12.4 Sampling procedure

12.4.1 Selection of sampling method

(1)P The sampling category and sampling method shall be selected in advance in accordance with the quality of the sample required for classification of soils and for the laboratory test to be performed.

(2) The sample diameter for soils containing large particles should be chosen by the size of the largest particles of the sampled material.

(3) Different disturbance of sample may be expected when using various sampling methods. The quality of a sample taken with the same sampler may vary depending on e.g. the soil type to be sampled, the presence of groundwater and the sampling operation.

(4) The sampling, transportation and storage procedures should be taken into account when selecting samples for laboratory tests and interpreting the laboratory test results.

(5) Examples of some of the most common sampling methods and their suitability to different categories of sampling methods in different soils are listed in annex K.

12.4.2 Drive sampling operation

(1)P In order to obtain good quality soil samples in stiff soils or when using open-tube drive samplers, a method of preboring shall be used. A boring technique shall be selected which will minimize soil disturbance. Boreholes in unstable soils shall be stabilized with casing or using drilling fluid.

(2)P When using open-tube drive samplers as category A sampling methods, or in boreholes without casings in soft cohesive soils and in cohesionless soils below the groundwater table, the borehole shall be filled with water or drilling fluid. The level of the fluid shall be maintained at or slightly above the level of the groundwater table.

(3) When using category A sampling methods above the groundwater level the borehole should preferably be kept dry. The borehole may be filled with drilling fluid, but with water only in case of artesian groundwater.

(4)P In order to obtain samples from the bottom of a prebored borehole by category A sampling methods the hole shall be cleaned of disturbed soil and segregated material. When using open-tube drive samplers in a cased borehole the hole shall be cleaned to the edge of the casing.

(5) No cleaning is required when the borehole is uncased and the closed piston sampler is forced into undisturbed soil.

(6)P A piston sampler shall be forced through the zone of disturbed soil before the piston is released and the actual sampling is started.

(7)P When using category A sampling methods in soft to firm cohesive soils the drive sampler shall be forced into the soil to the predetermined depth by continuous pushing. There shall be no rotation of the sampler during the downward movement.

(8) In stiff cohesive soils the sampler may be forced into the soil by a dynamic impact which may, however, cause additional disturbance of the sample.

(9)P The sampler shall be withdrawn slowly and carefully and not rotated.

(10) It is advisable to withdraw the sampler after waiting a few minutes so that sufficient adhesion can develop between the sample and the sampling tube or liner.

(11)P In sampling category A after the sampling tube has been disconnected from the sampler head seriously disturbed material from the upper part of the sample shall be removed. The top of the sample shall be sealed and the open space at the tube top shall be filled out e.g. by remoulded material, foil and sealed.

(12)P Samples obtained by category A and B sampling methods shall be sealed immediately after retrieval to prevent change in water content.

12.4.3 Handling and storing of samples

(1)P Samples obtained by category A sampling methods shall be handled in such a way that no disturbance will occur after withdrawal of the sample or during transportation and storage.

(2) Samples obtained by category A sampling methods should effectively be protected from heat, frost, vibration and shock during shipment and storage. Great care should be taken not to remove the seals of the samples and not to deform the sampling tubes.

(3) Samples obtained by category A sampling methods should be stored during the transportation in a container and in the laboratory in a room where the temperature and humidity are kept constant and as close as possible to that of the in situ conditions.

12.5 Reporting on boring and sampling

12.5.1 Boring record

(1)P In addition to the requirements given in 2.6 the boring record shall contain the following information:

  • date of boring;
  • coordinates and number of boring;
  • ground surface elevation at each boring or other reference level e.g. top of coating;
  • the depth of the free groundwater level;
  • the method of the preboring if used;
  • the use of the casing and the depth of the casing edge of each sampling;
  • the use of drilling fluid and the level of the drilling fluid in the borehole;
  • the specifications and the type of sampler used, e.g. reference for standard if applicable;
  • the diameter of each sample;
  • the depth of the top and bottom of the sample;
  • boring progress; any obstructions and difficulties encountered during the sampling operation.

12.5.2 Labelling of samples

(1)P All samples shall be numbered, recorded and labelled immediately after retrieval from a borehole or excavation and sealing.

(2)P The sample label shall show information about

  • identification data of the project;
  • date of the sampling;
  • number of the bore hole;
  • the sampling method and the type of the sampler used;
  • elevation or depths of the top and the bottom of the sample.

(3)P Samples shall be properly marked so that there can be no doubt about the top and bottom of the sample.

(4) The soil type according to the visual examination should be given on the label, whenever possible.

12.5.3 Sampling report

(1)P The field report of sampling operations included in the site investigation report shall be clear and accurate and it shall contain not only the data required for determination of the soil profile and the location of the samples obtained but also any observations which will contribute to an estimate of the condition of the samples and of the physical properties of the soil in situ.

(2)P Unsuccessful sampling operations shall be reported.

Eurocode 7 Geotechnical design — Part 3: Design assisted by fieldtesting