Mechanical Analysis On Self-bearing Capacity And Its Degradation Process Of Surrounding Rock

Currently,the construction scale and quantity of various rock engineering has increased significantly,such as lanes,mines,caverns,tunnels,roadways and all the other excavation structure.What's more,this is developing to a deeper and bigger way.The analysis and research of supporting parameters plays a crucial part in the construction which using convergence limit method.On the one hand,the key to the substructure support theory is the interaction mechanism between surrounding rock and support system.On the other hand,the self-bearing capacity of surrounding rock is time related.The time-varing self-bearing coefficient of surrounding rock is a comprehensive evaluation index under the combined action of multiple factors.It is assumed that the surrounding rock with visco-elastic-plastic behavior can be regarded as a rheological material,subject to the uniform strength theory.Visco-elastic-plastic stress field of surrounding rock is obtained by using this theory.Further more,the analytic expression of ime-varing self-bearing coefficient of surrounding rock is deduced based on Boltzmann-UST model and plastic flow law.The effects of aging,relaxation time,intermediate principal stress and more relevant parameters on the self-bearing capacity of surrounding rock are discussed based on the correctness and superiority of the analytical solutions.Then coupling it with LDP and GRC curves.Analyzing the data,results shows:(1)Parameter b has a great effect on time-varing self-bearing coefficient at the forming time.This is because of the influence that parameter b had on plastic zone radius.Due to the increase of parameter b,the plastic zone radius decreases,and the stored energy release in surrounding rock stays in a low level which make the self-bearing capacity is still high and not appropriate to carry out the secondary support.(2)The physical meaning of relaxation time shows the great influence on the time-varing self-bearing coefficient of surrounding rock.At the same time,the larger the value of the relaxation time,the greater the coefficient and the higher the bearing capacity of surrounding rock.(3)At the same time,time-varing self-bearing coefficient of surrounding rock decreases with the increase of crustal stress.It was found that the surrounding rock can not enter the plastic state when crustal stress was 10 Mpa.Due to the low level of energy release of surrounding rock,its self-bearing capacity maintains in a high level.Which means the tunnel remains stable.(4)Shear strength parameter are important index to evaluate the plastic mechanical behavior of surrounding rock.Which characterized the difficulty of yield strength of surrounding rock.With the increase of cohesion and internal friction Angle,the time-varing self-bearing coefficient of surrounding rock was increased at any moment.Since the self-bearing capacity of surrounding rock has been improving,which is coincide with the physical meaning of parameters.(5)The relationship between second supporting time and supporting force and the time-varing self-bearing coefficient of surrounding rock was obtained by coupling.The earlier the second supporting time,the greater the supporting force and the time-varing self-bearing coefficient of surrounding rock was increased.The result shows that the self-bearing capacity of surrounding rock has not been fully exploited.The decrease of the time-varing self-bearing coefficient of surrounding rock shows the exertion of the self-bearing capacity of surrounding rock.So that the supporting force will be reduced effectively.In general,the time-varing self-bearing coefficient of surrounding rock reach highest during the cave-forming,then decreased sharply and nonlinearly until it reaches steady state.So the tunnel supporting time should avoid the sharp decreasing stage.The theory of time-varing self-bearing coefficient of surrounding rock which under time effect and other factors was deepened.Also it can provide theoretical direction for determination of reserved deformation,support type,support rigidity and so on.Which was a progress in the methodology.