9703736 The objectives of this research program are to develop new instrumentation, test methodology, data acquisition, and field procedures for the direct in-situ and site-specific assessment of soil liquefaction potential by cone penetration testing. The program consists of a collaborative group effort between Georgia Tech and Virginia Tech, and is being co-funded with the United States Geological Survey. It includes the assembly of a vertically-vibrating piezocone penetrometer (piezovibrocone), laboratory calibration chamber testing, a companion series of laboratory cyclic triaxial and simple shear testing, and field trials at geotechnical experimentation sites. Current methods of assessing the liquefaction susceptibility of loose sands and silts during earthquake shaking rely strongly on empirical correlations and methodologies. Present state-of-practice procedures for liquefaction evaluation include both in-situ and laboratory test methods that require correction factors which are not fully understood, nor well defined. The vibrocone consists of a cone penetrometer coupled with a vibrating shaker mechanism that induces liquefaction of the soil in the vicinity of the probe during penetration into the ground. Vertical penetration tests are conducted under both static and dynamic excitation in paired side-by-side soundings. Comparisons of cone tip resistance values, sleeve friction values, and penetration pore water pressures from adjacent soundings are made to ascertain the liquefaction potential and other properties of the subsoils. The penetration test is designed to allow a rational interpretation by analytical theories which incorporate important soil behavioral aspects such as dynamic loading, cyclic pore pressure generation, initial stress state, and residual undrained steady- state strength. As envisioned, the piezovibrocone will thus offer an improved and systematic framework for evaluating the liquefaction susceptibility of loos e ground in seismically-active regions. Additionally, it should have value for assessing the applicability and effectiveness of ground modification techniques such as vibroflotation, vibro-replacement, and densification by blasting.
