Mechanical analysis and numerical simulation for deep and shallow bearing structures of soft and broken roadway surrounding rock

Surrounding rock plays a key role in the bearing structures of roadway according to the interaction system between surrounding rock and support. Stability control in the bearing structures of surrounding rock thus significantly influence the stability of roadway. Based on the engineering and geological properties of soft and broken surrounding rock,some theoretical models were established considering the strength characteristic,stress distribution and deforma- tion behavior of rock mass after excavation. The stress,displacement and plastic zone were then studied in the elastic zone,plastic soften zone and broken zone,respectively. Considering the influence of several key factors,such as the strength soften and dilation at post-peak state and the support resistance,based on the bearing characteristics of sur- rounding rock,two main bearing structures around the excavation which are the shallow and deep bearing structures were defined. A key bearing structure was found in the deep bearing structure,which was subjected to most part of the external load. Theoretical studies and numerical simulation using Flac3D code were performed to investigate the char- acteristics of the bearing structures and the deformation of roadway. The results show that the bearing structures will develop obviously with a big residual strength. The dilation effect occurs in the deep bearing structure,while it leads to the deformation of shallow bearing structure. The thicknesses of the two bearing structures increase with the increase of in-situ stress.