Numerical analysis of bonding stiffness for support effectiveness of pre-stressed bolts

To clarify the impact of bonding stiffness on bolts support effectiveness for stratified roof,the concept of bonding stiffness and its realization way in software FLAC3D were firstly introduced,then the roadway model with strat- ified roof was established using the interface elements of FLAC3D,and emulational bolts model was constructed by means of integrating pile structural elements with liner structural elements,whose pretension imposing method was also put forward. Based on these,the support effectiveness of different bonding stiffness for stratified roof were analyzed un- der the condition of in-situ stress. The results show that:Under certain conditions,the bonding stiffness determines the resistance-increasing characteristics of bolts,which vary from slowness to rapidness with the increase of bonding stiff- ness. Bolts support has definite control effectiveness for the separation of stratified roof. The greater the bonding stiff- ness,the better the control effectiveness. Supporting stress field of bolts can improve stress state distinctly,diminishing even eliminating the distribution of tension stress. The improving effect would get better if the bonding stiffness increa- ses. The bolts body would experience bending deformation under the influence of interlayer sliding of beddings,but the deformation degree would be relieved with the increase of bonding stiffness. In consideration of the importance of bond- ing stiffness,the technical approaches of improving the bonding stiffness were put forward,including optimizing the shape of bolts body,improving the contact condition of surrounding rock,strengthening the bonding behavior of anchor agent,and enhancing the installation quality of anchor agent.