Analysis of structural characteristics of karst conduit by time-concentration curve of tracer test

The structural characteristics of karst conduit have an important influence on the rational use and protection of karst water resources and the safe construction of underground engineering. At present, when using tracer test curve to analyze the structural characteristics of karst conduit, there are some problems, such as curve superposition shape, blunt front shape, irregular rise and fall of curve, connection relationship between multiple karst conduit, location of underground lake and groundwater state. In this paper, the time concentration curve of tracer test is used to explain the structural characteristics of karst conduit through the numerical simulation of the karst conduit flow tracer test and the change of water flow state. The results are as follows: (1) The number of curve peaks corresponds to the number of karst conduit, and there are three models for the parallel curve of double pipelines due to the difference of the length and velocity of karst conduit runoff. (2) The number of single karst conduit curve decline gradients corresponds to the number of blue hole, and the relationship between the decline gradients and the number of blue hole should be analyzed for multiple karst conduit in combination with the number of karst conduit and the location of blue hole. There are four types of parallel karst conduits. (3) The rapid change of curve shape indicates the mutual transformation of surface flow and pressure flow.