Geoscience Reference
In-Depth Information
Extension
Rod
Drill
Rod
Stop
Pin
2' Core
Barrel
Piston
Core
Liner
(A)
Sealed
Drive
Point
(B)
Core
(C)
(D)
Figure 2.14
Piston sampler: (A) piston sampler entering the hole with a sealed piston drive point
locked in place; (B) pin is then released from the surface with an extension rod, releasing
the drive point; (C) sampler is further driven into the soil; (D) discrete core sample is
collected (
Source
: http://www.esnnw.com/discrete.html).
the inner rods and piston are fixed in a locked position and the outer rods are pushed
down at a constant rate. After withdrawal of the sampler, the sample is sealed at the
top by not removing the piston when the cylinder is disconnected from the sampler
(Andersen, 1981).
The NGI 95mm piston sampler was developed and designed by NGI for use in
both soft and stiff clays. A tower is used during sampling in order to minimize the
number of connections and disconnections. The sampling tube can be connected and
disconnected to the sampler when it is hanging from the tower. The sampler tube is
made of cold-drawn mild steel tubes, with a polished inside surface. As for the 54mm
piston sampler, the displacement method is used for powering the sampler down to the
sampling depth. During penetration the piston is kept in its lower position by locking
the inner rods and pushing the outer rods at a constant rate. To prevent problems with
vacuum at the bottom of the sampling tube during withdrawal, in some cases a thin
plastic tube is fixed to the outer wall of the sampling tube, bringing water from the
surface down to the cutting edge (Andresen, 1981).
The Japanese Committee of Soil Sampling has proposed the Japanese 75mm fixed
piston sampler as the standard in Japan. The boring rod is connected to the upper end
of the sampler head and the sampling tube is connected to the lower end. A locking
