Use of CPTU data in clays/fine grained soils

Abstract

The Piezocone test (CPTU) continues to gain in popularity as a result of its potential, particularly in clay soils. In order to have confidence in the interpretation of CPTU results in clay soils, it is vital that the test results are accurate and representative of the in situ soil conditions. This can be achieved by using equipment and procedures following the new International Reference Test Procedure (IRTP) (and in future the forthcoming ISO document on CPTU). A particular feature of the IRTP is the introduction of Accuracy Classes according to what the results are to be used for. This aspect is discussed in some detail. Testing on land is normally done by pushing from ground level until refusal or to a predetermined depth. A new and very interesting method whereby CPT’s can be carried out while drilling is advanced facilitates continuous testing to large depths. The rest of the paper covers the use of CPTU for engineering purposes in clays soils. The aspects that are dealt with are: layering and identification of soil type, stress history, lateral stress ratio, undrained and remoulded shear strength, small strain shear modulus, coefficient of consolidation and in situ pore pressure.