Cut-Off Wall Construction of the Bastora Dam: Seepage Solution

While the vast urbanization and increasing demand for water led to the construction of embankments, selecting a suitable site proved challenging. This difficulty arose significantly due to soil type, which contributed to issues with seepage. This paper reports the use of a cut-off wall beneath the Bastora Dam, constructed in 2024, to control seepage. The wall, constructed using plastic concrete, was built to penetrate sandy gravel layers with high permeability coefficients 1×10−5 m/s. The cut-off wall, with a low coefficient of permeability of 8.76 × 10−10 m/s, extended 360 m in length and 1.2 m in width, fully penetrating up to 17.5 m the coarse deposit and reached 1.5 m into an underlying clay/claystone layer to control seepage. Due to its length and the complexity of pouring concrete, the wall was constructed in segments, each 10 m long. For each segment, the soil was excavated to the required depth and then backfilled with plastic concrete. The next 10-m segment was constructed in the same manner. To ensure interaction between the segments, a 4-in. (~10 cm) diameter borehole was drilled to a depth of 17.5 m at the contact point between the two dried segments and then filled with fresh plastic concrete. Additionally, the top part of the wall was embedded 0.9 m into the dam’s core material to enhance interaction and to minimize seepage. Field monitoring of seepage using five piezometers was conducted over a period of seven months immediately after the dam’s construction. Water elevations recorded via the installed piezometers showed consistent water levels (up to 11 cm) during the entire monitoring period, indicating effective seepage control.