6.5 Block sampling
6.5.1 Sampling from trial pits
6.5.1.1 In sampling from a trial pit, samplers with cutting procedure are used or block samples are recovered.
6.5.1.2 Block samples in cohesive soils can be cut by hand or by a handheld saw. The following precautions shall be taken:
- a) remoulded soil shall be carefully removed from the sampling spot;
- b) no extraneous water shall come into contact with the sample;
- c) the sample should be protected from sunshine, frost and winds;
- d) immediately after the sample has been cut, it shall be covered.
6.5.1.3 In soils with adequate cohesion, samples can be cut out by hand, care being taken to ensure that their dimensions are at least equal to those of the sampler tube shown in Figure C.31. Samplingfrom trial pits executed in such a way is usually used as category A or B sampling method.
6.5.1.4 In sampling from trial pits, samples are removed from the bottom,any slopes or walls of a trial pit using a sampling device as shown in Figure C.31. Sampler tubes according to Figure C.31 b) may only be used in soils with a maximum particle size up to 5 mm. The sampler tube shall be driven into the soil by hand or, where this is not possible, it shall be driven into the soil either by thrust or using a drop weight or sliding hammer and the sample recovered as shown in Figure C.31 c). In sampling dense sands, there is the possibility of losing sample material during extraction of the sampler tube. Such material shall be included in the sample to complete the sample.
6.5.2 Sampling using large samplers
6.5.2.1 The principles of sampling using a large sampler shall be as follows (see also C.15):
a) Preparation of the borehole:
The preparationof a borehole for a large sampler requires the useof a solid auger with a larger diameter. The borehole can be supported by mud, or be cased down to the sampling level. Before lowering a large sampler into the borehole, any loose debris or disturbed material shall be removed from the bottom of the borehole using a flat bottom auger with a larger diameter.
b) Sampling procedure and sample recovery:
A large sampler can be operated by any drilling rod system that enables the relevant modes of operations for the sampler. The large sampler should be advanced at a slow rate into the soil, using a combination of static thrust, rotation and/or flushing. The sample shall be carefully separated from the surrounding soil before recovery and brought to the surface with minimum disturbance. Precautions should be taken to reduce the effect of suctionwhen the sample is separated from the adjacent soil,and to avoid shocks and vibrations transferred to the rod system during upheaval of the sample.
6.5.2.2 Sampling using a large sampler is usually used as a category A sampling method.
| Soil type | Suitability depends on e.g. | Sampling method | ||
| Category A | Category B | Category C | ||
| Clay | Stiffness or strength sensitivity plasticity | PS-PU OS-T/W-PU b OS-T/W-PE a OS-TK/W-PE a, b CS-DT, CS-TT LS, S-TP, S-BB |
OS-T/W-PE OS-TK/W-PE CS-ST HSAS AS a |
AS |
| Silt | Stiffness or strength sensitivity groundwater surface | PS OS-T/W-PUb OS-TK/W-PE a, b LS, S-TP |
CS-DT, CS-TT OS-TK/W-PE HSAS | AS CS-ST |
| Sand | sizes of the particles density groundwater surface |
S-TP OS-T/W-PU b |
OS-TK/W-PE b CS-DT, CS-TT HSAS |
AS CS-ST |
| Gravel | size of the particles density groundwater surface |
S-TP | OS-TK/W-PE a,b HSAS |
AS CS-ST |
| Organic soil | state of decay | PS OS-T/W-PU b S-TP |
CS-ST HSAS AS a |
AS |
| a Can be used only in favourable conditions. b See also 6.4.2.3 for the detailed geometry. |
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| Key OS-T/W-PU Open-tube samplers, thin-walled/pushed OS-T/W-PE Open-tube samplers, thin-walled/percussion OS-TK/W-PE Open-tube samplers, thick-walled/percussion PS Piston samplers PS-PU Piston samplers, pushed LS Large samplers |
CS-ST Rotary core drilling, single tube CS-DT, CS-TT Rotary core drilling, double or triple tube AS Augering HSAS Hollow stem augering S-TP Sampling from trial pit S-BB Sampling from borehole bottom |
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