6.4.2.6 Sampling using the open-tube sampler

6.4.2.6.1 In addition to the components mentioned in 6.4.2.3, open-tube samplers (OS) consist of a sampler tube with overdrive space and a sampler head with non-return valve tube. The sludge tube shall provide an overdrive space into which the softened material in the borehole can pass. The non-return valve ball and seat shall be adequately sized, so as to permit the free escape of the contained water and air when the sampleenters the tube, and close tightly when the sampler is being withdrawn (see Figure 4). At its upper end, the sample tube is provided with a thread for connection to the sludge tube.

a) Schematic thick-walled open-tube sampler		b) Schematic thin-walled open-tube sampler

Key

6.4.2.6.2 Sampling using the thin-walled open-tube sampler is usually regarded as either a category A or B sampling method, depending the soil conditions (see Table 3).

6.4.2.6.3 Thick-walled open-tube samplers are mostly suitable for stiff and dense soils and for soils containing coarse particles (see line 2 of Table 3). For soil types that are difficult to sample, sample-retaining or closure devices are necessary.

6.4.2.6.4 The thick-walled open-tube sampler is usually regarded as a category B sampling method.

6.4.2.7 Sampling using the piston sampler

6.4.2.7.1 The piston sampler can be used in low-strength fine soils such as silt and clay, including sensitive clays. It can be used either in boreholes or be pushed directly into the soil.

6.4.2.7.2 The piston sampler consists of a sample tube containing a close-fitting sliding piston, which is slightly coned at its lower face. The sample tube is fitted to the sampler head, whereas the piston is fixed to separate rods. This passes through a sliding joint in the sampler head and up inside the drill rods. Clamping devices, operated at ground level, enable the piston and sample tube to be locked together or thepiston to be held stationary while the sample tube is driven down (see Figure 5). When shearing the sample, the piston shall be released or firmly fixed to the ground surface before further advance of the sampler is made. A movement of 1 % of the length of penetration in the piston rod due to tension is acceptable. The length of advance of the sampler shall not be more than the intended length of the sample to avoid compression of the sample.

6.4.2.7.3 Sampling using the piston sampler is usually regarded as a category A sampling method (see Table 3). In certain circumstances, the piston sampler can be used in sands by use of an appropriate core lifter. The sampling category in this case is usually regarded as a category B sampling method. For sampling in clay, a core lifter shall be avoided due to risk of disturbance. If used, it shall be noted in the sampling record.

Key

6.4.3 Sampling using the standard penetration test sampler (SPT)

6.4.3.1 The standard penetration test sampler is mostly used in the standard penetration test according to ISO 22476-3. It takes samples 35 mm in diameter, 450 mm in length and has an area ratio, C_a, of about 100 %.

6.4.3.2 Sampling using the standard penetration test sampler is usually used as a category C sampling method (see Table 3). In certain homogenous fine-grained soils, it can also be used as a category B sampling method.

6.4.4 Sampling using the window sampler

6.4.4.1 A window sampler consists of a hollow tube with a longitudinal slot cut along part of its length (window) and fitted with a shoe having a sharp cutting edge at its lower end. Window samplers are used to take samples by the application of static thrust, by dynamic impact or by percussion. After drivingand removal from the soil, the sample is removed from the window (see Figure C.23).

6.4.4.2 Sampling using the window sampler should only be done in the bottom of a borehole where the soil sample cannot be mixed with overlying soil layers, provided a shutter is not used.

6.4.4.3 Sampling using the window sampler is usually used as a category C sampling method (see Table 3).