The study of soil-reinforcement interaction by means of large scale laboratory tests

This thesis presents the results of an investigation into soil-reinforcement interaction by means of direct shear and pull-out tests. Scale and other factors affecting test results were studied; for this purpose an apparatus able to contain a 1 cu.m sample of sand was designed by the author in order to perform large scale tests. Plastic and metal sheet and grid reinforcements were used in conjunction with Leighton Buzzard sand. Direct Shear tests on unreinforced sand samples showed that soil strength parameters were not affected by the test scale, although the post peak behaviour and the shear band thickness at the centre of the sample were significantly affected by the scale of the test. The presence of a reinforcement layer inclined to the central plane of the box had a marked effect on the strength and behaviour of the sample. The reinforcement increased the vertical stress and inhibited the shear strain development in the central region of the sample. The behaviour of the reinforced sample was found to depend on the type and form of the reinforcement as well as its mechanical properties. Pull-out test results can be severely affected by boundary conditions, in particular by the friction on the front wall of the box. The results obtained in the series of tests showed that interference between grid bearing members is the main factor conditioning the pull-out resistance of a grid reinforcement. The intensity of such interference was quantified on the basis of results obtained in tests using single isolated bearing members and grids with different geometric characteristics. An expression for the bond coefficient between soil and grid, taking into account the degree of interference, was suggested. It was also observed that the maximum bearing pressure exhibited by a bearing member depends on the ratio of the member diameter to the mean particle size