an engineering geological characterisation of tropical clays - GBV
an engineering geological characterisation of tropical clays - GBV
an engineering geological characterisation of tropical clays - GBV
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
185<br />
On the other h<strong>an</strong>d, laboratory measured plasticity values (PImeas.) compare exactly <strong>an</strong>d are<br />
practically the same as calculated values (PILS) derived using the new relationship (PI =<br />
1,88*LS) developed <strong>an</strong>d established in this study for the black <strong>clays</strong>. The relationship<br />
between the calculated <strong>an</strong>d measured plasticity indices is practically identical at both depths<br />
<strong>of</strong> less th<strong>an</strong> 0,50m i.e.<br />
PImeas. = 1,00PILS (10.6)<br />
<strong>an</strong>d those <strong>of</strong> 0,50m <strong>an</strong>d greater, i.e.<br />
PImeas. = 1,01PILS (10.7)<br />
so that the black <strong>clays</strong> must be uniform <strong>an</strong>d homogeneous in their <strong>engineering</strong> character<br />
across the study area. An average relationship <strong>of</strong><br />
PImeas. = 1,005PILS (10.8)<br />
could be adopted for the two sets <strong>of</strong> plasticity indices.<br />
The red soils involved in this study were investigated <strong>an</strong>d <strong>an</strong>alysed in a similar way.<br />
Laboratory determined values <strong>of</strong> plasticity index are presented alongside those derived by<br />
calculation using the British St<strong>an</strong>dard relationship in Table (10.2). A comparison <strong>of</strong> the<br />
minimum <strong>an</strong>d maximum values as well as the medi<strong>an</strong>, mode <strong>an</strong>d me<strong>an</strong> values <strong>of</strong> the two sets<br />
<strong>of</strong> data reveals a slight overestimation <strong>of</strong> the calculated plasticity indices with respect to the<br />
laboratory measured values, <strong>an</strong>d this most probably due to reasons already stated above as for<br />
black <strong>clays</strong>. A covari<strong>an</strong>ce <strong>of</strong> 0,76 <strong>an</strong>d moderately strong correlation <strong>of</strong> 0,54 was also recorded<br />
for the two sets <strong>of</strong> data.<br />
A correlation <strong>of</strong> laboratory measured linear shrinkage (LS) <strong>an</strong>d plasticity index (PI) yielded<br />
new relationships for estimating the latter parameter from the former for the red soils (Fig.<br />
10.3), i.e.<br />
PI = 1,77LS (10.9)<br />
for the sampling area Rd1 <strong>an</strong>d<br />
PI = 1,90LS (10.10)<br />
for the sampling area Rd2, respectively. An average relationship <strong>of</strong><br />
PI = 1,83LS (10.11)<br />
was derived <strong>an</strong>d established for the red soils. Plasticity index values (PILS) derived by<br />
calculation from laboratory linear shrinkage (LS) values using this new relationship are also<br />
included in Table (10.2) for comparison purposes. The so calculated <strong>an</strong>d laboratory measured<br />
(PImeas.) plasticity index values are perfectly in close agreement <strong>an</strong>d/ or practically identical in<br />
terms <strong>of</strong> their maximum <strong>an</strong>d minimum values as well as medi<strong>an</strong> <strong>an</strong>d me<strong>an</strong> values. A<br />
covari<strong>an</strong>ce <strong>of</strong> 0,65 <strong>an</strong>d moderately strong correlation <strong>of</strong> 0,54 were registered for the two sets<br />
<strong>of</strong> data.