Excavation of underground spaces in large scale infrastructure projects encounters challenges with water ingress. A common method to reduce the water ingress is grouting to limit the zone of influence. Demands on lowering the water ingress are high, which reduces the excavation rate. Research aiming to make the grouting process more efficient is ongoing. One stage in the process is the time between completed grouting and continued excavation. Usually, it is determined that the grout needs to reach a certain shear strength before the excavation is continued. This pause in excavation is often set to five hours, to not mechanically degrade grout during excavation. 

The aim of the work presented in this thesis has been to study the necessary pause in excavation and to study the effective penetration length in a laboratory environment by implementing theories on viscous fingering. Rheometer measurements were done by conducting rheological and mechanical measurements on grout. Rotatory tests and oscillatory tests have been conducted in a Rheometer with different measurement geometries. A modified version of a three interval thixotropy test (3iTT) was used to measure the recovery time of grout, in conjunction with amplitude sweeps to measure shear strength and flow point. The cone and plate geometry were the most appropriate measurement geometry to study the properties early in the curing process. When longer tests were conducted, the plate and plate geometry was more suitable. 

The two predominant mechanical events affecting grout during tunnel excavation were the stress induced by the hydraulic gradient and the vibrations induced by blasting the rock mass. Theories on viscous fingering were implemented, and a mathematical equation was derived to describe the effective penetration length depending on hydraulic gradient. The theory was the region affected by viscous fingering is governed by the difference in pressure gradient of the grout and water. The effective penetration length is the region of grout which has not been affected by viscous fingering. Tests were conducted in a fracture replica in conjunction with rheological measurements to measure the effective penetration length. The results validated the theory, which suggested the flow, viscosity, fracture aperture and hydraulic gradient determines the effective penetration length. 

In addition to the lab tests, two field tests were conducted to investigate the blast’s influence on grout. The transmissivity of the rock mass was determined by water loss measurements. The rock mass was then grouted followed by another water loss measurement. The rock mass was charged and blasted within three hours of curing. Rheological measurements from the lab environment were analysed to mechanically describe the shear stress, shear strain and shear moduli in the grout. Triaxial vibration measurement devices were installed in the surrounding rock mass and a conceptual model was created to interpret vibrations as maximum shear strain. This study concluded grout only experiences high enough shear strain very close to the initiation point of the explosives to begin flowing. The shear strain was sufficiently great to temporarily damage the grout one meter from the detonation point. The temporarily damaged grout was more prone to erosion during the recovery time but later regained its shear strength.