Strength Criteria on Grouting Agents for Hard Rock- Laboratory studies performed on gelling liquid and cementitious grout

Licentiate thesis, 2006

Grouting is usually successful in excavations at moderate depths and groundwater inflow. At great depths, in post-grouting or in rock with a large inflow of water, grouting is more problematic due to the forces from groundwater. The thesis aims to increase the understanding of the groundwater forces that act on grouting agents in rock and characterisation of the required grout strength to withstand the forces. The outcome is a better understanding of the strength demands, thus providing an opportunity to perform more successful grouting. The strength of a gelling liquid for grouting in hard rock, silica sol, has been investigated. The strength of silica sol increases over a long time and the rate is depending on the humidity. In low humidities, silica sol shrinks but immersed in water, no shrinkage occurs. Further, a new robust method for determining the yield stress of cementitious grout in the field, termed the Yield stick, was developed. The method consists of a stick that sinks into the grout and the yield strength of the grout is determined by the sink depth. Good agreement was found between the Yield stick and reference tests made with rheometer. A study of the erosion process was performed where a Bingham fluid was injected into a pipe with flowing water. The study showed that the most important factor for the erosion process was the flow regime of water. To relate the conclusions with field conditions, grouting should always be done with shear strength of the grout that is higher than the shear stress from water, the grouting time should be sufficiently long and the grouting pressure should be resolute.