KARST DEVELOPMENT AT SHUJIACAO AND ITS INFLUENCES ON YIBA HIGHTWAY CONSTRUCTION

In the lower of Shennong river, it is widely covered by carbonatite with strong karstification, which has important influence on the construction of the Yiba highway. This paper takes Shujiacao area for example, researches on the karst development feature by in-site investigation and the data of geophysical prospecting and drilling. The results indicate that karst development is mainly controlled by formation lithology, topography and neoteetonics. The surface karst morphyology is multiple, and the underground karst cave and grike are development. The concrete development features are showed as below:(1)The surface karst becomes stronger from hill to valley, and the karst development depth is changed from several meters to hundred meters; the surface large karst morphology such as depression, doline etc.occur in the band distribution horizontally; depression and sinkhole are well developed at the intersection of valleys. (2)The caves and karst pipelines have four levels vertically, the elevation is 150~170m、220~250m and 310m respectively. At the same time, a mount of covered cave and karst pipelines are found in the Shujiacao valley. On the research above, the authors point out that stability of cave roof under bridge pile, covered karst collapse and different settlement of subgrade is the main engineering geological problems which have to take corresponding measures in the process of highway construction.