Johan Thörn

Fracture Deformation Measurements during Grouting in Hard Rock

When a fracture system in crystalline rock is grouted the rock mass may deform. Such deformations may reduce the grouting efficiency since new flow paths are opened. The work presented here show that deformations occur at hydraulic tests and grouting and that deformation can be measured and evaluated as stiffness from in situ tests. Deformation measurements, hydraulic testing, and grouting was conducted in spring 2010 in the Hallandsas tunnel and hydraulic testing in a service tunnel in Gothenburg (Runslatt and Thorn, 2010). For measuring physical deformation recently developed equipment from Chalmers University of Technology was used. Deformations were measured seven times in the same borehole. Three measurements were during grouting, and the remaining four from water pressure tests. Most deformations occurred at pump pressures of 1-1.4 MPa, which is lower than the calculated normal rock stress. Stiffness has been evaluated in several ways, including a new method, (Fransson, et al., 2010). Generally the evaluated stiffness is lower in the Hallandsas tunnel than in the Gothenburg tunnel. The results show agreement with other in situ experiments.

Statistical Evaluation of Groutability Using Data from Hydraulic Tests and Fracture Mapping Case Studies from Sweden

Sweden has a long history of research within the field of rock fissure grouting in hard crystalline rock mass due to strict environmental requirements regarding allowable ground water draw down. These requirements normally implies that fractures down to aperture size between 50 to 100 μm needs to be sealed and within these ranges the size of the particles for cementitious grouting agents becomes a limiting factor. For a grouting design it is therefore of importance to consider the aperture size distribution of the rock mass in order to predict the groutability for both cementitious and non-cementitious grouting agents. Transmissivity data from hydraulic tests (water pressure tests) and number of fractures along a borehole can be assessed from core logging for further use as input for a statistical interpretation of fracture data to simulate an aperture size distribution. A methodology developed at Chalmers University of Technology in Gothenburg, Sweden, is proposed. The method is a statistical evaluation of groutability (SEG) and is based on the Pareto distribution. A computational design tool has been developed to simplify the use of the statistical evaluation and to make the research more accessible to end users, designers, in the grouting industry. The aim of this article is to present two case studies where the statistical interpretation of fracture data is performed by using the computational design tool and how the outcome can be of great use in finding a more accurate grouting design. The case studies include fracture data sets from two large infrastructure rock tunnel projects in Sweden; a road tunnel in Stockholm and a railroad tunnel in Gothenburg.