Foundation System Analysis

4/23/13

The dam site area has a broad river valley; with the valley bottom’s width about 1,100 meters and the valley’s width at the dam crest elevation of 2,300 meters. The dam crest elevation is at 185 meters.

First, a diversion tunnel and coffer dams are used to divert the river flow around the dam site, allowing the river bed to dry completely. The riverbed is then stripped of overburden (usually soil, which is unsuitable for dam construction). The foundation of the dam is now prepared by removing the pockets and seams of weak material and replacing it with ‘dental concrete’, which gets its name because this work is like filling cavities in teeth. Next comes grouting, which involves drilling really deep holes and pumping them full of grout to fill up cracks in the rock foundation and prevent leakage from the reservoir. The foundation rock is now added to the site and compacted to allow for maximum density.

The foundation rock is crystalline, mostly made up of porphyritic granite with uniform lithology (characteristic of the rock) and high strength. This is great for dam construction. The rock is heavily tested to meet the requirements of foundation stability. This is to prevent from sliding and foundation deformation. There is no flat or loose debris interlayer within range of 5 meters below the dam foundation.

An anti-seepage grouting curtain is built in the dam foundation. This reduces the uplift pressure of dam foundation and decreases the seepage from within it. In the long term, this enhances the stability of soft fillings in the structural belt of the bed-rock.

Since the completion of the dam, the monitoring and testing shows that the dam deformation and seepage are within the range of the design’s allowance and the dam is operating safely.

By: Mansoor Sidiqui