Abstracts:Pre-excavation rock mass grouting is a common procedure for reducing water ingress into tunnels during construction in Norwegian tunnelling. The level of grouting pressure is a disputed subject and the knowledge of how the rock mass responds to the high pressure and how this inflicts on the grouting results is sparse and little investigated. For this reason, it is of interest to use data from high pressure grouting performed in Norwegian projects to investigate these matters. This paper presents the development of a method for identifying hydraulic jacking during rock mass grouting and the making of an algorithm to perform computerized detection of hydraulic jacking in grouting logs. The algorithm is the base for a larger study, where screening for hydraulic jacking is performed in over hundred grouting rounds, distributed on several Norwegian tunnels excavated in rock mass. The relation between grout flow and grouting pressure has shown to be vital for the understanding of the grouting progress and events occurring during the grouting. Interpretation of pressure and flow as two separate variables, which are affected by aliasing, caused by low and irregular sampling frequency is a challenging task, and it was found to be helpful to create a parameter to represent this relationship, named the PF index (Pressure Flow index). This parameter has also shown to be useful in other applications such as monitoring the grouting progress on site.

Abstracts:A modified Hopkinson pressure bar system with coupled static and dynamic disturbance is used to study the failure characteristics of a granite specimen with a cavity. Different coupled static pre-stress and dynamic loading experiments are conducted. The dynamic failure processes and characteristics of the granite specimen with a cavity under the test conditions are summarised. High speed camera images showed that moderate static pre-stresses of 27 MPa and 36 MPa coupled with moderate dynamic loading of 168 MPa lead to violent rock failure, which is the same as rock-burst. In addition, the coupled static pre-stress and dynamic loading processes are simulated, and the dynamic stress concentration factors (DSCFs) and strain energy density (SED) around the cavity under different coupled loads are investigated. The simulation results show that violent rock failure occurs at a higher DSCF and SED. The experimental and numerical setup used in this study provides useful results for investigating the characteristics of rock failure under coupled static and dynamic stress conditions.