Imaging A Soil Fragipan Using A High-Frequency MSAW Method

The objective of this study is to noninvasively image a fragipan layer, a naturally occurring dense soil layer, using a high-frequency (HF) multi-channel analysis of surface wave (MASW) method. The HF-MASW is developed to measure a soil profile in terms of shear (S-wave) wave velocity at depths up to a few meters. While conventional MASWs use geophones as surface vibration sensors, the present MASW uses an accelerometer as a sensor to detect Rayleigh wave propagation generated by an electromechanical shaker operating in a chirp mode to achieve high frequency and high spatial resolution. With the method, the subsurface soil properties at a test site were measured, visualized, and evaluated. A 2-dimensional S-wave velocity image was obtained and from the contrast of the image, the presence, depth, and extent of a fragipan were identified. The HF-MASW result was compared with those of site characterization made by invasive methods and a 2-dimensional image obtained by a penetration test. The results from the HF-MASW and soil characterization were in good agreement. The study demonstrates the capability of the HF-MASW technique for detection and imaging subsurface layers such as a fragipan.