AXPO - Extension and Optimization of Rüchlig Power Plant, Aarau

Comprehensive Engineering Solutions for Main and Dopant Power Plant Excavation

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As part of the relicensing of the Rüchlig power plant (Aarau), the main power plant was extended by a new group of machines and a new dopant power plant was constructed at the weir.

The excavation pit for the main power plant with a depth of approx. 12.5m (design water level at the top of the excavation pit) consisted of upstream and downstream cofferdams, an island-side overlapped bored pile wall (Ø = 1.3m, single anchored with Rak = 3,200kN in the original design) and sheet pile walls between the cofferdams and the existing power plant building (corner splices on cofferdams 3 or 2-ply). The cofferdams were secured with a layer of Gewi tie rods just above the mean water level.

Prior to this, anchor tests were carried out on vertical test anchors in the low-terrace gravels and in the Malm limestone formations for optimization purposes. The very good results in the Malm limestones with test forces of up to Ppv = 4,000kN for all 3 test anchors allowed optimization of the excavation design.

The excavation pit for the dopant power plant (depth up to 12m, design water level 0.5m below the top of the excavation pit) was constructed directly at the existing weir (built in 1928) and secured with three spillways. The uppermost rim was not allowed to transfer any loads to the weir, which is why an additional anchor layer was arranged. As an additional protective measure, stiffer bored piles were used in the area of the weir abutment instead of sheet piles.

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