EVALUATION OF SELF-BORING PRESSUREMETER TESTS IN BOSTON BLUE CLAY

Abstract

The research performed self-boring pressuremeter tests (SBPT) at tow sites in a deep marine clay deposit of moderate sensitivity (Boston Blue clay) having a decreasing over consolidation ratio with depth. The program involved 2 tests with the French PAFSOR and 14 tests with the English CAMKOMETER devices. The initial pressure recorded after self-boring was generally much less than the in situ total horizontal stress, perhaps mainly due to improper installation techniques. However, the Marsland--Randolph graphical interation method yielded quite reasonable estimates of total horizontal stress, especially in the upper stiff clay, and this technique should be further evaluated via SBPT programs in other clay deposits. Values of undrained shear strength obtained from elastic-plastic and various derived methods of analysis were very sensitive to the input data, often showed considerable scatter and generally exceeded the in situ undrained shear strength appropriate for bearing capacity and stability analyses. In particular, derived peak strengths in the deep soft clay were too high by a factor of two or more. However, most of the tests did give reasonable estimates of undrained shear modulus. (FHWA)