ABSTRACT

The concrete faced rockfill (CFR) dam of the Shuibuya Hydropower Project, with the maximum height of 233 m, is up to now the highest CFR dam built in the world. During construction and after completion of the project, however, a group of cracks were discovered on the concrete face slabs, which is the major measure for seepage control of the dam. Though measurements have shown that the cracks would not endanger the safety of the dam, sensitivity analysis is still needed to predict the seepage behavior of the dam in partial or complete deficiency of the face slabs on a coupled hydro-mechanical (HM) basis. In this study, a coupled saturated flow and stress process was considered to investigate the effects of the concrete face slab deficiency on the seepage behavior and safety of the dam. The deformation response of the rockfills is described by using the Duncan-Chang nonlinear elastic E-B model, together with the Desai's thin layer elements for the interface between the face slabs and the buffer material. The coupling effect of stress on hydraulic conductivity of the rockfill is described by the Gangi's model, which is embedded in the code for saturated flow process formulated with an adaptive variational inequality for eliminating the singularity at the outlet seepage points and resultant mesh dependency.

1 INTRODUCTION

The Shuibuya Hydropower Project is the third hydroelectric station constructed on the Qingjiang River, Hubei Province, China, with an installed capacity of 1840 MW. The concrete faced rockfill (CFR) dam of the project is up to now the highest CFR dam in the world, with the maximum height of 233 m. Seepage behavior of the dam and its control is one of the key technological issues on dam safety. In total, 73 monitoring sensors were deployed mainly at 3 cross sections (0+132 m, 0+212 m and 0+356 m) to record the evolutions of deformations, pore water pressures, seepage flow rates, among other relevant variables.

During construction and after completion of the project, however, a large group of cracks were observed on the concrete face slabs, as shown in Figure 1. Since use of the face slabs is the major measure for seepage control of the dam, the seepage behavior may deteriorate by the cracks. Though field measurements show that the cracks would not endanger the safety of the dam, sensitivity analysis is still needed to predict the seepage behavior, deformation and stability of the dam for partial or complete deficiency of the face slabs, as a coupled hydro- mechanical (HM) process.

In this study, a coupled saturated flow and stress process was established based on Biot's consolidation theory to examine the effects of the face slab deficiency on mechanical response and seepage behavior of the dam. The Duncan-Chang nonlinear elastic E-B model (Duncan et al. 1970) and Desai's thin layer elements (Desai et al. 1984) are used to model the deformation characteristics of the rockfills and its interaction with the stiffer concrete face slabs.

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