Abstract: During construction of shallowburied tunnel with small crosssection in uppersoft and lowerhard strata with rich water, rock breaking is hard to conduct in middle and lower benches, the arch foot of the top heading is not located on the bedrock, so the primary support cannot be closed in time, which may lead to the overall settlement of the primary support of the top heading. Therefore, a case study is conducted on the exit section of the Longquan tunnel, a excavation test section is set and the rock breaking efficiency is taken as the main index to comparatively analyze the feasibilities of four rock breaking technologies, namely, refitted blasting machine, hydraulic fracturing, CO2 phase change fracturing, and expansive agent fracturing, and the laws of tunnel convergence and surface settlement after rock breaking by refitted blasting machine are further analyzed. The results show the following: (1) The rock breaking efficiency of CO2 phase change fracturing is the highest, reaching 6 m3/h, followed by that of refitted blasting machine(about 4 m3/h), and those of hydraulic fracturing and expansion agent fracturing are lower, reaching 2 m3/h and 1.1 m3/h, respectively. (2) The rock breaking technology of refitted blasting machine has many advantages such as good stratum adaptability, controllable vibration, and easy trimming, which can reduce the surface and crown settlement.

Key words: waterdiversion tunnel, uppersoft lowerhard strata, settlement of primary support, rock breaking technology