Mechanical and energetic properties of rock-like specimens under water-stress coupling environment

Soft rock has the properties of low strength, poor integrity, and difficulty in core extraction. In order to study the deformation and failure of soft rock, this study used fine river sand as aggregate, cement and gypsum as bonding materials, and borax as a retarder to produce cylindrical rock-like samples (RLS) with a sand cement ratio of 1:1. Uniaxial compression tests were conducted on RLS under DIT (different immersion times) (0, 4, 8, 12, 24, and 48 h) in the laboratory. The mechanical and energy properties of RLS under water-stress coupling were analyzed. The results showed that the longer the IT of the RLS, the higher their water content (WC). As the moisture time increases, the uniaxial compressive strength, elastic modulus (EM), and softening coefficient (SC) of the sample gradually decrease, while the rate of change of EM is the opposite. The fitted sample SC exhibits a good logarithmic function relationship with WC. During the loading process of the sample, more than 60% of the U (total energy absorbed) during the loading process of the sample is accumulated in the form of Ue (releasable elastic energy), while less than 40% of U is dissipated by the newly formed micro cracks during the compaction, sliding, and yield stages of the internal pores and cracks of the sample. The U before the peak and the Ue of the RLS decrease exponentially with the moisture content; the relationship curves of Ue/U (released elastic energy ratio) and Ud/U (dissipated energy ratio) of RLS during uniaxial compression with the σ1/σmax (axial stress ratio) can be divided into three stages of change, namely the stage of primary fissure compaction and closure (σ1/σmax < 0.25), continuously absorbing energy stage (0.25 < σ1/σmax < 0.8), and energy dissipation stage (σ1/σmax > 0.8); the D (damage variable) was defined by the ratio of Ud (dissipated energy) to the Udmax (maximum dissipated energy) at failure time of RLS, the fitting of the relationship between the damage variable and axial strain conforms to the logistic equation.