Abstract:

Safe and rapid construction of tunnels in soft surrounding rocks becomes more and more important. Especially when tunneling through soft surrounding rocks with high ground stress, serious deformation may occur, which may jeopardize the construction safety and the construction progress. In this paper, the engineering geological properties of soft surrounding rocks, the deformation mechanisms of tunnels in soft surrounding rocks and the basic deformation control concepts are analyzed, and the criteria for the safety and stability of the support structures of tunnels in soft surrounding rocks and the construction countermeasures are proposed. Conclusions drawn are as follows: 1) Due to the improper support parameters and construction methods adopted, the strength and rigidity of the support structure cannot resist the huge surrounding rock pressure and therefore serious deformation and failure may occur; 2) 〖HJ2.2mm〗In soft surrounding rock section, the primary support takes all the loads during construction, the secondary lining needs to take the loads caused by the deformation of the surrounding rocks in the later stage, and the lining of the tunnel in soft surrounding rocks should be strengthened by means of adding steel bars and increasing the lining thickness. 3) Advance support and reinforcement can improve the selfsupport capacity of the surrounding rocks and can reduce the load acting on the support structure, therefore the advance support and reinforcement should be the focus of studies on construction technologies of tunnels in soft surrounding rocks; 4) For mountaincrossing tunnels in high ground stress area, ground stress measurement should be further implemented so as to select proper construction methods and support parameters.

Key words: mountaincrossing tunnel, soft surrounding rock, deformation mechanism, high ground stress, construction countermeasure