Construction of the Angren pressure tunnel

Conclusions

• 1. With the mining method of tunneling in rocks of average toughness it is extremely inexpedient to use auxiliary adits within the contour of the excavation, since this lessens the overall tunneling speed and increases the cost of the operations. Tunneling by the lower-bench method with the use of highly-productive drilling rigs, caterpillar rock-loading machines, and trucks can provide higher tunneling speeds.

• 2. Temporary timbering of the excavation (with the mining method), at first with metal arches with wooden braces and then by a protective concrete roof, with subsequent injection of cement-sand grout behind the temporary lining is a laborious process difficult to mechanize. Therefore, temporary strengthening of the excavation by anchors in combination with spray concreting is preferable.

• 3. Large-scale mechanization of the technological process of constructing the reinforced-concrete lining and dividing wall of a pressure tunnel is progressive and ensures suitably high rates of concreting the reinforced-concrete lining at comparatively low cost. The maximum rate of concreting of 83 m/month is not the limit. To increase this rate it is necessary to enlarge the reinforced block, increase the length of the run to 10 m, use two pneumatic concrete placers for concreting, and use two transporters for dismantling and assembling the formwork.

• 4. Continuous concreting of the lining of a pressure tunnel over its entire cross section proved feasible.

• 5. Pneumatic delivery of the materials for injection to a mobile hopper and simultaneous concreting of the lining and dividing wall, primary injection, testing injection, and stabilizing cementation ensure readiness of a tunnel in the shortest possible time.