Stability Assessment on Expressway Embankment by Automatic Survey System

Collapses of expressway embankments due to large earthquakes and heavy rainfalls have been reported. Those collapses often closed important transportation routes and resulted in serious damages in communities. Inappropriate groundwater treatment and slaking/weathering of embankment materials contribute to these collapses. In order to diagnose road embankment soundness, we have to visualize the inside the embankment. The automatic technology for surveys and evaluations of embankments by using surface wave logging and electric resistivity logging has been proposed. We performed initial diagnostics before the opening of the expressways to evaluate embankment materials and stability of the embankment, especially in the vicinity of the stiff structures, such as box culverts and around the boundary between embankment and cut section. The desired target inspection speed, 500 m per h (mean speed), was achieved. The stiffness of embankment was continuously obtained for many sections with different fill materials as the initial reference data for future inspection. Based on the comparison between initial reference data and those obtained in the future, it is possible to select the optimal countermeasures to ensure the continuous stability of the road embankment.