Foundations in low density chalk – a practitioner’s perspective

The assessment of the allowable bearing pressure for shallow foundations in chalk has historically been based on a combination of visual assessment and SPT N value. Research over many years has shown that chalk has a high initial stiffness at low strains up to a yield stress of around 200 kPa. Uncertainty over the stiffness of low density chalks often leads to conservative bearing pressures and routine adoption of piled foundation options. The wider use of geophysical techniques in routine ground investigation is advocated in order to determine site specific stiffness data and hence a less conservative approach to foundation design.