| With the implementation of "the Belt and Road",the tunnel and underground engineering in our country have obtained unprecedented development.At the same time,the geological conditions faced in the construction process are becoming more and more complicated,and the deformation of rock mass continue to increase,which has caused the instability and landslides disasters of the tunnlel and the engineering.In order to limit excessive deformation of rock mass and improve the strength of rock mass,the rock bolts are often used for reinforcement.As the main way of rock mass support,the rock bolt support effect has been widely recognized,but the long-term reinforcement mechanism of the rock bolt has not been well known.In the construction of tunnel transportation,water conservancy and hydropower,deep resource exploitation,etc.,it is necessary to consider not only the stability in the construction period,but also the long-term operational safety in the future.Therefore,it is of great theoretical significance and application value to explore the coordinated deformation mechanism and long-term variation law of rock mass supported with rock boltsIn this paper,the rock mass and rock bolts are regarded as independent rheological bodies respectively.Considering the different reinforced methods of the rock bolt,the coupling rheological properties of rock mass and continuously mechanically coupled(CMC)rock bolts、prestressed(DMFC)rock bolt of a circular tunnel is systematically studied.The main research content includes the following three parts.(1)The coupling rheological model of the rock mass-CMC rock bolts supporting structure in a circular tunnel is established.Based on the mechanism of load transfer at the interface between the rock bolt and the rock mass,the elastic solutions of the coupling model are solved.With the Mindlin displacement solution and the rock mass displacement solutions in the reinforced zone,the distributions of the shear stress and axial force along the rock bolt are calculated.Furthermore,based on the viscoelastic theory,the dynamic formulas of the stress,strain and displacement of the rock mass evolving with time are derived,and the distributions of the shear stress,axial force and neutral point are discussed.Based on the example analysis,a one-dimensional Kelvin model is used for rock bolt,a three-dimensional Maxwell model is used for rock mass.And the influence of the relative elastic modulus of the rock mass and rock bolt as well as the viscous coefficient on the support effect are analyzed.The results show that the radial stress and tangential stress of rock mass have an abrupt change at the interface between the reinforced zone and the unreinforced zone.The distribution of stress,strain and displacement field of rock mass are closely related to the relative elastic modulus and viscous coefficient,and show significant time correlation.On the other hand,the distribution of the interface shear stress of the CMC rock bolt is different from the shear stress distribution obtained by pull-out test.The absolute value of the shear stress reduces gradually from the rock bolt head to 0 in an approximately linear manner,that is the position of neutral point;After the neutral point,the shear stress increases to the maximum value with an approximate exponential mode;After the peak,the shear stress gradually decreases,eventually reaching a fixed value at the end of the rock bolt.In addition,the neutral point position is independent of time.(2)The coupling rheological model of rock mass and pre-stressed rock bolt support structure in a circular tunnel is established.The elastic solutions of the coupling model are obtained with the“distributed force model".Furthermore,based on material properties and dimensional effects,a rheological model conforming to the rock bolt and rock mass is selected,that is,a one-dimensional Kelvin model is selected for the rock bolt and a three-dimensional Burgers model for the rock mass,the analytical solutions of rock mass-pre-stressed rockbolt coupling model in Laplace space are solved,the viscoelastic solutions of the coupling model are obtained by Laplace inverse transformation.The influence of prestress and viscosity coefficients of rock bolt on rock mass stress,displacement field and axial force are explored.The results show that the support effect at the inner wall of the tunnel is positively correlated with the prestress,but when the prestress is too large,the support effect will no longer increase significantly;on the other hand,the viscosity coefficient of the first creep stage or the second creep stage is proportional to the displacement stability value.Moreover,the rheological state of the rock bolt is independent of the prestress.(3)Based on the theoretical model and the second development of finite difference software FLAC3D,the numerical simulation of the coupling rheological model of the rock mass-rock bolt support structure is carried out,and the analytical solutions and the numerical solutions are further compared and analyzed to verify the correctness and applicability of the analytical solutions.The results show that the analytical solutions and the numerical solutions are in good agreement,and the rationality of the model is evaluated. |
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