Preliminary exploration on the critical buried depth of the soil cave in karst area

The research area is situated in a karst area with shallow cover type of karst developed, where the overlying soil layer comprises cultivated soil, silty clay, muddy clay, breccia and gravel and the underlying bedrock is limestone. The soil caves are developed in the soil layer, which often cause the ground to collapse. A single soil cave’s size is 2 m to 5 m in both height and width, with a long longitudinal extension. The plane distribution of soil caves is consistent with the ground collapse. On the basis of their transverse section, the caves can be roughly as circular and tunnel types, the latter of which has the shape of semicircular upper part and rectangle lower one. The highway passing through the area normally has a road embankment of 5.5 m to 7.5 m high. In order to determine the scope of the treatment of the soil caves, it is necessary first of all to determine whether a cave will develop into ground collapse. Based on the detailed investigation of the site, the location, size and shape of the soil cave are recorded, from which a finite element analysis model is established. Taking the zone from ground surface or road embankment surface to underground plastic deformation area into account for the determination of critical buried depth of the soil caves which may develop into ground collapse, the critical buried depth of the soil cave stability in different depth, size, shape and different backfilling height is then analyzed. This research has showed that the critical buried depth of soil cave is closely related to the shape, size and location of the caves and the thickness of roadbed fillings. The critical buried depth has a minimum value at the circular cave, while it gets larger along with increasing cave size or roadbed filling thickness. The results of this research can be used as a basis for the treatment measures towards the soil cave collapse. When the buried depth of the cave is larger than the critical buried depth, there is no need to treat it. On the contrary, when the buried soil cave is shallower than the critical buried depth, it is necessary to deal with the soil cave. In order to ensure that the soil caves do not have harmful effects on the highway project, field monitoring should be carried out both during and after road construction; and it is accordingly suggested that immediate intervention measures need to be implemented for the problematic localities.