Karst development characteristics and collapse risk assessment along Shaoxing metro line 1

Abstract

Urban subway construction in karst areas can be seriously threatened by geological disasters, which impact the safety of subway construction and operation. Given the effects of geological conditions and human engineering activities, it is necessary to comprehensively analyze the influence of various factors and then evaluate the risk of karst collapse. With the section between Yanghe road station and Jianhu town station of Shaoxing metro line 1 as an example, crosshole seismic wave computed tomography (CT) was employed to prospect the geometric characteristics and spatial distribution of karst caves. Based on the survey results, ten influencing factors were selected as evaluation indexes for karst collapse susceptibility. Then, an assessment system was established, and each index was quantitatively rated through three grades. The analytical hierarchy process was used to determine the weight of these indexes, and the fuzzy transform principle and maximum membership degree principle were applied to quantitatively and comprehensively evaluate the collapse risk level in the study area. Results showed that karst cave development mainly occurred in the bedrock surface under 11 m. The caves were mostly 2–5 m high, and most of them were filled. Approximately 70% of the studied section had a moderate or high risk of karst collapse. As the subway passes through the karst area, appropriate measures should be implemented for the different risk sections to ensure the safety of construction and operation.