Interpreting the Mechanical Behaviour of Carbonate Sand-Fine Mixtures Using the Modified Interfine Void Ratio

Understanding the mechanical behaviour of carbonate sand-fine mixtures is crucial for modelling geotechnical-related gas exploitation problems in potential gas hydrate reservoirs. This paper presents a laboratory investigation of the mechanical behaviour of carbonate sand-fine mixtures with a carbonate sand content of no more than 40%. By means of computer tomography, the internal porosity of carbonate sand grains was measured, and the interfine void ratio was modified. For carbonate sand-fine mixtures with a similar void ratio, all mixtures exhibited strain-softening behaviour, and the peak strength decreased with increasing carbonate sand content. Compared to the mixture whose density was controlled by the void ratio, the change rule of mechanical behaviour influenced by the carbonate sand content was precisely the opposite for that controlled by the interfine void ratio. The mixture with the smallest modified interfine void ratio exhibited the highest peak strength and the strongest dilative volumetric behaviour. By adopting the modified interfine void ratio as a state variable, a unique critical state line can be identified with a carbonate sand content of no more than 40%, leading to a framework that coherently characterises the mechanical behaviour of these gap-graded soil mixtures.