Parameters of the Norwegian Q-system and geological conditions correlated with grout take in the JA1 Skaugum railroad tunnel

Abstract

Since its development in 1974 the Q-system for classifying rock masses has readily been used for dimensioning support measures in underground excavations in Norway and internationally. The Q-system, as it was originally developed, is based on 6 parameters where two and two make up ratios describing degree of fracturing, frictional conditions along joints and stress conditions in the rock mass.

During the past decade there has been an increasing interest in investigating any other fields of application for this classification system, for instance to predict leakage into tunnels and potential grout take.

In this thesis, it is of main interest to see whether or not the Q-value or the system parameter values determined along the trace of the JA1 Skaugum Railroad Tunnel exhibit any correlation to the amount of grout injected into the rock mass to control leakage. Unfortunately, the results of the re-working of data in this thesis cannot support a correlation between the Q-value or its parameters and the grout take. Secondly, it has been of interest to establish any relationship between the amount of injected grout and the geology within this specific section of the Oslo Region. This has given more promising results, as there seems to be a correlation between lithology and grout take, structural geologic variations and grout take, and orientation of the joint sets of the section and grout take. Additionally, there seems to be an indication that competent rocks, such as sand- and limestones have higher grout takes than clay- and nodular limestone shales. There also seems to be an indication that rock masses intercepted by dikes and folded strata have higher grout takes than faulted rock masses and adjacent rock. In addition, joint sets oriented perpendicular to the direction of the minor principal stress, exhibits increased grout take.

The conclusions from this thesis are that lithology, structural geologic features and joint orientations are reflected in the grout take to the tunnel and should be taken into account when a grouting scheme or prognosis is made for new projects. A routine application of Q-parameter values without the correlation with these features is too limited and does not seem fruitful.