cover soil placement and test sections are presented. Storage and seaming of the geosynthetics are discussed. Construction quality control and quality assurance programs are emphasized. In addition, relevant design issues pertaining to settlements, interface friction, and rigid-nonrigid connections are discussed.

Although these issues apply to all landfills, this paper is based on experience gained from design, review and construction oversight of CERCLA landfill covers by the US Army Corps of Engineers.     

Experimental study of the performance of geosynthetics-reinforced soil walls under differential settlements

The deformation performance and settlement failure mechanism of geosynthetics-reinforced soil (GRS) walls are the two key points of engineering design under the differential settlement. This paper presents model tests of deformation performance and failure mechanism of the GRS wall with and without lateral restriction under differential settlement conditions. The observation and measurement results, including force and vertical displacement of geosynthetics and lateral deformation of facing panels, indicate good settlement control performance of GRS wall during construction and under differential settlement. Results indicate that the influence of the stress state of facing panels on the settlement control performance of GRS wall cannot be ignored. And the differential settlement failure of GRS wall is likely to occur in the joint of facing panels and geosynthetics. For good illustrations, two analytical approaches about deformation and stress of geosynthetics were proposed based on elastic cable theory, in GRS wall with and without lateral restriction. The expressions exclude the necessity to carry out sophisticated numerical analyses to stress and deformation and may help to develop the design guidelines for such GRS wall.     

土工布加筋基础的一维非线性模型(英文)

本文推导出一个代表软土双曲线弹簧支撑的土工布加筋基础一维非线性模型。该模型的数学形式是两个非线性二阶常微分方程组。给出了解常微分方程组的迭代格式，并着重讨论了非线性弹簧参数对加筋基础的沉降和土工布拉力的影响。     

土工合成材料与土界面作用特性的研究

土工合成材料加筋土工程中 ,土工合成材料与填料的界面作用特性是最关键的技术指标 ,因此利用直剪试验和拉拔试验研究土工合成材料与填料的界面作用特性是非常必要的。本文以 5种不同种类的国产土工合成材料为加筋材料 ,以砂和石灰粉煤灰为填料 ,通过直剪试验和拉拔试验比较各种国产土工合成材料与填料的界面作用特性 ,得到一些有益的结论 ,可指导土工合成材料的优选和研究加筋机理。     

The prediction of long-term geosynthetic strength using cumulative damage theory

This paper presents cumulative damage theory and compares predictions obtained using this theory with the observed performance of several geosynthetics. Cumulative damage theory, which is based on the separation of the processes of reversible non-elastic deformation and damage, may be used to forecast the long-term strength of geotextiles and geomembranes. Such forecasts are made for transient or permanently applied loads which allows assessment of the relative resistance of materials to damage.     

砂土颗粒级配对筋土界面抗剪特性的影响

为了研究砂土与土工合成材料相互作用时筋土界面的抗剪强度以及剪胀特性,采用3种不同级配的砂土分别与土工格栅和土工织物进行室内大型直剪试验,研究不同颗粒级配、密实度、筋材种类以及竖向应力对界面剪切特性的影响,并对界面剪胀系数进行分析。试验结果表明：粗砂和细砂与筋材的界面剪切强度要明显大于粗细混合砂;松砂剪切过程中只有剪缩效应的存在,但密实砂土呈现出明显的剪胀过程;当竖向应力较大时,筋土界面达到峰值剪切强度所需的剪切位移比低应力时大;粗砂与土工格栅作用时达到峰值剪切强度所需的剪切位移比与土工织物作用时大,而细砂则相反。     

Zum Einsatz von Geokunststoffen bei der Flachgründung von Windenergieanlagen

The use of geosynthetics for construction of windmills on spread foundation. The spread foundation is most favourable for the construction of that larger and higher performance windmills regarding the economic criteria. The ground improvement is most proper for such spread foundations on soft soils with high settlement potential by using the base course installation (reinforced and unreinforced). Additional reinforcement elements like geosynthetic can be installed for the further increase of the bearing capacity, from which a more favourable distribution of load impact on the underground, stress peaks will be diminished and the resulting settlement will be more uniformly. For the analysis of the bearing capacity and stability‐increasing characteristics of geosynthetic reinforced base course under spread foundation of windmill in low load‐carrying soil, a numerical investigation with the program system PLAXIS 2d, version 8.2, was performed, whereby both the separate contribution of the filling soil as well as the reinforcing element was determined. It could be proven that the use of geosynthetics in reinforced base course entails a significant increase of safety as well as a tilting reduction.     

Geosynthetics used to stabilize vegetated surfaces for environmental sustainability in civil engineering

Geosynthetics, factory-manufactured polymer materials, have been successfully used to solve many geotechnical problems in civil engineering. Two common applications are earth stabilization and erosion control. Geosynthetics used for earth stabilization include but are not limited to stabilized slopes, walls, embankments, and roads. Geosynthetics used for erosion control are mostly related to slopes, river channels and banks, and pond spillways. To enhance environmental sustainability, vegetation has been increasingly planted on the facing or surfaces of these earth structures. Under such a condition, geosynthetics mainly function as surficial soil stabilization while vegetation provides green appearance and erosion protection of earth surfaces. Recently, geosynthetic or geosynthetic-like material has been used to form green walls outside or inside buildings to enhance sustainability. Geosynthetics and vegetation are often integrated to provide combined benefits. The interaction between geosynthetics and vegetation is important for the sustainability of the earth and building wall surfaces. This paper provides a review of the current practice and research in the geosynthetic stabilization of vegetated earth and building surfaces for environmental sustainability in civil engineering with the emphases on geosynthetic used for erosion protection, geosynthetic-stabilized slopes, geosynthetic-stabilized unpaved shoulders and parking lots, and geosynthetic-stabilized vegetated building surfaces.     

Performance of geosynthetic-reinforced flexible pavements in full-scale field trials

The paper presents the results of a series of full-scale trials carried out in Thailand examining the performance of geosynthetics as reinforcement for flexible pavements. The geosynthetics were embedded at different pavement depths and the structural response was monitored across four test sections by means of strain gauges, pressure sensors, deflection points and deflection plates. The results show that all reinforcement configurations helped reduce the vertical static stresses developed at the base of the pavement by up to 66% and by up to 72% for dynamic stresses. The performance enhancement expected to prolong the lifespan of the base layers. The reinforcement layers closer to the base experienced the highest lateral strains of up to 0.13%, providing evidence that geosynthetics can also effectively reduce lateral spreading. All reinforcement configurations helped enhance rut resistance with maximum traffic benefit ratio (TBR) of 13.70, effectiveness ratio (EF) of 12.70 and minimum rutting reduction ratio (RRR) of 0.74. The best configuration included a geotextile within the asphalt concrete layer and a geogrid under the base layer. Non-linear finite element analyses of the test sections predicted very well the strains and stresses in the pavement. The study provides a benchmark for future studies in this field and concludes that geosynthetics can help increase maintenance periods and extend the lifetime of flexible pavements.