Development characteristics of the epikarst zone in Wuhan area

In order to find out the development characteristics of the epikarst zone in the Wuhan area, the statistical analysis and research have been carried out by using a large number of engineering drilling data and hydrogeological test results. The result shows that the average thickness of the epikarst zone is from 11 to 16 m, and the average linear karst rate for per meter depth is from 3.93% to 10.52%, the maximum of which is from 5.83% to 17.25%; the karst is moderately to strongly developed in the epikarst zone, and the lower part karst development is weak. About half of the karst caves in the zone are less than 1.8 m in height, and the average height is of 1.50 to 2.18 m ,with the characteristics of small in size and large quantity in cave number. 2/3 of the karst caves are fully filled, while about 1/3 of the caves are non-filling or semi-filling, with their filling material mainly came from the upper overburdens. In the epikarst zone, rock masses and soils occur together in one place, and as a result their property for building foundation ground is poor. The average hydraulic conductivity is from 0.04 to 6.60 m·d-1, which falls in the range of weak to medium permeability. These characteristics of the epikarst zone are of great significance to the selection of building foundation types, the bearing layer of pile foundation and the construction method of the tunnel, which is also important for the utilization and treatment of groundwater in the foundation pits and underground engineering.