The significance of hydraulic jacking for grout consumption during high pressure pre-grouting in Norwegian tunnelling

Pre-grouting is a common measure for reducing water ingress into tunnels. This study has investigated parameters which are expected to have an impact on grout consumption during high pressure pre-grouting of rock mass in Norwegian tunnelling, with special attention to the occurrence of hydraulic jacking of fractures. A significant positive correlation between grout consumption and hydraulic jacking was found, especially when grouting with microfine cement, but it was not established to what extent hydraulic jacking contributes to the total grout consumption. Also, there was found to be a general increase in time consumption for grout holes where hydraulic jacking was indicated. It was concluded that hydraulic jacking does not tend to be a good choice for the economy of the projects, because it involves longer grouting time and higher grout consumption, particularly when using microfine cement.