Dilatometer Test (DMT)
Dilatometer test is an accurate flat instrument, designed to measure the dimensional changes of a wide range of material. This steel blade has a circular expandable steel membrane of 60 mm diameter on one side.
As this figure shows, first the steel blade is driven into the ground by usual in-situ penetration equipment. Next, a gas pressure unit inflates the membrane. Two pressure gages measure the amount of pressure required to expand the DMT membrane. Generally three readings are recorded:
- the pressure needed to lift the membrane off its seat (“lift off”).
- The amount of pressure needed to expand the membrane by one mm.
- A third measurements, which is not compulsory, is related to deflating the membrane.
These readings are repeatedly recorded at different penetration depth (usually every 30 cm) to give and insight about the profile of the soil. The results of DMT are correlated with some soil properties such as in-situ lateral stress and lateral soil stiffness. However, the test can be carried out for a variety of soils, its highest accuracy is when soil grains are smaller than the membrane diameter (60 mm) .The precise procedure of performing DMT is described in ASTM D6635-01