63.1 Contents common to all reports
Interpretation is a continuous process, which should be begun in the preliminary stages of data collection with the construction of the initial ground model. Further interpretation of the ground conditions should be carried out as information from the site studies and ground investigation becomes available; this information should be used to detect and resolve anomalies as field and laboratory work progresses. At all stages the current version of the ground model should be used to allow the known information and unknowns to be identified, so that the questions that need to be addressed by the next phase of study or investigation can be formulated. The progressive resolution of these questions should be the aim of the investigation, although it is also normal for new questions to come forward as more becomes known about the site.
Engineering problems should also be evaluated along with the ground model as the data 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. These should be addressed in a geotechnical risk register.
The compiled GIR and GDR should include a number of parts, as outlined in Table 43.
NOTE 1 Full details of the items to be covered are given in BS EN 1997-1 and BS EN 1997-2.
A report should be prepared with the understanding that it is intended to eventually be the only record of what was found, as samples are likely to be destroyed or rendered unrepresentative.
NOTE 2 Traditionally, the results are normally issued in the form of a limited number of bound or unbound copies of an official written report. An increasing number of reports and the data contained therein are presented as computer files; this may be as copies of the prepared report.
Data should be maintained in parallel with the formal reporting recommended and this requirement should be included in specifications on all ground investigations. The requirements for data management are given in BS 8574.
NOTE 3 A suitable format in which to provide the date is prepared by the AGS and is known as AGS format.16)
The formal report should contain a description of the site and the procedures used, together with tables and diagrams giving the results. Copies of field and laboratory report forms and data sheets may be included in the formal report, but the originals should be preserved for a suitable period so that they are available for later reference. The practice of binding copies of these forms as a report volume for permanent reference has much to commend it; the client's requirements in this regard should be specified in the tender document.
63.1.2 The introduction
The report should have an introduction stating for whom the work was done, the names of parties involved, the phase of the investigation, the geotechnical categories of the proposed structures, the dates of commissioning and the dates of various activities, and nature of the investigation, and its purpose, scope and general location.
126.96.36.199 Description of site
The report should contain an unambiguous description of the geographical location of the site, so that the area covered can be readily located at a later date, when possibly most, if not all, of the existing landmarks might have disappeared. Where appropriate, this should include street names and the National Grid reference. The report should incorporate relevant findings of the field reconnaissance visit, desk study or notable features identified during the course of the works, including a reproduced section of the relevant Ordnance Survey map of the appropriate scale for clarity. Details of all relevant topographic features should be included.
An account should be given of the geology, geomorphology and hydrogeology of the site, and the sources from which the information was obtained should be stated.
NOTE The amount of the data included depends on the complexity of the ground conditions in line with the nature of the work being planned and the amount of available data.
63.2 Ground investigation and testing reports
Report form templates should be provided in the field for recording information, and these should have prompts (questions, spaces or boxes) to ensure that all the required information is recorded at the time.
NOTE 1 Templates may be paper forms or digital input screens. The latter have the advantage of not allowing the operator to move off an input screen unless all required data has been entered.
Field report forms should require the operator to record all the data necessary for the eventual interpretation of the borehole or field test in accordance with BS EN ISO 22475-1. Most of the information called for is needed to draw appropriate conclusions from the results of boring and field tests, and whatever layout is adopted, all such items should be recorded somewhere. The information should include flush type, core barrel type, bit used from/to, drill rig and over specific depths used.
NOTE 2 Other data, such as that which might be needed for administrative purposes, have not been included.
The reference number, location and depth of each investigation point, sample and test should be recorded. The location may take the form of a reference that can be related to the national or other appropriate grid, and marked on a drawing in such a way that it can be easily located at a later date if needed. The ground level at the test position should be measured and included when available; however, this is often not surveyed until after the test and so might not be available for inclusion in the field report.
NOTE 3 Drilling foremen, technicians, engineers or geologists, as appropriate, fill in field report pro formas on paper or digitally. Certain of the more complex tests might have several pro formas, and are often referenced in more than one report; for instance, bearing or permeability tests in boreholes or trial pits. It is usual to require copies of the field reports to be made available soon after the tests, normally within a few days, or as specified, to demonstrate that the field data has been satisfactorily collected. These then form a complete contemporaneous record, although further processing of the data is usually necessary to derive a satisfactory presentation for the field report and the parameters for use in design. Inclusion of the relevant field records in the final report might be beneficial (see 63.1).
Detailed information on the procedures and results should be reported in accordance with the standard under which the test is being carried out.
An account should be given of the methods of investigation and testing used and the standards followed. A summary of the scope of work should be provided and should detail the spacing and depths of the investigation points. It should include a description of all the equipment used, e.g. types of drilling rigs and tools, together with the relevant standards for testing, sampling or drilling to which the work has been carried out. A note should be made stating any limitations of the results and any difficulties experienced, e.g. ground disturbance or problems in recovering samples. Any testing for gases and other contaminants or observations of these in the boreholes and around the site should be reported. The dates when the exploratory work, ground gas monitoring and groundwater monitoring was done should also be recorded, together with a note about the weather conditions, if relevant.
The report should contain a drawing indicating the positions and ground levels of all pits, boreholes, field tests, etc. It should contain sufficient topographical information so that the exploratory hole positions and particularly monitoring installations can be located at a later date.
63.2.2 Exploratory hole logs
The exploratory hole log should be a record that is as objective a record as possible of the ground conditions at the investigation position before the ground was subjected to disturbance and loss by the drilling or excavation process. Some interpretation is necessary, if only to link sets of samples with a stratum description, but the degree of interpretation should be kept to a minimum unless this is necessary to provide information, in which case it should be clearly identified; the use of words such as "probably" or "possibly" is useful in this regard.
The exploratory hole log should be part of the factual data arising from the investigation. The final logs should be based on the visual examination and description of the exposures, the laboratory test results, the driller's daily report forms and what is known of the geology of the site. All the relevant data should be recorded.
NOTE The logs can only be finalized when the appropriate field and laboratory work has been completed.
Although there are no set rules on the method of presentation of the data, the logs should present all the data obtained in a readable form and give a picture in diagrams and words of the ground profile at the particular point where the hole was bored. The extent to which minor variations in soil and rock types should be recorded, together with any discrepancies, depends on the various purposes to which the information is to be put. Detail indents should be used on the log to clearly represent variability or complexity of the ground.
Most organizations carrying out ground investigations have standard forms for exploratory hole logs but it is seldom practical within these to make allowance for all data that might need to be recorded. A standard form can be made more flexible by leaving one or more columns without headings, so that these can be used for whatever particular data needs to be recorded. Full use should be made of any unused space on the last sheet of a log.
The information to be included on logs should be in accordance with BS EN ISO 22475-1.
COMMENTARY ON 63.2.3
Further guidance on photography is given in Annex H.
Rock and soil cores should be photographed when fresh and before any destructive logging is carried out. The photographs should be in colour, to a consistent format on any investigation, including job, borehole and depth references, together with a scale and standard colour chart, and be sensibly free from distortion. The photographs should be presented in the report. Core should preferably take up over half the area of a photograph.
NOTE High resolution scanning or imagery is also available and can be a useful alternative to conventional photography, particularly when a large-scale viewable image of the core is required.
Trial pit photographic records should include one or more faces and the spoil heap; all photographs should include a suitable and legible reference board. Artificial or flash lighting should normally be used.
63.2.4 In-situ tests
For in-situ tests, the information to be recorded should be as outlined in Section 7; more detailed requirements for many tests should be presented in accordance with the relevant parts of BS EN ISO 22476 or BS 1377.
NOTE The contract specification might have special or additional requirements.
63.2.5 Incidence and behaviour of groundwater
To obtain a clear understanding of the incidence and behaviour of groundwater, all data collected on the groundwater should be included and, where no groundwater was encountered, this too should be recorded. In addition, where it was not possible to carry out groundwater observations this should be noted; for instance, drilling with water flush or overwater, or boring at a rate much faster than water can make its way into the borehole.
Where the information derived from boreholes and excavations is concise, it should be included in the logs. When this is not possible, the data should be given elsewhere in the report, and the exploratory hole logs cross-referenced.
The position of the borehole casing and the borehole depth at the time of an observation should be stated.
All other data, including those from separate observation wells, should be given in a separate table. Where water has been added to or removed from the ground by the boring or drilling process, this should be recorded.
63.2.6 Location of investigation points
The report should contain tabulated coordinates and a plan showing the precise position of each investigation points so that it is possible to locate each position accurately even after demolitions and excavations have taken place. The locations of any abortive or cancelled investigation points might also usefully be reported.
Where extensive tracts of open featureless country are encountered, the position of the investigation point should be linked to a land survey. Ground levels related to a permanent datum should also be provided.
Coordinates and ground levels at investigation points should preferably be given to National Grid and Ordnance Datum. If a site or local grid is used, its origin and orientation should preferably be given.
63.2.7 Results of laboratory tests and visual description of samples
Guidance on the use of laboratory tests is provided in BS EN 1997-2. Where the test is covered by International Standards (e.g. BS EN ISO 17892 [all parts]) or British Standards (e.g. BS 1377 [all parts]), the reporting of the results should be in accordance with those standards; where a test is not so covered, all relevant details and data should be given. Where an extensive programme of testing has been undertaken, a summary should be provided in addition to the detailed results. Test results may also be presented in line with specific contract requirements. The precise test carried out should also be stated without ambiguity. Where the test is reasonably standard, for instance "consolidated, drained, triaxial, compression test on 100 mm diameter samples", the name alone suffices; but where the test is not standard, a full description should be given.
The visual descriptions (see Clause 60) may be shown on the same sheets as the results of the laboratory tests, or in a separate table.
If the tests indicate a soil different from that visually described, the description should not be discarded on that account but should be preserved as a record of the observer's opinion. The laboratory report forms and data sheets should be filed for possible future reference or separately bound and presented (see Section 9).
If the results of contamination testing, ground gas monitoring and groundwater monitoring are included, this should be done in accordance with the requirements of BS 10175, BS 8576 and BS EN ISO 22475-1, respectively.
NOTE BS 10175 states that it is not sufficient to simply present contamination results in the form of a compilation of analytical certificates. The results are to be presented in the main text in such a way that they can be easily assimilated by the reader.
63.2.8 Special reports
The results of any specialized study, e.g. detailed mineralogical analysis, should be identified in the main report text, with all results and details included as an annex. Where relevant, specialized reports should include details of the analysis undertaken, the standards adhered to and any relevant calibration certificates.