3.5 Rock sampling
3.5.1 Categories of sampling methods
(1)P Samples shall contain all the mineral constituents of the strata from which they have been taken. They shall not be contaminated by any material from other strata or from additives used during the sampling procedure.
(2)P The discontinuities and corresponding infilling materials existing in the rock mass often control the strength and deformation characteristics of the material as a whole. Therefore, they shall be defined as closely as possible during the sampling operations, if such properties have to be determined.
(3)P Three sampling method categories shall be considered (see EN ISO 22475-1), depending on the quality of sample:
- category A sampling methods;
- category B sampling methods;
- category C sampling methods.
(4) By using category A sampling methods, the intention is to obtain samples in which no or only slight disturbance of the rock structure has occurred during the sampling procedure or in handling of the samples. The strength and deformation properties, water content, density, porosity and the permeability of the rock sample correspond to the in-situ values. No change in constituents or in chemical composition of the rock mass has occurred. Certain unforeseen circumstances such as variations of the geological strata may lead to lower sample quality being obtained.
(5) By using category B sampling methods, the intention is to obtain samples that contain all the constituents of the in-situ rock mass in their original proportions and with the rock pieces retaining their strength and deformation properties, water content, density and porosity. By using category B sampling methods, the general arrangement of discontinuities in the rock mass can be identified. The structure of the rock mass has been disturbed and thereby the strength and deformation properties, water content, density, porosity and permeability for the rock mass itself. Certain unforeseen circumstances such as variations of the geological strata can lead to lower sample quality being obtained.
(6) Category C sampling methods lead to the structure of the rock mass and its discontinuities being totally changed. The rock material may have been crushed. Some changes in constituents or in chemical composition of the rock material can occur. The rock type and its matrix, texture and fabric can be identified.
3.5.2 Rock identification
(1)P Visual rock identification shall be based on examination of the rock masses and samples including all observations of decomposition and discontinuities. The identification shall conform to EN ISO 14689-1.
(2)P Weathering classification shall be related to the geological processes and shall cover the grades between fresh rock and rock decomposed into soil. The classification shall conform to 4.2.4 and 4.3.4 of EN ISO 14689-1:2003.
(3)P Discontinuities such as bedding planes, joints, fissures, cleavages and faults shall be quantified with respect to pattern, spacing and inclination using unambiguous terms. The quantification shall conform to 4.3.3 of EN ISO 14689-1:2003.
(4)P Rock quality designation (RQD), total core recovery (TCR), and solid core recovery (SCR), as defined by EN ISO 22475-1, shall be determined.
3.5.3 Planning of rock sampling
(1)P The characteristics and number of samples to be recovered shall be based on the aim of the site investigations, the geology of the area and the complexity of the geotechnical structure and of the construction to be designed.
(2)P The category of the sampling methods to be prescribed shall be selected according to the rock characteristics to be preserved, as detailed in 3.5.1. and the expected rock and groundwater conditions.
(3)P The requirements of EN ISO 22475-1 shall be followed for the selection of the drilling or excavation methods and sampling equipment.
(4) For a given project, specific sampling equipment and methods may be required within the rock sampling categories defined in 3.5.1.
3.5.4 Handling, transport and storing of samples
(1)P After sampling and visual inspection has taken place, the obtained cores shall be preserved, handled and stored according to EN ISO 22475-1.