Large Excavation Behavior at Petacalco, Mexico

The pumping sump for the Petacalco, Gro. Power Plant required for its construction an excavation 100 x 87 m plan and 11 m depth. The calculated flow towards the excavation was 370 l/s. Two perimetral systems were proposed to control the inflow water: Cut-off wall or conventional pumping system. After a technical-economical analysis, the first one was selected. Due to construction delays of the cut-off wall and program construction demands, the excavation began simultaneously and advanced faster than the wall. The observed inflow water was ten times lesser than the predicted one, so that the construction of the wall was suspended. The excavation finished using a 6 diameter pump working continuously with a 35 l/s flow. During the excavation randomly thin layers and pockets of peat and organic clay were observed. These materials were not detected in the geotechnical exploration. The flow reduction is attributed to the presence of those materials