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The purpose of this thesis has been to design and develop a practical apparatus for determining the residual strength of clay soils. To provide background for the study, current knowledge regarding residual strength is reviewed, including the following points. 1. Residual strength, defined as the lowest drained strength a soil can exhibit, is attained at large shear displacements. 2. Residual conditions result when particles located in shear bands within the failure zone become aligned in the direction of shear. 3. Residual strength, derived from interparticle bonding, is influenced by crystal structure and, in active clay minerals, by pore water chemistry. The ring shear test, performed by applying a torsional shear load to an annular shaped specimen, is particularly suited for residual strength determinations because of unlimited uni-directional strain capabilities. The UBC Ring Shear Device was designed to combine versatility with uncomplicated operation. Features of the design are as follows. 1. Variable sample height up to 0.75 inches. 2. Smoothly variable normal stress up to 200 psi delivered through an air piston. 3. Smoothly variable rate of shear from 3-2 inches per year to 9 inches per hour. 4. A non-tilting loading platen which reduces required machine tolerances and improves control of sample losses during testing. 5. Automatic data acquisition. 6. A simple method of sample placement. Residual strength determinations obtained with the UBC Ring Shear Device demonstrate its efficient and effective operation. Minimal supervision is required and test results are easily interpreted. Multi-reversal direct shear tests for residual strength were undertaken for comparison with the ring shear results, but no satisfactory results were obtained due to excess pore pressures within the test specimens. Recommendations for improvements to both ring shear and direct shear devices are given. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

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