DMT – SDMT
A dilatometer test (DMT) consists of pushing a flat blade located at the end of a series of rods. Once at the testing depth, a circular steel membrane located on one side of the blade is expanded horizontally into the soil. The pressure is recorded at specific moments during the test. The blade is then advanced to the next test depth, typically in 20 cm steps.
The seismic dilatometer (SDMT) is the combination of a dilatometer blade with an add-on tubular element equipped with two sensors, for measuring the shear wave velocity Vs.
The DMT blade is normally pushed using a penetrometer – no borehole. Alternatively the blade can be pushed by a drill rig, starting from the bottom of a borehole. The blade can also be advanced by driving, e.g. using an SPT tripod.
The test can be executed in soils from semiliquid to soft rock, composed of soil grains small compared with the membrane diameter (60 mm).
Soil Parameters. DMT provides estimates of the oedometer modulus M, shear strength Su, OCR and Ko in clay, liquefaction resistance CRR.
Settlement Prediction. Many world experts consider DMT one of the best tools for predicting settlements (see citations on settlements).
Compaction Control. DMT has been recognized to be twice more sensitive than CPT to compaction. Before-after DMTs are increasingly used to monitor not only the gain in modulus but also the gain in OCR due to compaction.
Liquefaction. A just published Asce paper (2016) provides an updated KD-CRR correlation for estimating the liquefaction resistance CRR from KD. The paper also includes a chart for estimating CRR based at the same time on CPT and DMT (see citations on liquefaction).
Detecting Slip Surfaces in Clay Slopes. Values of the DMT parameter KD = 2 found in a slope signal the presence of slip surfaces, active or quiescent.
Laterally Loaded Piles. DMT was originally conceived to provide estimates of the horizontal soil modulus for laterally loaded piles.
Stress History Information. The DMT parameter KD is considerably more sensitive to Stress History than other in situ tools. Stress history is important, as it significantly increases moduli and liquefaction resistance. If Stress History is not felt, its benefits are wasted, leading to an uneconomical design.
G-Gamma Decay Curves. SDMT provides the small strain modulus Go and the working strain modulus MDMT, i.e. two points of the G-γ curve. The availability of two points is helpful while selecting the design G-γ curve.