Subsurface profiling of a region in Jamshedpur city using active MASW: a case study

This paper deals specifically with the active MASW method, which was applied for subsurface exploration of a region in Jamshedpur city, India, to study the various lithological and stiffness properties of subsurface materials. The study investigates the impact of data acquisition parameters on obtaining a high-resolution dispersion image, based on the ongoing MASW survey. A linear array of 24 numbers of 4.5 Hz geophones was used to collect raw wavefield traces generated by a 10 kg sledgehammer. Wavefields were regulated using a range of sampling frequencies (500 Hz, 1000 Hz, 2000 Hz, 4000 Hz, and 8000 Hz), as well as offset distances (1, 2 m, 4 m, 6 m, 8 m, 10 m, and 12 m) and inter receiver spacing (1 m and 2 m). Based on the results, the best data collection parameters for a high signal-to-noise ratio were determined to be: 1000 Hz sampling frequency, 8 m offset distance, and 1 m inter receiver spacing, resulting in a sufficient resolution dispersion image. Moreover, 1D and 2D shear-wave velocity profiles for the chosen site were derived. The stiff silty clay soil (up to a depth of 5 m) and dense to very dense weathered mica schist was found (at variable locations and depths from 8 to 30 m or beyond). The average V s30 is 402 m/s, and the site is classed as Type C as per NEHRP Site Classification. The shear-wave velocity profiles show a high level of agreement with borehole data, demonstrating the effectiveness of the non-invasive technology for sub-surface investigation.