抄録
The stress-strain behaviour of clay around a pressuremeter was investigated using the program DACSAR, a finite element program based on an elasto-plastic constitutive model. To check the program, a series of miniature pressuremeter tests were conducted in a sample of soil in a triaxial chamber, and the results were compared to those predicted using the program. The input parameters for the modelling were obtained from standard laboratory tests. This exercise showed that the clay behaviour could be reasonably well simulated using of the DACSAR program. In addition, it was demonstrated that the miniature pressuremeter test was not an accurate model of an in situ test, because of the effect of the finite dimensions of the sample in the triaxial cell on the pressure-expansion behaviour. Partial drainage was also shown to have an effect on the response in the model tests, and this effect was also reproducible with the DACSAR program. The DACSAR program was also used to investigate in situ pressuremeter tests in clay. The analysis showed that the stress-strain behaviour of the soil around the pressuremeter may be strongly influenced by partial drainage, with this effect being dependant on the permeability of the soil and the rate of testing. Consequently, when the so-called "Sub-Tangent" method was used to deduce the stress-strain curve from the numerical "tests", the derived "undrained" shear strength was higher than the true value, because the assumptions of undrained behaviour and plane-strain deformation, on which the method is based, are violated to some extent.
