The Upper Cretaceous Chalk Group of the UK covers a significant area of the south-east and east of England, and underlies several major cities, including London. This widespread distribution has led to several major infrastructure projects involving chalk. Weathering in chalk is difficult to identify and its distribution is poorly documented within current literature. Weathering is known to affect both
geomechanical and hydrogeological properties but there are uncertainties as to the extent of these physical changes, both on the material and rock mass scale.
This study combines observational field techniques with industry best-practice to investigate chalk weathering. It introduces novel field-based uniformity surveys using non-destructive methods and develops novel sampling methods to enable laboratory testing. Laboratory testing underpins
observations made in the field and allows characterisation of de-structured chalk.
Field measurements have shown that current industry standard methodologies produce consistently higher CIRIA density grades compared measured grades. Laboratory testing demonstrated that CIRIA D-grade chalks are observed to be one CIRIA grade lower than structured chalks and are not close to saturation like their parent material. Geomechanical testing showed that de-structured chalk is 11 – 12 times weaker than structured chalk and can behave as both a stiff soil or weak rock (exhibiting both brittle and ductile failure), while permeability testing identified a reduction in permeability with increasing effective stress.
This research has developed knowledge of the types of weathering present at select field sites and has characterised their extent. Novel methods of sampling and testing have been developed, which has enabled the characterisation of geomechanical and hydrogeological properties of de-structured chalk deposits. Laboratory testing has identified significant differences between de-structured chalk deposits compared to parent material, and has produced quantified useful parameters. This thesis lays a clear path for the further study of chalk weathering.