Using Pressuremeter unload/reload data to determine the elastic shear modulus

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High resolution pressuremeter tests are used to determine the shear modulus of soils and the degradation of modulus with increasing strain using unload/reload data. A limitation of this procedure is the need to impose relatively large changes of shear stress on the soil in order to determine the consequent shear strain response. The minimum verifiable shear strain that can normally be observed is about 10^-4, too high to give the elastic shear modulus, G_max. Although for design purposes the pressuremeter degradation response is valuable, for modelling purposes and the wider use of pressuremeter data the lack of a means of determining G_max is a weakness. The paper collates data from sites and projects where multiple insitu techniques for measuring the maximum shear velocity of the ground have been deployed, a measurement that is easily converted to G_max. The methods include the widely used seismic cone penetrometer (SCPT) and downhole/cross-hole testing (DCH). Data are taken from the investigation for the second UK high speed rail project (HS2), the former UK soft clay research site at Bothkennar, and some recent testing in chalk for the SOURCE project. Recent work has suggested that it is possible to infer G_max from the shear modulus that applies when the full strength of the material has been mobilized. This suggestion is tested and shown to be reasonable. It is a significant finding, because it is often not practical or possible to deploy SCPT or DCH methods in the full range of soils accessible to the pressuremeter.

8th International Symposium on Pressuremeters (ISP2025)

Data Interpretation and Analysis