Abstract: The overburden layer above the karst rock is often used as the bearing layer of buildings, and its moisture content characteristics have both the theoretical and the practical significance. In this paper, the relationship curve between the elevation and the water content is divided into four different types: gradual decline curve, steep decline-stable curve, steep decline-slow rise curve and stable-steep decline-stable curve. Each of these curves can be superimposed with the inclusion of the overburden with the extreme water content to form a composite curve. The peak value and the valley value of the curve have engineering significance, or can reflect the prominent hard layer in the overburden, or can represent the soft underlying layer buried deeply in the overburden. The study area is in a limestone belt, and the karst geological structure type is the Type IV. The porous medium in the overburden is less affected by the seasonal precipitation and more affected by the fissure water in the deep strata. Highdensity resistivity method can be used to analyze the characteristics of the water content in overburden soils. The water content decreases with the increase of the resistivity, and the resistivity value increases with the increase of depth. The abnormal areas with a high resistivity and a low resistivity can be characterized as abnormal areas with the water content in the engineering practice.

Key words: Moisture Content, High Density Electrical Method, Karst Rock Cavity, Overburden Layer, Electrical Resistivity