APPLICATION OF TRACER TEST IN THE PRELIMINARY SURVEY OF TUNNEL CONSTRUCTIONA CASE STUDY OF THE PROPOSED QIGANSHAN TUNNEL IN CHENGKOU COUNTY, CHONGQING

Because of the high degree of heterogeneity and complexity of karst aquifer media, there are many uncertainties in the tunnel construction. This paper takes the proposed Qiganshan Tunnel of Chengkai Expressway in Chengkou county as an example, using on-line tracer technique, getting high-resolution tracer data, combining with the method of quantitative interpretation to analyze the potential flow direction and flow field of karst groundwater in the tunnel area. By putting the tracer into the borehole to carry out work, the test results identify the relation between the groundwater of the testsite and outlets of several underground rivers. This result could be a useful tool to identify the karst underground water ridge and calculate the hydro-stress gradient of the tunnel area. This test greatly improves the precision of hydrogeology investigation in the tunnel area. By this example, it is indicated that the on-line tracer technique is of great value for popularization and application in the study of aquifer media and its related exploration in karst areas of Southwest China.