Current stage of gunite in tunnel construction

Abstract

1. Under present-day conditions Gunite is used widely as a support material of tunnels and chambers of various uses. As applied to underground hydraulic structures, the ways to improve it should be directed mainly to automation of the spraying process (Gunite spray trucks), improvement of the properties of the material (addition of various types of fibers), and combination of gunite coverings with other types of support (ordinary and prestressed’ anchors, rigid and pliant metal arches, reinforcement meshes, sheet reinforcement of perforated casing panels). 2. In hydraulic tunnels-conduits Gunite linings are quite economical, but their use following the mining method of driving should be limited to fractured stable rocks with which the adhesion of Gunite is not less than 8 kgf/cm2 in the absence of tectonic zones with clay interlayers in the rock. The velocity of the water in the tunnels usually should not exceed 10 m/sec. In tunnels driven by tunneling machines the indicated limitations are largely removed. 3. For pressure tunnels with an outside monolithic or sectional lining (including that forced into the rock) it is necessary to conduct extensive investigations of the crack resistance and crack formation of the inside Gunite linings containing fibers of steel or other materials (nylon, glass, etc.) under the effect of various loads. Such linings can apparently be used instead of those made of reinforced concrete or reinforced Gunite, which will greatly reduce labor costs.