Geomechanical Model Tests and Infrared Detection of Rock Responses for Tunnels Excavated in Sedimentary Rocks

Rock mass behavior is controlled mainly by weak planes in sedimentary rocks. Geomechanical model tests were conducted for simulating tunnel excavations in horizontal, the 45° and vertical inclined rock strata. Infrared thermography was employed for detecting rock responses during the excavations. Infrared temperature (IRT) curve obtained by averaging the matrices of the infrared sequence can be viewed as temporal observation of the overall energy release from the rock under excavation. The IRT curve characterizes the horizontal and vertical strata as linear behavior and the 45° inclined strata as piecewise linear behavior over the full-face excavation and the three strata as plastic-like behavior over the staged excavation, respectively. The constitutive heterogeneity can be represented by the Weibull modus obtained by curve-fitting to the Weibull model using the probability distribution of the IRT temporal observations. The vertical strata has the smallest Weibull modulus values corresponding to the higher heterogeneity compared with the else two strata models. The structural response of the rock under excavation was characterized by the IRT distribution of the infrared image. IRT distribution of the horizontal strata evolved from scattering distribution to localized high-temperature zone around the face. In contrast, IRT distribution for the 45° and vertical strata distributed as belt-like IRT parallel to the weak surface; indicating the frictional sliding damage mechanism. Most intense friction was observed in the excavation in the 45° inclined rock strata.