Demand-Assessed Grouting—Hydrogeologically Based Methodology

Rock tunnel projects in Sweden always have an environmental demand linked to the acceptable effect on the groundwater level. In order to keep the impact from tunneling acceptable, continuous pre-grouting is usually practiced. However, the benefits of grouting measures vary along a tunnel and with it the need for grouting. This article presents a structured methodology that can be used to evaluate and identify preferential areas for grouting, and the results of its applications to existing projects. The methodology is based on a hydrogeological area description, combined with an analysis of the groutability of the fracture system and environmental demands to estimate the grouting demand along the tunnel. For low-permeable areas with low environmental demands, no grouting is needed. This is referred to as demand-assessed grouting. This paper presents an evaluation of four Scandinavian tunnels and the result indicates that continuous pre-grouting is only needed along 15-30% of the tunnel stretches. This indicates that substantial time and cost savings can be achieved by applying the methodology.