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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knowledge <strong>of</strong> the consolidation characteristics would serve as a basis for safeguarding against<br />
overloading <strong>of</strong> the piles due to this effect.<br />
Results <strong>of</strong> consolidation tests could also be used to monitor ch<strong>an</strong>ges in effective strength in<br />
structures such as earth-dams <strong>an</strong>d emb<strong>an</strong>kments (which usually consolidate under their own<br />
weight); as well as in the underlying soil strata. This would ultimately serve to aid in the<br />
<strong>an</strong>alysis <strong>of</strong> the long-term stability <strong>of</strong> the structures.<br />
The use <strong>of</strong> results <strong>of</strong> oedometer consolidation tests is, however, usually limited when it comes<br />
to the estimation <strong>of</strong> rates <strong>of</strong> settlement <strong>of</strong> foundation soils. According to Rowe (1972), the<br />
underestimation is attributed to the small size <strong>of</strong> laboratory test specimens used which make it<br />
impracticable to represent m<strong>an</strong>y <strong>of</strong> the natural features <strong>of</strong> soil fabric (fissures, pores,<br />
laminations, other discontinuities), <strong>an</strong>d which have a pr<strong>of</strong>ound effect <strong>an</strong>d control on drainage<br />
<strong>an</strong>d therefore the rate <strong>of</strong> consolidation-settlement. As a result, a given proportion <strong>of</strong> the<br />
ultimate consolidation-settlement is reached in a shorter time in real field situations, th<strong>an</strong> that<br />
predicted from laboratory test data. In addition, extent <strong>of</strong> consolidation is based only on<br />
measurements <strong>of</strong> ch<strong>an</strong>ge in height <strong>of</strong> the specimen; while me<strong>an</strong>s for measuring excess pore<br />
pressure, the dissipation <strong>of</strong> which actually controls the consolidation process is, however, not<br />
provided for in the oedometer consolidation cell.<br />
9.5 Percentage swelling <strong>an</strong>d swelling pressure effects<br />
Results <strong>of</strong> swelling tests show that, in general, black <strong>clays</strong> would exhibit high percentage<br />
swelling (S > 75%) when imposed loads from light <strong>engineering</strong> structures located on <strong>an</strong>d/ or<br />
within, fall below 5 kPa. On the other h<strong>an</strong>d, external imposed loads greater th<strong>an</strong> 80 kPa would<br />
me<strong>an</strong> minimal swelling <strong>of</strong> the <strong>clays</strong>, i.e. S < 10% [S% in this case is the amount <strong>of</strong> swelling<br />
(S mm) under a given load decrement, expressed as a percentage <strong>of</strong> ultimate swelling (Smax<br />
mm) which occurs under zero external loading]. In addition, swelling pressure tests have<br />
shown the black <strong>clays</strong> to exhibit swelling pressures <strong>of</strong> 49-104 kPa. It would therefore be<br />
appropriate that in practice, light <strong>engineering</strong> structures are initially designed to impose loads<br />
<strong>of</strong> well over 100 kPa in order to minimise potential destabilisation effects that may arise from<br />
possible swelling <strong>of</strong> the <strong>clays</strong> on wetting.
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