Geotechnical parameters from integrated geophysical methods: Laboratory measurements and regression models
Seismic and electrical measurements are performed in the laboratory on unconsolidated geomaterials with well-characterized geotechnical properties. The measured seismic parameters are compressional wave velocity (V p) and shear wave velocity (V s), and the electrical parameters include the amplitude and phase of electrical response. Measurements are conducted on 32 samples with wide variability in mineralogical composition, texture and geotechnical properties. Each sample is saturated with fresh water and subjected to varying effective stress levels of 5, 10, 15, 20 and 25MPa for measurements of the seismic and electrical parameters. The geotechnical properties, porosity, fines content, particle size distribution, plastic and liquid limits are determined for each sample. The relationship between the geotechnical properties and geophysical parameters is investigated and regression models are developed. It is shown that porosity decreases slightly with increasing fines content to a threshold of about 15%, after which the linear decrease is sharp, for all the effective stress levels. The variation of resistivity with stress is also found to be dependent on the amount of clay and fines present in the sample. Resistivity correlated all the geotechnical properties with higher accuracy. The best prediction is for fines content with R 2 of 0.93. Fines content is also found to be the best geotechnical parameter which has better relationship with both resistivity and velocity. Combinations of resistivity and velocity also predicted plastic and liquid limits reasonably. The relationships developed will be useful in the geophysical interpretation of field measurements as well as the rapid estimation of geotechnical properties in the preliminary investigation of a project.
