Effect of layered joints on rockburst in deep tunnels

The existence of joints in the surrounding rock mass has a considerable efect on tunnel rockbursts.Herein,we studied the efect of layered joints with diferent inclination angles and spacings on rockburst in deep tunnels and investigated the failure area,deformation process of the surrounding rock mass,stress change inside the surrounding rock mass,velocity of the failed rock,and the kinetic energy of the failure.The failure type of the surrounding rock mass can thus be determined.The results showed that the intensity of rockburst increases as rock quality designation(RQD)decreases,while the deformation rate of the surrounding rock mass frst increases and then decreases.The deformation rate exhibits a turning point between RQD=50 and 70,below which the deformation rate of the surrounding rock mass gradually decreases,ultimately ceasing to be a rockburst.Rockburst always occurs perpendicular to the direction of the joint.Whenσ_(x)=σ_(y),as the joint inclination angle changes from 45°to 90°,the intensity of a rockburst frst decreases(from 45°to 60°),and then increases(from 60°to 90°).When combined with the evolution law of stress and strain energy,the rockburst process can be divided into four stages.

Experimental investigation on the anisotropy of friction property for dry and water-saturated rock

Friction properties of rock are closely connected with the anisotropy.The anisotropy of rock friction can provide a valuable assessment for geotechnical and geological engineering.In this study,the rotary friction tests were conducted to analyze the water effect on the friction property and the friction anisotropy of the four types of rock.The drilling response model(DD-model)was employed to characterize the rotary friction behavior of the rocks.The parameters of this model include the three types of friction parameters:1/ς,μ,and f,where 1/ςandμare constant,and f is a variable.A quantitative method is proposed for assessing the anisotropy of rock friction.The results of the rotary friction tests indicate that the relation between torque force and thrust force conforms to the DD-model.The changes of two friction constants 1/ςandμfrom dry state to water-saturated state suggest that the water effect on the friction strength of the rocks exhibits significant anisotropy.The friction strength determined by the friction variable f increases first,then decreases,and finally stabilizes with the increasing of depth.AIf is an anisotropy index calculated by the proposed method.The percentage difference of the average value of AIf between water-saturated and dry states shows the degree of the water effect on the friction anisotropy of the rocks,mudstone(MU)>granite(GR)>fine sandstone(FS)>argillaceous siltstone(AS).The quantitative model is hopefully constructed for characterizing the relation between the anisotropic friction strength of rock and the moisture state in future.