Mechanical response of a medium-fine-grained decomposed granite in Hong Kong

Completely decomposed granite (CDG) is abundant in Hong Kong. It has been used extensively as fill materials in various applications, such as back-filling materials for retaining structures and pavements. In this paper, results of a series of triaxial tests, including isotropic and anisotropic compression, and drained and undrained shearing tests, on a medium-fine-grained re-compacted CDG with overconsolidation ratio ranged between 1 and 8 are reported. The tests aim to understand the mechanical behavior of the soil in its saturated state under various initial states, stress paths and drainage conditions. It is found that the material is highly compressible during virgin isotropic and anisotropic compression. Moreover, the virgin compression lines are uniquely associated with their stress ratios and they appear to parallel to each other in an e-lnp′ plane. All specimens exhibit strain-hardening type response during drained shearing. In undrained shear, normally consolidated specimens reveal contractive response until the ultimate states are reached. Overconsolidated specimens, however, show complex stress paths and volumetric tendency. Dilatancy responses of the soil during a constant stress ratio compression and deviatoric shear are discussed respectively. Unique isotropic compression line (ICL) and critical state line (CSL) are reported for the studied soil.

► A detailed triaxial testing procedure of re-compacted decomposed granite is presented.
► Mechanical behavior of normally and over-consolidated re-compacted completely decomposed granite is studied.
► Stress-strain response of the material is interpreted under the critical state soil mechanics framework.