The short DMTA dissipation test

Abstract

The CPT is used either in a continuous advance mode or in a rheological testing mode. Both periods are present in the short local side friction and in the short cone resistance dissipation tests made in the technical breaks of continuous penetration of the old CPT S832 equipment. The pause is a few second long. A statistical study previously made revealed that the local side resistance increased in sand and decreased in NC plastic soils with time in the first seconds after the stop of the steady penetration, the decrease was sometimes larger than 50%. The rate of stress variation was depending on the permeability and thus on the soil type. In this research, a similar, new test is considered. Before taking the standard Areading in a DMT, a short dissipation can be measured in a generally 15 s long time period, with the Medusa DAS, being able to sample an A-reading in every 20 millisecond. A series of them made at the Araquari test sites are statistically analysed here. The results are similar to the ones related to the short local side friction dissipation tests which is explained by the different residual stress state in sands and in NC clays, and by the different permeability of sands and NC clays.