Stress and time-dependent properties of crushed chalk

Abstract

Although nearly all occurrences of putty/remoulded chalk can be problematic for geotechnical engineers, laboratory studies of its mechanical properties remain infrequent. This paper presents results of a laboratory programme to characterise the mechanical behaviour of reconstituted samples from crushed chalk. Using non-destructive wave velocity propagation measurements by bender elements, a full characterisation of the small-strain shear stiffness (G0) for a range of stress levels and overconsolidation ratios is provided for the first time. The time-related small-strain stiffness and strength gains have also been investigated by ageing fully saturated reconstituted chalk samples under different isotropic stresses for a period up to 72 d. While the increase in strength was found to be negligible, an increase of the soil shear stiffness with time was recorded. Such increase appears to be mostly related to secondary (creep) deformations, although some further increase was also observed when measurable deformations ceased. Beyond the initial shear stiffness, the overall shear behaviour appears to be unaffected by the ageing and is mostly governed by the consolidation stress history and density. These experimental results are expected to benefit the design of geotechnical structures in contact with remoulded or putty chalk, in particular when assessment of small deformation behaviour (serviceability) is required.