Creep behaviour and remediation concept for a deep‐seated landslide, Navistal, Tyrol, Austria

In the valley of Navis, the village of Kerschbaum with 84 houses stands on a slowly downhill moving, relatively corase grained, aqua bearing earth‐flow/‐slide about 40 m thick. This secondary movement overlies a deep‐seated rock slide. The rates of movement at the surface of the earth‐flow/‐slide were between 1 und 3 cm/a before the implementation of remedial works. Starting from the geotechnical and geomechanical model of the slope, measures were developed, which were intended to reduce the movement. A monitoring system was installed to provide information about the movement and slope water conditions of the earth‐flow/‐slide and the sliding rock mass. In order to estimate the creep behaviour of the earth‐flow/‐slide, the ductility index ILZR was determined from shear tests. A simple flow law was assumed for the estimation of the change of creep rate. Measurements over a period of about 18 months after the first phase of remedial works show rates between 0.5 and 1.2 cm/a. The reduction of the rate of movement is compared with the creep model applied and the viscosity index ILZR to check the validity.