Imaging a soil fragipan using a high-frequency multi-channel analysis of surface wave method

The objective of this study was to noninvasively image fragipan layers using a high-frequency multi-channel analysis of surface wave (HF-MASW) method. The HF-MASW method is developed to measure the soil profile in terms of the shear wave velocity at depths up to a few meters in the vadose zone. The present MASW method uses an accelerometer as a vibration sensor to detect Rayleigh wave propagation generated by an electrodynamic shaker operating in a frequency-sweeping mode in three overlapped frequency bands. With the method, a subsurface image was obtained, i.e., the soil properties in terms of shear wave velocity of a vertical cross-section of the test site were measured, visualized, and evaluated. From the contrast of the image, the presence, depth, and extent of a fragipan were identified. The HF-MASW result was compared with field observations of a soil pit face and a 2-dimensional image obtained by penetration tests. They were in good agreement. The study demonstrated the capability of the HF-MASW technique for detection and imaging soil subsurface hard layers such as fragipan.