Development of a Practical Test Method for Friction Between Cohesive Soil and Structure Foundation

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The purpose of this study is development of a practical test method for estimating the frictional resistance between cohesive soil and structure foundation. To start with, several sets of friction tests (1. and 2.) were carried out systematically to evaluate the efficiency of the test apparatus andto have a good grasp of the fundamental behavior of the friction. After that, friction tests (3.) were practiced with in-situ soil samples for estimating the skin frictions around piles.The knowledge acquired through this study are as follows :1. Friction tests between clay and steel :(1) There is only the shear deformation of a clay sample until the shear stress reaches the maximum value.(2) For smooth surface steel, the interface sliding occurs and the shear deformation of a clay sample stops after reaching the maximum shear stress.(3) There is the boundary steel roughness, R_b : if the steel roughness is larger than R_b, the interface sliding does not occur and the frictional resistance reaches the upper limiting value which is equal to the shear strength of a clay sample.2. Friction tests between cohesive soil and steel :Clay-sand mixtures have been used as cohesive soil samples.(1) The maximum shear stress is not affected by the clay-sand mixture ratio and steel roughness.(2) The more richly a soil sample has sand, the larger R_b is.(3) There is a complex behavior that the shear deformation of a soil sample occurs simultaneously with the interface sliding.3. Friction tests with in-situ soil samples :Two sets of friction tests were practiced by using undisturbed soil samples extracted from the ground around piles.Since the frictional resistances were in reasonably agreement with the skin frictions around piles, there is a possibility of the application of the test method of this study to practical use.