Deep, In Situ Nonlinear Dynamic Testing of Soil with Controlled Blasting: Instrumentation, Calibration, and Application to a Plastic Silt Deposit

Abstract

Abstract This study presents a novel test method to obtain dynamic properties of soil in situ using controlled blasting. Experimental and calibration protocols have been developed to conduct such investigations for any soil at any depth to obtain the coupled response between nonlinear shear modulus and pore pressure generation in soil. Controlled blasting using buried explosives with different charge weights at various depths were used as an active seismic source and the soil response measured. Micro electro mechanical system (MEMS) accelerometers, geophones, pore pressure transducers, and the MEMS-based inclinometers were calibrated to develop unique excitation voltage-to-unit relationships. Procedures to determine the post-installation sensor locations and orientations were developed to quantify the appropriate body wave velocity and shear strain in the soil. The conversion of calculated strains to a constant-volume direct simple shear-equivalent shear strain facilitated direct comparison to previously reported shear modulus reduction curves. Although this manuscript primarily focuses on instrumentation and calibration protocols, an example of the results of a test blast program is provided to demonstrate observation of the in situ, coupled, nonlinear fluid-mechanical response of an instrumented plastic silt deposit at a depth of 9 to 11.5 m below ground surface.