The stated purpose of the document is to "...deal(s) with the investigation of sites for the purposes of assessing their suitability for the construction of civil engineering and building works and of acquiring knowledge of the characteristics of a site that affect the design and construction of such work...".
The document gives guidance on legal, environmental and technical matters relating to site investigation and includes a section on the description and classification of soils and rocks.
BS5930:1999 was amended in December 2007 to avoid conflict with the newly introduced Eurocode 7 "Geotechnical Design" and the code is to be retained as a normative reference.
Section 1 Preliminary Considerations Pages 3–6[1] Seven factors to be cognizant of at this stage are: suitability of the site for the proposed works, economic and adequacy of design, optimum method of construction with reference to potential issues due to ground and groundwater.
Existing records, local authorities, industry, libraries, present or past OS maps and aerial photography or even anecdotal information are to be used.
A site reconnaissance should also be conducted at this stage and includes a thorough visual inspection of any exposed cuttings and note taken of level of vegetation.
Section 2 Ground investigations Pages 7–23[1] This is a natural follow on from the desk study, the objectives are similar – acquiring sufficient information for design, assessing the hazards.
Temporary or permanent changes should be investigated this involves changes in stresses and strains, moisture content, strength and compressibility.
Due to the potential flexibility and size of an investigation, adequate supervision, equipment, testing, personnel, and audits should be provided in a safe manner.
The extent of the GI can depend on many variables such as, character of site, availability of equipment and personnel and costs of methods.
The GI should give sufficient information to make good decisions on design, construction material selection.
Frequency of sampling and testing can be decided with the following in mind, the determination of the character and structure of all the strata and ground water conditions, the determination of the properties of the strata and the use of special techniques should ‘normal’ techniques not give satisfactory results.
Samples are taken from deep trial pits and shafts at certain sites if necessary and if below the water table can become a more complicated process.
Sampling quality can be classified to determine depending on their disturbance and other factors such as, wet or dry ground.
Laboratory samples are at times not considered to be representative and of insufficient quality, stress, pore pressure, and degree of saturation.
The van test is used to determine the shear strength of a soil - material with coarse silt or sand can mean unreliable results.
Packer tests are also used to measure the impermeability of grouted ground and permeability of dam foundations, strength and deformation data can also be taken.
Mainly used at a preliminary stage, it is also useful to check surrounding ground but is unsuitable in soils with boulders and cobbles.
Geophysical surveying can be useful in site investigation for determining layers of rock other geological features, locating aquifers, mineral deposits, voids – natural or man-made and engineering properties of the ground.
Nature of ground and soil type, quality and how representative the sample is, method of analysis proposed, requirement of the design along with laboratory capabilities are all key factors in lab testing.
Sample quality should be borne in mind when testing, and finally reporting unambiguous results is desirable.
after a time, samples are destroyed and the only record maybe the field report, for this reason it should be composed and written in properly.