Potential karst collapse assessment along a bridge foundation of high-speed rail, Anshan, China

Abstract

Mingjiashan Bridge is constructed along the high-speed rail (HSR) connecting two metropolitan cities, Harbin and Dalian, northeastern China. Sixty two cores were drilled into limestone bedrock. Caves occurred in 8 cores and soil voids appeared in 6 cores. Quaternary sediments on top of the bedrock are loose alluvial and fluvial deposits with a thickness of more than 50 m, which were categorized into three sections (A, B, and C) based on sediment types and structures. Daily water level fluctuations were 33, 20, and 10 cm in sections A, B, and C respectively. Maximum groundwater declining rates were 0.87, 2.0, and 0.26 cm/min in sections A, B, and C respectively. Seepage deformation experiments demonstrate that threshold hydraulic gradients causing deformation are 1.59, 2.38, and 0.79 in sections A, B, and C respectively. Results from hydrogeological and geotechnical investigations indicate that potential karst collapses may form in section A. Socketed piles should be used in this section and friction piles can be used in other sections. Existing voids and cavities need to be treated with grouting to reduce potential risk of collapse events in the future.