Concept
The Flat dilatometer, or DMT, is an in-situ device used to determine the soil in-situ lateral stress and soil lateral stiffness and to estimate some other engineering properties of subsurface soils. It is a relatively simple test and its use in geotechnical investigations becomes more and more common. However, it is not yet as common as Standard Penetration Test and Cone Penetration Test in geotechnical investigation.
Description and procedure
The main part of the flat dilatometer consists of a flat stainless thin steel blande with a circulat expandable steel membrane of 60 mm diameter on one side. The test involves driving this steel blade into the ground, inflate the steel membrane and measure the corresponding pressure and deformation. Penetration of the steel blade is ususally done using common in-situ penetration equipments as for instance those used for Standard Penetration Test. The membrane of the blade is connected to a gas pressure unit on the surface which provide the pressure to inflate the steel membarne.
At a given penetration depth, the measurements are done by inflating the membrane and making two readings: (i) the pressure required to just begin to move the membrane against the soil "lift off", and (ii) the pressure, required to move the center of the membrane 1.1 mm against the soil. Sometimes a third measurements is made corresponding to deflating the membrane. These readings are repeated at different penetration depth increments.
The DMT pressures readings are used to estimate the in-situ lateral stress and lateral soil stiffness. DMT results have been interpreted and correlated with other soil properties and used as the basis for some engineering design methodologies.
The test can be applied to variety of geomaterials from extremely soft soils to hard soils/soft rocks. However, the common the soil grains should be smaller than the membrane diameter (60 mm) in order to acheive representative results.
Standards
- ASTM D6635-01 Standard Test Method for Performing the Flat Plate Dilatometer Link
References - External Links
- Use of the Flat Dilatometer Test (DMT) in geotechnical design, G. Totani, S. Marchetti, P. Monaco & M. Calabrese, Preprint : IN SITU 2001, Intnl. Conf. On In situ Measurement of Soil Properties, Bali, Indonesia, May 2001
- The Flat Dilatometer Test (DMT) in Soil Investigations,The Flat Dilatometer Test (DMT) in soil investigations, A Report by the ISSMGE Committee TC16, Marchetti S., Monaco P., Totani G. & Calabrese M. IN SITU 2001, Intnl. Conf. On In situ Measurement of Soil Properties, Bali, Indonesia
- Simple description of DMT with photos,R. W. Boulanger, University of California at Davis