OR/15/065 Data format
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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. |
Field descriptors
The data fields that are common throughout all the dataset are described below. Full class descriptions as they appear in the dataset are provided in the Appendices.
General lithology (GEN_LITH)
This is a simplified geological description of the parent material and is derived from the original DiGMapGB-50 LEX-RCS coding compared with the hierarchical classification of UK geological materials from the BGS RCS system. In general, the aim is to provide the user with a simplified a lithological description as possible.
Lexicon Rock Classification Scheme (LEX_RCS)
This field is the standard DiGMapGB-50 code that describes the geological units found in Great Britain. It provides the starting point for the parent material characterisation. It comprises a Lithostratigraphic code (LEX) and ‘Lithology’ code (RCS).
Nominal Scale (Nom_Scale)
This field describes the notional x-y spatial scale of the data. Most geological map data in the dataset is presented at a scale of 1:50 000. The field identifies a combination of scales used to create the map from the bedrock and superficial map sources. The scales used are shown in Table 1 below.
| Field Value | Meaning |
| 50 | No superficial data is present for this sheet and bedrock data is available at 1:50 000 scale |
| 250 | No superficial data is present for this sheet and bedrock data is available at 1:250 000 scale |
| 625_50 | Superficial data is present for this sheet at a scale of 1:625 000 and Bedrock data is available at a scale of 1:50 000 |
| 50_50 | Superficial data is present for this sheet at a scale of 1:50 000 and Bedrock data is available at a scale of 1:50 000 |
| 35_50 | Superficial data is present for this sheet at a scale of 1:35 000 and Bedrock data is available at a scale of 1:50 000 |
| 35_250 | Superficial data is present for this sheet at a scale of 1:35 000 and Bedrock data is available at a scale of 1:250 000 |
Each dataset then has individual fields describing the specific engineering properties as in Table 2 below:
| Field name | Description |
| EXCAVATABILITY | |
| (STR_TYP_EX) (DEN_TYP_EX) | The mode of equipment required to excavate the typical deposit present (see Appendix 1 - Excavatability classification terms and descriptions for full descriptors). |
| STRENGTH | |
| Strength_Minimum (STR_MIN) | The minimum strength or consistency expected for this unit. Where there is more than one lithology present (heterolithic units) the strength of the weakest lithology is given. This does take into consideration weathering and alteration. |
| Strength_Maximum (STR_MAX) | The maximum strength or consistency expected for this unit. Where there is more than one lithology present (heterolithic unit) the strength of the strongest lithology is given. In general, this will be unweathered material and found at depth. However, in some situations the maximum strength might be where weak rocks or soils are altered and includes calcrete, silcrete and ferricrete. |
| Strength_Typical (STR_TYP) | The typical strength expected of the rock or soil. This is a simplification but provides guidance as to the typical strength and can be taken in relation with the Minimum and Maximum values. For example in a mixed lithology of strong to very strong sandstone with subsidiary weak mudstone, the rock may exhibit predominantly strong characteristics and, therefore, its typical or dominant strength is strong. |
| Density_Minimum (DEN_MIN) | The minimum density expected for this unit, including rocks that are weathered or altered to coarse soil, generally near surface. |
| Density_Maximum (DEN_MAX) | The maximum density expected for this unit, including rocks that are weathered or altered to coarse soil, generally near surface. |
| Density_Typical (DEN_TYP) | The typical density expected of the soil. This is a simplification but provides guidance as to the typical density and can be taken in relation with the Minimum and Maximum values. For example for a soil that is moderately dense to very dense sand and gravel with subsidiary loose sand, the soil may exhibit predominantly moderately dense characteristics and, therefore its typical or dominant density is moderately dense (see Appendix 2 - Strength, consistency and density classification terms and descriptions for full descriptors). |
| DISCONTINUITIES | |
| DISCO_S TEXT | This field describes the minimum and maximum spacing between stratification planes, the dividing planes that separate each layer in a rock or soil from layers below and above it. |
| DISCO_1 TEXT | This field is the code used for DISCO_S |
| DISCO_F TEXT | This field describes the typical foliation or range of foliations likely to be present within the formation. Includes the parallel orientation of platy minerals or mineral banding present in metamorphic rocks, layered structures formed by the separation and/or orientation of minerals in igneous rocks and strongly developed, very closely spaced, bedding fissility which is found in some un-metamorphosed argillaceous rocks (shales). (see Appendix 3 - Discontinuities classification terms and descriptions for full descriptors). |
| DISCO_2 TEXT | This field is the code used for DISCO_F |
| DISCO_RM TEXT | This field describes the overall shape of the blocks that form a rock mass at a metre to decimetre scale. (see Appendix 3 - Discontinuities classification terms and descriptions for full descriptors). |
| DISCO_3 TEXT | This field is the code used for DISCO_RM |
| DISCO_ADD TEXT | This field describes other types of discontinuities that may be present and that are not accounted for by the other three fields. (see Appendix 3 - Discontinuities classification terms and descriptions for full descriptors). |
| DISCO_4 TEXT | This field is the code used for DISCO_ADD |
| BULKING OF SOILS AND ROCKS | |
| Bulking factor class
(BULK_CLASS) |
This is the class or classes of the ‘bulking factor’ and is derived from the original DiGMapGB-50 LEX-RCS coding compared with the hierarchical classification of UK rocks from the BGS RCS system. It relates to lithology type, as described in Table 1 above. |
| Bulking factor values (BULK_FACTR) | This field contains the bulking factor (range or ranges) expected for each LEX-RCS code, as indicated by the bulking class or classes. The range is separated by ‘to’, and where there are two bulking classes the ranges are separated by ‘,’. They are described as primary and secondary factors. (see Appendix 4 - Bulking of soils & rocks classification descriptions for full descriptors). |
| SULFATE AND SULFIDE POTENTIAL | |
| Sulfide class (SUL_CLSS) | The primary and secondary sulfate classifications as used in the GIS are a short alpha-numeric code for GIS purposes. |
| Sulfide description (SUL_DESC) | This field describes the primary and secondary sulfate/sulfide classifications. Full descriptions are given in Appendix 5 - Sulfate/sulfide potential classification descriptions. |
| CORROSIVITY (FERROUS) | |
| Class | The primary classification as used in the GIS is a short alpha-numeric code for GIS purposes. |
| LEGEND | This field provides a brief explanation of the ground conditions |
| RECOMMENDA | This is a description of recommendations and factors to consider in designing or mitigating for potentially corrosive conditions. |
| BACKFILL | This is a description on suitability of material for backfill. |
| SCORE | The total score of all the contributing factors taken into account (pH, moisture conditions, resistivity, redox status and sulphate/sulphide). see Appendix 6 - Corrosivity classification descriptions for full descriptions. |
| USE AS ENGINEERING FILL | |
| Use as engineering fill (FILL_CODE) | This is the code used by BGS to identify a type of ‘use as engineering fill’. It is provided to enable identification of properties of a geological unit and for data management purposes. |
| Use as engineering fill (FILL_TYPE) | This is a description of the broad type of ‘engineering fill’ associated with the geological materials. The values are used are provided in Appendix 7 - Use for engineered fill classification descriptions. |
| Use as engineering fill (FILL_USES) | This is a description of the typical USE of the ‘engineering fill’ associated with the geological materials. It is a slightly more informative version of the FILL_TYPE field as it identifies key ‘fill’ characteristics that are important to test for, or ascertain, at an early stage of site investigation. For example it identifies fill types that may be ‘partly’ unsuitable. See the DETAIL section below for further description). see Appendix 7 - Use for engineered fill classification descriptions. |
| Use as engineering fill (DETAIL) | This is a description of the ‘engineering fill’ associated with the geological materials. It is a more descriptive and informative version of the FILL_USE and FILL_TYPE fields as it identifies key ‘fill’ characteristics that are important to test for, or ascertain, at an early stage of site investigation. It outlines the full range of subdivisions of fill-use in this dataset. see Appendix 7 - Use for engineered fill classification descriptions. |
| Use as engineering fill (OTHER_USES) | A description of known alternative uses of the geological materials, as defined in the BritPits database. (List is not exclusive). |
Scale
The Engineering Properties datasets are produced for use at 1:50 000 scale providing 50 m ground resolution.
Format
The data are released in ESRI shapefile formats. Other formats such as MapInfo TAB are available on request. The standard data supplied to customers has polygons or areas in a single layer or theme.
Coverage
Data is provided to indicate the strength of rocks and soils across Great Britain. The scale of map data available to create this dataset is shown in Appendix 9 - Mapping scales.
Data history
The release dates of the datasets are in Table 3.
| Dataset name | Version release | Year of release |
| Strength | Version 1: Derived from DiGMapGB-50 version 6. | 2012 |
| Excavatability | Version 1: Derived from DiGMapGB-50 version 6. | 2012 |
| Discontinuities | Version 1: Derived from DiGMapGB-50 version 6. | 2015 |
| Bulking of soils and rocks | Version 1: Derived from DiGMapGB-50 version 6. | 2015 |
| Sulfate and sulfide potential | Version 1: Derived from DiGMapGB-50 version 6. | 2015 |
| Corrosivity (ferrous) | Version 1: Derived from DiGMapGB-50 version 6. | 2012 |
| Use for engineering fill | Version 1: Derived from DiGMapGB-50 version 6. | 2014 |
Limitations
- The Engineering Properties datasets have been developed at 1:50 000 scale and must not be used at larger scales. All spatial searches against the data should be done with a minimum 50 m buffer.
- The spatial distribution of the data is limited by the distribution of the site investigation exploratory holes from which the geotechnical data have been extracted (shown in Appendix 3 - Discontinuities classification terms and descriptions) and digital geological map data (DiGMapGB-50) (Appendix 8 - Distribution of source data). Although the National Geotechnical Properties Database is the ‘first port of call’ for data it has limited coverage so other descriptive data from exploratory borehole logs or from Site Investigation Reports has been used.
- The presentation of the data are created as vector polygons and are available in a range of GIS formats, including ArcGIS (.shp), ArcInfo Coverages and MapInfo (.tab). Other formats might be available and might incur additional processing costs.
- The datasets are concerned with the properties of natural geological units and not those altered by man. It does NOT cover any man-made constructions, such as engineered fill or made ground.
- The data are based on, and limited to, an interpretation of the records in the possession of The British Geological Survey at the time the dataset was created.
- Engineering properties data are based on the mechanical and chemical properties rather than a physical property and are usually measured in the laboratory or occasionally in the field or described in the field. Earth materials are varied by their very nature, particularly in the top metre or so, where they are often affected by surface processes such as weathering. Thus, a geological unit is unlikely to have a homogenous characteristic. This is indicated in the datasets by providing the minimum, maximum and ‘typical values’ (or ranges of values) and descriptors for each units’ characteristics.
- Site specific assessments should be carried out by suitably qualified and experienced professionals and using appropriate methods. The descriptions provided in these data are designed for DESK STUDY phases.
- Some of the engineering properties in the vicinity of faults or fault zones such as Discontinuities and Excavatability will be different from the mass of the unit. The effects of faults are not included in these assessments. An appropriate ground investigation should be used to assess the effect of faulting on the properties as required by the project.
- For engineered fill, the ‘dataset’ is for the lithology or lithologies as identified for each geological unit and does not include mechanical mixing of lithologies. This assessment can only be done on site and depends on the size of the site and the lithologies and quantities available on site. Such an assessment can only be made by inspection of the fill materials by a qualified professional.