SYNOPSIS

The paper presents the elastic and elasto-plastic analyses of a gravity dam on jointed rock foundation using distinct element method. The Universal Distinct Element Code (UDEC) is used for carrying out the dam foundation analysis. A concrete gravity dam of 85 m height and 72 m base width is analyzed under loading conditions A and B as per IS-6512 (1984). A total of 26 cases have been analyzed and the behaviour of the dam founded on the jointed rock mass in comparison with the intact rock is studied. It is inferred from the analyses that the presence of joints and joint inclination has a pronounced effect on the stress-deformation response of the dam-foundation system. The deformation of the crest is maximum when the joint inclination is horizontal under loading condition A. Under loading condition B; the crest deformations are maximum when the joint inclinations are between 75° to 105°. The stress-deformation response of the dam on the intact rock and jointed rock is presented in the paper.

1.0 INTRODUCTION

The rapid development of water resources in a country necessitates the construction of dams for water storage, flood control and power generation. The foundation of a dam is a critical structural component and requires special attention throughout the lifetime of the project. The foundation has a threefold function, namely

  • to provide stability,

  • to provide sufficient stiffness for limiting the deformations of the dam-foundation system and

  • to provide control of seepage (ICOLD, 2005). If any one of these functions is satisfied only marginally, the performance of the dam is jeopardized.

The construction of gravity dam requires a foundation of competent rock with high bearing capacity and resistance to percolation as these structures are sensitive to foundation deformations. With more and more ideal sites being exhausted, it is inevitable that less favourable foundations are to be used for dam construction. Proper design involving a complete stress-deformation analysis is required for dams constructed on rock formations exhibiting material non-homogeneity, anisotropy and non-linear behaviour. The presence of foundation weaknesses such as joints, faults and shear seams cause excessive deformations which are inconsistent to the usual assumption of linear elastic and homogeneous nature of the foundation medium. Presence of discontinuous zones substantially affects the distribution of stresses in the dam-foundation and the overall stability of the system. Joint inclinations also have a marked effect on the deformation pattern and the distribution of stresses. For dams on rock foundations, a critical requirement in the stability analysis is the identification of planes of weakness or discontinuities that combine to give a kinematically possible sliding block mechanism. Failure to identify potential blocks may have disastrous consequences, e.g. the Malpasset dam (Londe, 1987). Numerical models, particularly finite element models, are routinely used in the analysis of the global mechanical and hydraulic behaviour of dam-foundation system under normal operating conditions. Discontinuities may be modelled finite element analysis by incorporating special interface elements to simulate the behaviour of joints, shear zones and faults.

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