Model studies of prestress in the rock mass surrounding a tunnel excavation

Abstract

The method for hlgh-pressure grouting the rock surrounding an underground excavation has recently come into increasingly widespread use in hydraulic construction as a means of increasing its bearing capacity. St is assumed that under certain conditions, high injection pressure may lead to the development of prestress not only in the lining itself, but also in the rock mass surrounding it. In a number of cases, this apparently makes it possible to dispense with the massive concrete and reinforced-concrete linings of underground excavations and construct in their place thin smoothinglinings with deep high-pressure rock grouting.Pressurized tunnels have been constructed abroad with the use of this effect, e.g., in the Roselend-Bati tunnel in France, the Festinnyoung tunnel in England, the Capivari-Cachoeira tunnel in Brazil, the Wainberg and Reizach tunnels in the Federal Eepublic of Germany, etc. [1, 2]. Major complex studies of problems associated with the efficiency of high-pressure grouting were conducted in Yugoslavia during construction of the Rama hydroelectric plant [3, 4]. Grouting of the rock surrounding an excavation with the installation of only a thin smoothing jacket was first employed in the USSE during construction of the diversion tunnel for the Inguri plant.No special studies of the process of rock prestress by grouting or its effectiveness were conducted in test passageways during construction of the ~ngurl and Charvak hydroelectric plants~ the only indicator of quality improvement in the rock mass revealed in the investigations was a significant reduction in seepage and an increase in the elastic-resistance fac-There are many examples of study of the prestress condition of concrete linings formed by the pressure injection of grout both in our country and abroad. Examples of the measurement of the prestress state developed directly in the rock mass itself by grouting are lacking, however| i.e., in describing the qualitative possibility of creating a prestress condition in the rock surrounding a tunnel by the injection method, not one of the authors cites quantitative indicators for this condition. Prestressing of the rock forming the unsealed opening around the tunnel lining by the injection of grout under a pressure of 1 MPa into cracks was investigated by the V. V. Kulbyshev Moscow Order of Red Labor Banner Civil Engineering ~nsti-tute. The investigations were conducted on a large-scale three-dimensional model of a tunnel excavation with a lining in a fissured rock mass of average toughness (Fig. i).The model of the structure had an outside diameter of 136 cm and a length of 80 cm and represented a tunnel excavation with a thin nonrelnforced lining with an inside diameter of 50 cm, a thickness of 3 cm, and a fissured rock mass surrounding the lining to a depth of 0.8 the diameter.Since the model makes it possible to examine the effect of grouting at a considerable distance from the lining, a grouting depth of 0.8 of the tunnel diameter, which is the maximum depth recommended for this purpose~ wa...

Use of crack-resistant linings of hydraulic tunnels with consolidation grouting of the rock

“…Prestressing of the rock mass was achieved by grouting under a pressure of 1 MPa to a depth of 0.gD, which after relaxation (during the course of 3 months) amounted to 0.4-0.5 MPa [3]. Prestressing of the rock mass was achieved by grouting under a pressure of 1 MPa to a depth of 0.gD, which after relaxation (during the course of 3 months) amounted to 0.4-0.5 MPa [3].…”