The investigation should be carried out to BS 5930 (1999) standards. More information can be found from the Institution of Civil Engineers. Soil testing must be carried out to BS 1377 (1990), by a United Kingdom Accreditation Service (UKAS) accredited laboratory.
Site investigation is considered to be a construction activity and should therefore comply with the Construction, Design and Management Regulations (CDM) 2007.
Please note that under the CDM specific legal duties are placed on organisations or individuals for whom a construction project is carried out. Please contact the Health and Safety Executive for further information.
The ground model
The overriding objective of the investigation is to produce a ground model, against which predictions may be made regarding the ground response to the proposed works. The ground model requires interpretation of the geology, ground conditions including groundwater and other factors (including existing structures), by a suitably qualified person, normally a geotechnical engineer or engineering geologist.
The ground model should be described clearly using plans, cross-sections, block diagrams and other sketches as appropriate. Areas of assumption or interpolation should be clearly identified.
A detailed geotechnical survey and appraisal will be required.
Ground investigations should include the following information where the proposal connects to or interferes with the impermeable lining of an artificial cut or canalised navigation:
- location and depth of all boreholes and trial pits
- full log of boreholes and pits including description and classification of soils and ground water levels
- location and depth of samples
- an interpreted ground model with quantitative information on characteristics such as plasticity index, permeability (horizontal and vertical), classification by particle size distribution, angle of friction, cohesion, dry density and bulk density, and dispersivity index
- ground levels not only to Ordnance Datum but also relative to normal water level in the canal and, where appropriate, levels of flood defences, maximum flood, mean low water of spring and neap tides, and mean high water of spring and neap tides
- quantitative information on contaminated land and ground water, where applicable. We may require water quality monitoring during construction and subsequently during operation.
It is important that the level and the quality of information provided is consistent with the complexity of the proposed works and that any subsequent design assumptions used in the temporary and permanent works are supported by the findings of such an investigation. Where insufficient ground investigation data is available, designers will have to use conservative soil parameters in the design of the works that may result in substantial additional costs.
The ground investigation should be sufficient to reduce the risks associated with unforeseen ground conditions to a tolerable level.
It should be noted that the connection to the waterway, unless agreed otherwise with us, will need to be undertaken in dry conditions. This will require the use of temporary works and/or a pre-agreed canal stoppage/partial stoppage to create a dry working area. Consideration should be given to this in the ground investigation and in the programming and pricing of the works.
Care should be taken not to disturb wildlife when carrying out any intrusive investigations (boreholes, trial pits, etc). Of the wildlife most likely to be encountered, badgers (and their setts), nesting birds, bats, water voles and all reptiles require special attention as they are all legally protected.
No borehole shall be drilled or trial pit excavated within six metres of the water's edge or within the water channel without our written permission. Normally, this will be necessary as it is a requirement to determine the composition and properties of the bed/lining material, to assess whether the lining extends behind the bank protection, or to locate services or other buried structures, to provide the level of detail for us to fully assess your proposals for construction of the marina entrance.
Waterway walls can be up to 200 years old and are generally not capable of bearing loads. Plant should be lightweight only and must not load the wall or edge of the canal. A condition survey and risk assessment will be required.
Whilst undertaking site investigation works within or adjacent to the canal, appropriate measures must be taken to avoid disturbing the existing canal lining. However, if it will be necessary to affect the navigation channel, within the existing waterway width, for temporary or permanent works, then bed profiling for a sufficient distance either side of the works should be carried out. In such cases, any investigations must be agreed in detail with us in order to minimise the risk of damage to the canal.
Other conditions which must be observed are as follows.
- Unless pre-agreed with us, and required for safety reasons, at no time shall the waterway or towpath be blocked. Signage and suitable fencing or other barriers must be used to segregate the public from the working area. Some towpaths are public rights of way and will require Local Authority consents for closure/ diversion.
- No trial pits are to be excavated on embankment slopes below the level of the waterway or within five metres of the toe of such embankments.
- No water is to be pumped into or out of the waterway.
- No borehole or trial pit spoil or grout shall be allowed to enter the waterway and all such arisings shall be removed in compliance with waste management legislation.
- Boreholes are to be sealed and backfilled with cement-bentonite grout of an agreed specification, except for any borehole within the existing waterway width. Where alternative backfilling is required (for example, for a particular installation), this must be agreed with us.
- Trial pits are to be carefully backfilled and adequately compacted in layers.
- Any variations from these conditions require our prior agreement.
All access roads used, and fences and hedges disturbed during the investigation, should be fully reinstated to our satisfaction.
Where it is necessary to leave apparatus such as piezometers or survey stations on our land, the design of the installations, including details of covers, etc, must be acceptable to us and a commercial agreement may also be required.
Provision of information
Relevant logs, test data and other field information must be submitted. The preferred format is paper, backed up by electronic (e.g. pdf format) copies, as well as AGS data (current version). Interpretative reports should be provided as a paper copy, together with an electronic (e.g. Word or pdf) version.
All exploratory holes must be accompanied by a 12-figure national grid reference, as well as a level to Ordnance Datum. Where it is not practical to provide levels to OD (for example where no benchmarks are present locally), then it may be acceptable to provide a relative level to an agreed datum (not water level), with a suitable witness drawing of any temporary benchmark used.
Useful references and links
- Institution of Civil Engineers
- UKAS United Kingdom Accreditation Service
- Construction, Design and Management Regulations (CDM) 2007
- AGS (2004) A Client's Guide to Site Investigation, AGS Information Sheet, AGS, Beckenham, Kent
- BS 5930 (1999) - Code of Practice for Site Investigations
- BS 10175 (2001) - Code of Practice for the Investigation of Potentially Contaminated Sites