Development of classification charts for Q index of shale from the parameters

Abstract

Construction of tunnels, slopes, deep basements, foundations and retaining walls are common in shale. Quality of shale can be assessed based on the Q index system. This paper presents the analysis of charts developed for Q index of shale from three different parameters such as block size (RQD/Jn), inter-block shear strength (Jr/Ja) and active stress (Jw/SRF). For the range of values chosen for RQD/Jn, Jr/Ja and Jw/SRF a Q index was estimated and charts were established between Q index and RQD/Jn for various values of Jr/Ja and Jw/ SRF. The charts presented in the paper for Q index can be used to classify the shale. Shale should have minimum Jr/Ja, Jw/SRF and RQD/Jn as 0.5, 0.2 and 10 respectively to be classified as good to very good category.