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| '''Sliding criterion (Discontinuity)'''
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| The '''sliding criterion''' is a tool to estimate easily the [[Shear strength (Discontinuity)|shear strength]] properties of a [[Discontinuity (Geotechnical engineering)|discontinuity]] in a [[Rock (geology)|rock]] mass based on visual and tactile (i.e. by feeling) characterization of the [[Discontinuity (Geotechnical engineering)|discontinuity]].<ref name=HackPrice1995/><ref name=Hack1998/><ref name=HackPriceRengers/><ref name=Price2008/> The shear strength of a discontinuity is important in, for example, [[tunnel]], [[Foundation (engineering)|foundation]], or [[Slope stability analysis|slope]] engineering, but also stability of [[Slope stability|natural slopes]] is often governed by the shear strength along discontinuities.
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| The ''sliding-angle'' is based on the ease with which a block of rock material can move over a discontinuity and hence is comparable to the ''tilt-angle'' as determined with the [[Tilt test (Geotechnical engineering)|''tilt test'']] but on a larger scale. The ''sliding criterion'' has been developed for stresses that would occur in slopes between 2 and 25 m, hence, in the order of maximum 0.6 MPa. The ''sliding criterion'' is based on back analyses of slope instability and earlier work of [[ISRM]]<ref name=ISRMbluebook/> and Laubscher.<ref name=Laubscher/> The ''sliding criterion'' is part of the [[Slope Stability Probability Classification]] (SSPC)<ref name=HackPriceRengers/> system for slope stability analyses.
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| {| align="right" class="wikitable" style="text-align:left" width="30%"
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| |+ Table 1. Discontinuity characterization & factors.
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| | colspan="3" style="border-top: 3px solid red" | characterization
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| ! scope="col" align="center" style="border-top: 3px solid red"| factor
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| |-
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| | rowspan="5" style="border-top: 3px solid red" | Roughness large scale (''Rl'')
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| | colspan="2" style="border-top: 3px solid red" |wavy
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| |align="center" style="border-top: 3px solid red"| 1.00
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| |-
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| | colspan="2" |slightly wavy
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| |align="center"| 0.95
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| |-
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| | colspan="2" |curved
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| |align="center"| 0.85
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| |-
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| | colspan="2" |slightly curved
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| |align="center"| 0.80
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| |-
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| | colspan="2" |straight
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| |align="center"| 0.75
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| |-
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| | rowspan="9" style="border-top: 3px solid red" | Roughness small scale (''Rs'')
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| | colspan="2" style="border-top: 3px solid red" |rough stepped/irregular
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| |align="center" style="border-top: 3px solid red" | 0.95
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| |-
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| | colspan="2" |smooth stepped
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| |align="center"| 0.90
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| |-
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| | colspan="2" |polished stepped
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| |align="center"| 0.85
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| |-
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| | colspan="2" |rough undulating
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| |align="center"| 0.80
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| |-
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| | colspan="2" |smooth undulating
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| |align="center"| 0.75
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| |-
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| | colspan="2" |polished undulating
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| |align="center"| 0.70
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| |-
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| | colspan="2" |rough planar
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| |align="center"| 0.65
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| |-
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| | colspan="2" |smooth planar
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| |align="center"| 0.60
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| |-
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| | colspan="2" |polished planar
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| |align="center"| 0.55
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| |-
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| | rowspan="11" style="border-top: 3px solid red" | Infill material (''Im'')
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| | colspan="2" style="border-top: 3px solid red" |cemented/cemented infill
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| |align="center" style="border-top: 3px solid red" | 1.07
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| |-
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| | colspan="2" |no infill - surface staining only
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| |align="center"| 1.00
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| |-
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| | rowspan="3" | non-softening & sheared material, e.g. free of clay, talc
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| | coarse
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| |align="center"| 0.95
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| |-
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| | medium
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| |align="center"| 0.90
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| |-
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| | fine
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| |align="center"| 0.85
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| |-
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| | rowspan="3" | softening & soft-sheared material, e.g. clay, talc
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| | coarse
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| |align="center"| 0.75
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| |-
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| | medium
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| |align="center"| 0.65
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| |-
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| | fine
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| |align="center"| 0.55
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| |-
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| | colspan="2" |gouge < irregularities
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| |align="center"| 0.42
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| |-
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| | colspan="2" |gouge > irregularities
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| |align="center"| 0.17
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| |-
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| | colspan="2" |flowing material
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| |align="center"| 0.05
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| |-
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| | rowspan="2" style="border-top: 3px solid red" | Karst (''Ka'')
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| | colspan="2" style="border-top: 3px solid red" | none
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| |align="center" style="border-top: 3px solid red" | 1.00
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| |-
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| | colspan="2" |karst
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| |align="center"| 0.92
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| |}
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| ==Sliding-angle==
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| The '''sliding-angle''' is calculated as follows:
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| ::<math>''sliding-angle'' =\frac{Rl * Rs * Im * Ka}{0.0113}</math>
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| ::''sliding-angle'' in degrees
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| ::''Rl'' = roughness large scale
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| ::''Rs'' = roughness small scale
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| ::''Im'' = infill material in the discontinuity
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| ::''Ka'' = karst; presence of karst (solution) features along the discontinuity
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| (The values for the parameters are listed in table 1 and explained below)
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| [[File:SlidingcriterionRl.jpg|right|thumb|Figure 1. Large scale example roughness graphs.]]
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| ===Roughness large scale (''Rl'')===
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| The roughness large scale (''Rl'') is based on visual comparison of the trace (with a length of about 1 m) or surface (with an area of about 1 x 1 m<sup>2</sup> of a [[Discontinuity (Geotechnical engineering)|discontinuity]] with the example graphs in figure 1. This results in a descriptive term: ''wavy, slightly wavy, curved, slightly curved'', or ''straight''. The corresponding factor for ''Rl'' is listed in table 1.<br />
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| The ''roughness large scale (Rl)'' contributes only to the friction along the discontinuity when the walls on both sides of the discontinuity are fitting, i.e. the [[Asperity (Geotechnical engineering)|asperities]] on both discontinuity walls match. If the discontinuity is non-fitting, the factor ''Rl'' = 0.75.
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| [[File:SlidingcriterionRs.jpg|right|thumb|Figure 2. Small scale example roughness graphs.]]
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| ===Roughness small scale (''Rs'')===
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| The roughness small scale (''Rs'') is established visually and tactile (by feeling).
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| The first term ''rough'', ''smooth'', or ''polished'' is established by feeling the surface of the [[Discontinuity (Geotechnical engineering)|discontinuity]]; ''rough'' hurts when fingers are moved over the surface with some (little) force, ''smooth'' feels that there is resistance to the fingers, while ''polished'' gives a feeling about similar to the surface of glass.<br />
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| The second term is established visually. The trace (with a length of about 0.2 m) or surface (with an area of about 0.2 x 0.2 m<sup>2</sup> of a [[Discontinuity (Geotechnical engineering)|discontinuity]] is compared with the example graphs in figure 2; this gives ''stepped'', ''undulating'', or ''planar''. The two terms of visual and tactile give a combined term and the corresponding factor is listed in table 1.<br />
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| The visual part of the ''roughness small scale (Rs)'' contributes only to the friction along the discontinuity if the walls on both sides of the discontinuity are ''fitting'', i.e. the [[Asperity (Geotechnical engineering)|asperities]] on both discontinuity walls match. If the discontinuity is non-fitting, the visual part of the ''roughness small scale (Rs)'' should be taken as ''planar'' for the calculation of the ''sliding-angle'', and hence, the ''roughness small scale (Rs)'' can be only ''rough planar, smooth planar, or polished planar''.
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| ===Infill in discontinuity (''Im'')===
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| Infill material in a discontinuity has often a marked influence on the shear characteristics. The different options for infill material are listed in table 1, and below follows a short explanation for each option.
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| ====Cemented discontinuity or cemented infill====
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| A ''cemented discontinuity'' or a ''discontinuity with cemented infill'' has higher shear strength than a non-cemented discontinuity if the cement or cemented infill is bonded to ''both'' discontinuity walls. Note that cement and cement bounds that are stronger than the surrounding intact rock ceases the discontinuity to be a mechanical plane of weakness, and, hence, the 'sliding-angle' has no validity.
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| ====No infill====
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| ''No infill'' describes a discontinuity that may have coated walls but no other infill.
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| ====Non-softening infill====
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| ''Non-softening'' infill material is material that does not change in shear characteristics under the influence of water nor under the influence of shear displacement. The material may break but no greasing effect will occur. The material particles can roll but this is considered to be of minor influence because, after small displacements, the material particles generally will still be very angular. This is further sub-divided in ''coarse'', ''medium'', and ''fine'' for the size of the grains in the infill material or the size of the grains or minerals in the discontinuity wall. The larger of the two should be used for the description. The thickness of the infill can be very thin, sometimes not more than a dust coating.
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| ====Softening infill====
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| Softening infill material will under the influence of water or displacements, attain in lower shear strength and will act as a lubricating agent.
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| This is further sub-divided in ''coarse'', ''medium'', and ''fine'' for the size of the grains in the infill material or the size of the grains or minerals in the discontinuity wall. The larger of the two should be used for the description. The thickness of the infill can be very thin, sometimes not more than a dust coating.
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| ====Gouge infill====
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| Gouge infill means a relatively thick and continuous layer of infill material, mainly consisting of clay but may contain rock fragments. The clay material surrounds the rock fragments in the clay completely or partly, so that these are not in contact with both discontinuity walls. A sub-division is made between ''less thick'' and ''thicker'' than the amplitude of the roughness of the discontinuity walls. If the thickness is less than the amplitude of the roughness, the shear strength will be influenced by the wall material and the discontinuity walls will be in contact after a certain displacement. If the infill is thicker than the amplitude, the friction of the discontinuity is fully governed by the infill.
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| ====Flowing material infill====
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| Very weak and not compacted infill in discontinuities flows out of the discontinuities under its own weight or as a consequence of a very small trigger force (such as water pressure, vibrations due to traffic or the excavation process, etc.).
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| ===Karst (''Ka'')===
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| The presence of solution ([[karst]]) features along the discontinuity.
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| ==See also==
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| * [[Discontinuity (Geotechnical engineering)]]
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| * [[Shear strength (Discontinuity)]]
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| * [[Slope stability probability classification]] ([[Slope stability probability classification|SSPC]])
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| * [[Tilt test (Geotechnical engineering)]]
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| == References ==
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| <references>
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| <ref name=HackPrice1995>{{Cite conference | last1 = Hack | first1 = H.R.G.K. | last2 = Price | first2 = D.G. | title = Determination of discontinuity friction by rock mass classification | booktitle = Proceedings 8th International Society for Rock Mechanics ([[ISRM]]) congress | volume = 3 | place = Tokyo, Japan | date = September 25–29, 1995 | editor1-last= Fujii |editor1-first= T. | publisher = Balkema, Rotterdam, [[Taylor & Francis]] | pages = 23-27 | ISBN = 978-90-5410-576-3 | url = http://www.xs4all.nl/~hack/WORKHack/Publications/1995%20Japan/Japan1995.pdf }}</ref>
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| <ref name=Hack1998>{{Cite book | last1 = Hack |first1 = R. | year = 1996 1998 | title = Slope Stability Probability Classification (SSPC) | publisher = [[Technical University Delft]] & [[Twente University]] - International Institute for Aerospace Survey and Earth Sciences ([[ITC Enschede]]), Netherlands | series = ITC publication 43 | ISBN = 90-6164-154-3 | page = 258 | url = http://www.itc.nl/library/papers_1996/general/hack_slo.pdf }}</ref>
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| <ref name=HackPriceRengers>{{Cite journal |last1 = Hack |first1 = R. | last2 = Price |first2 = D. |last3 = Rengers |first3 = N. | year = 2003 | title = A new approach to rock slope stability – a probability classification (SSPC) |journal = Bulletin of Engineering Geology and the Environment | volume = 62 | number = 2 | pages = 167–184 | doi = 10.1007/s10064-002-0155-4 }}</ref>
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| <ref name=ISRMbluebook>{{Cite book | last1 = [[ISRM]] | year = 2007 | title = The Blue Book - The Complete ISRM Suggested Methods for Rock Characterization, Testing and Monitoring: 1974-2006 | editor1-last = Ulusay | editor1-first = R. | editor2-last = Hudson | editor2-first = J.A.
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| | publisher = [[ISRM]] & ISRM Turkish National Group | place = Ankara | ISBN = 978-975-93675-4-1 | page = 628 | url = http://www.isrm.net/gca/index.php?id=935 }}</ref>
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| <ref name=Laubscher>{{Cite journal | last1 = Laubscher |first1 = D.H. | year = 1990 | title = A geomechanics classification system for rating of rock mass in mine design | journal = Journal South African Institute of Mining and Metallurgy | volume = 90 | number = 10 | pages = 257–273
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| | ISSN = 0038-223X }}</ref>
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| <ref name=Price2008>{{Cite book | last1 = Price | first1 = D.G. | editor1-last = De Freitas | editor1-first = M.H. | year = 2008 | title = Engineering Geology: Principles and Practice | publisher = [[Springer Science+Business Media|Springer]] | page = 450 | ISBN = 3-540-29249-7 }}</ref>
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| </references>
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| ==Further reading==
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| * {{Cite journal | last1 = Andrade |first1 = P.S. | last2 = Saraiva |first2 = A.A. | year = 2008 | title = Estimating the joint roughness coefficient of discontinuities found in metamorphic rocks | journal = Bulletin of Engineering Geology and the Environment | volume = 67 | number = 3 | pages = 425–434 | doi = 10.1007/s10064-008-0151-4 }}
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| * {{Cite journal |last1= Filipello |first1= A. |last2= Giuliani |first2= A. |last3= Mandrone |first3= G. |year= 2010 |title= Rock Slopes Failure Susceptibility Analysis: From Remote Sensing Measurements to Geographic Information System Raster Modules |journal= American Journal of Environmental Sciences |volume= 6 |number= 6 |pages= 489–494 |doi= 10.3844/ajessp.2010.489.494 }}
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| * {{Cite book |first1 = Geertsema | last1 = A.J. |year = 2003 |title = The shear strength of rock joints with special reference to dam foundations; PhD Dissertation | publisher = Faculty of Natural and Agricultural Sciences, School of Physical Sciences, Department of Geology, University of Pretoria, South Africa |urn= etd-09252008-170958 |url= http://upetd.up.ac.za/thesis/available/etd-09252008-170958/ }}
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| * {{Cite conference|last1= Huisman |first1= M. |last2= Hack |first2= H.R.G.K. |last3= Nieuwenhuis |first3= J.D. |year= 2004 |title= Observed rock mass degradation and resulting slope instability |booktitle= Rock Engineering – Theory and Practice. EUROCK 2004 & 53rd Geomechanics Colloquium |location= Salzburg, Austria |editor1-last= Schubert |editor1-first= W.| publisher= Verlag Glückauf, Essen, Germany |page= 449-452 |ISBN= 3-7739-5995-8 }}
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| [[Category:Geotechnical engineering]]
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| [[Category:Mining engineering]]
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| [[Category:Rock mass classification]]
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| [[Category:Rocks]]
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| [[Category:Tunnels]]
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