Thick wall samplers are those having the area ratio greater than 10 percent. The samplers are classified as thick wall or thin wall samplers depending upon the area ratio. The non-retum valve, invariably provided in samplers, should permit easy and quick escape of water and air when driving the sampler. Lower value of inside clearance allows the elastic expansion of soil and reduces the frictional drag. The walls of the sampler should be smooth and should be kept properly oiled so that wall friction is minimum. The inside clearance should lie between 1 to 3 percent and the outside clearance should not be much greater than the inside clearance.
It should not be greater than 25 percent for soft sensitive soil, it should preferably not exceed to porcent. The area ratio should be as low as possibie. The following terms are defined with respect to the diameters marked in Fig. 2.18 shows a typical cutting edge of a sampler, with the lower end of the sampler, with the lower end of the sampler tube. The design features of the sampler, that govern the degree of disturbance are (i) cutting edge (ii) inside wall friction and (iii) non-return valve.įig. The sampling tube when forced into the ground should cause as little remoulding and disturbance as possible.
To take undisturbed samples from bore holes properly designed sampling tools are required. The sample disturbance depends upon the design of the samplers and the method of sampling. An undisturbed sample is that in which the natural structure and properties remain preserved. Such a soil sample should, however, be representative of the natural soil by maintainlng the original proportion of the various particles intact. A disturbed sample is that in which the natural structure of soil gets partly or fully modified and destroyed although with suitable precautions the natural water content may be preserved.
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