Abstract
A series of laboratory tests was undertaken to investigate the prolonged time taken by soft chalk and soft chalk/clay mixtures placed in embankments on the M4 motorway to stabilize sufficiently for further fill to be placed on top. It is shown that the presence of the clay both severely increases the setting time and reduces the ultimate bearing strength of the chalk. Also, that the air voids of uncontaminated soft upper chalk should be between 5% and 10% for maximum bearing strength immediately after compaction. It is argued that minimum compaction compatible with acceptable long-term settlement is the most effective method of forming soft chalk embankments with minimal risk of interruption due to instability of the chalk mass. (Author/TRRL)
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