mac beauty powder Subway tunnel support systems Nu

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Subway tunnel support systems Numerical Simulation of

Abstract: CRD engineering methods and the two short-step construction method more commonly used in the construction form and the supporting means carried out by FLAC numerical simulation analysis of different parameters on the tunnel support the stress and displacement fields around the the impact of the plastic zone obtained on the distribution and the relationship between support patterns, and various support methods were compared and analyzed.
Keywords: subway tunnel; FLAC; numerical simulation
1 Introduction Guangzhou Metro is located in the Pearl River Delta region, with varying degrees of soft and hard layer of the tunnel location, its physical comparison of discrete mechanical properties, and rich groundwater. Upper Quaternary strata alternating land and sea and river alluvial deposits such as the artificial soil, including loose fill soil, silt and silty alluvial soil and red soil ~. Fu rock under it to have greater strength and hardness of granite, including the entire weathering zone, strong weathering zone, and the weathering and weathered zone, is characterized by rock hard. In short, the Metro Line section of the geological conditions along the large difference, and some lots in the soft soil layer, while others have lots of soil in a semi-semi-rock formations , and the rock strength is still very great. In this construction of the tunnel formation is difficult, especially in the form of their support to keep the situation under the rock around to adjust. Although the reinforced concrete construction of the role of monitoring and measuring, to measure various parameters of the results of any amendment, but he still followed the preliminary design of the inside of the relevant content and not the real essence of the data based on measurements take reasonable the supporting form, that is basically the entire tunnel on the use of one or two support programs, which obviously does not meet the requirements of varied rock around the tunnel. The main content is the situation for a rock to simulate different forms of the supporting and support parameters, analysis of the displacement and stress field around the tunnel effect, and reasonable support to find a way to meet the subway tunnels on the security and durability requirements. 2 model calculation software 2.1 for a cross-section tunnel, axial impact is negligible, can be seen as a plane strain problem, Select this article as a model calculation program FLAC22D differential analysis software. The program uses Lagrange yen method using node displacement continuity conditions, the large deformation continuum calculation and analysis. Will be calculated in the calculation process is divided into a number of regional grid (cell), each unit in the given boundary conditions follow the specified linear or nonlinear constitutive relation. In solving large deformation,[link widoczny dla zalogowanych], because each time step of the deformation is small, can be approximated by the constitutive relation and a number of small deformation theory and theorems, the last step of the deformation of the superposition of all time, that are the result of large deformation. FLAC offers a variety of plastic material constitutive model, the elastic model, Mohr - Coulomb model, masonry joint model, strain softening and strengthening of other materials for model use empty cells to simulate the underground excavation; have static, dynamic, creep, flow, temperature calculation model, and coupled with each other between the various modes to be used to simulate complex problems in geotechnical and civil engineering . Can simulate the stress field generated, the slope or underground excavation,[link widoczny dla zalogowanych], concrete lining, or the anchor bolt settings, underground seepage. Within the program also set a variety of structural forms, such as rock, soil and other material entities, beams, columns, shells and artificial structures, such as support, lining, bolt, cable, friction piles, sheet piles. Lever beam elements which can be used to simulate the excavation of the pole ground and the concrete tunnel lining project; bolt anchor unit can be fixed, or you can anchor along the length of mortar can also be used to simulate the prestressing cable tension or pressure such as the supporting components. 2.2 Meshing and boundary conditions 2.2.1 calculation conditions and calculation process of calculating an infinite desirable to analyze the experience from the engineering knowledge, away from the tunnel excavation surface at 4 times the diameter of the boundary conditions can be ignored. The simulation of the tunnel diameter of about 7 ~ 10m, so the model length to take 110m, height to take 57m, of which the tunnel depth of about 17m. 2.2.2 rectangular unit by unit, in the tunnel section at the local refinement, divided into 400 × 320 units. 2.2.3 Model boundary conditions on both sides of the boundary conditions for limited horizontal movement of the sliding support, the model boundary conditions at the bottom of the vertical displacement of the slide for a limited support, top model for the free boundary, as shown in Figure 3.1 and Figure 3.2.
Figure 1 Single-hole single parallel tunnel model
Figure 2 span the tunnel model 2.3 model physical and mechanical parameters and yield criterion 2.3.1 selection of mechanical parameters ; in the selection of calculation parameters, geotechnical, rock and experimental rock to be removed between the size effect, it is desirable experimental parameters of the 1 / 10 ~ 1 / 5 as the calculation parameters. 2.3.2 yield criterion to the calculation of the background of Guangzhou Metro Line, on a single hole and single hole single two-lane tunnel were calculated and analyzed in parallel, the construction method using the new Austrian law, lining for the composite lining. For different rock types and different soil materials with different mechanical calculation model. Of Ⅰ, Ⅱ and Ⅲ surrounding rock, mainly by the fill, sand and rock weathering product of the composition of a strong plastic plastic geological materials, prominent nature of soil, in the material reaches the yield limit, can produce large plastic flow. These types of materials used Moerkulun (Mohr2Coulomb) yield criterion to simulate them. 2 1 + sinφ 1 + sinφ fs = σ1-σ3 1-sinφ + 2 c 1-sinφ ft = σ1-σ3 including: σ1, σ3 are the largest minimum principal stress, c is the cohesive strength, \ T if fs <0 the shear failure of material, material yield limit is reached, the constant stress level in the plastic flow. If the tensile stress exceeds the tensile strength of tensile stress that: ft <0, the material tensile breaking occurs. Of Ⅳ and Ⅴ surrounding rock, mainly rock material, the nature of the rock is more obvious strain softening can be used for simulation and analysis criteria. In this criterion, the yield function, potential function, plastic flow rule and the stress correction of a Coulomb criterion with the mole is completely consistent, the only difference is that the cohesive strength, internal friction angle, shear angle and tensile strength up through the After the plastic yield point, the strain softening model appears softened. Support the tunnel using bolt and composite lining, which simulate the bolt with a rod element, composite lining is mainly a concrete, the deformation follows the Moore 2 Coulomb yield criterion. 2. 4 method of calculation and simulation program tunnel surrounding stress field, displacement field and other parameters not only by the geological conditions, bolt, lining and other factors, and also affected by the construction method of the constraints. Therefore, according to tunnel condition in which Sections of the tunnel span, construction methods and the development of support measures adopted by the following calculation and analysis program and the results under different scenarios were compared. (1) rock category Ⅰ and Ⅱ, medium-span, CRD construction method, the use of <42 ahead of the small pipe grouting, length L = 4. 5m, circumferential spacing 0. 35m, the vertical spacing of 3 . 0m; full steel grille ring, spacing, 0. 6m; arch wall WTD25 hollow grouting anchor, length L = 3. 5m, spacing 0. 8 × 0. 6m, diamond-shaped arrangement; full-face single Set steel mesh, specifications Φ8 × Φ8, pitch 150 × 150mm. Lining by the early C20, S6 injection early strength concrete, the thickness of 350mm; secondary lining is built model C25, S8 reinforced concrete, the thickness of 600mm. (2) rock category Ⅰ and Ⅱ, medium-span, CRD construction method, the use of <108 bassoon studio hot rolling seamless steel pipe grouting, pipe wall thickness of 8mm, double layout, from top to bottom row 1000mm, the row spacing of 414mm, the next row spacing 399mm, length of pipe roof 2. 5m, outside Chajiao 1 °. The remaining parameters are the same (1). (3) rock category Ⅰ and Ⅱ, the small span, step construction method, the use of <42 ahead of the small pipe grouting, length L = 4. 5m, circumferential spacing 0. 40m, the vertical spacing of 3 . 0m; full steel grille ring, spacing 1. 0m; arch wall hollow grouting anchor set; single full-face setting steel mesh, size <6. 5 × <6. 5, distance 150 × 150mm. Lining with early C20, S6 injection early strength concrete, the thickness of 350mm; secondary lining is the model built C25, S8 reinforced concrete, the thickness of 600mm. (4) rock category Ⅰ and Ⅱ, the small span, step method applied,[link widoczny dla zalogowanych], the use of hot rolling seamless steel pipe grouting studio bassoon, double layout, from top to bottom row of 800mm,[link widoczny dla zalogowanych], pipe length of 2. 0m. The remaining parameters are the same (3). 3 results selected in the calculation of plastic zone around the tunnel to analyze the stress distribution. Because the calculation does not consider the impact of horizontal loads, so select only the vertical displacement curve of the displacement around the tunnel to see the trend. The calculation results are as follows: 3. 1 of the plastic zone around the tunnel
Program in Figure 1 Distribution of a plastic zone
Option II in Figure 2 Distribution of plastic zone Figure 1 and Figure 2 can be seen: For the span of the tunnel, pipe roof small pipe grouting grouting will make the scope of the plastic zone has been reduced, the force bolt lower end, but the overall shape of plastic zone and the emergence of shear plastic is basically unchanged position. The same time, by comparing Figures 3 and 4, for a small single-hole single-span tunnel, the same will occur with a large span tunnel similar results. Were compared again in Figure 1 and Figure 3 and Figure 2 and Figure
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