DETECTION OF PIPING LEAKAGE AT SHIJIAO SECTION OF BEUIANG DYKE WITH SYNTHESIZED TRACER METHOD

摘要

In Shijiao Section of BeiJiang dyke, Guangdong province, there exist serious potential dangers of piping leakage. Even after strengthening for several times, a large piping accident happened in 1994 and 1997 with 120m3 and 250m3 sands surging out respectively. Therefore, it is necessary to find out the real reason of piping before making effective strengthening measures. Comprehensive isotope tracer method was used to detect the leakage passage. Firstly, natural tracer methods, mainly including temperature and environmental isotopes, was used to analyze primarily the recharge sources of the groundwater behind the dyke. Then, the bedrock penetrability and strong leakage areas were determined by affusion tests and artificial radioactive tracer method. Eventually, the existence and location of leakage passage were proved by interconnection test. From above detection methods, such result was proposed and proved that the water conductive faults in the study area caused the piping. These faults were mainly located in the red sand layer under pebble gravel layer. By the long-term chemical and physical erosion, several water conductive solution caverns should be formed, and caused piping eventually. The analysis of water level and the piping located behind groundwater lowering wells also proved above results. At the end, some problems of previous studies are discussed about the seepage of Shijiao Section of Beijiang dyke. The previously used seepage calculation should have its applying conditions; otherwise we will get wrong results from such calculation.