Experimental investigation of solute transport in unsaturated fractured rock

An experiment is designed to perform tracer tests in an unsaturated fractured rock with a horizontal fracture. Data from an intact and an artificial sandstone sample was collected and used to discuss the effect of the fracture on tracer migration. The delay time of the tracer in the fracture was further determined in terms of the fracture aperture involved. An alternative electrical conductivity (or electrical resistance) method was developed to measure the change in the tracer concentration with time and space. The method causes no disturbance to the flow and concentration fields, and is convenient to use. The test results show the fluctuations in the tracer concentrations and there were 2–3 peak values of concentration in the monitored sections related to the heterogeneity of the water content and pore distribution. Also, the fracture was found to delay migration of the tracer before it is filled with the tracer solution and quicken the velocity of migration afterwards. This results in accumulation of the tracer near the fracture. Furthermore, the delay time of the tracer increases with fracture aperture in a nonlinear manner.