Section 6 Ground investigation report
6.1 General requirements
(1)P The results of a geotechnical investigation shall be compiled in the Ground Investigation Report which shall form a part of the Geotechnical Design Report.
(2)P The Ground Investigation Report shall consist of the following:
- a presentation of all appropriate geotechnical information including geological features and relevant data;
- a geotechnical evaluation of the information, stating the assumptions made in the interpretation of the test results.
(3) The information may be presented as one report or as separate parts.
(4) The Ground Investigation Report may include derived values.
(5) P The Ground Investigation Report shall state known limitations of the results, if appropriate.
(6) The Ground Investigation Report should propose necessary further field and laboratoryinvestigations, with comments justifying the need for this further work. Such proposals should be accompanied by a detailed programme for the further investigations to be carried out.
6.2 Presentation of geotechnical information
(1)P The presentation of geotechnical information shall include a factual account of all field and laboratory investigations.
(2) The factual account should include the following information, as relevant:
- the purpose and scope of the geotechnical investigation including a description of the site and its topography, of the planned structure and the stage of the planning the account is referring to;
- a classification of the structure into a geotechnical category;
- the names of allconsultants and subcontractors;
- the dates between which field and laboratory investigations were performed;
- the field reconnaissance of the site of the project and the surrounding area noting particularly:
a) evidence of groundwater;
b) behaviour of neighbouring structures;
c) exposures in quarries and borrow areas;
d) areas of instability;
e) any exposures of mining activity at the site and in the neighbourhood;
f) difficulties during excavation;
g) history ofthe site;
h) geology of the site, including faulting;
i) survey data with plans showing the structure and the location of all investigation points;
j) information from aerial photographs;
k) local experience in the area;
l) information about the seismicity of the area.
(3)P The presentation of geotechnical information shall include documentation of the methods, procedures and results including all relevant reports of:
- desk studies;
- field investigations, such as sampling, field tests and groundwater measurements;
- laboratory tests.
(4)P The results of the field and laboratory investigations shall be presented and reported according to the requirements defined in the EN and/or ISO standards applied in the investigations.
6.3 Evaluation of geotechnical information
(1)P The evaluation of the geotechnical information shall be documented and include, as-appropriate:
- the results of the field investigations and laboratory tests evaluated according to Sections 3 to 5 of this standard;
- a review of the results of the site and laboratory investigations and all other information listed in 6.2;
- a description of the geometry of the strata;
- detailed descriptions of all strata including their physical properties and their deformation and strength characteristics, referring to the results of the investigations;
- comments on irregularities such as cavities and zones of discontinuous material.
(2)P It shall be documented, if appropriate, that:
- the results were interpreted taking into account the groundwater table, ground type, drilling method, sampling method, transport, handling and specimen preparation;
- the strata subdivision assumed from desk studies and site inspections were reconsidered in light of the results obtained.
(3) The documentation of the evaluation of the geotechnical information should include as appropriate:
- the tabulation and graphical presentation of the results of field investigation and laboratory testing in cross-sections of the ground showing the relevant strata and their boundaries including the groundwater table in relation to the requirements of the project;
- the values of the geotechnical parameters for each stratum;
- areview of the derived values of geotechnical parameters (see 6.4).
(4) Averaging can mask the presence of a weaker zone and should be used with caution. It is important that weak zones are identified. Variations in geotechnical parameters or coefficients can indicate significant variations in site conditions.
(5) The documentation should include comparisons of the specific results with experience for each geotechnical parameter, giving special consideration to anomalous results for a given stratum when compared with any results from other types of laboratory and field tests capable of measuring the same geotechnical parameter.
(6) The documentation of the evaluation should substantiate the following aspect: strata in which ground parameters differ only slightly may be considered as one stratum.
(7) A sequence of fine layers with greatly differing composition and/or mechanical properties may be considered as one stratum if theoverall behaviour is relevant, and the behaviour can be adequately represented by ground parameters selected for the stratum.
(8) When deriving the boundary between different ground layers and the groundwater level, there may be interpolated linearly between the investigation points provided the spacing is sufficiently small and the geological conditions are sufficiently homogeneous. Such application of linear interpolations and their justification should be reported.
6.4 Establishment of derived values
(1)P Ifcorrelations have been used to derive geotechnical parameters or coefficients, the correlations and their applicability shall be documented.