Foreword 
Grouting research has been part of the BeFo programme for 30 years and is an important part of Scandinavian rock construction. Carefully executed grouting is a cheaper alternative to sealed lining. Stricter stipulations regarding low ingression levels are pushing up the cost of grouting, making cost calculation more difficult. Grouting largely takes place in conjunction with rock extraction. The lifespan of the grout is affected by the roundwater, possible stress movements, the materials used and the design that is adopted. Many of these factors can be influenced and there is a demand for greater predictability and a better financial outcome for grouting. Grout that fails to harden or flows back could result in erosion of the grout and deterioration in the quality of the work. Strength is linked to groundwater pressure and fan geometry in the grouting design. The threshold for how watertight the rock can be made without lining is being raised constantly. Research in recent years has led to a new type of grout, silica sol, which when used correctly offers excellent functionality. It was introduced onto the Swedish market as a grout for hard rock in 2002 and since then it has been used in several tunnels. The grout is suitable as a complement to traditional cement grouting in order to meet strict water ingression stipulations in tunnels. The aim of this current project is to provide a guide to grouting with silica sol. The guide is aimed at contractors, consultants and clients. The purpose is threefold: to provide a design and implementation tool for industry, to address the problems that could arise and to present measures that can be taken to rectify such problems. The guide summarises the research that has been conducted in this area, in particular at Chalmers University of Technology, as well as the projects in which the University has been involved. The reference group that contributed to the project comprised Gunnar Gustafson, Chalmers University of Technology, Bjarne Liljestrand, STRABAG, Magnus Zetterlund, Vattenfall, Kenneth Rosell, Swedish Transport Administration, Hans-Olov Hognestad, BASF, Inger Jansson, Eka, and Mikael Hellsten, BeFo. 
Stockholm, October 2012 
Per Tengborg