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UBC Theses and Dissertations

A simple shear machine for soil Pickering, D. J.

Abstract

The new shear machine enforces more uniform deformations than the conventional triaxial test. A low compliance pore pressure measuring device is an integral part of the machine. The machine described is capable of applying cyclic normal stress up to 1000 lb. per sq. in. and alternating cyclic shear stress up to ± 500 lb. per sq. in. Static loads can be taken 50 percent higher. The test specimen can be cut from an ordinary undisturbed drill hole sample, being 2 ins. square and 1 1/8 in. high. Height variation of ± 1/8 in. is permitted during testing, but there is no "dead" zone; the entire sample is subjected to the applied shear. An analytic solution is presented, for the boundary value problem of an anisotropic elastic sample in the tests to be described. This solution shows the variation of the stress field and deformations throughout the sample. For the benefit of any future simple shear machine designs, the theoretical relationship was also examined between the ratio of sample length to height and the uniformity of stresses and displacements within the sample. In comparing test results from the new machine with conventional triaxial tests, it was found that the measured strengths are different. Some of the results suggest that the triaxial test could over-estimate the strength of undrained sand. The difference between simple shear and triaxial conditions is, therefore, of more than theoretical interest. Liquefaction of undrained sand was readily induced by alternating shear in the new machine. It was found that liquefaction alters the structure of a sand sample, rendering it more susceptible to re-liquefaction.

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