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Construction Method of Metro Tunnel Crossing the Existing Railway Liu Hui-jun Study in central south university [email protected] Wang Xiao-feng Li Shuai-shuai Study in central south university Changsha Construction Science Research Institute, Changsha 410011, China School of Civil Engineering, Central South University, Changsha 410075, China Funding project: Hunan natural science foundation (2012GK3005); Changsha science and technology projects (10908) ABSTRACT Based on the shield construction of Changsha metro line 1 that crossing the Beijing- Guangzhou railway, using numerical software MIDAS GTS for simulation calculation, analyzing strata displacement caused by the subway shield tunnel drive and the influence on deformation because of the existence of pile foundation. The results show that shield tunnel construction loads to effect that the top sinks while bottom hunch-up. And reinforcing railway with method lifting lintel through vertical and horizontal can effectively weaken the effect and can be conducive to the stability of the soil. KEYWORDS: Numerical simulation; Shield driven; vertical and horizontal lifting beam; horizontal displacement; settlement; axial force of pile shaft INTRODUCTION With the development of subway, more and more subway engineering goes through the existing railway. A large number of subway tunnel engineering practice shows that urban tunnel construction is bound to cause ground subsidence and deformation[1,2]. The ground movement causes differential settlement of existing railways .If the D-value overruns, it will create sub grade settlement in the railway roadbed and bend distortion in track structure, and thus cause the change of track geometry, harm to the existing line operators[3,4]. The stress of the deformed track greatly increased. Over-sized railway embankment settlement can cause track fracture or even derailments[5]. The engineering example of Changsha Subway Line 1 - 5393 - Vol. 18 [2013], Bund. W 5394 Underpass Beijing-Guangzhou railway is studied in this paper. In this project, to ensure safety we should adopt a method of vertical and horizontal lifting beam to reinforce the track. Shield tunnel construction is an integrated engineering which affected by many uncertainties. Shield drive caused deformation of the railway line exacerbating the track irregularity, it not only increased the impact force between wheel and rail, accelerated the destruction of foundation bed and track structure .The operation safety of the railway is also seriously affected. This paper focuses on the engineering example of Changsha metro 1 underpass Beijing- Guangzhou railway, using numerical analysis software MIDAS GTS to simulate it to studying the effect of shield-driven tunnel underpass the track which reinforced by vertical and horizontal lifting beam. PROJECT OVERVIEW The project next to the New Road overpasses of Furong Road in Changsha, influenced by the bridge piles of New Road overpasses and east Cambridge building (under construction) in the south of Beijing-Guangzhou railway, the left and right line of Railway section between Tu-chong Station to Railway College Station Underpass the Beijing-Guangzhou railway respectively at mileage K1575 +75 and K1575 +100. We use shield-driven method to construct, the right line is straight and the left line is a horizontal curve with Radius of 600 meters. Vertical section of the line is a longitudinal slope of 14.103% (uphill), the subway tunnel is covered with soil of approximately 8 meters thick, inner diameter of the tunnel structure is 5.4m, diameter is 6.0m. Its segmental lining uses reinforced concrete of C50. Shield tunnel located in 1# and 3# turnouts in the North of Xin Kai-pu Station of Beijing- Guangzhou railway. The cross segment is located in turnout area of single crossover of Beijing-Guangzhou railway. Its model is P60-1/12. Beijing-Guangzhou railway line spacing down the line. The distance between the uplink and downlink line is 5m, thickness of the track bed is approximately 0.45 m. Here the railway roadbed is in the form of cutting subgrade, Type of slope protection of railway sides: anchor piles are used in the north, we use mortar rubble masonry in the south. Slope pile is hand-dug pile, the diameter is1.8m, bottom elevation is approximately 41.5m. The vertical spacing between the slope protection piles and shield zone is approximately 2.4m. North and south sides of railway lay a surface drainage. Respectively, dimensions are approximately: 5m×1.3m(Width x depth, north)and 0.5m×0.5m(Width x dept, south). The entities figure is shown in Figure 1, the positional relationship between Metro and reinforcement pile of railway is shown in Figure 2. Vol. 18 [2013], Bund. W 5395 Figure 1: Entities Figure of the Railway 016电化柱 隧道右线中心线 隧道左线中心线 转辙机 015电化柱 广州方向 东边 电气化立柱临时桩 旋喷桩 Figure 2: Plane diagram of relationship between the tunnel and reinforce pile of rail NUMERICAL MODEL AND PARAMETERS The project will use the final settlement of foundation as the control standards in order to simulate the influence of metro shield drive under railway to tracks project characteristics. When analyzing metro shield which under railway segments, the railway uses the method of "Vertical and horizontal lintel" to reduce the impact of the metro shield on the track and assert control standards to similar construction. Diameter of hole digging pile all use 1.5m hand-dug piles and main buckle rail is 16.5m and vice buckle rail pile is 8m, then the temporary electronic column L15 foundation pile is 16m. Digging holes use C30 concrete pile body and Vol. 18 [2013], Bund. W 5396 wall all adopt C20 net shotcrete. During construction remove turnout crossing the line from 1 to 3 #, lock 1 # and 3 # turnouts as well as . Numerical analysis model is specifically as this : horizontal strata 60m, portrait 20m, depth calculated according to the surface 20m, taken straight up to the surface. Subway tunnel depth H is 10m,the hole diameter D is 6.0m, concrete lining thickness h is 0.3 m, the pile diameter d is 2.0 m. Stratigraphic layers from top to bottom are the artificial filled soil, silty clay layer (shield layer), gravel layer. Formation of mechanical parameters is shown in Table 1, three-dimensional numerical analysis simulation is shown in Figure 3, and the model mesh is in Figure 4. Table 1: Physical and mechanical parameters of the model material Friction Bulk density Cohesion Modulus Poisson's angle Category ρ 3 2 E/MPa ratio µ b ()kN m c() kN m ϕ ()° Artificial 6 0.24 19.5 12 10 filled soil Silty clay 22 0.26 19.4 36 15 Pebble 24 0.21 22.5 4 40 Lining 20 550 0.30 25.5 - - Pile 30 000 0.28 24.5 - - Girder 220 000 0.31 76.9 - - Figure 3: Three-dimensional map of numerical analysis model Vol. 18 [2013], Bund. W 5397 Figure 4: Grid divided of model In order to analyze the calculation results conveniently, the rock is divided symmetrically into I (away from the hole axis), II (near from the hole axis), III (between the axes of two holes) regions .Each region selects pile A, B, C as a representative to discuss, the pile shown in Figure 5. Ⅰ区 Ⅱ区 Ⅲ区 Ⅱ区 Ⅰ区 桩A 桩B 桩C 桩C 桩B 桩A Figure 5: Representative piles and rock zoning map SIMULATION RESULTS AND ANALYSIS Vertical surface subsidence First, shield tunnel surrounding soil disturbed by shield construction, they formed excess pore water pressure zone around the tunnel. When the shield construction leave the formation, pore water pressure around the tunnel will drop due to the surface stress of the soil released, pore water discharge, causing ground deformation, the nearer tunnel hole axis the impact is Vol. 18 [2013], Bund. W 5398 greater. Second, it causes secondary disturbance to the soil because of the tunnel support and unconsolidated sediments have a long time, so the vertical settlement of the completed support to be slightly larger than tunnel excavation. Third, due to there are being piles and beams, the overall vertical deposition of surface decreases, in a pile position the influence is more significant, and the vertical and horizontal lifting beam can significantly protect soil subjected to secondary perturbations. When tunnel construction, pile-soil deformation of pile C is close to symmetric in zone III, soil bear the upward side friction by piles, so preventing soil subsidence, and the closer to piles the impact is more obvious, so the vertical displacement of the surface soil has decreased when there are piles compared to no piles, the largest deformation is 5mm. Pile-soil deformation of pile B is asymmetric in zone II, resulting the friction that at the side adjacent hole shaft of pile decreases, making the soil load of pile lateral decreases, the upper soil layer bear upward friction load, so pile is able to prevent soil settlement here. Comparing to no piles the vertical displacement of the surface soil layer in the zone II decreases slightly. Because at the piles the impact to soil is the greatest, there will be a sudden reduction of vertical displacement at that places. As region I relatively far away from the axis of the tunnel hole, so stratigraphic vertical subsidence caused by tunnel excavation is small in zone I, and pile A is short, it cannot guarantee a good supporting force to prevent the formation of the settlement of soil, and it may settle with stratigraphic settlement. Formation of the region I subsidence decreases the minimum amount. Tunnel shield construction will lead to uneven soil settlement, and increase the rail irregularity; also it will impact safety of the railway. Figure 6: Cloud images of vertical displacement after subway built Vol. 18 [2013], Bund. W 5399 Figure 7: Vertical subsidence before vertical and horizontal lifting beam built Figure 8: Vertical subsidence after vertical and horizontal lifting beam built Surface horizontal displacement Horizontal displacement of the surface is the surface tension and compression, and it is great damage for the rail even affect the rail irregularity.

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