Abstract
Construction of a dam cut-off wall is one of the most challenging tasks in dam engineering given the deep excavations involved and the complex interactions between stiff cut-off walls and soft surrounding soils. Here, we present innovative solutions for the development of the Karkheh dam’s complementary cut-off wall in southwest Iran which is among the largest structures of this type worldwide with a maximum depth of 115 m. Due to excessive water seepage and high hydraulic gradient following the reservoir impoundment, additional measures were considered among which was the extension of the existing cut-off wall. The main goal was to decrease the hydraulic gradient of the seepage through the dam foundation. The construction of this new wall, which is called as the complementary wall here, was associated with a number of technical challenges among which were: the connection between the new and old walls; trenching and placing of plastic concrete wall through different dam body zones; and slurry loss during trenching through the dam body zones. The complementary wall was constructed successfully producing invaluable engineering experiences including: design of a U-shaped panel as the connecting panel; design of a new method for grouting through uniformly distributed filter/drain materials; and adding cement-based grouts to the cut-off wall panels to prevent slurry loss. The complementary wall helped to decrease both total seepage and the hydraulic gradient; for instance, in the right abutment, total seepage was cut for 25% and the hydraulic gradient was reduced from 0.2 to 0.095.
Highlights
Introduction and geological backgroundWater sealing of the foundations of large dam projects are usually archived by a number of ways including plastic concrete cut-off walls [1, 2], multiple-row grouting curtains [3, 4], and soil-bentonite slurry trench cut-off walls [5]
For the connection region, where the new cut-off wall is connected to the old wall, trenching at depths of up to 115 m was inevitable because the connecting panel had to be executed from the dam crest
Since water seepage from Karkheh dam foundation and abutments were higher than expectation, it was necessary to take remedial measures
Summary
Water sealing of the foundations of large dam projects are usually archived by a number of ways including plastic concrete cut-off walls [1, 2], multiple-row grouting curtains [3,. Excavation of 100-m deep trenches and placing of plastic concrete diaphragm walls as well as the associated complex computer modeling makes the choice of plastic concrete cut-off wall an expensive and challenging choice in dam engineering Such a choice is sometimes unavoidable; especially when the engineer is faced with a highly permeable foundation in a project with a giant reservoir water volume whose failure may endanger the lives of millions of downstream people. The permeability of conglomerate was continuously monitored during the dam construction and first reservoir filling Based on these comprehensive investigations, the average permeability of the conglomerate was estimated in the relatively wide range of (4–9) × 10−4 m/s [8].
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