an engineering geological characterisation of tropical clays - GBV

67
Q: Quartz (1%)
H: Haematite
K: Kaolinite
F: Fluorite (CaF2-Standard)
Tr: Specimen holder
204
16
H
0.0
Figure 6.10. X-ray diffraction diagram of red soils collected at 4,0m depth.
6.4 Scanning electron microscope (SEM) analysis
6.4.1 Scope and method
The scanning electron microscope technique was applied on fresh undisturbed soil specimens
sliced into suitable volume (2cm*2cm*2cm). The analysis was also performed on prepared
specimens of the underlying phonolitic and trachytic rocks. The analysis involved establishing
the morphology, mode of occurrence relative to clayey matrix and diagenetic features of clay
and other minerals. Possible alterations of clay minerals to form other minerals (and vice
versa) were also sought and identified; while relative abundance and type of texture and/ or
fabric (flocculation, randomness, orientations, lamination) of minerals were also investigated
and established. In addition, the porosity, interconnection of pores and permeability
(possibility of water movement/ percolation) of the soils were assessed.
The analysis employed a Leiz Scanning electron microscope (Modell: ISI Super 40/3A)
manufactured by International Scientific Instruments (ISI, 1972). The microscope
incorporated a Eumex detector having Lithium fitted with an ultra-thin Beryllium window to
facilitate element measurements in the range of carbon (C) to Uranium (U). Use was also
made of Hardware for High Performance X-ray Micro-analysis (EDX: WINEDS) as well as
Wineds 3.0 & Edisson 32 Software for element analysis (Thomson Scientific Instruments Pty
Ltd. & Fa.Getac, 1995). In addition, Hardware for digital photo-processing with
Rasterelektronenmikroskop (REM PC Einsteckkarte); as well as WinDISS 2.0 Software for
digital photo-taking, were employed (Fa.Point Elektronic GmbH, 1997).