Study On Fast Construction Technology For Moxi NO.2 Tunnel

This paper is a brief introduction regarding to construction method and project management for Moxi No. 2 Tunnel, which covers the selection of fast construction proposal, plant & equipment and site management.This project, i.e Chongqi-Huaihua Railway, Contract 10, has a total length of tunnel 5,580 m. The construction period of the tunnel is critical for the successful completion of the whole Contract.81.2% of the tunnel length is in Grade II and Grade III rock mass which is difficult to be blasted. Excavation operation is a key working procedure for the whole construction period.At the portal, there is a long section of soft and poor rock mass at where the tunnel will be advanced with a small embedment depth. A large area of shape "V" lining has to be constructed in Grade V surrounding rocks from DIK 140+950 to DIK141+290, 340m in length.The tunnel site is located in Karstic area with limestones gravels, where is easy to cave in when construction in raining season.This project commenced on 20 August 2001 and completed on 20 November 2003, with a total construction period of 27 months.The construction is divided two groups, inlet portal group for construction length of 2890m and outlet group for construction of 2690m. An adit was constructed and connected with the main tunnel at No.4 diversion tunnel for tunneling purpose. The other diversion tunnels were also constructed for ventilation and drainage purpose.Inlet Portal Section Construction:From DK140+950 to DK 141+290, 340M in length was excavated with centre cut method. Whole section bench cut method is employed in Grade IV rock mass for the excavation of single tunnel advancing and Full face cut method was applied for excavation of Grade â…¢ rock mass.The section from the Portal to No.1 diversion tunnel, DK 140+950 to DK 141+ 430, was excavated with multi-function platform and jack hammer boring method, the muck was transported by dump trucks and WA320-3 side loader.When advancing from No. 1 diversion tunnel location (DK 141+430), in July 2002, rail transport proposal was used, with LW backhoe loader and 12t battery car and 14m3 muck shifter. Wet shot-concrete was applied in initial support.The parallel adit was excavated in full face cut method with jack hammer. Apart from the beginning section of 70m long was excavation with removal of mucks by loader and trucks, the mucks in other sections were handled by LW-150 backhoe loader and transported on rail with 8t battery car and 14m3 muck-shifter. Wet shot-concrete was applied in initial support.