Counterface Soil Type and Loading Condition Effects on Granular/Cohesive Soil – Geofoam Interface Shear Behavior

Tanay KARADEMİR
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Abstract

The primary function of the geofoams consists of providing; i) lightweight fill for construction on soft ground (i.e. embankment), ii) relatively stiff base for subgrade installation below a highway (i.e. roadway, runway foundation), bridge approach (i.e. abutment backfill), and iii) slope stabilization for retaining structures. In those applications, the geofoams are in direct contact with soils and this interaction results in development of an interface where likelihood of a failure to initiate is higher. For this reason, the frictional resistance and the type of shear response mobilizing at these soil – geofoam interfaces control the stability of composite system, and hence, govern the integrity of the infrastructure. Soil – geofoam interfaces have been studied through an extensive experimental program by performing multiple series of interface shear tests using two different granular soils (i.e. beach sand and construction material sand) and one cohesive soil (i.e. bentonite clay) as well as a soil mixture containing 75% sand and 25% clay by dry weight at distinct loading conditions (i.e. normal stresses: 25, 100, 250; low, moderate, high loading conditions, respectively). Using the shear stress versus horizontal displacement curves obtained, some important engineering design parameters including peak shear stress, residual shear stress, interface sensitivity (i.e. peak/residual ratio) and displacement required to reach peak stress have been determined and the variations in those interface mechanical properties as a function of loading condition and counterface soil type have been investigated. It was seen that the peak as well as residual shear stresses increased with an increase in normal stress. Further, granular soil (sand) interfaces demonstrated relatively larger frictional strengths (both peak and residual) as compared to that of not only cohesive soil (clay) interface but also soil mixture (sand and clay) interface. Additionally, the higher the angularity of granular soil particles became, the larger the interface shear strengths (peak and residual), when sheared against geofoams, developed in light of experimental results attained as a result of interface shear tests on different material combinations.
面土类型和荷载条件对颗粒/粘性土-土工泡沫塑料界面剪切性能的影响
土工泡沫的主要功能包括提供;I)在软土地(即路堤)上进行施工的轻质填充物,ii)在高速公路(即道路、跑道基础)、桥梁引道(即桥台回填)下面安装路基的相对坚硬的基础,以及iii)用于挡土结构的边坡稳定。在这些应用中,土工泡沫与土壤直接接触,这种相互作用导致界面的发展,在这种界面中,启动失败的可能性更高。因此,摩擦阻力和在这些土工泡沫界面调动的剪切响应类型控制着复合体系的稳定性,从而控制着基础设施的完整性。通过广泛的实验程序,通过使用两种不同的颗粒土(即沙滩砂和建筑材料砂)和一种粘性土(即膨润土粘土)以及含有75%沙子和25%粘土的土壤混合物在不同的加载条件下(即正常应力:25,100,250;分别为低、中、高负荷工况)。利用得到的剪应力与水平位移曲线,确定了一些重要的工程设计参数,包括峰值剪应力、残余剪应力、界面灵敏度(即峰值/残余比)和达到峰值应力所需的位移,并研究了这些界面力学特性随加载条件和界面土类型的变化规律。随着法向应力的增大,峰值剪应力和残余剪应力均增大。此外,颗粒土(砂)界面的摩擦强度(峰值和残余)不仅比粘性土(粘土)界面大,而且比混合土(砂和粘土)界面大。此外,根据不同材料组合的界面剪切试验结果,颗粒土颗粒角度越高,与土工泡沫塑料剪切时的界面剪切强度(峰值和残余)越大。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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