Section 2: Desk study and field reconnaissance
The desk study and field reconnaissance should be carried out as the first stage of an investigation to enable an initial ground model to be developed, based upon the available information, and to plan the scope of the initial and subsequent stages of the investigation. A desk study and field reconnaissance should be carried out before a ground investigation programme is designed in accordance with the sequence specified in BS EN 1997-2:2007, 2.1.
NOTE 1 Field reconnaissance has historically been referred to as site inspections, walkover surveys, site visits, etc.
The desk study (or preliminary sources study as it is sometimes referred to) should identify the likely ground-related hazards which inform the initial project risk register. Subsequent phases of the investigative process should take into account these hazards in relation to the proposed development and should quantify, address and attempt to mitigate the risks associated with each hazard.
From the outset, knowledge of planning application status and conditions including discharge requirements should be identified.
The field reconnaissance should be carried out once the factual information for the site and its environs has been compiled and preliminary proposals for any ground investigation prepared.
NOTE 2 Additional information on the geology and hydrogeology and potential construction and access constraints for ground investigation might be revealed by the field reconnaissance.
Interpretation should be carried out as a continuous process, starting in the preliminary stages of data and information collection with the construction of the initial ground model. Further interpretation of the ground and groundwater conditions should proceed as information from the investigation, for example the ongoing desk studies and field reconnaissance, becomes available (by using this information it is often possible to detect and resolve anomalies as work progresses). At all stages the current version of the ground model should be used to identify the known/unknown information and so formulate the questions that need to be addressed by the next phase of study or investigation. The progressive resolution of these questions should be the aim of the investigation, although it is also usual for new questions to arise as more becomes known about the site.
NOTE 3 A robust ground model, which is then interrogated and developed through the whole investigation process, is critical to the success of a ground investigation. By identifying the uncertainties in the knowledge of the ground and groundwater conditions sensible decisions can be made as to the need for further investigation, including additional intrusive investigation, examination of exposures within the construction or by monitoring of the structure during its construction and operation.
The engineering design and construction proposals should also be taken into account along with the ground model as data and information becomes available, so that the geotechnical adviser can decide either what additional exploration and testing needs to be carried out or, where appropriate, what reductions in the original programme/scope are possible.
NOTE 4 BS 10175 gives guidance on the design and execution of preliminary investigations (desk study and field reconnaissance, as well as preliminary risk assessment) for potentially contaminated sites and sites where there might be naturally elevated concentrations of potentially hazardous substances. This guidance is supplemented by additional guidance in BS 8576 for sites where there might be elevated concentrations of hazardous ground gases.
The results of all studies and surveys should be formally presented in a report, bringing together details of:
- site topography;
- geology, hydrogeology and geomorphology;
- ground and groundwater conditions;
- preliminary geotechnical parameters;
- potential geotechnical problems;
- previous and existing uses of the site;
- services/utilities at the site (see 19.2.4);
- anticipated construction hazards; and
- the proposed ground investigation.
NOTE 5 High risk areas have been defined where development is likely to be affected by hazards from historical coal mining. Sites which fall within these areas require the submission of a Coal Mine Risk Assessment (CMRA) as part of their Planning Application. This assessment needs to be obtained if completed by others, or produced by the responsible expert prior to any investigation being planned. To determine if a site requires such a risk assessment, an online interactive map can be viewed via a link from <https://www.gov.uk/planning-applications-coal-mining-risk-assessments> [last viewed 24 June 2015].
11 Desk study
The desk study should comprise a factual core supplemented by interpretative elements which summarize physical, geoenvironmental and geotechnical aspects in order to aid the formulation of a ground model or a conceptual site model. The successive stages of assessment and investigation should identify potential geotechnical, environmental and health and safety issues that are likely to detrimentally affect the site, its investigation and its development.
NOTE 1 The typical scope of the factual core of the desk study is presented in Table 1 while those typical geotechnical aspects requiring further consideration are summarized in Table 2. An example format for such a report is given in Design manual for roads and bridges, Vol 4 .
NOTE 2 Annex B outlines the kinds of information that might routinely be needed for a desk study. Where there is a choice of site, information obtained from this study could well influence such choice. Much information might already be available about a site in existing records. A summary of the most important sources of information is given in Annex C; a more detailed catalogue is given elsewhere (see Perry and West, TRL Report 192 ).
NOTE 3 For most projects, the design and planning of construction requires a detailed examination of the site and its surroundings (a CIRIA project to develop guidance covering all the key stages in the planning and set-up of a construction site was underway at the time of publication of this British Standard). See Annex D. This examination might necessitate a detailed land survey (see D.2), or an investigation of liability to flooding. The investigation of ground conditions is dealt with in other sections of this British Standard, e.g. Section 3. Other subjects might be studied, such as unexploded ordnance (see D.5), hydrography (see D.6); climate (see D.7); hydrology (see D.8); sources of materials (see D.9); disposal of waste materials (see D.10); and other environmental and ecological considerations as appropriate.
|Site details||Location (address, grid reference); boundaries; land ownership; present/proposed land use; site protection and environmental status; topography, services/utilities and other relevant information.|
|Site history||Review of historical maps, photographs, remote sensed images (aerial photographs and satellite imagery) and documents to determine past site usage. Identification of changes in topography and unstable ground; the presence of watercourses and potential for flooding; archaeological potential; the presence of Designated Heritage Assets (World Heritage Sites and their Buffer Zones, Listed Buildings, Scheduled Monuments, Areas of Archaeological Importance, Protected Wreck Sites, Registered Parks and Gardens, Registered Battlefields and Conservation Areas), man-made structures including foundations, infrastructure (e.g. tunnels, pipes, cables) and mine workings; the potential for contamination given current/past uses of the site.|
|Site geology||Review of all available geological, geomorphological and hydrogeological maps and memoirs, reports and other documents including digital data; exploratory hole record sheets and well records; past ground investigations in the vicinity.|
|NOTE The above list is non-exhaustive and other searches might be required for such things as utilities, invasive weeds, biocontamination (e.g. anthrax).|
|Ground- related site constraints||Cataloguing of the identified site-specific factors that might affect the ground investigation and subsequent development proposals.|
|Ground- related hazards||Listing, describing and prioritizing the identified ground hazards (both site- and project-specific) together with proposals for further investigation and subsequent mitigation. Ground hazards can be topographic, geological, hydrogeological and man-made. Assessment of the information available for reliability and completeness in terms of identifying all sensibly possible hazards.|
|Ground investigation||Recommendations for the scope of the ground investigation required; specific site/project-specific issues identified which require particular investigation.|
Where mining and quarrying, whether past, present or prospective, is likely to be a factor affecting the site, reference should be made to Annex C. Where contamination of the ground or the presence of ground gases is possible, reference should be made to BS 10175 and BS 8576.
Local sources of information should also be referred to, including:
- local authorities and local/regional statutory undertakers (for example, Engineer's and Surveyor's Offices) for earlier uses of the site and the results of excavations in the area;
- repositories of information on previous investigations on or near the site;
- repositories of information on local industry, commercial premises and land uses;
- museums and libraries for historical maps, photographs, etc;
- local press publications;
- professional or amateur societies' journals, papers and other publications; and
- local oral tradition (although of variable reliability) and information.
NOTE 4 It is possible to purchase reports from a number of private companies that provide a collation of some of the available information relevant to a site's history, geology, hydrogeology and environmental setting, etc. Although very helpful, these are not sufficient on their own to fully characterize a site. It is important to cross-check information from the various sources as there might be errors in the data banks from which they are derived (e.g. they might not be up-to-date) or they might be incomplete, not site-specific or insufficient for the project.