Determination of frictional resistance pair Jr/Ja using a friendly – graphical approach in the Q-slope empirical method

Abstract

The Q-slope index is a new geomechanical classification for slope [1] that has become popular and is spreading throughout the world. It is currently being applied in various lithologies, in different countries, mining and civil projects. The Q-slope allows engineers to adjust and optimize slope based on field observations of some geomechanical and geometric parameters that are easy to obtain. The selection of the value of each of the different parameters is made based on tables [2] some of whose parameters are the same as in the tunnel Q index, e.g. roughness (Jr), alteration (Ja), RQD etc. However, if the rock engineering has to analyse many slope with different properties, it is not so intuitive to work with very detailed tables and descriptions. We have therefore based ourselves on the concept of the graphic Geological Strengh Index [3] that uses short descriptions and designs. In this investigation we have selected the two parameters that form the pair of frictional resistance Jr / Ja (joint roughness number and joint alteration number. This Jr / Ja coefficient is very important since it is the multiplied by a correction factor for favorable or unfavorable orientation called O-factor. This O-factor is one of the novelties of the Q-slope compared to the “classic” Q of tunnels. Throughout the investigation we have simplified the descriptions of Jr and Ja (referring the reader to the previous works to know these parameters in grater detail) and created some graphic images that are easy and friendly to implement on site with a multiple choice table.