Interface Friction Between Organic Soil and Construction Materials

In this study, interface frictional resistance between organic soil and some of construction material was investigated. Construction materials used in this work are concrete, metal, and wood. Interface friction angle were determined for three different water contents values of organic soil dry, 25%, 50%, and 75% respectively. Different face roughnesses were tested for different water content. All tests were carried out using direct shear test device. Three different normal forces were used and shear stress at 10% strain rate was taken as maximum shear stress. Test results showed that water content of the organic soil, material type, and surface roughness should be considered while selecting interface friction angle between organic soil and construction materials. INTRODUCTION Organic soil is a mixture of fragmented organic material formed in wetlands under appropriate climatic and topographic conditions and it is derived from vegetation that has been chemically changed and fossilized. This type of soils has low shear strength and high compressive deformation which often result in difficulties when construction work is undertaken on the deposit. Bearing capacity and settlement problems are generally solved using pile foundations or different improvement methods. Pile foundation used in this type of soil is generally friction piles where loads transferred to soil through interface friction between soil and pile material. One of the important parameter for frictional resistance is friction coefficient between pile material and soil. Many geotechnical problems involve estimation of stresses transferred along the interface between soils and solid surfaces. Pile foundations and earth reinforcements involve the estimation of interfacial friction between soils and such structures. It is essential to determine the interface friction angle between soil and pile material in order to make a good estimation of the axial capacity of the pile. Also, knowledge of the interface friction angle in the determination of the magnitude and line of action of the wall reaction is significant. Various studies on interfacial friction between soil and other materials were carried out in the past. Different kinds of apparatus were used in the literature to determine interface friction angle between soil and solid construction material such as direct shear test apparatus [1-6], simple shear apparatus [7-8], ring torsion apparatus [9], dual shear apparatus [10], miniature pile test apparatus [11], and soil-pile slip tests apparatus [6]. Previous researchers found that several factors affecting the value of the interface friction angle. Among those factors are: (i) soil properties such as mineralogical composition, density, grain shape, grain size and gradation; and (ii) the properties of the material surface such as hardness and surface roughness.