![]() The piston acts as a sample protector since it prevents water or loose soils from entering the tube. The tube and piston are locked together by means of a clamping device at the top of the rods. During the sampling process, the sampler is lowered into the borehole with a piston located at the lower end of the tube. The piston is attached to length of rod, which passes through sampler head and run inside the hollow-boring rod. It consists of a thin-walled tube fitted with a piston. Among different type of piston samplers, the one designed by Osterberg has greater advantage to other samplers and is shown clearly in the fig.1 (d). In market, several types of piston samplers are available. This type of sampler ensures the availability of samples of first class quality. In particular situations, when soils are much sensitive to disturbance or soil consists of silts and silty sands, which have some cohesion piston sampler is preferred. ![]() In addition to these dimensions, the inside clearance ratio of the sampler shall be between 0.5 to 3 %. Generally, the diameter of the sampler varies from 40 mm to 125 mm and thickness ranges from 1.25 to 3.15 mm. In case of sensitive clays, Shelby tubes are not considered suitable. The top and bottom of the sampler are carefully waxed, capped and labeled for identification. After driving the Shelby tube, sampler is turned to shear the soil at base of the hole.Īfter taking out the sampler from the hole, the head and shoe of the sampler is removed. However, the tube should not be driven beyond 90 per Cent of its total length. The clear sketch of Shelby tube is shown in Fig.2.6 (a). They are generally used to take undisturbed samples for routine site investigation works. The thin walled seamless steel tubes are called Shelby tubes.
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