Study Of Safe Construction Technique Of Four-Lane Highway Tunnel Under Shallow Covered Slope In Weak Surrounding Rock

Four-lane highway tunnel has obvious advantage of traffic such as increasing speed, save time, reduce the mileage, ease the traffic. But it also has more construction process and more complicated mechanical effect because of its large cross section, wide span, staged excavation, under shallow covered slope in weak surrounding rock. In this paper, the safety of construction technique of four-lane highway tunnel under shallow covered slope in weak surrounding rock is studied based on rock mechanics and NATM construction with Niu Zhaishan tunnel in Fujian Province. The main research contents and results are as follows:(1) Through using the method of literature and engineering example, realize the difficulties in design and construction of four-lane highway tunnel under shallow covered slope in weak surrounding rock, summarizes the relevant design methods, construction methods and auxiliary method etc.(2)Monitoring for a period of one year of Niu Zhaishan tunnel in Fujian Province which is a typical four-lane highway tunnel under shallow covered slope in weak surrounding rock. According to the measured data, points out that inverted arch build in time is crucial to control surface subsidence and tunnel displacement of four-lane highway tunnel under shallow covered slope in weak surrounding rock, also is conducive to the improvement of the tunnel structure stress environment(3)According to the characteristics of four-lane highway tunnel under shallow covered slope in weak surrounding rock, do the three-dimensional finite difference numerical simulation of outlet section of Niu Zhaishan Sounth tunnel. It emphatically analyzes the displacement field, stress field, plastic zone distribution of surrounding rock and supporting structure during the actual excavation of tunnel. Combining with mechanical response of primary support, temporary support, twice primary support, secondary lining, judging the safety and rationality of the construction site. Pointing out the important function of temporary support during the construction process, it should reduce the damage of temporary support and determine the reasonable time of demolition. And the time during excavate lower part of tunnel to construct twice primary support is the greatest risk time in the whole process of construction, it should ahead of time to construct twice primary support and inverted arch reasonably.(4)Analysis the existing tunnel monitoring datum through the literature and related engineering example, combined with monitoring situation of Niu Zhaishan tunnel, discussing the monitoring datum briefly of four-lane highway tunnel under shallow covered slope in weak surrounding rock. Establishing the monitoring datum for its characteristics and setting up the applicative early warning procedure. And it points out the standard of monitoring and early warning procedure cannot rely on displacement limit and permissible value simply, it should be combined with displacement rate, actual site conditions and so on to analysis comprehensively.