Undisturbed samples are may be obtained from boreholes by open drive samplers or piston samplers. Open drive samples consist of thin-walled tubes which are pushed or driven in to the soil at the bottom of the hole and then rotated to detach the lower end of the sample from the soil. Most soft or moderately stiff cohesive soil can be sampled without extensive disturbance in thin-walled seamless steel tubes having diameter not less 50 mm. the lower end of the tube is sharpened to from a cutting edge and the other end is machined for attachment to the drill rods. The entire tube is pushed or driven in to the soil at the bottom of the hole and is removed sample with inside. The two ends of the tube are then sealed and sample shifted to the laboratory.

Undisturbed samples which are to be tested after some time should be maintained in such a way that the natural water content is retained and no evaporation are allowed.

Usually, two coats of 12mm thick paraffin wax and petroleum jelly are applied in molten state on either end of the sample is preserved in a humidity controlled room. In the absence of such facilities, the sampling tubes should be covered by Hessian bags and sprinkled with water from time to time. Block samples may be coated with 6mm thick paraffin wax and kept in air-tight box with saw dust filling the annular space between the box and the sample.