BGS Civils: discontinuities

BGS Civils is a suite of national maps of engineering properties based on geological data and the digital 1:50 000-scale geological map — BGS Geology 50K.

It comprises eight layers: 

• bulking volume
• corrosivity (ferrous)
• discontinuities
• engineered fill
• excavatability
• foundation conditions
• strength
• sulfate/sulfide

The primary goal of the product is to provide the key engineering characteristics of the geology of Great Britain to professional users who need simple and rapid access to such information. You might be planning pipeline routes avoiding difficult ground conditions, calculating tender costs for trench excavation or you might need knowledge of ground properties in order to plan your daily activities.

The data is provided as GIS shapefiles that are available to licence individually or as a bundle to meet your own requirements.

This dataset

This theme provides information on the discontinuities in bedrock and superficial deposits as part of a suite of GIS layers for different engineering parameters.

The spatial model covers England, Scotland and Wales at 1:50 000 scale and is based upon bedrock and superficial geology from BGS Geology 50K.

Discontinuities within rocks and soils are an important factor in all engineering activities.

What are discontinuities?

For the purposes of this engineering theme in BGS Civils, discontinuities are defined as ‘any break in the continuity of a rock mass that has the potential to have zero or very low tensile strength’.

As such the theme includes all stratification planes (bedding; layering; lamination), all foliation planes (fissility; cleavage; banding) and all fractures (joints; faults; fissures) as defined in BS5930 and ISRM.

It will not include interfaces (other than stratification planes or depositional interfaces) and chemical-solution breaks (such as solution cavities) that are included within the BGS discontinuity classification system. (No further reference shall be made to the BGS discontinuity classification system as it is not considered appropriate for engineering geology applications.)

Classification

The discontinuity parameters proposed for attributing the BGS Civils: discontinuities dataset are:

• stratification planes:
  • lamination
  • bedding
  • layering
• foliation:
  • bedding plane fissility/slaty cleavage
  • lineation/linear schistosity
  • schistose foliation
  • gneissose foliation
• rock mass:
  • massive
  • blocky
  • tabular
  • columnar
  • irregular
• additional discontinuities:
  • fissured
  • sheared
  • sheet/exfoliation joints

As previously stated, not all stratification planes and foliation planes are mechanical discontinuities. However, at the scale proposed, it would not be possible to differentiate between those that are and those that are not. As such, it is proposed that all potential discontinuities within the rock mass be described.