Scheme Analysis And Optimization Study On Chaotianmen Underground Interchange Of Underwater Overpass Tunnels In Chongqing

As rapidly development of China's economic and acceleration of urbanization process, Development and utilization of urban underground Space attaracted serious concern of more and more people. Urban underground interchange is one of utilization of underground space forms in recent years, and construction of large-scale underground interchange in the city. The difficult is intensive buildings on ground surface; complicate conditions of geological and terrain, stringent restrictions on the site region, large width and height of main tunnels, layered staggered tunnels, the clean distance of tunnels is complex and changalbe.Based on the planning of Chongqing's Chaotianmen underwater overpass tunnels underground interchange tunnels project, the paper discuss reasonable form of underground interchange and construction method. Using of finite element numerical simulation method to analyse stability of underground interchange under varous surrounding rock conditions and excavation methods, deformation regular of ground surface after excavation and underground interchange and construction mechanical effects of trumpet-like tunnel of underground Interchange. The following are major conclusions①Basing on existing roads net of Chao Tianmen underground interchange site,comparative analyze through the security, ease of construction and engineering factors,Y-shaped semi-directional interchange form is suitable for the Chao Tianmen underwater overpass tunnel.②Comparative analysis of construction mechanical effect of full section method, bench excavated method, unilateral pilot tunnel method showed that: displacement of tunnel, internal forces of lining, distribution of plastic zone by unilateral pilot tunnel excavation method is smaller than the other two excavation methods. Thus, unilateral pilot tunnel excavation method should be the reasonable approach for Chao Tianmen interchange underground interchange.③By Studying mutual impact of two tunnels as their net space changes in differernt surrounding rock conditions, and raised the mutual impact of two tunnels by relative influence degree of arch crown. The results showed that when the tunnel Net Space span of more than 4.13 times the tunnel, the mutual effect of two tunnels become stabilizing. ④Surface deformation regular after the excavation of the underground tunnels at different condition of surrounding rock grade, supporting condition, surface loading, and depth of tunnel was numerical simulated. The results show that as the rock conditions become worser, the settlement amount and tilt value of ground surface accelerates to increase afer tunnel excavation without supporting and the settlement amount and tilt value of ground surface will become basically constant percentage growth afer tunnel excavation with supporting. Surface tilt is decreasing as depths increasing in a word.⑤By analysing construction mechanical effects of the trumpet tunnel through the displacement, initially supporting internal forces, rock stress and plastic zone. The results showed that the early support of trumpet cross parts and the angle of tunnel always exit greater internal forces, and early support at those parts will fail easily. The poor mechanisc state of mid-board, always simultaneously exit tensile and presure stress, acute disturbance of bios pressure when net space of two ramps is small.