Detailed information for design and construction
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 is underway at the time of publication). Such requirements 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 in this British Standard, e.g. Section 3. Other requirements might entail studies of subjects 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); and disposal of waste materials (see D.10).
D.2 Detailed land survey
The following information can be gathered when carrying out a detailed land survey.
- a) Detailed survey of site and its boundaries (particularly marked changes in ground levels), including levels referring to Ordnance datum, means of access, public and other services, and natural drainage network (see Annex C).
- b) Present and previous use of site and particulars of existing structures and obstructions, and whether they have to be maintained or demolished.
- c) Adjoining property and differences in ground levels with particulars of any adjacent structures including heights, floor levels, type of foundation and other details, and whether support is needed for these adjacent structures.
- d) Location and depth, where known, of any underground obstructions, and features such as cavities and mine workings and tunnels with a full description (see Annex F).
- e) Location with co-ordinates of triangulation and traverse stations (Ordnance Survey and site) positions and levels of Ordnance Survey and site bench marks, true north points and date of survey.
- f) Establish site bench marks and record their nature, location and description.
- g) Establish whether easements are required.
- h) Location, height and type of trees especially where site is underlain by fine soils and shallow footings are likely to be used.
D.3 Aerial photography
D.4 Ground conditions
Ground conditions, including the possibility of contaminated ground, are dealt with elsewhere in this British Standard, e.g. Section 2, and also in BS 10175 and BS 8576.
D.5 Unexploded ordnance
For areas where there is known to be a risk of encountering unexploded ordnance, impact assessments of the study areas can be made following the guidance given in CIRIA C681 .
Geophysical methods can be used to search for potential UXOs (see Clause 27). From the surface a grid form survey can be used:
- Magnetometer — This locates ferrous features to around 4 m — 5 m depth. Responses typical of UXOs can be differentiated in size and depth to some degree, though false anomalies can be expected. The value of this survey is dependent upon the localized environment being clear of ferrous debris, services, etc.
- Electromagnetic (EM) — This detects both non-ferrous and ferrous metallic objects. It is typically less sensitive to background noise than the Magnetometer, and is slightly more limited in depth penetration than the Magnetometer but provides additional information on the nature of the materials.
- GPR can be used for location of specific features, but is not typically recommended for most sites.
The exact nature of the targets to be located with these techniques can only be determined by excavation. As such, these techniques are used to minimize risk of unforeseen obstructions.
When drilling, techniques such as combined magnetometer CPT cone can be used to minimize risk of encountering UXOs below the depth of resolution of surface techniques.
D.6 Hydrography and hydraulic models
Structures in, adjoining, or near waterways require information on some or all of the following.
- a) Requirements of statutory bodies controlling waterways, such as port authorities, environment agencies, water companies, planning authorities and fisheries.
- b) Topographical and marine survey data to supplement, where appropriate, Ordnance Survey maps and Admiralty charts and publications (see Annex C).
- c) Detailed information about rivers, size and nature of catchment areas, tidal limits, flood levels and their relations to Ordnance datum.
- d) Observations on tidal levels (referred to Ordnance datum) and the rate of tidal fluctuations, velocity and directions of currents, variations in depth, and wave data.
- e) Information on scour and siltation, movement of foreshore material by drift; stability conditions of beaches, dunes, cliffs, breakwaters and training works.
- f) Location and details of existing river and marine structures, wrecks and other obstructions above and below the water line. Include effect of obstructions and floating debris, etc., on permanent and temporary works, including clearances.
- g) Observations on the condition of existing structures, such as attack by marine growth and borers, corrosion of metal work, disintegration of concrete and attrition by floating debris or bed movements.
Information on the following can be obtained from publications of the Meteorological Office (see C.5) and, where necessary, supplemented from local sources:
- a) annual rainfall and seasonal distribution;
- b) severity and incidence of storms;
- c) direction and strength of prevailing and strongest winds with their seasonal distributions;
- d) local air flow characteristics;
- e) liability to fogs;
- f) range of temperature, seasonal and daily; and
- g) humidity conditions.
Some sites might be liable to flooding. Information on sources of published data is given in Annex C. It can sometimes be advantageous to set up data collection, initially on-site, specifically orientated to the investigation, and then again later, at the construction stage. Parameters such as rainfall, wind, river and tide levels, maximum and minimum temperature and ground water levels can be measured, preferably on a regular daily or weekly basis. Where appropriate, the continuation of data collection might be possible with the liaison of the controlling statutory bodies. Even short-term data collection can provide a better understanding of the site conditions in the context of all previously recorded data.
Data is also available giving local and regional precipitation and flow data.
D.9 Sources of materials for construction
The following are all sources of materials for construction:
- a) topsoil;
- b) fill for earthworks and reclamation;
- c) road base and surfacing materials;
- d) concrete aggregates;
- e) stone for building, rip rap or pitching; and
- f) water.
D.10 Disposal of waste and surplus materials
The following information is needed to dispose of waste and surplus materials:
- a) location and capacity of spoil tips, including those for surplus dredged materials;
- b) requirements to safeguard nearby structures from ground movements and slips;
- c) liquid waste and standards of pre-treatment required;
- d) solid waste;
- e) access to spoil tips;
- f) transport requirements; and
- g) effect on environment, particularly in respect of any contaminated waste materials.