Shear behavior of single-joint bolted sandstone subjected to dryewet cycles:Experimental and analytical approaches

A series of direct shear tests under constant normal loading conditions were carried out on specimens of bolted sandstone single-joint treated with different numbers of dryewet cycles.The experimental results show that the peak shear strength and shear stiffness of bolted sandstone joints were significantly reduced after 12 dryewet cycles.The decrease in the shear strength of rough joints is more significant than that of flat joints.Due to the decrease in the strength of the surrounding rock,the deformation characteristics of the bolts are significantly affected by the number of dryewet cycles performed.With an increase in the number of dryewet cycles,the plastic hinge length of the bolt gradually increases,resulting in an increase in the corresponding shear displacement when the bolt breaks.Compared with the tensileeshear failure mode of the bolts in flat joints,the tensileebending failure mode arises for bolts in rough joints.A shear curve model describing the whole process of bolted rock joints is established based on the deterioration of rock mechanical parameters caused by dry‒wet cycles.The model proposed considers the change in the friction angle of the joint surface with the shear displacement,which is applied to the derivation of the model by introducing the dynamic evolutionary friction angle parameter.The reasonably good agreement between a predicted curve and the corresponding experimental curve indicates that this method can effectively predict the shear strength of a bolted rock joint involving rough joint under dryewet cycling conditions.

Effects of the Tensile and Shear Properties of Bolts on the Shear Properties of Bolted Rock Joints

The mechanical properties of bolts are important factors affecting the shear behavior of bolted joints.In this study,tensile and pure shear tests were conducted on five kinds of bolts made from different materials to measure their tensile and shear parameters.Direct shear tests were conducted to analyze the effects of tensile and shear strength parameters on the shear behavior of bolted joints.The test results showed that the mechanical properties of bolts made from different materials were clearly different and that these differences mainly affected the plastic deformation stage of the bolted joints.The larger the bolt elongation was,the larger the joint shear displacement at bolt failure.The tensile and shear strengths of the bolts were positively correlated with the shear strength of the bolted joints.According to the standard regression analysis,the bolt shear strength had a greater influence than the bolt tensile strength on the bolt contributions when the bolts were perpendicular to the joint surface.Based on the empirical equation for the bolt contribution proposed by Spang,the maximum shear loads in the pure shear test were introduced,and a new equation was established to predict the contributions of bolts.The prediction results obtained using the modified equation were in good agreement with the experimental results.