OR/15/065 Appendix 3 - Discontinuities classification terms and descriptions
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| Entwisle, D, Lee, K A, and Lawley, R S. 2015. User guide for ‘BGS Civils’ - a suite of engineering properties datasets. British Geological Survey Internal Report, OR/15/065. |
Explanation of bedding descriptors (mostly sedimentary rocks)
| Description | Definition (DISCO_1) | Code (DISCO_S) |
| Laminated | Stratification spacing <0.02 m | La |
| Thinly bedded/layered | Stratification spacing 0.02–0.20 m | Bn |
| Medium bedded/layered | Stratification spacing 0.20–0.60 m | Bm |
| Thickly bedded/layered | Stratification spacing 0.6–2.0 m | Bk |
| Very thickly bedded/layered | Stratification spacing >2.0 m | Bv |
| Not bedded | The unit has no bedding/layering, bedding/layering is not persistent, or bedding/layering is inconspicuous. | NB |
| Null | Application of stratification description is not possible or is inappropriate for this unit. |
Explanation of foliation descriptors (for suitable metamorphic rocks)
| Description | Definition (DISCO_F) | Code (DISCO_2) |
| Bedding fissility/ Slaty cleavage | Strongly developed, very closely spaced (mm), highly fissile parallel planes along which the rock can be parted into thin plates indistinguishable from each other in terms of lithological characteristics. May not be persistent throughout unit. | Fs |
| Schistose Foliation | Strongly developed, closely spaced (mm–cm), highly fissile to poorly fissile, parallel and sub-parallel planes. All traces of bedding destroyed. May not be persistent throughout unit. | Sc |
| Gneissose Foliation | Well developed regular alternating bands (cm) of schistose material (highly to poorly fissile) and granofelsic material (unfoliated and unfissile). Foliation is more irregular and discontinuous than schistose foliation. All traces of bedding destroyed. May not be persistent throughout unit. | Gn |
| Not Foliated | The unit has no foliation, foliation is very rare or the foliation is non fissile and imparts no strength anisotropy to the unit. | NF |
| Null | Application of foliation description is not possible or is inappropriate for this unit. |
Explanation of rock mass descriptors
| Description | Definition (DISCO_RM) | Code (DISCO_3) |
| Massive | There are less than three pervasive discontinuity sets and/or the discontinuity sets are widely spaced (>5 m between discontinuities). | Ma |
| Blocky | The rock mass is made up of approximately equidimensional blocks. | Bl |
| Tabular | The rock mass is made up of blocks where one dimension is considerably shorter than other dimensions. | Ta |
| Irregular | The rock mass is made up of fragments which have a wide variation in size and shape. Includes shear and crush zones. | Ir |
| Not a Rock Mass | Rock mass description not applicable to artificial deposits, superficial deposits and very weak bedrock. | NR |
| Null | Application of rock mass description is not possible or is inappropriate for this unit. |
Explanation of additional discontinuity descriptors
| Description | Definition (DISCO_ADD) | Code (DISCO_4) |
| Sheet jointing/ Exfoliation jointing |
A pervasive, surface parallel, joint set may be present and extend up to 1 m below the surface. | Sj |
| Columnar jointing | Layers within the formation may have pervasive columnar jointing producing blocks where one dimension is considerably larger than other dimensions. | Cl |
| Sheared | Low angle fault planes with low residual shear strength may be present. | Sh |
| Fissured | Near surface joints associated with weathering extending from the surface downward may be present. | Fi |
| No additional discontinuities | No additional discontinuity types are known for this unit. | NS |
| Null | Application of additional discontinuity description is not possible or is inappropriate for this unit. |