Hard sandwiched soil layer detection using higher mode in active MASW test

Abstract

This study focuses on detecting hard sandwiched soil layers using higher modes in the active multichannel analysis of surface waves (MASW) survey. The higher modes refer to the highest phase velocity spectrum over the fundamental mode in the dispersion image obtained from the active MASW test. Detection of the hard sandwiched soil layers can be challenging when the same magnitude of shear wave velocities (Vs) occur at two different depths in the Vs profile obtained from fundamental modes. To address this issue, the dispersion curves were analyzed using surface wave partial derivative (SWPD) and finite element (FE) simulation for soil models. The depth variations of hard sandwiched soil layers were investigated experimentally and numerically, utilizing mode-mixing and mode-separation phenomena in the dispersion images. In cases of uncertainty in identifying the fundamental modes, the depth of the hard sandwiched soil layer was directly determined by half of the wavelength of the higher modes. Additionally, irregular soil profiles were examined using various multi-layer FE models and field MASW tests to detect the hard sandwiched soil layers of Vs values ranging from 700 to 800 m/s at depths ranging from 3 to 8 m. The advantages of Vs values using the higher modes were evaluated to detect the hard sandwiched soil layer compared to those using fundamental modes and downhole seismic test results. The hard sandwiched soil layers were correctly identified at depths of 4.8 m and 7.2 m in multi-layer soil models by focusing on the higher modes without analyzing the fundamental modes.