Calculation tool for hydraulic characterization during grouting design
Paper in proceedings, 2016
An understanding of the fracture aperture distribution facilitates design of grouting measures in crystalline rock masses, this since both the penetrability (ability of grout to enter the fractures) and penetration length is linked to the aperture. This is considered in a design process for rock grouting that has been developed at Chalmers University of Technology. The process suggests that fracture aperture distribution can be estimated based on transmissivity data from hydraulic tests combined with fracture data from boreholes. However, hydraulic tests seldom contain information that can be linked to individual fractures and measurement data need to be further processed using probability distributions. To resemble a rock mass where few fractures dominate the flow Fransson suggested the use of a Pareto distribution and combinatorics to estimate transmissivity of individual fractures.
A freely available computational tool for the statistical analyses based on this concept with Pareto distributed fractures was developed previously. The purpose of the tool is to process field data and create probability distributions that can be used as input to grouting design and approximate tunnel leakage estimates. The methodology has been developed with tunnel data, which sofar has been the main application. For dam and open cut grouting, with higher proportions of surficial rock the validity of the connectivity assumptions may need to be investigated. This paper briefly present the design process and calculation tool in its context using real datasets from a Swedish tunneling project, to provide advice on usage and to give examples of pitfalls in data collection.