Q-Slope: Rock Slope Engineering 10 Years on

Abstract

The Q-slope method for rock slope engineering provides an empirical means of assessing the stability of rock slopes in the field. It enables geotechnical engineers and engineering geologists to make adjustments to slope angles as ground conditions become apparent during the excavation of reinforcement-free slopes in civil engineering and mining projects. Q-slope was developed by supplementing the Q-system which has been extensively used for 50 years for characterising rock exposures, drill core and tunnels under construction. 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 (O-factor) 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 (strength reduction factor) categories have been developed for slope surface conditions, stress–strength ratios and major discontinuities such as faults, weakness zones or joint swarms. Through over 600 case studies in 36 rock types across 5 continents, a simple relationship between Q-slope and long-term stable slope angles has been established. It includes several failure modes and applies to slopes ranging from less than 5 m to more than 250 m in height. This paper discusses Q-slope application and use for the last 10 years. It presents updated Q-slope stability charts and discusses the time-dependent behaviour of rock slopes.