Abstract: The electronic-magnetic computed tomography (CT) is an important means and method for the engineering exploration of karst cavities. The development type and degree of the underground karst cavities and their distribution characteristics have important reference value for the engineering design. This paper presents a case history of a subway station in Wuhan. The chemical and mineral composition analysis of the soluble carbonate at the site were analyzed to investigate the karst type and development degrees. The CT scan method was used to study the spatial distribution characteristics of the karst from the vertical height of karst anomalies, elevation distribution, and spatial relationship with bedrock. Meanwhile, borehole technology is used to verify the detection results. The results show that, the structures of the soluble rock are mainly marl, bioclastic limestone and micrite, and the mineral composition is mainly composed of calcite and dolomite, and karst is moderately developed in the field. The locations of the karst anomalies inferred by the geophysical CT are consistent with those revealed by borehole methods. The vertical height of karst anomalies is mainly distributed in 0~4m, and there are few anomalies with the vertical height greater than 4m. The elevation of the karst anomaly points mainly distributed in 27m ~ 13m, accounting for 70% of the total, while the proportion of karst cavities exposed by the drilling is 60% affected by factors such as the drilling density. Karst anomalies and karst cavities are concentrated within 6m below the bedrock surface, accounting for about 63% of the total, and the number of the karst anomalies and karst anomalies decreases with the increase of the depth. The above research indicates that CT detection of karst cavity development and distribution is completely feasible.

Key words: Karst Cavity Development, Karst Cavity Type, Geophysical CT, Space Distribution