| The deformation of deep soft rock tunnels is a complex mechanical process.The high floor heave and the common inward movements are usual engineering disasters for deep soft rocks tunnels when the excavation were finished.Mechanical state of surrounding rock in deep soft rock tunnel is analyzed through the nature of the surrounding rock,mechanical characteristics,deformation mechanism and so on.Three-dimensional elastoplastic solution of axisymmetric circular tunnel is obtained with power-hardening model based on Drucker-Prager failure criterion,which adopt the intermediate principal stress expression,and the dilatancy effect is took into account.Under this condition,the time-varying displacement analytical solution of the surrounding rock was deduced considering dilatancy for the deep tunnel in soft rock.The non-associated flow rule and the Burgers creep model are utilized to calculate the visco-elastoplastic creep behaviors for tunnels in soft rocks,to further deepen Hou’s viewpoint.The results are compared with the measured data of soft rock tunnel(clay rock),and it is found that the results of this paper can well reflect the time-dependent deformation of soft rock tunnels.Finally,considering the water swelling of the soft rock tunnel under the condition of water,it is discussed based on the improved Burgers model.On the basis of,the sensitivity of the parameters related to the mechanical properties such as strain enhancement,expansion and water absorption is explored from multiple angles.The following conclusions can be drawn:1.With the effects of strain-hardening and dilatation of surrounding rock,the power-hardening model can fully describe mechanical state for tunnels in soft rocks,the result show that it’s error in physical significance in the theory of volume incompressible which don’t consider dilatancy.2.With the increase of the dilatancy angle,the surrounding rock stress of the deep soft rock tunnel increases gradually,and the radius of the plastic zone also increases,which is consistent with the physical meaning of the parameter.The displacement of the surrounding rock is obviously increased and the development becomes faster,which show the displacement is more sensitive when the power-harding parameter become severer.Exploring the deformation at the viscoplastic zone became an important consideration for the engineering stability.3.The strain-hardening effect and the dilatancy effect of tunnel surrounding rock have a significant synergistic effect on the mechanical state.Increasing the dilatancy angle or power-harding index,the sensitivity of the displacement increases.Within the effects of dilatancy characteristic and/or power-harding,the deformation is obviously larger than that of without the effects of these factors.4.Regardless of whether the effect of water absorption is considered,with the increase of the power-harding index,the strain hardening effect is strengthened,the creep displacement is increased,And the creep behavior of the surrounding rock is more sensitive to time.The displacement is obviously increased and the development becomes faster when the dilatancy angle become higher.Within the effects of water absorption,the deformation is obviously larger than that of without the effects under water conditions.It’s unfavorable to the long-term stability of surrounding rock.In view of the problem of the mechanics for deep tunnels in soft rocks,this paper deepens and extends the deformation mechanism of such tunnels,and explores time-dependent deformation under different water conditions.further enrichs design theories of hydraulic,mining and transportation tunnels excavated in swelling rocks.The analytical results can be used as theoretical basis for the tunnels excavated in soft rocks. |
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