An Integrated Approach to Rock Grouting

Fransson, Ǻ. (Golder Associates and Chalmers University of Technology) | Stille, H. (Geokonsult Stille AB) | El Tani, M. (Rockgro)

OnePetro 

Abstract

Grouting of rock is a trans-disciplinary and trans-stadial topic. It is trans-disciplinary in the sense that grouting involves defining the geological and hydrogeological conditions and what to achieve at a specific site in relation to e.g. decrease in flow and hydraulic conductivity or maintaining ground water levels. Further, the grouting materials to be used to modify and improve the geological and hydrogeological conditions have to be characterised and have properties in line with both rheological and environmental demands. Hydrogeological conditions and grouting material properties in combination with analytical solutions allow estimates of penetration length, thus facilitating grouting design. Grouting is trans-stadial due to its importance in all stages from early planning to long term maintenance. In all stages, hydrogeological conditions and environmental impact are key issues. For the grouting design and construction a step-wise approach based on the observational method including prediction, observation and action is advantageous considering the uncertainties related to hydrogeological conditions and environmental impact. This paper aims at presenting theoretical development using a number of references and case studies to highlight the importance and usefulness of an integrated and theoretically based approach to grouting.

1. Introduction

Sealing of fractured rock using permeation grouting is one way to reduce flow, decrease hydraulic conductivity (i.e. the ability of rock or soil to transmit water) and to maintain groundwater levels. Tunnels and dams are constructions in rock where a reduction in flow can be necessary. Reasons for rock grouting can e.g. be to provide proper function of the construction, maintain water table level, improve working conditions or reduce environmental impact. Damage to buildings can be one consequence if groundwater levels and heads are not maintained. Other possible consequences are loss of energy well efficiency, depletion and dry wells, water shortage for vegetation and settlement of soft soil in urban areas (above a tunnel in rock or due to a tunnel or shaft at a rock-soil interface).

According to Eurocode (1997) verification of the design of the construction works at a site (tunnel, dam, shaft etc) can be based on use of calculations, adoption of prescriptive measures, experimental models and load tests or an observational method. Normally, in rock engineering, adoption of observational method is applied due to related uncertainties. Prediction of actual behavior, which is the base for observational method, should be based on calculation or adoption of prescriptive measures. Adequate theories are prerequisite for calculations.

Fig. 1 suggests a principal flow chart starting with data (and knowledge) related to a site (upper box), resulting in construction drawings (middle box) and finally performance, monitoring and control (lower box). The left (dashed) arrow has its origin in site data and points at construction drawings resulting from a design process based on e.g. adoption of prescriptive measures. The grey, vertical arrow also has its origin in site data but continues with a theoretically based design process that is the main focus of this paper. The design process aims at integrating geology, hydrogeology, rheological behavior of grout and grouting technique and relate to requirements set for a specific site. Requirements can e.g. be formulated as a reduction in flow (hydraulic conductivity) or point at hydraulic heads (groundwater pressure levels) that should be maintained.