Rock Slope Design using Q-slope and Geophysical Survey Data

Abstract

The Q-slope method for rock slope engineering provides an empirical means of assessing the stability of excavated rock slopes in the field. It enables rock engineers and engineering geologists to make potential adjustments to slope angles as rock mass conditions become apparent during the construction of reinforcement-free road or railway cuttings and in open cast mines. Q-slope was developed by supplementing the Q-system which has been extensively used for characterizing rock exposures, drill core and underground mines and tunnels under construction for over 40 years. The Q׳ parameters (RQD, Jn ,
Jr and Ja) have remained unchanged in Q-slope, although a new method for applying Jr /Ja ratios to both sides of a potential wedge is used, with relative orientation weightings for each side. The term Jw has been replaced with the more comprehensive term Jwice , which takes into account long-term exposure to various climatic and environmental conditions such as intense erosive rainfall and ice-wedging effects. SRF categories have been developed for slope surface conditions, stress-strength ratios and major discontinuities such as faults, weakness zones or joint swarms. Through case studies across Europe, Australia, Asia, and Central America, a simple relationship between Q-slope and long-term stable slope angles was established. The Q-slope method is designed such that it suggests stable, maintenance-free, bench face slope angles of, for instance, 40–45°, 60–65° and 80–85° with respective Q-slope values of approximately 0.1, 1.0 and 10. Q-slope has also been found to be compatible with P-wave velocity and acoustic and optical televiewer data obtained from borehole and surface-based geophysical surveys to determine appropriate rock slope angles.