Geoscience Reference
In-Depth Information
The sample collection process must fulfil numerous regional requirements as well.
These requirements are determined by a variety of factors that affect how samples
should be collected for an individual sampling event. These factors include:
1. The type of samples being collected (organic/inorganic, aqueous or soil/sediment)
2. How the samples will be analyzed
3. Acceptance or performance criteria
The processes by which a sample can be disturbed during sampling and laboratory
testing are (Hvorslev, 1949):
1. Change in stress conditions
2. Change in water content and void ratio
3. Disturbance of the soil structure
4. Mixing and segregation of the soil constituents
This disturbance can be related to sampler design, sampling, handling and storage.
Many authors have discussed the factors that influence sample quality, in particular
Hvorslev (1949) and Kallstenius (1963).
Peat often contains more than 90% water but has fibrous/spongy layers that are
difficult to cut without causing compression, particularly if using a tube sampler. This
has to be relatively wide, sharp, possibly toothed and inserted gradually, preferably
by rotation or rapid vibration. There are two primary potential problems: improper
sample collection and selection of the sampler for specific soil conditions. This causes
disturbance of the matrix, resulting in compaction of the sample or inadequate homog-
enization of the samples where required, resulting in variable, non-representative
results.
Soil samples may be collected using a variety of methods and equipment depending
on the depth of the desired sample, the type of sample required and the soil type. Near-
surface soils may be easily sampled, while sampling at greater depths may be performed
using a hand auger, continuous flight auger, a trier or a split-spoon.
2.5.1 Disturbed but representative sampling
Samples that are disturbed in a geotechnical sense (changed density and mechanical
properties) but representative of the type and proportion of the constituents and water
content can be obtained at shallow depths by manually operated samplers such as a
Hiller borer, Davis sampler, Finnish piston-type sampler or Scottish Macaulay sampler
(
Muskeg Engineering Handbook
, 1969; Peat Testing Manual, 1979). Macaulay sam-
pler has a vane or cover. It is inserted into position by pushing with the vane closed.
Rotating the sampler opens the vane and the edge of the vane removes a one-half cylin-
der of material that is relatively undisturbed by rotation. It is evaluated to be the best
available sampler for one-person operation (Peat Testing Manual, 1979). Two types
of shallow sampler are reportedly used in Japan: a sampler with a cover (similar to
a Macaulay sampler) and a piston sampler (Noto, 1991). Split-spoon samplers can
