Q-slope

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The Q-slope method for rock slope engineering and rock mass classification is developed by Barton and Bar. [1] [2] [3] 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:

Q-slope utilizes similar parameters to the Q-system [4] which has been used for over 40 years in the design of ground support for tunnels and underground excavations. The first four parameters, RQD (rock quality designation), Jn (joint set number), Jr (joint roughness number) and Ja (joint alteration number) are the same as in the Q-system. However, the frictional resistance pair Jr and Ja can apply, when needed, to individual sides of a potentially unstable wedges. Simply applied orientation factors (0), like (Jr/Ja)1x0.7 for set J1 and (Jr/Ja)2x0.9 for set J2, provide estimates of overall whole-wedge frictional resistance reduction, if appropriate. The Q-system term Jw is replaced with Jwice, 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 erosive intense rainfall, 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.

Q-Slope Stability Chart Q-Slope Stability Chart.jpg
Q-Slope Stability Chart

A simple formula for the steepest slope angle (β), in degrees, not requiring reinforcement or support is given by:

Q-slope is intended for use in reinforcement-free site access road cuts, roads or railway cuttings, or individual benches in 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, weathered and saprolitic rock slopes. [1] [2] [3] [5] Q-slope has also been applied in slopes with interbedded strata, [6] in faulted rocks and fault zones, [7] and in alpine and Arctic environments, which are susceptible to freeze-thaw and ice wedging. [8]

Rock slope design techniques have been derived using Q-slope and geophysical survey data, primarily based on Vp (P-wave velocity). [9]

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. [10]

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, [11] RHRS, [12] and SMR. [13]

See also

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References

  1. 1 2 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.
  2. 1 2 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.
  3. 1 2 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.
  4. ↑ 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.
  5. ↑ 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.
  6. ↑ 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
  7. ↑ 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
  8. ↑ 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.
  9. ↑ Bar, N.; Barton, N.R. (2018) (2018). "Rock Slope Design using Q-slope and Geophysical Survey Data". Periodica Polytechnica Civil Engineering. doi: 10.3311/PPci.12287 .{{cite journal}}: CS1 maint: numeric names: authors list (link)
  10. ↑ 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
  11. ↑ 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.
  12. ↑ 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.
  13. ↑ 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.
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