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cores bore very little similarity to Chalk Grades obtained from SPT ‘N’ values. These results
suggest that the SPT values should be treated separately from a Grade Classification.
The site investigations at Mundford and Bury St Edmunds, combined with geological and
engineering geology logging at Grimes Graves (Mortimore, 1979), provided invaluable
information on the stratigraphy, structure and sedimentology of the Chalk in north-west
Suffolk and south-west Norfolk. In the Mundford investigations, Gallois (in Ward et al.,
1968) illustrated the stratigraphy (Fig. 11) and showed that the ‘high-strength’ high density
Mundford Grade I chalks were associated with the lithological unit then known as the
Melbourn Rock. In the overlying equivalent of the New Pit and Lewes Chalk formations
Gallois (in Ward et al., 1968) recognised the presence of intraformational channels (Gallois
pers. comm.; Ward et al., 1968, fig. 5a) which locally cut out marker beds such as the Twin
Marls. In addition, the Mundford investigations illustrated the presence of local low amplitude
folding in the Chalk.
Correlations between the Mundford Site and the Bury St Edmunds Sugar Silo boreholes (Fig.
11) indicated that there were lateral changes in thickness and the degree to which nodular
chalks and/or hardgrounds were developed, and changes in their stratigraphic range. It seemed
likely that the nodular chalk layers characteristic of the Lewes Chalk present at Bury St
Edmunds possibly died-out northwards into south Norfolk.
Both the Mundford and Bury St Edmunds investigations illustrated the relationship between
Chalk Grade and mechanical properties (e.g. Ward et al., 1968, table 6), especially in relation
to ground settlement beneath cyclically loaded foundations. The CERN site at Mundford was
located with the simplicity of the underlying geology in mind, particularly the low angle of
stratal dip, relatively uniform and consistent lithologies, and lack of Quaternary palaeovalleys
cut into the Chalk.