Geoscience Reference
In-Depth Information
For shallow samples, block samplers can be obtained. Typically a pit is excavated
and blocks of peat are removed from the pit wall. Large block samples (250mm
square) can be obtained from below the ground and groundwater surface (down to
a depth of 7m) using a block sampler for peat described by Landva
et al
. (1983). It
provides somewhat disturbed samples, but retains their general structure. There are
other large-size down-hole block samplers, such as the Sherbrooke sampler (250mm
in diameter) and Laval sampler (200mm in diameter), which have been developed for
sampling clays but can also be used for organic soils and probably for peat. Hebib
(2001) describes a novel method that was employed to obtain 1m
3
block samples of
Ballydermot peat, Co. Offaly, Ireland. Samples were taken from a vertical face, 2.5m
high, using a custom-made block sampler attached to the lifting arm of a tracked
excavator. The sampler was fabricated from a steel box that had three faces removed.
Each of the remaining exposed faces had sharpened edges so as to minimize disturbance
during sampling. The retrieved samples were wrapped in polythene to prevent loss of
moisture and placed in wooden boxes for transportation to the laboratory.
A sampler for collecting undisturbed peat was developed by Duraisamy
et al.
(2009). It consisted of a hollow cylinder of 150 mm internal diameter connected to a
100 cm long stem. The top of the stem was provided with a handle 60 cm wide for
pushing the sampler into the peat. The sampler was formed from a hollow cylindrical
body with a cover plate at the top, and a thin tube with a valve was provided. The valve
was designed to be left open during sampling to release both air and water pressure.
Meanwhile, the lower part of the cylindrical tube was kept sharpened to cut roots
as the auger slowly rotated into the peat ground during sampling. Once the augur
reached the desired depth of sampling, the valve was closed prior to withdrawal of the
tube with the peat sample enclosed, thus providing a vacuum effect to help hold the
sample in place. Soon after the sampler was withdrawn, the sample was sealed in the
cylindrical tube with paraffin wax (Figure 2.17).
Once in the laboratory, the top cover of the cylindrical tube is opened to extract
the sample. The auger enables the extraction of peat core samples 150mm in diameter
and 230mm long. The top and bottom of the sample were trimmed. As fibrous soil,
such as peat, is easily disturbed, the trimming process was done very carefully and
quickly to minimise any change to the soil sample's water content. All tests reported
here were performed inside the lab maintained at a constant temperature of 20
2
◦
C
±
(Kazemian and Huat, 2009; Duraisamy
et al.
, 2009).
2.5.3 In situ tests
There are no special tools available for determining the
in situ
properties of peat.
Therefore select methods that have been developed for use in soft clays are used either
directly or in a somewhat modified manner to test peat and organic soils. Because of
the nature of these soils, certain methods have gained prominence over others. The
methods of interpreting the
in situ
test results as applied to peats and organic soils are
limited in the literature, and direct use of methods primarily developed on the basis
of mineral soil experience should be conducted with great caution. Because of the
greater variability and fabric effects in organic deposits, larger numbers of
in situ
tests
and complementary sampling and laboratory testing are required to arrive at design
properties. Some of the more common approaches to
in situ
testing in such deposits
