Time-Lapse Shear-Wave Velocity Changes Corresponding to Stages of Soil Arching Using a Trapdoor and the Multichannel Analysis of Surface Waves

In this study, a subsidence simulator, also known as a trapdoor, is used to evaluate stages of soil arching (a load transfer mechanism), and related failure features are imaged using time-lapse surface-wave analysis in near real time. The trapdoor was reinforced with a nonwoven geotextile to simulate void roof sagging due to increased loading during void development. This soil behavior was uniquely monitored with three methodologies, namely, multiple horizontal layers of earth pressure cells, photography, and time-lapse seismic surface-wave surveys. Pressure measurements were recorded after every 1 mm of trapdoor downward displacement, along with time-lapse photographs, to visually monitor the development of failure features. Time-lapse seismic surface-wave surveys were conducted after every 7 mm of displacement with pseudo-2D shear-wave velocity (Vs) sections generated for each survey using surface-wave inversion techniques. Vs variations were consistent with the progressive development of shear planes that formed an arch above the trapdoor. A simplified ground reaction curve was then derived from pressure measurements with the estimated stages of soil arching supported by each experimental method. Based on this physical model, Vs variations from surface-wave surveys can be used to successfully and noninvasively image and monitor stress-field variations related to progressive void roof collapse and associated deformation features.