Minimum steel percent of hydraulic pressure tunnel linings

Conclusions

The lining of the pressure diversion tunnels of the Irganai hydrostation designed by Lengidroprotekt in accordance with type 1-a, representing an invert block reinforced with two rows of mesh and a monolithic part on the remaining perimeter and having a thickness of 50 cm, can be realized with a steel ratioμ=0.15% instead of 0.5% recommended by par. 4.19 of SNiP 2.06.09-84.

• 2. The grounds for departing from the requirements of SNiP under the giver, conditions were an analysis of the engineering-geological conditions of occurrence of the tunnels, static and seepage calculations of the linings, results of model investigations of the linings, use of tunneling machines without the use of drilling and blasting operations, and possibility of performing driving, concreting, and grouting operations with a high quality in the tunnels of the Irganai hydrostation.

• 3. The engineering-geological conditions of using the lightweight type 1-a lining withμ=0.15% should be characterized by homogeneous sedimentary rocks with a Protod'yakonov rock-hardening ratio of 8–10 and modulus of deformation in the mass of more than 11,000 MPa. The rocks should be supported by gunite and rock bolting as the tunnel is being driven before constructing the lining.

• 4. Driving of tunnels with a type 1-a lining should be done full section by a tunneling machine without the use of drilling and blasting.

• 5. It is recommended to reinforce the lining withμ=0.15% with a mesh consisting of 5 Ø 14 A-III main steel and 4 Ø 10 A-II distribution steel. The mesh consists of three parts with 300 mm overlap each. The length of the free lengths of the reinforcement of the invert block should not be less than 400 mm to avoid extreme opening of the working joints.