BGS Civils: excavatability

BGS Civils: excavatability sample.
BGS Civils: excavatability coverage.
Selby Bypass cutting: mechanical excavation of a fine soil.
Scale 1:50 000
Coverage Great Britain
Format

GIS line and polygon data. (ESRI, MapInfo, others available by request.)

Price

Product 1: BGS Civils bundle (all 8 layers)

£0.50 per km2

Product 2: BGS Civils individual layers

£0.30 per km2

Product 3: BGS Civils web viewer (subscription service)

£500 per layer for the first layer. £100 for each additional layers.

Or, £1000 for all 8 layers.

BGS Civils comprises 8 layers: bulking volume, corrosivity (ferrous), discontinuities, engineered fill, excavatability, strength, sulfate/sulfide, foundation conditions.

All products are subject to number of users, licence fee and data preparation fee.

Downloads

This theme provides information on the excavatability of geological deposits at surface. The values supplied are the indicative minimum, maximum and typical values we would normally expect to encounter per geological unit but limited to the top 2–3 m.

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, archive data of engineering soil strength from the National Geotechnical Properties Database coupled with the Soil Parent Material Map and displayed via dictionaries of 'excavatability classes'.

Excavations are dug for a range of civil engineering purposes including cuttings, borrow pits and quarries. Typically excavations to 2–3 m are for foundations, utilities infrastructure, cellar construction, grading and burial pits.

What is excavatability?

Excavatability is a measure of how easy it is to remove earth materials and is used to determine appropriate excavation methods. It is a function of the geotechnical properties of the material (strength or density) and mass characteristics, in particular mechanical discontinuities.

The stronger the material, the more difficult it is to penetrate, break and consequently remove. However, mechanical weaknesses, in particular discontinuities, are exploited to aid excavation. A very strong rock may be readily excavatable if it has closely spaced discontinuities while a moderately strong rock with widely spaced discontinuities may require greater effort to excavate.

Additional factors that may affect excavatability include the maximum depth of penetration, bulk density, bulking volume and susceptibility to running (flow).

Definition

The description and classification of excavatability depends on the type of deposit. In engineering geology, earth materials are split into two groups: soils and rocks.

Soil

Soil is an aggregate of mineral grains or organic material that can be separated by gentle means such as agitation in water. Soil behaviour is determined by the particulate nature, specifically the particle size, shape and mineralogy, and water content and material density. The mass properties of a soil are largely influenced by its material characteristics. The principal soil types are clay, silt (fine soils), sand, gravel (coarse soils), cobble and boulder (very coarse soils). Whether the soil is classified principally as fine or coarse is dependent upon the behaviour of the material. Discontinuities affect the mass strength of some soils, primarily clay and silt.

Rock

Rock is an aggregation of minerals connected by strong and permanent forces. The behaviour of the rock material depends on the material characteristics. The behaviour of the rock mass depends on a combination of the material characteristics and the discontinuities including spacing, roughness, persistence, filling, orientation and the number of sets.

Classification

The categorisation of excavatability is based on strength data collated for geological formations as identified in the BGS lexicon and rock classification scheme (LEX-RCS). The strength data is derived from the BGS Civils: strength dataset and is derived from the British Standards Institute (1999) code of practice for site investigation (amended in 2003 and 2009). The classification has been further subdivided to account for regional/lateral geological variation where sufficient data exists. The degree of weathering of the geological unit has also been incorporated where possible. This dataset will be updated to include the new BGS Civils: discontinuities information during 2015.

Contact

Contact Digital Data for more information.

Hutton field: well correlation diagram.