"Profiling Stress History by In-situ Tests" by Paul Mayne

Piezocone penetration tests are a convenient and expedient means to determine the geostratigraphy because at least continuous measurements are obtained: cone tip stress (qt), sleeve friction (fs), and penetration porewater pressures (ub). The qt and ub readings may be used separately, or jointly, to map the magnitudes of preconsolidation stresses in clays and silts. The approach has a theoretical basis in a hybrid formulation based on cavity expansion & critical state soil mechanics. From a practical standpoint, the methodology has been calibrated with oedometric data on undisturbed samples in complement with electric piezocone results from 209 fine-grained soil sites worldwide. A simplified statistical approach is also available. The CE-CSSM formulation also provides a compatible interpretation for porewater dissipation tests whereby the excess values decay with log time and depend upon the coefficient of consolidation (and permeability) of the medium. Similar procedures can be applied in anapproximate scheme to the flat plate dilatometer, but not rigorously because of the non-axi-symmetry of this device.

The in-situ lateral stress state relates to the geostatic stress history. In this regard, the normalized form for the preconsolidation stress is defined by the overconsolidation ratio (OCR) which strongly influences Ko (lateral stress coefficient). Consequently, expressions can be used to relate piezocone and flat dilatometer readings to Ko states in soils.