A new approach for compensation grouting in highly permeable gravel

The Oberau Tunnel is located in southern Bavaria near Garmisch-Partenkirchen. A sector of the tunnel crosses the highly permeable gravel of the Giessenbach Valley. The shotcrete driving of the two tunnel tubes is carried out in this area with only a small overburden under settlement-sensitive buildings. In order to reduce the expected settlements of several centimetres to a tolerable level, compensation grouting was carried out underneath the buildings. This paper deals with the problem of compensation grouting in coarse-grained soils and presents a concept of compensation grouting, which was successfully applied in the highly permeable gravel of the Giessenbach Valley. In addition to the findings from the compensation grouting on a test field, the uplift of a 6000 m(2) industrial hall is shown. The successful execution of the compensation grouting could be demonstrated on the basis of geotechnical deformation measurements in the subsurface, real-time measurements on the structure and the efficiency of the compensation grouting derived from them.