Use and interpretation of a research dilatometer

Abstract

The flat dilatometer (DMT) test was introduced by Marchetti (1980) as a new in situ penetration test for soils. The equipment and test procedures are simple, and the test provides repeatable, nearly continuous data that has been empirically correlated to soil type, undrained shear strength (su), coefficient of earth pressure at rest (K0), overconsolidation ratio (OCR), and constrained modulus (M). To better understand the measurements from the DMT, a research flat dilatometer was developed at the University of British Columbia (UBC). The research dilatometer is identical in size, shape, and operation to the Marchetti blade except that instrumentation was added which made passive measurements of pore pressure and deflection at the centre of the membrane, inflation pressure at the membrane, verticality of the blade, and penetration force immediately above the blade. Results from several well-documented sites near Vancouver, British Columbia, using the research DMT are presented and discussed. Results from the research DMT have provided useful insight into the test procedure and interpretation methods of the standard Marchetti DMT. Stress-deflection curves for the DMT are remarkably similar to both self-bored and full displacement pressuremeter test results. Alternate DMT procedures are proposed to estimate ø′ of sands and coefficient of consolidation in clays. A procedure incorporating the closing pressure (P2) using a standard Marchetti DMT is proposed and evaluated. Key words: flat dilatometer test, in situ, research, cone penetration test, pore pressures.'