The Construction Scheme Analysis and its Application of the Southern Portal Section of Urban Mountain Large-span Road Tunnel Under Shallow-buried Bias and High Voltage Tower in Zhuhai

Abstract

The Heibaimian Jiangjun Mountain road tunnel is located in Nanwan District, Zhuhai City. The topography and geological conditions are complicated with challenges of high-voltage tower protection, shadow-buried bias load, under-passing water-supply tunnel and large-span section tunnel. To tackle these extremely unfavourable site conditions, the original construction scheme includes: i) a gravity retaining wall to overcome shadow-buried bias load, ii) a both side drift method with static blasting, controlled blasting, and conventional blasting and a tunnel body using a composite lining with curved wall and invert to resist section deformation of tunnel and protect existing infrastructures. However, this scheme involving multiple blasting techniques has seriously affected the construction progress of the west-line tunnel, becoming the primary threat to construction progress. To solve this problem, an flexible and pragmatic engineering countermeasure with a controllable cost and without sacrificing safety is proposed, by adjusting location of a south construction adit between the east and west tunnels. Besides, improvements on tunnel face excavation method and relative blasting parameters, as well as the optimization of construction scheme at the southern portal section, are proposed to accelerate the construction progress of the west tunnel. The proposed countermeasure provides important technical support for tunnel construction and is successfully applied to this engineering practice.