Ground Investigation Report

The requirement for a Ground Investigation Report (GIR) appears in EN 1997-2:

The results of a geotechnical investigation shall be compiled in a Ground Investigation Report which shall form part of the Geotechnical Design Report. [EN 1997-2 §6.1(1)P]

The contents of the GIR are specified both in EN 1997-1 (as an Application Rule) and in EN 1997-2 (as a Principle):

The Ground Investigation Report [should normally consist of]/[shall consist of, if appropriate] a presentation of all available geotechnical information including geological features and relevant data; [and] a geotechnical evaluation of the information, stating the assumptions made in the interpretation of the test results. [en 1997-1 §3.4.1(3)] and [en 1997-2 §6.1(2)P]

In simple terms:

GIR = Presentation + Evaluation ... of geotechnical information

The contents of the GIR are illustrated in Figure 16.5 and discussed in the following sub-sections. Physically, the GIR may form a single volume or span several volumes, depending on the size and nature of the investigation.

16.3.1 Presentation

The presentation of geotechnical information is set out in three Principles and one Application Rule in §6.2 of EN 1997-2.

The GIR must provide a factual account of all field and laboratory investigations, presented in accordance with the EN and/or ISO standards used in those investigations. The report must document the methods and procedures used — and results obtained — from desk studies, sampling, field tests, groundwater measurements, and laboratory tests.

The factual account should include a description of the site and its topography, in particular: evidence of groundwater, areas of instability, difficulties during excavation, local experience in the area, and a further eight items given in a checklist. [en 1997-2 §6.2(2)]

fFirst wording from EN 1997-1, second from EN 1997-2.

Ground Investigation Eurocode Ppt
Figure 16.5. Contents of the Ground Investigation Report

The level of detail given in Section 6 of EN 1997-2 is less than that provided by Section 7 of BS 5930. It is important to refer to the guidelines provided in BS 5930 when preparing reports intended to meet the requirements of Eurocode 7. It is likely that BS 5930 will be updated to remove any information that conflicts with EN 1997-2.

The results of field and laboratory investigations must be included in the GIR in the format specified in the appropriate European (EN) or International (ISO) standard used to perform the investigation. The requirements of these standards, which are separate from but relied upon by Eurocode 7, are discussed in Section 16.2

16.3.2 Evaluation

The evaluation of geotechnical information is set out in two Principles and six Application Rules in §6.3 of EN 1997-2.

The first Principle requires that the GIR must provide an evaluation and review of the field and laboratory results; detailed description of all strata, including their geometry, physical properties, and strength and deformation characteristics; and comments on irregularities such as cavities and discontinuities.

The second Principle ensures that in situ and laboratory test results are interpreted accounting for various factors including: groundwater, ground type, sampling, handling, transportation, and specimen preparation. Further, it requires that the ground model be revisited in the light of the test results.

The six Application rules provide guidance on presentation of the data, derivation of geotechnical parameters, consideration of anomalies, grouping of similar strata, and deriving boundaries between various geological units across a site.

Importantly, EN 1997-2 requires known limitations of the results to be stated in the GIR. [en 1997-2 §6.1(5)P]

It can be the case that engineers are reluctant to highlight limitations in the data, as it could be construed that contract obligations had not been fully met or their level of competency had been questioned. However, in order that data can be reliably analysed in the future, accurate recording of all the difficulties is essential. For example, when standard penetration tests (SPTs) are carried out below the water table, it is important to record whether the water level in the borehole is maintained above that in the surrounding ground. If this is not the case, then artificially low SPT blow counts could be recorded if the imbalance in water pressure loosens the base of the borehole.

16.3.3 Derived values

Any correlations that have been used to derive geotechnical parameters must be documented in the GIR. Typically this might include such correlations as the relationship between standard penetration test blow count and Young's modulus, consistency index and undrained strength, or plastic limit and California bearing ratio (see Chapter 5).

+1 -1

Post a comment