5 General requirements prior to sampling and groundwater measurements
The type and extent of sample recovery and groundwater measurements shall be specified in advance according to the purpose of the project, the geological and hydrogeological conditions and the anticipated field and laboratory testing (see EN 1997-2).
5.2 Selection of techniques and methods
5.2.1 The techniques and methods for sampling and groundwater measurements shall be selected according to the purpose of the investigations in relation to the expected geological and hydrogeological conditions.
5.2.2 Sampling techniques, sample transportation and storage procedures shall be selected on the basis of the required
- sample quality class according to EN 1997-2,
- sample mass, and
- sample diameter,
depending on the type of laboratory tests to be carried out.
5.2.3 A specific sampling category shall be selected in order to achieve a required sample quality class according to EN 1997-2 (see 6.2).
5.2.4 Different disturbance of sample can be expected when using different sampling methods. The quality class of a sample taken with the same sampler can vary depending on, e.g. the soil type to be sampled, the presence of groundwater and the sampling operation. The following sample disturbance can be generated by the drilling and sampling methods:
- mechanical sample disturbance due to compression, shearing, flushing or vibration during drilling or excavation;
- sample disturbance due to release of in situ stresses and related rebound;
- changes in material and chemical constituents such as water content and gases.
5.2.5 The sample diameter for soils containing large particles should be chosen with respect to the size of the largest particles of the sampled material.
5.2.6 If investigation below the groundwater surface or to greater depths is necessary, stable or stabilized boreholes are required.
5.2.7 Trial pits, headings and shafts give the possibility to investigate the ground in a larger scale e.g. to get information on the composition, sequence, structure and orientation of strata and possible rock surface. Without groundwater lowering, the depth is often limited to shallow depth above the groundwater surface. Large samples can be taken in order to analyse boulder content, bearing capacity, compactibility and permeability. At the same time, the excavability could be assessed and photographic documentation made.
5.3 Requirements for ground investigation sites and points
5.3.1 Site investigation points on land shall be marked on the site before the investigation process commences. Their location and elevation shall be surveyed and entered in a site plan on completion of the investigation.
5.3.2 Investigation sites shall be checked with respect to relevant hazards, underground utilities and unexpected, unexploded ordnance and, if necessary, appropriate actions have to be taken. Investigation locations on contaminated ground have to be dealt with by special procedures.
5.3.3 Trial pits should be situated outside the planned foundation area as the excavation can loosen the ground. There should have a distance between the nearest excavation wall and the planned foundation edge of at least 0,5 m plus half the intended excavation depth below the foundation level.
5.3.4 Trial pits (with or without access), headings and shafts shall be constructed in accordance with appropriate national or international standards and national safety regulations. They shall be sufficientlylarge to permit inspection, sampling and testing to be carried out in situ. Where necessary, they shall be protected against the effects of disturbance and weathering.
5.3.5 If visual logging, photographic evidence of the soil strata, sampling and in situ tests are to be carried out, this has to be done immediately after excavation.
5.3.6 The environmental impact of drilling and sampling shall be considered. Special principles have to be applied in water supply areas.