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Chapter 5
Sampling probes
Shelby soil sampler
| SHELBY SOIL SAMPLER 5.3 | ||
| General principles The Shelby sampler (Figure 44) is a thin-walled soil sampling system. The system is used to sample soils that are particularly sensitive to sampling disturbance as it has a very low wall thickness-to-sample area ratio. The sampler consists of a thinwalled steel tube whose lower end is shaped to form a cutting edge. It is pushed into the soil by continuous static thrust from a hydraulic jack. This sampler is usually only suitable for cohesive soils up to a firm-to-stiff consistency and free from large particles. It normally gives Class 1 samples of fine cohesive soils, including sensitive clays. Samples of 75, 100 or 150 mm in diameter can be obtained. The thin-walled Shelby sampler is not fitted out with a core catcher. However, a thicker-walled sampler with a core catcher is available. |  | |
| Disturbance It should be noted that disturbance occurs at the base of the borehole in weak soil below a certain depth due to stress relief resulting from reduced over-burden pressure. Therefore, pushing the Shelby sampler in using CPT equipment can overcome this to some degree. At the end of the sampling process the thin steel tube containing the sample is removed from the sampler head, waxed, capped at both ends and labelled. The steel tube is used as a container to transport the sample to the laboratory thus avoiding any damage to the sample. Cohesive soils The Shelby sampler is ideally used for normally-consolidated and over- consolidated cohesive soils such as London Clay. It is not suitable for granular non-cohesive soils. The disadvantage of the Shelby sampler – in comparison to the Mostap sampler which can take samples at preselected depths – is that it has an open end (no cutting mouth) so it is necessary to start from ground level or pre-drill a borehole. Further problems are encountered where the sample hole does not remain open. In these situations the hole must be cased to prevent sampling of ‘fall-in’ materials. |