Vurdering av fjellskråningsstabilitet og sikringstiltak i Dolstad

Abstract

This report starts with a comprehensive review of the theory conserving rock slope stability. This theory will form the foundation for the assessment of the rock slope stability behind a future building in east Mosjøen. The site was poorly documented with very little information from previous studies online. Two field surveys were carried out to assess the slope and identify parameters needed to calculate the risk for rock falls. This report fully documents these findings.

The preliminary investigation shows that the slope should consist of calcite marble. The consequences if there should be a rock fall in the future would be huge as there will be a terrace estate in the middle of the rock fall path. This report concludes that the risk for a rock fall should be decreased through implementation of tensioned rock bolts.

To calculate the risk for rock falls and rock slides several simulations have been performed using the geotechnical software Geo5 – Rock Stability. This report deals with the axis where the biggest change in slope geometry will occur. Through several simulations, the need for rock bolts is well supported and documented. To determine the sensitivity of the analysis all simulations have been performed several times using small subtle differences in the input parameters. The findings show that Rock Stability is very sensitive to the water level in the tension cracks. A downside to the program is that it does not take the same seismic parameters into consideration as the one used for hand-based calculations. A calculation with pen and paper has been performed to confirm the quality of the program and its findings.

The calculations in this report shows that blown and fractured rocks can be used to stabilize the mountain side before the pre tensioned bolts are installed. The calculations also show that the use of bolts with capacity up to 400kN will ensure that the slope meets the governmental standard of a potential risk for rock fall under 0,1% per year.

This report and all its calculations have been performed according to: - Byggteknisk forskrift (from now on called TEK17) - NS-EN 1997-1:2004+A1:2013+NA:2016 (from now on called EC.7) - NS-EN 1998-1:2004+A1:2013+NA:2014 (from now on called EC.8)