5.4 Preparation of rock specimens for testing

5.4.1 Objective

(1) The objective of preparing specimens for testing rock is to provide specimens that are as representative as possible of a rock formation.

NOTE Annexes T, U to W and X.2 provide more detail on the preparation of rock specimens for testing and some guidelines.

5.4.2 Requirements

(1)P It shall be specified how a rock specimen is prepared. If these specifications cannot be met, the specimen shall be prepared as near to the specifications as possible and it shall be reported how the specimen has been prepared.

(2)P All instruments and assemblies for determining straightness, flatness and perpendicularity of end surfaces shall be controlled on a registered regular time basis with tolerances satisfying at least the requirements of the specific rock tests.

(3)P The following shall be specified:

  • the storage conditions for rock samples (short term and/or long term storage);
  • the moisture condition of the test specimens at the time of the test;
  • the method for preparing rock core specimens;
  • the method for determining dimension and shape tolerances.

(4)P Any change in water content should be avoided. If a change in the natural water content should occur, its effect shall be counteracted as part of the preparation for testing, if relevant.

(5) The cause and effect of any change in water content should be reported.

(6)P The need for re-coring to a specified dimension shall be defined with reference to the laboratory coring method, coolant applied and the need for re-saturation of the test specimens.

(7) Together with the data and results for the particular test, the following should be recorded and reported:

  • the source of test specimen, including depth/level and orientation in space;
  • the dates of specimen preparation and testing;
  • comments on the representativeness of the specimen(s) tested;
  • all dimension and shape measurements, including conformity to requirements;
  • the water content of the sample/specimen (as received, during preparation, saturated);
  • the conditions for drying (air- or oven-drying, pressurised or partial vacuum).

(8) The following information on the samples should be given for the interpretation of the test results:

  • a physical description of the specimen including rock type (such as sandstone, limestone, granite, etc.), location and orientation of inherent rock structural features and any discontinuities, and inclusions or non-homogeneities;
  • a sketch of the test specimen or a colour photograph for other than monotonous homogeneous rock types;
  • a Core Recovery and Rock Quality Designation, where possible;
  • data to substantiate the tolerance checks on deviations of the right cylindrical form of the test specimen, from the flatness of the end bearing surfaces and perpendicularity of the end surfaces with respect to the axis of the core.

Eurocode 7: Geotechnical design — Part 2: Ground investigation and testing