An Experimental Approach to Analyze the Effect of Impact Loading on Shallow Tunnels in Weak Rockmass

The threat to underground structures has emerged as a vital issue and attracts the attention of researchers worldwide. Underground tunnels prove to be an essential mode of transportation for sustainable development. Urban tunnels are primarily located in the upper few kilometers in the ground. Therefore, most of these urban tunnels are situated in weathered rockmasses. Hence, these tunnels are highly susceptible to deformations under low-to-high-frequency dynamic loading. Therefore, it is essential to determine the dynamic response of tunnel lining under different sets of dynamic loading conditions. Thus, in the present study, a new impact testing facility (ITF) of 40 kg capacity was conceptualized, designed, and developed at the Indian Institute of Technology Delhi, India, for the physical modeling of tunnels at certain depth subjected to impact loading. The developed system is multifaceted, and testing is possible for a wide range of drop weights. The small-scale rock tunnel physical models of different cover depths can be tested under a sudden loading stress state, simulating in-situ stress conditions. The system consists of an impact load unit, air compressor unit, eight-channel data acquisition system, and a personal computer to record all load and deformation data. The working of the ITF facility was verified by conducting trial impact tests on several model specimens of rock tunnel blocks with three C/D ratios 1.0, 0.7, 0.5, and surrounding synthetic rockmass. The test results of a few rock tunnel models with surrounding material GM1 and with C/D 1.0 under varying drop energie conditions are discussed in the current study.