Section 3 Soil and rock sampling and groundwater measurements
3.1 General
(1)P Sampling of soils and rocks by drilling and excavations and groundwater measurements shall be conducted so comprehensively that the necessary geotechnical design data are obtained.
3.2 Sampling by drilling
(1)P The drilling equipment shall be selected according to:
- the sampling categories required, as defined in 3.4.1 and 3.5.1;
- the depth to be reached and the required diameter of the sample;
- the functions required from the drilling rig, e.g. recording of the drilling parameters, automatic or manual adjustment.
(2)P The requirements of EN ISO 22475-1 shall be followed.
3.3 Sampling by excavation
(1)P If samples are recovered from trial pits, headings or shafts, the requirements of EN ISO 22475-1 shall be followed.
3.4 Soil sampling
3.4.1 Categories of sampling methods and laboratory quality classes of samples
(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 Three sampling method categories shall be considered (EN ISO 22475-1), depending on the desired sample quality as follows (for sample quality see Table 3.1) :
- category A sampling methods: samples of quality class 1 to 5 can be obtained;
- category B sampling methods: samples of quality class 3 to 5 can be obtained;
- category C sampling methods: only samples of quality class 5 can be obtained.
(3) Samples of quality classes 1 or 2 can only be obtained by using category A sampling methods. The intention is to obtain samples of quality classes 1 or 2, in which no or only slight disturbance of the soil structure has occurred during the sampling procedure or in the handling of the samples. The water content and the void ratio of the soil correspond to those in-situ. No change in constituents or in chemical composition of the soil has occurred. Certain unforeseen circumstances such as variations in geological strata may lead to lower sample quality classes being obtained.
(4) Using category B sampling methods will preclude achieving samples of quality classes better than 3. The intention is to obtain samples that contain all the constituents of the in-situ soil in their original proportions and for the soil to retain its natural water content. The general arrangement of the different soil layers or components can be identified. The structure of the soil has been disturbed. Certain unforeseen circumstances such us variation in geological strata may lead to lower sample quality classes being obtained.
(5) By using category C sampling methods, samples of quality classes better than 5 cannot be obtained. The soil structure in the sample has been totally changed. The general arrangement of the different soil layers or components has been modified so that the in-situ layers cannot be identified accurately. The water content of the sample needs not represent the natural water content of the soil layer sampled.
(6)P Soil samples for laboratory tests are divided in five quality classes with respect to the soil properties that are assumed to remain unchanged during sampling and handling, transport and storage. The classes are described in Table 3.1, together with the sampling category to be used.
| Soil properties / quality class | 1 | 2 | 3 | 4 | 5 |
| Unchanged soil properties particle size water content density, density index, permeability compressibility, shear strength |
* * * * |
* * * |
* * |
* |
|
| Properties that can be determined sequence of layers boundaries of strata - broad boundaries of strata - fine Atterberg limits, particle density, organic content water content density, density index, porosity, permeability compressibility, shear strength |
* * * * * * * |
* * * * * * |
* * * * |
* * * |
* |
| Sampling category according to EN ISO 22475-1 | A | ||||
| B | |||||
| C | |||||
3.4.2 Soil identification
(1)P Soil identification, based on the examination of the samples recovered, shall conform to EN ISO 14688-1.
3.4.3 Planning of soil sampling
(1)P The quality class and number of samples to be recovered shall be based on the aims of the soil investigations, the geology of the site, and the complexity of the geotechnical structure and of the construction to be designed.
(2) Two different strategies may be followed for sampling by drilling.
- Drilling aimed at recovering the complete soil column, with samples obtained by the drilling tools down the borehole and by special samplers at selected depths at the borehole bottom.
- Drilling to recover samples only at specific predetermined elevations, e.g. by separately conducted penetration tests.
(3)P The sampling categories shall be selected considering the desired laboratory quality classes, as detailed in Table 3.1 the expected soil types, and groundwater conditions.
(4)P The requirements of EN ISO 22475-1 shall be followed, for the selection of the drilling or excavation methods and sampling equipment adequate to the soil sampling category prescribed.
NOTE The recovery of completely undisturbed samples is practically impossible due to, among other factors, the mechanical disturbance caused by the sampling operations and to the unavoidable stress release when recovering the sample. The effect of these factors on the degree of disturbance depends on the sampling category used and the types of soil being sampled. The type of soil being sampled has a decisive influence on the degree of disturbance of samples obtained by the same sampling methods. Thus very sensitive soils are prone to disturbance, while less sensitive soils, such as most stiff clays, may require less restrictive methods of sampling for obtaining fairly undisturbed samples. On the other hand, each problem requires a different degree of accuracy for the soil parameters to be used. As a consequence, when preparing a sampling programme, the factors mentioned above should be considered in order to decide the degree of disturbance that can be accepted and therefore the sampling methods to be required.
(5) For a given project, specific sampling equipment and methods may be required within the sampling categories defined in 3.4.1. For instance, this is the case when the deformation moduli (stiffness) at small strains have to be determined in undisturbed samples.
(6)P The dimensions of the samples to be recovered shall be in accordance with the type of soil and the type and number of tests to be performed.
NOTE See Section 5 and Annexes L, M, N, P, Q, R and S.
(7) Samples should be taken at any change of stratum and at a specified spacing, usually not larger than 3 m. In inhomogeneous soil, or if a detailed definition of the ground conditions is required, continuous sampling by drilling should be carried out or samples recovered at very short intervals.
3.4.4 Handling, transport and storing of samples
(1)P Handling, transport and storing of samples shall be carried out in accordance with EN ISO 22475-1.
NOTE For handling and storing in the laboratory, see Section 5.
