2.4.1.4 Sampling
(1)P The sampling categories (see 3.4.1 and 3.5.1), and the number of samples to be taken shall be based on;
- the aim of the ground investigation;
- the geology of the site;
- the complexity of the geotechnical structure.
(2)P For identification and classification of the ground, at least one borehole or trial pit with sampling shall be available. Samples shall be obtained from every separate ground layer influencing the behaviour of the structure.
(3) Sampling may be replaced by field tests if there is enough local experience to correlate the field tests with the ground conditions to ensure unambiguous interpretation of the results.
(4) Further details on sampling are given in Section 3.
2.4.1.5 Groundwater
(1)P Groundwater measurements shall be planned and carried out in accordance with 3.6.
2.4.2 Laboratory tests
2.4.2.1 General
(1)Prior to setting up a test programme, the expected stratigraphy at the site should be established and the strata relevant for design selected to enable the specification of the type and number of tests in each stratum. Stratum identification should be a function of the geotechnical problem, its complexity, the local geology and the required parameters for design.
2.4.2.2 Visual inspection and preliminary ground profile
(1) Samples and trial pits should be inspected visually and compared with field logs of the drillings so that the preliminary ground profile can be established. For soil samples, the visual inspection should be supported by simple manual tests to identify the soil and to give a first impression of its consistency and mechanical behaviour.
(2) If distinct and significant differences in the properties between different portions of one stratum are found, the preliminary soil profile should be further subdivided.
(3) Where practicable, the quality of the sample should be assessed before laboratory tests are performed. Quality classes for soil samples are defined in Table 3.1.
2.4.2.3 Test programme
(1)P The type of construction, the type of ground and stratigraphy and the geotechnical parameters needed for design calculations shall be taken into account when setting up the laboratory test programme.
(2) The laboratory test programme depends in part on whether comparable experience exists. The extent and quality of comparable experience for the specific soil or rock should be established. The results of field observations on neighbouring structures, when available, should also be used.
(3)P The tests shall be run on specimens representative of the relevant strata. Classification tests shall be used to check whether the samples and test specimens are representative.
NOTE This can be checked in an iterative way. In a first step, classification tests and strength index tests are performed on as many samples as possible to determine the variability of the index properties of a stratum. In a second step, an assessment of how representative the samples used for the strength and compressibility tests are of the stratum can be checked by comparing the results of the classification and strength index tests for the samples with all results from the classification and strength index tests for the stratum.
(4) The need for more advanced testing or additional site investigation as a function of the geotechnical aspects of the project, soil type, soil variability and computation model should be considered.
2.4.2.4 Number of tests
(1)P The necessary number of specimens to be tested shall be established depending on the homogeneity of the ground, the quality and amount of comparable experience with the ground and the geotechnical category of the problem.
(2) To allow for difficult soil, damaged specimens and other factors, additional test specimens should be made available, whenever possible.
(3) Depending on the test type, a minimum number of specimens should be investigated.
NOTE A recommended minimum number for some test types can be taken from the tables in Annexes L to W (except Annexes O and T). The annexes can also be used to check whether the extent of the testing was sufficient.
(4) The minimum number of tests may be reduced if the geotechnical design does not need to be optimised and uses conservative values of the soil parameters, or if comparable experience or combination with field information applies.
2.4.2.5 Classification tests
(1) Soil and rock classification tests should be performed to determine the composition and index properties of each stratum. The samples for the classification tests should be selected in such a way that the tests are approximately equally distributed over the complete area and the full depth of the strata relevant for design. Thus the results should give the range of index properties of the relevant layers.
(2) The results of the classification tests should be used to check if the extent of the investigations was sufficient or if a second investigation stage is needed.
(3) Suitable routine classification tests for ground samples with various degrees of disturbance are presented in Table 2.2. The routine tests are generally performed in all phases of the ground investigation (see 2.2 (3)).
