CRACK FORMATION PROCESS IN ARCH DAM FOUNDATION

M. A. KALABEGISHVILI
(Georgia)

This report presents theoretical solution and analysis of stress state and correspondingly seepage process in arch dam tectonic foundation.  Such as demonstrative object is represented Enguri HPP arch dam.

Foundation of Enguri HPP dam (height of 271.5 m) has complex geological structure. The bedrock consists of carbonate rock strata of Lower Cretaceous stage, represented by non-uniform, strongly fissured limestone and dolomite. The rock massif is layered with clayey marl at every 40-50 m of depth, with the thickness of the layers ranging from 3-10 cm to 50 cm. This rock actually screens the seepage flow and strengthens the anisotropy of the foundation. There is a 120 m-deep grout curtain and drainage arranged on the entire perimeter of the gorge, which play a role in the seepage regime in the dam foundation.

In the dam operation period, the seepage pressure significantly increased behind the grout curtain in the central section, and the pressure dynamics can be tracked back as follows: the first peak occurred in 1989, followed by a certain drop, and then a rise again. Therefore the area was assessed as an anomalous one. Since 1999 to date, when the cracks started to fill with mud, the seepage pressure behind the grout curtain has restored to normal regime parameters.

According to general evaluation, processes ongoing behind the grout curtain are linked to the existence of tensile stresses in the tectonic foundation of the dam, potentially followed by opening of the cracks, damaging of the curtain, and then mud filling of the cracks.

In 2006-2007, grout curtain and drainage rehabilitation works were conducted in the frame of a rehabilitation program, which resulted in reduction of seepage discharge in the dam galleries.

This study aimed to evaluate the anomalous seepage and its causes in the central part of the dam foundation. For this purpose, the study consisted of:

- Analysis of foundation’s static stress state and current seepage processes, taking into account the grout curtain behavior, both independently, and together with the drainage, during reservoir filling/emptying (as part of unsteady regime);

- Evaluation of crack development in view of decreased pressures and friction resulting from the crack mud filling process).

The static and seepage analyses have been conducted using a 3D Finite Element Model  of the dam-foundation, whereas crack development was evaluated using 2D models based on fracture mechanics approaches. This report presents some results of the study.

BRIEF DESCRIPTION OF THE COMPUTER PROGRAM FOR THE OPTIMIZATION OF  INTERNAL REGIMES OF HYDRO POWER PLANTS

J. Kilasonia, P. Samsonashvili
(Georgia)

Brief description of the computer program for the Optimization of Internal Regimes of Hydro Power Plants has been given. The program is based on dynamic programming method. Therewith it includes a set of sub-programs that is oriented on analytic solution of simplified variants of regime problems, which gives possibility to control the correctness of solutions with numerical methods.