Equivalent Elastic Model and Deformation Characteristics of X-Type Cross-Jointed Rock Mass

The conjugated X-type cross joints are one of the main forms of rock mass in nature. It is a composite geological material with macrodefects like joint fissures, and microdefects like microjoints and microvoids. From the perspective of composite damage, an equivalent elastic model considering macro- and microdefects of rock mass is formulated. First, the micro- and macrodamages caused by cross joint and wing crack propagation are used to build a composite damage model of nonpenetrated cross-jointed rock mass based on the strain equivalence principle. Next, considering the interaction between cross joints and the conditions of wing crack propagation, the stress intensity factor at the tips of cross joints before propagation and that at the tips of wing cracks after propagation are derived, respectively. Third, the macrodamage variables involving the geometric characteristics of cross joints and the friction coefficient of joint surface are derived based on fracture mechanics and strain energy theory. Finally, the proposed model is tested on the samples of similar materials in the cross-jointed rock mass; the interference effect between cross joints is analyzed using digital image correlation technology; the calculated results of the model are compared with the experimental results. The model calculation coincides with the test results, proving the rationality of the model. The model helps understanding the influence law of the interference effect of cross joints on the damage and deformation characteristics of rock mass and has guiding significance for related rock mass engineering practice.