The Q-slope method was developed to allow geotechnical engineers to assess the stability of excavated rock slopes in the field and make potential adjustments to slope angles as rock mass conditions become visible during construction. Q-slope was developed over the last decade by modifying the Q-system for characterizing rock exposures and drill-core, and estimating single-shell support and reinforcement needs in tunnels, caverns and mining roadways. Assessing slope stability in highly weathered rocks and saprolites (in-situ, soft, friable, weathered rock that retains the original rock's structure but with a lower bulk density) is considered complex since failure mechanisms often involve a combination of shearing and rotational sliding through a weak rock mass, and sliding on relic geologic structures. Q-slope was applied to several highly weathered and saprolitic slopes in Far North Queensland and has shown that a simple correlation exists between Q-slope values and long-term stable and unsupported slope angles.
The original Q-system for characterizing rock exposures, drill core and tunnels under construction was developed from rock tunneling related and rock cavern related case records and has been used by engineers across the world for over 40 years (Barton et al. 1974; Barton & Grimstad 2014). Single-shell B+S(fr) tunnel support and reinforcement design assistance, and open stope design, utilizing Q' (the first four parameters) have also been the principal focus of application in civil and mining engineering.
The Q-slope method (Barton & Bar 2015) is intended for use in reinforcement-free site access road cuts, road or rail cuttings or individual benches in open cast mines. It is not intended for assessing the stability of large slopes developed by several excavation stages over significant periods of time, such as inter-ramp or overall slopes in open cast mines.
Q-slope was developed from case records in six countries, spanning 17 rock types (igneous, sedimentary and metamorphic) and some saprolites for slope heights ranging from 5 m to 30 m.