The 1D normal compression line and structure permitted space of low–medium density chalk

Abstract

The one-dimensional (1D) normal compression behaviour of low–medium density chalk is investigated by way of high-pressure oedometer tests on intact and reconstituted specimens. Test results reveal that a single 1D normal compression line (NCL) exists for reconstituted chalks within the assessed density range, a feature that has not been reported previously. Laser diffraction particle-size analyses and scanning electron microscopy indicate that the ‘uniqueness’ of the NCL may be associated with comparable grain shapes and size distributions, and to grain breakage. These observations underscore the applicability of critical state concepts to describe the mechanical behaviour of reconstituted chalk. The compression paths of intact samples and the NCL for reconstituted chalk define an intact density-controlled structure-permitted space, which is used to estimate macroscopic bond strength. These calculations show that low-density intact chalk is far more reliant on cement bonds than medium density intact chalk to tolerate loading without exhibiting plastic straining. Therefore, the increase in intact strength observed with greater densities appears to result principally from stronger fabric, rather than stronger bonding.