What Does Piston Sample Mean?
A piston sample, in cable percussion boring, is a soil sample obtained by a piston sampler. The cable percussion boring method is used to conduct geotechnical site investigations and can drill boreholes up to 60 meters in depth to obtain different sample types, such as:
- Piston samples
- Cohesive disturbed samples
- Granular disturbed samples
- Undisturbed samples
- Split-barrel samples
Piston samples are obtained from soil layers below the groundwater table that are less cohesive, such as sand as well as sediments with sand content.
Trenchlesspedia Explains Piston Sample
To obtain piston samples, a piston sampler is assembled on a drill rod and lowered to the bottom of a borehole. Additionally, a water swivel is attached to a hose line coupled to the swivel and a pressure pump. When water or air pressure is applied to the drill rods, the piston forces the sample tube into the soft soil or clay to extract a sample. When the sampler has reached its end, the water or air used to press it downward exhausts through a relief hole. The piston sample is then retrieved for analysis.
The piston sampler can only be used below the water table in moderately cohesive soils. Thin-walled aluminum or steel tube samplers are normally used to take the samples.