Stress history profiling in soils using OCD–G anisotropy relationship

The stress history profile in soils is evaluated on the basis of paired shear wave velocity measurements in different propagation directions (vertical and horizontal) with both waves horizontally polarised. Specifically, using a specially compiled database of sites with well-defined stress histories, the level of prestress, or overconsolidation difference (OCD = $σ′p−σ′vo$⁠), relates directly to the ratio of shear moduli (G_0,HH/G_0,VH) as measured by field geophysical testing. The G_0,VH profile is obtained from standard downhole tests using a horizontal surface source and either a cased borehole or direct-push technology, such as seismic cone or seismic dilatometer, whereas the G_0,HH profile is determined from a crosshole array using a torsional or rotary source at the same elevation as the geophones. In soil formations that are mechanically prestressed, the OCD is constant and permits the calculation of the profile of preconsolidation stress (⁠$σ′p$⁠) with depth and corresponding overconsolidation ratio.