Approach for early engineering geological prognosis adapted to rock grouting design

Paper in proceeding, 2013

Planning of suitable water-mitigating measures, such as grouting, can be valuable for feasibility studies of underground construction projects. However, grouting design work becomes more difficult if hydraulic properties of the rock mass are insufficiently investigated and the geological information presented in the engineering geological prognoses mainly focus on stability-related parameters. The purpose of this study has been to demonstrate how geological information useful for grouting design can be compiled in engineering geological prognoses during early phases of tunnel projects. Attention is also given to relating geological settings to grouting design classes during the construction phase. The suggested approach was exemplified for the Hallandsås project, Sweden, using low-cost geological information available during the original feasibility study of the project. The prognosis included a conceptualisation of the hydraulic behaviour of the rock mass at the project site, with hydraulic domains representing the flow regimes found in different geological units. The need for sealing measures along the tunnel alignment was expressed with inflow estimates based on data from the SGU Wells archive. This combination of qualitative and quantitative estimates indicated grouting design prerequisites for both favourable and unfavourable scenarios, which could be useful for grouting design classification during construction. The hydraulic domains facilitate the understanding of the relation between geology and grouting design, which is essential for tunnel construction work.