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    A Servo System for Controlled Stress Path Tests

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    This paper describes a servo system capable of imposing a prescribed stress path for the study of soil behavior in the laboratory. Various conditions were examined: (1) stress paths resembling those in the field, (2) both axisymmetric and plane strain shearing, and (3) large strain or post failure (or yield) state.

    The servo system is composed of two main parts: A minicomputer and an electric-pneumatic (E/P) transducer. The minicomputer collects and processes data while the experiment is in progress. The appropriate electrical signals are transmitted to the E/P transducer, which regulates the pressure connected to the back-pressure line of the triaxial or plane strain apparatus. With the axial load applied at a constant strain rate, it is possible to measure the complete stress-strain behavior, including that at large strains, along a prescribed stress path.

    A series of tests was carried out to illustrate the capability of the servo system. For the particular case of slope stability analysis, another series of tests was conducted from which peak and post-peak strength envelopes were obtained.


    servo system, computerized soil tests, controlled stress paths, triaxial tests, plane strain tests, strength envelopes, peak, post peak

    Author Information:

    Law, KT
    Research Officer, National Research Council of Canada, Ottawa, Ontario

    Committee/Subcommittee: D18.12

    DOI: 10.1520/STP28750S