BGS Civils: foundation conditions - British Geological Survey

Key information

Scale:

1:50 000

Coverage:

Great Britain

Availability:

Licensed

Format:

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

Price:

BGS Civils bundle (all eight layers) £0.53 per km²

BGS Civils individual layers £0.32 per km²

Subject to number of users, licence fee and data preparation fee.

Uses:

Local-level use

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Our free data is available under the Open Government Licence. Please acknowledge reproduced BGS materials.

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Supporting documents

BGS Civils user guide

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:

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, which are available to licence individually, or as a bundle, to meet your own requirements.

BGS Civils: foundation conditions sample. BGS © UKRI.

BGS Civils: foundation conditions coverage. BGS © UKRI – Contains OS data © Crown copyright 2020.

This dataset

This theme provides information on the suitability of a geological material for foundations 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 the Soil Parent Material Model, the National Geotechnical Property Database and BGS Geology 50k dataset. It characterises bedrock and superficial deposits in terms of their engineering properties related to the suitability for foundations.

What are foundation conditions?

The foundation is the interface of some form of construction and the ground. Design of the foundations takes into consideration a number of factors, including the response of the ground to the stresses produced by the construction. The behaviour, or ‘condition’, of the ground may be assessed by in situ and/or laboratory tests during a typical site investigation.

This dataset highlights common factors to consider when planning for a site investigation or land-suitability assessment.

The foundation conditions of rocks and soils are an important consideration for determining how surface construction loads are transmitted into the ground safely and for the lifespan of the project.

The main considerations are:

strength or bearing capacity
settlement (compressibility) and differential settlement
volume change of the ground due to climatic conditions
subsidence due to natural voids beneath the foundation, leading to ground failure

Other considerations include:

weathering and alteration
aggressive ground conditions of soluble sulfate, sulfide, low pH or high chloride content
foundation excavations protection

Classification

The primary classifiers give a qualitative assessment of the likely ground conditions for foundations. This is based on characteristics including bearing capacity (strength), compressibility, rate of consolidation and the variability of the ground conditions for each unit. A special case for construction above mapped coal seams is also given, which is also relevant for units that contain coal seams. In these cases this is one of the subsets.

Condition	Additional hazard considerations
Generally good foundation conditions	Probable volume change (shrink–swell) hazard Sulfate/sulfide might be present Sand or silt might be frost susceptible Possible variable ground conditions (clay and mudstone) Low potential for collapse when loaded and saturated Possible variable ground conditions due to lithological variability Boulders at/just below foundation level might result in differential settlement Possible variable ground conditions near surface due to weathering Possible variable foundation conditions at interface between granite and altered granite Fine-grained head deposits, if present, might contain shear surfaces affecting stability in pits and trenches Possible variable ground conditions due to sand/sandstone lithological variability: excavations might be unstable
Generally good foundation conditions but might be locally moderate or poor	Possible dissolution of gypsum at or near foundation level: collapse breccia and differential settlement might occur Sulfate might be present Voids or infilled voids in limestone might result in differential settlement
Generally good foundation conditions but may be locally variable or poor	Voids or infilled voids in limestone might result in differential settlement Weathered chalk (silt) might be frost susceptible
Generally good foundation conditions but may be locally poor	Coal present at foundation level requires remedial measures assess emissions of dangerous gases might be mined out and backfilled Possible highly compressible ground and variable bearing capacity; possible differential settlement Sand and silt might be frost susceptible Excavations might be unstable
Good to poor foundation conditions	Possible variable compressibility Local low bearing capacity and differential settlement Flooding of alluvium should be considered Might contain shear surfaces Excavation might be unstable Dissolution of gypsum at or near foundation level: collapse breccia and differential settlement might occur Sulfate might be present
Good to very poor foundation conditions	Possible highly variable ground conditions Might contain chemical and physical hazards
Generally unsuitable for most foundation types	Water changes in water levels possible poor foundation conditions beneath water Likely highly compressible ground Possible large and differential settlement and aggressive acidic conditions Excavations might to be unstable
Generally very poor foundation conditions or poor to moderate conditions (where ground is no longer tidal)	Highly compressible ground; possible differential settlement Salt and sulfide might be present Excavation might be unstable
Variable foundation conditions from poor (in dynamic environment) to good (in stable environment)	Possible dynamic environment: deposition and erosion might occur Silt and some sand might be frost susceptible Shells, if present, might crush under load Excavations might be unstable
Generally unsuitable foundation conditions (unless assessed as stable or stabilised by engineering works)	Possible unstable ground (assess for stability) Excavations likely to be unstable
Difficult foundation conditions (due to the presence of boulders)	Boulders where present can obstruct foundations Potential for differential settlement
Foundation conditions unknown because lithologies are unknown	Hazards not known