Solution:Sampler–Many types of samplers are in use for extracting the soil called undisturbed samples. Only two types of samplers are described here they are–
1. Open drive sampler
2. Piston sampler.
Open drive sampler–The wall thickness of the open drive sampler used for sampling may be thin or thick according to the soil conditions met in the field. A thin walled tube sampler is called as shelby tube sampler, consists of a thin wall metal tube connected to a sampler head.
The thin wall tube which is normally formed from 1/16 to 1/8 inch metal, is drawn in at the lower end and is reamed so that the inside diameter of the cutting edge is 0.5 to 1.5 percent less than that of the inside diameter of the tube.
The thin-wall tube sampler is primarily used for sampling in soft to medium stiff cohesive soils.
Note : Option (b) is correct according to commission.