ABSTRACT

The objective of this paper is to study the feasibility of using a seismic surface wave method to investigate seasonal and weather effects on shallow surface soils. In the study, temporal variations of subsurface soil properties were measured and monitored by using a combination of a new seismic surface method and an existing acoustic probe system. A laser Doppler vibrometer (LDV)-based multi-channel analysis of surface wave (MASW) method is developed to measure the soil profile in terms of shear wave velocity at depths up to a few meters. While the conventional MASW uses geophones as surface vibration sensors, the present MASW uses a moving LDV as a non-contact sensor to detect Rayleigh wave propagation generated by an electromagnetic shaker operating in chirp mode. A long-term survey was conducted by measuring the S-wave velocity profile with the MASW along with measurements of soil temperature, water content, water potential, and P-wave velocity with the acoustic probe system. The results from the two methods are compared and interpreted with the concept of the effective stress, governed by soil suction stress for top unsaturated soils and by overburden pressure for deeper layers of soils. This study demonstrates that the S-wave velocity images obtained from the LDV-MASW method can effectively monitor and visualize the temporal and spatial variations of subsurface soil properties caused by seasonal and weather effects.

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