Hangsicherung Roggwil-Wynau: Stabilisierung eines seit 150 Jahren bekannten Rutschhangs

Stabilization of the long known landslide in Roggwil-Wynau (Switzerland).

Along the new railway line between Bern and Zürich a landslide known for several decades had to be redeveloped because the deformations had exceeded the tolerable level. The cause of the deformations in up to 30 mWS artesian mountain water (up to 75 mWS total pressure level) has been detected by intensive monitoring of water pressure conditions. Previous attempts to stabilize the slope by anchors failed. Re-analyses confirmed the adequate slope stability by reducing the acting pore-water pressure. As a redevelopment measure three 15 m deep drainage shafts were carried out, which have been joined by a micro-tunnel and connected to the main outfall. Afterwards up to 50-m-long horizontal filter wells have been drilled which lead away the mountain water. Through the measure the hydraulic pressure could be lowered by 30 mWS; about 120 l / min are drained permanently. Through the drainage action stress redistribution occurred which caused at the first time an increase in deformation. For about six months after the end of the measure, the slope behaves stable and no significant deformations longer be recorded. The case study illustrates the significant influence of pore water pressure ratio on slope stability and shows that remediation measures are usually only successful in reducing the impacts.