View source for Q-slope

{{COI|date=November 2021}}

The '''Q-slope''' method for [[rock (geology)|rock]] [[Slope stability|slope]] engineering and rock mass classification is developed by Barton and Bar.<ref name=":0">Barton, N.R.; Bar, N. (2015). "Introducing the Q-slope method and its intended use within civil and mining engineering projects". In Schubert W (ed.), ''Future Development of Rock Mechanics; Proc. ISRM reg. symp. Eurock 2015 & 64th Geomechanics Colloquium, Salzburg 7–10 October 2015''. OGG, pp. 157-162.</ref><ref name=":1">Bar, N.; Barton, N.R. (2016). "Empirical slope design for hard and soft rocks using Q-slope". In ''Proc. 50th US Rock Mechanics / Geomechanics Symposium, Houston 26–29 June 2016''. ARMA, 8p.</ref><ref name=":5">Bar, N.; Barton, N.R. (2017). "The Q-slope Method for Rock Slope Engineering". ''Rock Mechanics & Rock Engineering'', Vol 50, Springer, Vienna, https://doi.org/10.1007/s00603-017-1305-0.</ref> It expresses the quality of the rock mass for [[slope stability]] using the Q-slope value, from which long-term stable, reinforcement-free slope angles can be derived.

The Q-slope value can be determined with:

<math>Q_{slope}= \left ( \frac{RQD}{J_n} \right ) \times {\left ( \frac{J_r}{J_a} \right )_0} \times \left ( \frac{J_{wice}}{SRF_{slope}} \right ) </math>

Q-slope utilizes similar parameters to the [[Q-system (geotechnical engineering)|Q-system]]<ref>Barton, N.R.; Lien, R.; Lunde, J. (1974). "Engineering classification of rock masses for the design of tunnel support". ''Rock Mechanics and rock engineering.'' Vol. 6, Springer-Verlag, pp. 189-236.</ref> which has been used for over 40 years in the design of ground support for [[tunnel]]s and underground excavations. The first four parameters, RQD ([[Core recovery parameters|rock quality designation]]), J<sub>n</sub> (joint set number), J<sub>r</sub> (joint roughness number) and J<sub>a</sub> (joint alteration number) are the same as in the Q-system. However, the [[friction]]al resistance pair J<sub>r</sub> and J<sub>a</sub> can apply, when needed, to individual sides of a potentially unstable wedges. Simply applied orientation factors (<sub>0</sub>), like (J<sub>r</sub>/J<sub>a</sub>)<sub>1</sub>x0.7 for set J<sub>1</sub> and (J<sub>r</sub>/J<sub>a</sub>)<sub>2</sub>x0.9 for set J<sub>2</sub>, provide estimates of overall whole-wedge frictional resistance reduction, if appropriate. The Q-system term J<sub>w</sub> is replaced with J<sub>wice</sub>, and takes into account a wider range of environmental conditions appropriate to rock slopes, which are exposed to the environment indefinitely. The conditions include the extremes of [[Erosion|erosive]] [[rainfall intensity|intense rainfall]], [[frost weathering|ice wedging]], as may seasonally occur at opposite ends of the rock-type and regional spectrum. There are also slope-relevant SRF (strength reduction factor) categories.

Multiplication of these terms results in the Q-slope value, which can range between 0.001 (exceptionally poor) to 1000 (exceptionally good) for different rock masses.
[[File:Q-Slope Stability Chart.jpg|thumb|Q-Slope Stability Chart]]
A simple formula for the steepest slope angle (β), in degrees, not requiring reinforcement or support is given by:

<math>\beta = 20\log_{10}Q_{slope}+65^\circ </math>

Q-slope is intended for use in reinforcement-free site access road cuts, roads or railway cuttings, or individual benches in [[Open-pit mining|open cast mines]]. It is based on over 500 case studies in slopes ranging from 35 to 90 degrees in fresh hard rock slopes as well as weak, [[weathering|weathered]] and [[Saprolite|saprolitic]] rock slopes.<ref name=":0" /><ref name=":1" /><ref name=":5"/><ref>Bar, N.; Barton, N.R.; Ryan, C.A. (2016). "Application of the Q-slope method to highly weathered and saprolitic rocks in Far North Queensland". In Ulusay et al. (eds.), ''Rock Mechanics and Rock Engineering: From the Past to the Future Development of Rock Mechanics;'' Taylor & Francis Group, London, pp. 585-590.</ref> Q-slope has also been applied in slopes with interbedded strata,<ref>Bar, N.; McQuillan, A. (2021). Q-slope application to coal mine stability. ''IOP Conference Series: Earth and Environmental Science,'' 833(1):012043, DOI: 10.1088/1755-1315/833/1/012043</ref> in faulted rocks and fault zones,<ref>Barton, N.R., Bar, N. (2019). The Q-Slope Method for Rock Slope Engineering in Faulted Rocks and Fault Zones. ''Proc. ISRM 14th International Congress of Rock Mechanics,'' Iguassu Falls, Brazil</ref> and in alpine and Arctic environments, which are susceptible to freeze-thaw and ice wedging.<ref>Bar, N.; Barton, N.R. (2020). "Q-Slope addressing ice wedging and freeze-thaw effects in Arctic and Alpine environments". ''Proc. ISRM International Symposium Eurock 2020, Trondheim 14–19 June 2020.''</ref>

Rock slope design techniques have been derived using Q-slope and geophysical survey data, primarily based on V<sub>p</sub> (P-wave velocity).<ref>{{cite journal|last1=Bar|first1=N.|last2=Barton|first2=N.R. (2018) |title=Rock Slope Design using Q-slope and Geophysical Survey Data|journal=Periodica Polytechnica Civil Engineering|year=2018 |doi=10.3311/PPci.12287|doi-access=free}}</ref>

Q-slope has been applied in conjunction with remote sensing (aerial photogrammetry) to assess slope stability in hazardous and 'out-of-reach' natural and excavated slopes.<ref>Bar, N.; Borgatti, L.; Donati, D.; Francioni, M.; Salvini, R.; Ghirotti, M. (2021). Classification of natural and engineered rock slopes using UAV photogrammetry for assessing stability. ''IOP Conference Series: Earth and Environmental Science,'' 833(1):012046. DOI: 10.1088/1755-1315/833/1/012046</ref>

Q-slope is not intended as a substitute for conventional and more detailed slope stability analyses, where these are warranted.

Q-slope has been correlated with other rock mass classifications including BQ,<ref>Song, Y.; Xue, H.; Meng, X. (2019). Evaluation method of slope stability based on the Qslope system and BQ method. ''Bulletin of Engineering Geology and the Environment'', 78(4). DOI: 10.1007/s10064-019-01459-5.</ref> RHRS,<ref>Saito de Paula, M.; Maion, A.V.; Campanha, G.A.C.; Castilho, L.M.N.; Cunha, M.A. (2019). Q-Slope and RHRS for the evaluation of highway rock slopes – Serra do Mar, Brazil. ''Proc. 14th International Congress on Rock Mechanics and Rock Engineering'', Igaussu Falls, Brazil.</ref> and [[Slope mass rating|SMR]].<ref>Jorda-Bordehore, L.; Bar, N.; Cano, M.; Riquelme, A.; Tomas, R. (2018). Stability assessment of rock slopes using empirical approaches: comparison between Slope Mass Rating and Q-Slope.  ''Proc. XIV International Congress on Energy and Mineral Resources. Slope Stability 2018. Seville, Spain.''</ref>

==See also==
* [[Slope failure]]
* [[Rockfall]]
* [[SMR classification]]

== References ==
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[[Category:Rock mechanics]]
[[Category:Slope landforms]]
[[Category:Soil mechanics]]
[[Category:Rock mass classification]]
[[Category:Geotechnical engineering]]