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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30<br />
Chapter 4<br />
Field methods<br />
4.1 Introduction<br />
The principal objectives <strong>of</strong> the field study were to:<br />
(i)<br />
(ii)<br />
(iii)<br />
(iv)<br />
Provide information on the nature <strong>an</strong>d distribution <strong>of</strong> black cotton soils (exp<strong>an</strong>sive<br />
<strong>an</strong>d reactive soils) <strong>an</strong>d red soils <strong>of</strong> the study area.<br />
Acquire site specific information on environmental characteristics which impact<br />
on in situ soil behaviour (groundwater conditions, climate, vegetation).<br />
Investigate <strong>an</strong>d model depth variation <strong>of</strong> soils across the study area.<br />
Compare in situ soil properties, behaviour <strong>an</strong>d derived parameters with those<br />
predicted <strong>an</strong>d/ or derived from laboratory studies.<br />
The cone penetration sounding, soil augering, in-situ description <strong>of</strong> soils <strong>an</strong>d underlying rock,<br />
tests for possible carbonate content, as well as undisturbed <strong>an</strong>d disturbed soil sampling were<br />
carried out, among others. Documentation <strong>of</strong> results was done according to known st<strong>an</strong>dards<br />
(BGR, 1996; DIN 4021/ 4096, 1980; IAEG, 1981; ISRM, 1978; NLfB & BGR, 1991).<br />
The sampling technique was selected <strong>an</strong>d pl<strong>an</strong>ned in such a way as to facilitate collection <strong>an</strong>d<br />
provision <strong>of</strong> high quality <strong>an</strong>d detailed data for validating models <strong>an</strong>d assessing variation <strong>of</strong><br />
<strong>engineering</strong> soil properties across the project area.<br />
4.2 Investigation <strong>an</strong>d sampling scheme<br />
A number <strong>of</strong> site investigation <strong>an</strong>d sampling schemes have been devised by practical<br />
statistici<strong>an</strong>s, <strong>an</strong>d are available for use by geologists (Koch <strong>an</strong>d Link, 1970; Krumbein <strong>an</strong>d<br />
Graybill, 1965; Meyer, 1975; Wetherill, 1966; ). According to Cheeney (1983), the principal<br />
motivation for the diversity <strong>of</strong> available procedures is the need to achieve maximum<br />
efficiency <strong>an</strong>d precision within constraints <strong>of</strong> cost, time, effort, available facilities, m<strong>an</strong>power<br />
skills <strong>an</strong>d specimen accessibility. However, the application <strong>of</strong> these schemes may be<br />
hampered <strong>an</strong>d/ or limited by the fact that, <strong>geological</strong> materials <strong>an</strong>d observations are frequently<br />
hard won under difficult circumst<strong>an</strong>ces.<br />
A site investigation/ sampling pl<strong>an</strong> is a fundamental part <strong>of</strong> the study <strong>of</strong> soils, especially as<br />
may regard the assessment, <strong>an</strong>alysis <strong>an</strong>d evaluation <strong>of</strong> the spatial distribution <strong>of</strong> import<strong>an</strong>t<br />
<strong>engineering</strong> <strong>geological</strong> characteristics <strong>an</strong>d/ or parameters. The use <strong>of</strong> <strong>an</strong> unsuitable <strong>an</strong>d<br />
inadequate procedure could lead to bias in the observation <strong>an</strong>d selection <strong>of</strong> specimens, with a<br />
consequent distortion <strong>of</strong> the outcome <strong>of</strong> import<strong>an</strong>t soil studies <strong>an</strong>d evaluations such as<br />
hypothesis testing <strong>an</strong>d statistical tests. It is therefore essential that the field investigation/<br />
sampling method adopted is such as to allow for the acquisition <strong>of</strong> necessary information <strong>an</strong>d<br />
soil samples which are free as much as possible from bias. This is because a biassed set <strong>of</strong><br />
observations <strong>an</strong>d/ or sample would only serve to give a biassed impression <strong>of</strong> the parent<br />
population from which it was drawn (Cochr<strong>an</strong>, 1977).<br />
In the present study, field investigations <strong>an</strong>d sampling were carried out with the aim <strong>of</strong><br />
achieving both descriptive <strong>an</strong>d <strong>an</strong>alytical objectives <strong>of</strong> soils. Among the <strong>an</strong>alytical objectives<br />
is hypothesis testing, the methods <strong>of</strong> which are based on samples. Attempts were therefore<br />
made to avoid choosing <strong>an</strong>d applying defective site investigation <strong>an</strong>d sampling practices that