Analysis of the stress state of a pressure tunnel considering nonlinear deformation of the rock massif

Abstract

The presented study is based on the calculation of the “tunnel-surrounding massif”, a unified system taking into account the nonlinear operation of the surrounding massif, where a hyperbolic model of rock material is used. Numerical calculations were carried out on the example of the Aspindza HPP diversion tunnel. The Aspindza HPP hydro node (on the Mtkvari River) includes a diversion tunnel, the operation of which is envisaged in the pressure mode and, together with the equalization reservoir, partially receives a hydraulic shock, taking into account which the pressure from inside the tunnel reaches 25 m. It was accepted that the nonlinearity of the material has a significant impact on the construction and operational stress states of the tunnel. In particular, the influence of nonlinearity reduces extreme stresses in the construction and, accordingly, reveals strength reserves, which allows for optimization of reinforced concrete construction. The horizontal tensile stresses identified by nonlinear calculations in the tunnel bottom cross-section were significantly reduced compared to linear calculations, and when taking into account the phased nature of the tunnel construction (compared to the sudden construction scheme), the tensile stresses were completely eliminated.

The paper presents some results of the calculation of the derivation tunnel for the construction and operation periods, taking into account the nonlinear operation of the surrounding massif.