Study On The Construction Techniques Of Railway Tunnels In Complicated Geological Conditions

To fit for the active demand of the successively, rapidly, harmoniously development of national economy, a prospective developing ideology of the modernization construct in China shall be carried out. The scale of railway net are enlarged quickly and the frame of railway net are perfected, the new ideas of the construction of railways are fully canied out, particularly in the during of the Development of the West Regions in China, the mountain railway which runs thought in type of tunnel are optimum choice, and the proportion of railway tunnel are more in the whole railway line.The section of Xiangfan-Hujiaying of the second new building Xiangfan-Ankang railway, which one part of Shanghai- Wuhan- Chengdu reconstructed railway, runs through the region of low-mid river vally in the northwester of Hubei province. For complicated geological conditions, a good few issues of the being construction of railway tunnel occurred, especially for geological hazards and tunnel lining deformation collapse.This paper based on the section of Xiangfan-Hujiaying of the second new building Xiangfan-Chongqing railway, the principle issues of railway tunnel constructing in complicated geological conditions are studied carefully, for examples, geological hazards, tunnel lining issues, tunnel monitoring and so on, and derived following results:(1) Forbidding digging road cutting in the front of tunnel portal, early entering and lately exiting, not destroying mountain entironments, as possible as not disturbing the upward slope, advocating "the supernatural appearance of enter the hole", and as soon as possible accomplishing the circumference drain system of the entrance of the tunnel.(2) The complicated geological conditions region, for entrance of tunnel, shallow cover, deviation pressure, soften-weaked cracked zone, closed net distance to the built tunnel and son forth, resulted easely in collapsing and deformation destroying, in which the importance of the safe and construction difficulty should be detected early, the construction detailed scheme, e.g. field arrangement, pre-reinforcement measurements, construction method etc, should be attached importance before entering hole to construction, and forbidded changing randomly the warranted construction scheme in the during of constructing.(3) The regions of the disadvantageous geological conditions, for shallow cover, deviation pressure, soften-weaked cracked zone, the wall rock of tunnel should be controlled firstly instead of the release deformation of wall rock in the during of tunnel construction, detailed construction methods: (1) primary support stronger, that is to say, primary support in time with higher stiffness material can only control effectively the wall rock deformation and the ground subsidence; (2) secondary lining adopted in appropriate time, not limited the rate of deformation velocity is less than 0.2mm/d.(4) Following the principle of reinforcement firstly, then excavation, implementing strictly 27 words guide line "water-control, firstly, then reinforced with tube, grouting carefully, excavation in short time, weakly burst, reinforcement strongly, closing in time, repetitious measurement and building tunnel door in time", this is a reliable principle for railway tunnel runs through the unfavorable regions to prevent deformation destroy and control ground subsidence.(5) The region of shallow cover, deviation pressure, soften-weaked cracked zone etc, short benching tunnelling method must be adopted, as possible as shortened steps length, closed invert arch into loop early. And the method of more steps with core soil circle excavation should be employed for the intricated section to restrain tunnel arch top settlement and convergence deformation.(6) The key of tunnel construction were the monitoring and measurement, and achieved results quickly, predominated the characteristics of the variation of tunnel hole, especially attached importance to the stability of the position beteewn the range of one radius time and the top and bottom of step site. Space-time variation effects should be recognition fully, supporting, asurement, feedback, modification four principles must be carried in time.(7) The guideline of the dynamic design, dynamic construction and dynamic management will be implemented. The informationization feeded back to design, informationization construction, informationization dynamic management should be obeyed.(8) The safety-risk hierarchical management and the high quality-high price management at the construct of tunneling should be prompted, and correspond to the managerial system should be established to reduce security level accidents and quality hidden trouble problems of tunneling.