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 1 - CHAPTER 1 SUPPORT SYSTEM TYPE D1-1

1- Input data

1.1 Tunnel Cross Section

Figure 1: Typical cross section of D1 pattern

1.2 Cross Section of Support System

Support System is includings:

- Shotcrete with thickness t = 200mm

1.3 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

C.L

C.L PHASE-2 PHASE-1 C.L C.L

F.G

Figure 2: Cross section of D1 support system

+ 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

4- Calculation Result of MISES3: 4.1 Diagram element:

4.2 Construction sequence:

4.3 Stress state:

4.4 Deformation:

d1-1 - with invert

4- Calculation Result of MISES3: 4.1 Diagram element:

4.2 Construction sequence:

4.3 Stress state:

4.4 Deformation: