Implementation of a 3D Multilaminated Hydromechanical Model for Analysis of an Unlined High Pressure Tunnel

Abstract

In fractured rock masses in the presence of water, modelling of the excavation of an underground opening and of its infilling with water under high pressure needs to take into consideration the interaction between the hydraulic and the mechanical problems as an integrated process.

The purpose of this paper is to report the first stage of the implementation within FLAC ^3D of a coupled hydromechanical model using an iterative procedure between two independent hydraulic and mechanical sub-models. The fracture network of the rock mass is considered using the multilaminated medium concept. The implemented model is illustrated through its application to the hydraulic circuit of the Venda Nova II hydroelectric power scheme, in Portugal [1]. Hydromechanical interaction is of particular relevance in this project, owing to the high water pressures involved and to the fact that the pressure tunnel is unlined.

The paper starts with a short description of the main characteristics of the Venda Nova II hydraulic circuit. The main assumptions and the conceptual model are then presented, namely as regards the geometry of the openings, the mechanical and hydraulic behaviour of the rock mass and the hydromechanical interaction [2]. The main characteristics of the numerical model and the implementation of the hydromechanical interaction mechanisms are described. Finally, some results corresponding to the first infilling of the unlined pressure tunnel are presented.