Simple and inexpensive pressure control equipment for conventional and stress path triaxial testing of soils

Abstract

The equipment controls a standard hydraulic stress path cell for 38 mm dia samples with conventional instrumentation monitored by a simple transducer reading device. Similar equipment has been built for sample sizes up to 100 mm dia. Pore pressure, cell pressure and axial ram pressure are supplied by electromanostats which are air pressure regulators adjusted by stepper motors. The apparatus can carry out routine strain controlled triaxial tests or tests in which the axial stress is controlled and it can change from stress control to strain control during a test with little disturbance to the observed stress-strain curve. With other stresses varying simultaneously the apparatus can follow simple stress paths although it may be necessary to adjust the loading rates from time to time to bring the stress path close to the desired path. With the addition of a microcomputer the apparatus described becomes a fully automatic stress path facility capable of applying stress paths with a high degree of accuracy. (TRRL)