an engineering geological characterisation of tropical clays - GBV
an engineering geological characterisation of tropical clays - GBV
an engineering geological characterisation of tropical clays - GBV
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could otherwise lead to erroneous decisions regarding assessments <strong>an</strong>d estimation <strong>of</strong><br />
parameters <strong>of</strong> parent populations (<strong>of</strong> selected soil types). The boundaries/ limits <strong>of</strong> the areas to<br />
be site investigated <strong>an</strong>d sampled were clearly defined <strong>an</strong>d marked. The investigation <strong>an</strong>d<br />
sampling points were then arr<strong>an</strong>ged <strong>an</strong>d distributed in such a way that they covered the<br />
population (or projected area <strong>of</strong> interest) more or less uniformly.<br />
A systematic site investigation <strong>an</strong>d/ or sampling technique was employed in the current study<br />
as the st<strong>an</strong>dard procedure for the black <strong>clays</strong> (Fig. 4.1). The procedure generally involves<br />
dividing the population or the projected area <strong>of</strong> investigation <strong>an</strong>d sampling into a number <strong>of</strong><br />
mutually exclusive subpopulations or strata, over the spatial r<strong>an</strong>ge <strong>of</strong> interest. In this way,<br />
there would be as m<strong>an</strong>y strata as there are to be specimens in the projected sample. During<br />
site investigation <strong>an</strong>d sampling, the position <strong>of</strong> the first specimen taken from the first stratum,<br />
is decided at r<strong>an</strong>dom. Succeeding specimens would then be taken from the same/ similar<br />
position but in their respective strata. According to Cheeney (1983), systematic investigation<br />
<strong>an</strong>d sampling is straightforward, easy to execute, fast; <strong>an</strong>d involves relatively low labour<br />
input. In addition, this site investigation/ sampling scheme is usually adopted as <strong>an</strong> effort<br />
towards improving on the precision <strong>of</strong> estimation <strong>of</strong> some population parameter.<br />
Figure 4.1 illustrates the field arr<strong>an</strong>gement <strong>of</strong> systematic site investigation <strong>an</strong>d sampling as<br />
effected for the black <strong>clays</strong> in this study. Site investigation (soil augering & cone penetration)<br />
points were located at equal intervals <strong>of</strong> 250 m dist<strong>an</strong>ce along pl<strong>an</strong>ned field pr<strong>of</strong>iles. A total<br />
<strong>of</strong> five parallel field pr<strong>of</strong>iles (A, B, C, D, E) in <strong>an</strong> east-west direction, as well as <strong>an</strong>other five<br />
similar pr<strong>of</strong>iles (F, G, H, I, J) in a north-south direction; were used over the extent <strong>of</strong><br />
investigation interest <strong>of</strong> black <strong>clays</strong> across the study area. The interpr<strong>of</strong>ile separation dist<strong>an</strong>ce<br />
was 1000 m for the east-west running pr<strong>of</strong>iles <strong>an</strong>d 2000 m for the north-south pr<strong>of</strong>iles.<br />
Disturbed <strong>an</strong>d undisturbed soil sampling were effected in h<strong>an</strong>d-dug excavation pits (Plates 4.1<br />
& 4.2).<br />
Plates 4.1(a) & (b) H<strong>an</strong>d-dug excavation pits <strong>an</strong>d undisturbed sampling in black <strong>clays</strong>.
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