the residual shear strength parameters required for an assessment of the limiting strength of soil may be measured in the laboratory by a shearbox method. in this method the strength along the shear plane formed in the specimen is made to approach a lower limiting or residual value by repeated reversal of the direction of travel of the shearbox. this report describes the apparatus in use at the laboratory for carrying out residual shear strength tests. the standard shearbox has been modified to enable the direction of travel to be reversed automatically. the movement of the box and the shearing force developed are measured by use of linear variable differential transducers (lvdt) fitted to the strain dial-gauge and the proving-ring dial-gauge respectively. the output from the transducers is automatically recorded by a chart-recorder and on punched paper tape. the procedures for carrying out a shear test and calibrating the transducers are described together with an account of the interpretation of the results obtained.(a)

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