Evaluation of the multi‐channel surface wave analysis approach for the monitoring of multiple soil‐stiffening columns

Abstract

ABSTRACTSurface wave spectral analysis is a well‐known technique in the characterization of layered media, where individual layers are assumed to be laterally homogeneous. This technique was later extended into the multi‐channel surface wave analysis approach by using an array of sensors to offer higher signal‐to‐noise ratio and faster data collection as well as in aiding the identification of surface wave propagation from the source. The objective of this article is to assess the performance of the MASW technique for the monitoring of multiple soil‐stiffening columns. The key difference in this application is the strong lateral heterogeneity due to the columns, while being relatively homogeneous in depth. The application of this technique may alleviate the constraints associated with traditional field techniques such as plate loading tests, dynamic probing and field vane shear tests. A laboratory‐scale experiment was carried out using materials with controlled properties in order to validate the proposed technique. Two concrete mortar blocks were built, one as a control and another with mild‐steel columns installed. A piezo‐ceramic transducer was acoustically coupled to the block using a padded weight in order to introduce a stepped‐frequency excitation from the surface. Four accelerometers were used to capture the excitation signal. Data were collected from multiple excitations and averaging was then applied to maximize the signal‐to‐noise ratio. By reconfiguration of the exciter and receivers’ arrangement, the area containing the columns was sequentially surveyed. The experimental measurements were processed to obtain the phase velocity as a function of wavelength. Approximated inversion was then applied in order to obtain the phase velocity versus depth and this was repeated for all survey points in order to build a 2D plot of phase‐velocity across the line of survey and with respect to depth. The results provided experimental evidence on the performance of this technique in the assessment of stiffening columns, evaluated against the requirements of spatial resolution of columns, the consistency of phase‐velocities within the columns and the comparison of the measured stiffness profile against known empirical values.