Undrained mechanical behavior of unsaturated completely weathered granite: Experimental investigation and constitutive modeling

Abstract

The undrained mechanical behavior of unsaturated completely weathered granite (CWG) is highly susceptible to alterations in the hydraulic environment, particularly under uniaxial loading conditions, due to the unique nature of this soil type. In this study, a series of unconfined compression tests were carried out on unsaturated CWG soil in an underground engineering site, and the effects of varying the environmental variables on the main undrained mechanical properties were analyzed. Based on the experimental results, a novel constitutive model was then established using the damage mechanics theory and the undetermined coefficient method. The results demonstrate that the curves of remolded CWG specimens with different moisture contents and dry densities exhibited diverse characteristics, including brittleness, significant softening, and ductility. As a typical indicator, the unconfined compression strength of soil specimens initially increased with an increase in moisture content and then decreased. Meanwhile, an optimal moisture content of approximately 10.5% could be observed, while a critical moisture content value of 13.0% was identified, beyond which the strength of the specimen decreases sharply. Moreover, the deformation and fracture of CWG specimens were predominantly caused by shear failure, and the ultimate failure modes were primarily influenced by moisture content rather than dry density. Furthermore, by comparing several similar models and the experimental data, the proposed model could accurately replicate the undrained mechanical characteristics of unsaturated CWG soil, and quantitatively describe the key mechanical indexes. These findings offer a valuable reference point for understanding the underlying mechanisms, anticipating potential risks, and implementing effective control measures in similar underground engineering projects.

Keywords

completely weathered granite / undrained mechanical behavior / environmental variable / unconfined compression test / constitutive model

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