Environmental Engineering Reference
In-Depth Information
Samplers
Drive samplers (Figure 2.71):
Either split-barrel samplers or tubes are driven with a 176 lb
(80 kg) hammer dropped 10 ft (3 m) by release of a wire-hoisting drum. Penetration is only
approximated by measuring sample recovery since the sampler is attached to the wire, not
to drill rods. Recovery is related to the blow count for a rough estimate of relative density.
Tube samples recovered in deep water at substantial depths below the seafloor in stiff
clays will undergo significant strength decrease from stress release upon extraction from
the seabed and extrusion in the shipboard laboratory.
Pushed-tube and piston samplers:
See
Section 2.3.4
for operations offshore.
Sampling to Shallow Penetration without Drill Rigs and Casing
General
Various devices and methods are available for sampling shallow seafloor conditions without
the necessity of mounting a drill rig on a platform and maintaining a fixed position for
extended time intervals. Sampling procedure involves operating the equipment from the side
of a vessel equipped with a crane. Sampling is generally not feasible in strong materials or to
bottom penetration depths greater than about 40 ft (12 m), depending upon the device used.
Wire
Drop
weight
Drive
length
Sample
tube
FIGURE 2.71
Wireline drive sampler: (a) before driving, (b) after driving.
(a)
(b)
