GEOTECHNICAL & CIVIL ENGINEERING
MECHANICAL CHARACTERISATION OF TIME AND STRESS-DEPENDENT PROPERTIES OF PUTTY CHALK GRZEGORZ BIAŁOWAS
University of Bristol | UK
While nearly all occurrence of putty/remoulded chalk can be problematic for geotechnical engineers because of the degraded strength and stiffness characteristics, laboratory studies of its mechanical properties remains infrequent. The results of an extensive laboratory campaign aiming to provide an advanced mechanical characterization, from small strain stiffness to large strain strength and deformation properties of reconstituted samples from crushed chalk (i.e. putty chalk). Using non-destructive wave velocity propagation measurements by bender elements, a full characterization of the small strain shear stiffness (G0) for a range of stress levels and over-consolidation ratios is provided for the first time. By aging fully saturated reconstituted chalk samples under different isotropic stresses (period up to 72 days), the age related small-strain and strength gains have also been investigated. While strength increases were found to be negligible, a consistent increase of the soil shear stiffness with time was recorded by wave propagation measurements. Such increase appears to be mostly related with secondary (creep) deformation. The main focus of this research was to characterise and clarify some fundamental aspects of the mechanical behavior of reconstituted chalk for civil engineering purposed. The project’s objectives have been pursued by carrying out an extensive experimental investigation on reconstituted chalk samples from slurry. The emphasis of this research was directed to explore the influence of the stress levels, stress history and ageing on the evolution of the principal mechanical properties, such as strength and stiffness, during the samples’ consolidation and shearing. This parameters are commonly used in everyday engineering practice.