Tính Hầm xuyên núi

Thi công hầm theo công nghệ NATM là một công nghệ thi công hầm được dùng hầu như toàn bộ cho các hầm trên Việt Nam hiện nay. công nghệ này được áp dụng lần đầu tiên ở dự án Hầm Hải Vân, và cho đến nay có rất nhiều hầm áp dụng công nghệ này. Bản Thuyết minh tính toán này sẽ cung cấp cho Sinh viên, kỹ sư nắm bắt được cách thức tính toán áp dụng trong công nghệ hầm NATM. Bản tính được thực hiện bằng phương pháp phần tử hữu hạn thông qua phầm mềm MISES

CHƯƠNG - CHAPTER SUPPORT SYSTEM TYPE D1-1 1- Input data 1.1 Tunnel Cross Section D1-PATTERN concrete lining Shotcrete bê tông phun TUNNEL C.L PHASE-2 C.L C.L PHASE-1 C.L S.P.L F.G i=2,0~2,5% 1.2 1.3 Figure 1: Typical cross section of D1 pattern Cross Section of Support System Support System is includings: - Shotcrete with thickness t= 200 mm - Rock bolt D25 L= 4000 mm - Steel Rib H 125x125 mm - Wire mesh 150x150 D mm Construction Sequence Tunnel conruction sequence as below: - Stage 1: Crown excavation ( Upper bench as Figure 2) - Stage 2: Install steel rib, shotcrete, rock bolt for crown Install monitoring equipment, control stress and deformation - Stage 3: Bench excavation ( Lower bench as Figure 2) - Stage 4: Install steel rib, shotcrete, rock bolt for bench Install monitoring equipment, control stress and deformation - Stage 5: Tunnel lining concrete construction (PROFILE D1) C/L 7,45 TUNNEL CENTER 3,3 UPPER BENCH LOWER BENCH 14,9 Figure 2: Cross section of D1 support system 1.4 Materials 1.4.1 Linning concrete: - Compression strength: f'c = - Modulus of elasticity: - Poisson’s ratio - Unit weight 20 MPa E = 24037731 kN/m2 ν= 0.2 γ= 25 kN/m3 1.4.2 Shotcrete: - Compression strength: - Modulus of elasticity: - Poisson’s ratio - Unit weight f'c = 30 MPa E = 29440087 kN/m2 ν= 0.2 γ= 25 kN/m3 1.4.3 Rock: - Modulus of elasticity: - Poisson’s ratio - Unit weight - Angle of friction - Cohesion E = 3162277.7 kN/m2 ν= 0.35 γ= 25 kN/m3 φ= 20 Degree C= 139 kN/m2 1.4.4 Rock bolt: - Modulus of elasticity: E= ν= γ= 2.10E+08 kN/m2 0.25 2.10E+08 kN/m2 - Poisson’s ratio E= ν= - Unit weight γ= 78.5 kN/m3 - Poisson’s ratio - Unit weight 78.5 kN/m3 1.4.5 Steel Rib: - Modulus of elasticity: 2- 0.25 Element model: - Software: Mises3 - Structure of tunnel cross section is calculated by the plane (2D) model (for 1m tunnel length) According NATM theoretical, elastic deformation and plastic deformation rock mass around the tunnel appear in the range of 3-5 diameter of the tunnel Beyond that, stress state and deformation of the surrounding rock is hardly affected by the tunnel construction On that basis, the scope of the surrounding rock to be considered takes into calculation as following: + Top of the tunnel: Thickness of tunnel cover + Bottom of the tunnel: 50m from tunnel center line + Beside of the tunnel: 50m from tunnel center line - By symmetry of tunnel cover, in this model we describe the half of tunnel cross section and the surrounding rock to calculate 3- Stress state and deformation in the tunnel construction (Design load): According construction sequence above, stress state and deformation of support system and surrounding rock in construction stage as following: - Stage 1: Determination of stress formation in the original rock mass - Stage 2: Crown excavation Stress state and deformation of surrounding rock is changed Assuming that 40% of the change of stress state and deformation due to crown excavation (40% load of crown excavation) in the structure without shotcrete - Stage 3: Shotcrete for crown; 60% of the change of stress state and deformation of remaining (60% load of crown excavation) in the structure with shotcrete - Stage 4: Bench excavation Stress state and deformation of surrounding rock is changed Assuming that 40% of the change of stress state and deformation due to bench excavation (40% load of bench excavation) in the structure without shotcrete - Stage 5: Shotcrete for bench; 60% of the change of stress state and deformation of remaining (60% load of crown excavation) in the structure with shotcrete d1-1 - without invert 44.1 Calculation Result of MISES3: Diagram element: 4.4 Deformation: