Assessment of stabilised soil strength with geophysical methods

Soil stabilisation by deep mixing is performed to improve the strength and compression properties of soft soils. The determination of strength and of deformation moduli of stabilised soils in the laboratory can be performed in different ways. In addition to the unconfined compression test, which is the most common method for routine testing, seismic non-destructive methods may be employed. In order to evaluate strength parameters from these methods, correlations between the wave velocity and the undrained shear strength are required. At the Swedish Geotechnical Institute, the unconfined compression tests have routinely been preceded by shear wave velocity measurements with bender elements and resonant column free-free test to determine the shear wave and compression wave velocities in the same test specimens. This has allowed comparisons to be made of the results obtained with the two test methods. Fairly good and reliable relations between shear wave velocity and undrained shear strength have been established for stabilised clays of initial medium and high plasticity.