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Deformation and properties of cohesive soil in relation to soil-machine systems Kim, Joo Ick

Abstract

Methods of determining the deformation characteristic physical properties and dynamic response of cohesive soils were evaluated in order to obtain design parameters for soil-machine systems. The study was limited to simple scaled soil-machine systems on Haney clay and on mixed Haney clay and Ottawa sand in the semi-solid to plastic range. A special moire method was successfully developed to study large deformation and translation paths of soil as a function of tool shape and position. Compression, direct shear, stress wave and forced vibration methods were used to measure mechanical properties of soils. Advantages and disadvantages of each method were evaluated. Quasi-static stress-strain relationships were established from improved unconfined compression tests to produce unixial compression. Yield stress and strain hardening effects could be observed from these tests. Rate dependency of cohesive soil was verified by observing stress wave propagation in soil. It was observed that stress wave propagation velocity was more sensitive to soil particle size than to soil strength. Forced vibration methods were used to evaluate elastic constants such as Young's modulus and shear modulus which are useful in determining the contribution of elastic strains to the total force required to deform a soil. The theory of plasticity was successfully used in conjunction with experimental observations to establish stress-strain relationships in the soil on the assumption that strain hardening was linear and elastic strains were negligible. The maximum difference between theoretical forces deduced on the above basis and measured forces was less than twenty percent. The use of gelatin as a simulated soil was investigated to determine whether its use could provide a useful qualitative aid to design of soil-machine systems. It was found that the gelatin study gave stress trajectories and slip lines which resembled the results observed by the moire method in actual soil. Results obtained from the application of soil-machine systems on simulated soil and prototype soil were compared.

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