Seepage monitoring and leaks detection along an earth dam with a multi-sensor thermal-active system

Thermal investigation using linear sensors installed in the ground is currently one of the most effective methods for analyzing seepage processes in the bodies of earth dams or dikes and their subsoil, including leaks detection. However, linear, fiber-optic temperature sensors present several limitations when applied to existing structures, including installation difficulties and substantial costs. To enhance the applicability of the thermal method for studying subsurface water flow, a novel Multi-Point Thermal-Active Monitoring method has been devised. The approach consists of installing, through hammering, thermal-active sensors side-by-side in the ground, at the same depth in a single line thereby achieving quasi-continuous measurements along the structure. Small openings from sensor installation are secured with bentonite and do not pose a threat to the structure. Each sensor is equipped with a micro-heater, which enables the use of the thermo-active method to determine in-situ seepage velocity. This article describes this method and its initial application in 2014 on one of the Polish earth dams. This application enabled the detection of two leakage zones and the monitoring of their flow velocities, leading to the successful validation of the described technology.