6 Soil sampling methods

6.1 General

6.1.1 Techniques for obtaining soil samples can generally be divided into the following groups:

• a) sampling by drilling (continuous sampling);
• b) sampling using samplers;
• c) block sampling.

6.1.2 Combinations of these sampling methods are possible and sometimes required due to the geological conditions and the purpose of the investigation.

6.2 Categories of soil sampling methods

6.2.1 There are three categories A, B and C of sampling methods. For given ground conditions, they are related to the best obtainable laboratory quality class of soil samples (defined in EN 1997-2) as shown in Table 1 and Table 2, column 9:

• category A sampling methods: samples of quality classes 1 to 5 can be obtained;
• category B sampling methods: samples of quality classes 3 to 5 can be obtained;
• category C sampling methods: only samples of quality class 5 can be obtained.

6.2.2 Samples of quality class 1 or 2 can only be obtained by using category A sampling methods. The intention is to obtain samples in which no or only slight disturbance of the soil structure has occurred during the sampling procedure or in handling of the samples. The water content and the void ratio of the soil correspond to that in situ. No change in constituents or in the chemical composition of the soil has occurred. Certain unforeseen circumstances, such as varying of geological strata, can lead to lower sample quality classes being obtained.

6.2.3 By using category B samplingmethods, this will preclude achieving sampling quality class better than 3.The intention is to obtain samples containing all the constituents of the in situ soil in their original proportions and the soil has retained 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 as varying of geological strata, can lead to lower sample quality classes being obtained.

6.2.4 By using category C sampling methods, this will preclude achieving sampling quality class better than 5. The soil's structure in the sample has been totally changed. The general arrangement of the different soil layers or components has been changed so that the in situ layers cannot be identified accurately. The water content of the sample may not represent the natural water content of the soil layer sampled.