Drill parameter analysis in the Løren tunnel : Normalization and interpretation of automatically collected borehole data

Abstract

During the last decades, the Norwegian method of tunneling has been reviewed and continuously updated with the latest information and research results available. Despite the effort of making the practice of tunnel construction as efficient and safe as possible, the analysis of drill response parameters has not yet become a standard in the field. The use of drill parameter response in underground openings and tunnels is a helpful tool in assessing information on structural and mineralogical features. When drilling in hard rock with rotary percussive drilling, the drill data are in most cases automatically collected, but hardly analyzed. In this study drill parameters collected in the Løren tunnel, a road tunnel surrounding central Oslo, Norway, have been normalized and compared to engineering geological mapping collected by on site engineering geologists. The normalization process itself has been evaluated regarding the sensitivity and reliability of the method and the normalized parameters have been put to test. Results show that normalized drill parameters such as penetration rate and torque pressure respond to changing rock conditions, but the sensitivity of the normalization process is high and measures has to be taken in order to use single drill parameters for rock characterization. Also research of the penetration rates dependency to uniaxial compressive strength has been evaluated and a relationship has been found.