Infrared thermography for detecting cracks in pillar models with different reinforcing systems

The overburden pressure is concentrated in the pillar in between twin tunnels and hence monitoring is required for the stability of the pillar. In this paper, an experimental study was conducted to understand the behavior of pillars by simulating unreinforced, concrete reinforced and steel rib reinforced pillars. In order to define the initial crack and propagation pattern in the pillar, the crack was detected by using an infrared thermal camera as well as strain gauges. In a pilot test with cylindrical gypsum samples, crack friction and crack opening were determined according to the temperature change pattern at the crack point. In the compressive load test of the unreinforced pillar, cracks occurred and propagated in the pillars. After the initial crack, having an instantaneous temperature increase of about 0.1 °C, the temperature increased by about 0.3 °C to 0.4 °C continuously. The differential temperature occurring at the crack in the concrete reinforced pillar is higher than that of unreinforced pillars due to the larger overburden pressure. Three types of crack propagation occur with different features depending on the location of crack occurrence in the concrete reinforced pillar. In the steel rib reinforced pillar, an arch is created by the steel rib and hence there was no failure in the pillar.