Stressed state of the rock mass during excavation of the underground machine gallery for the Inguri hydroelectric plant: Fid-Bau Portal

Stressed state of the rock mass during excavation of the underground machine gallery for the Inguri hydroelectric plant

Yufin, S. A. / Chincharauli, T. G.

Conclusions These field studies and computations provide the basis for us to draw the following conclusions.The development of deformations over an entire chamber periphery is undesirable, even in cases where its surface is rigidly braced, as has taken place in the underground machine gallery of the Inguri hydroelectric plant. The most vigorous process of strain development (≈80–90% of the total) is observed just during the period when the chamber is being opened. Active strain development with time does not exceed 4–5 months on the average, after which the deformations are stabilized prior to the start of excavation on the next stage of the compartment. The outer face of the softened zone reaches ≈ 1/2 the span of the chamber under favorable geological conditions; beyond the limits of this zone, the rock mass may be considered virtually nondeforming.In avoiding the development of high stresses in the mass surrounding the chamber and, consequently, significant peripheral deformations, the use of any rigid support, or type of reinforced-concrete crown, is not promising. It is expedient to use the bearing capacity of the rock itself by including it in the working scheme by the creation of a semielastic lining with deep-seated stressed anchors whose length exceeds the zone of active deformations.Use of the results of field observations as initial data to determine the stress-strain state of the rock mass surrounding a chamber in computations performed by the finite-element method make it possible to obtain good convergence between the computation results and real deformations of the chamber periphery. This demonstrates the expediency of the broad use of complex studies in designing large-scale underground structures.