Study On Surrounding Rock Displacement Of Soft Rock Tunnel Considering Expansion And Dilatancy Effect

With the continuous development of the central and western regions of China,the construction of transportation networks in these regions is of utmost importance.The central and western regions of China are mostly mountainous areas,with complex landforms.In the construction process of highway and railway tunnel projects in the central and western mountainous areas,especially when crossing soft rock formations,construction difficulties often arise.Because the strength of soft rock is generally low,the structure is broken,and most soft rocks have characteristics of poor integrity or low bearing capacity.After reaching the peak strength,there will be softening,expansion and dilatancy,which can lead to large deformation and even major safety accidents during the construction process.Therefore,studying the deformation law of surrounding rock displacement in soft rock tunnels is particularly important.Although there are currently many analysis studies on the displacement of surrounding rock in soft rock tunnels,the research results on the displacement of surrounding rock in soft rock tunnels with expansion and dilatancy effects are very limited.Therefore,this article will consider the characteristics of expansion and dilatancy of soft rock.Based on the Anlan Expressway Xiejiapo Tunnel,a combination of theoretical derivation,numerical software simulation,and on-site monitoring measurement will be used to conduct in-depth research on the deformation law of surrounding rock displacement during the construction process of soft rock tunnels.This has important theoretical and engineering significance for the design and construction of soft rock tunnels.The main content and conclusions are as follows:(1)In response to the characteristics of expansion and dilatancy of surrounding rock caused by soft rock tunnel excavation,a viscoelastic plastic mechanical model for softening and expansion was analyzed,and theoretical analytical formulas for stress,strain,and displacement in the viscoelastic stage,viscoplastic stage,and viscoplastic residual stage were derived.(2)On the basis of the above theoretical analysis and research,the viscoelastic plastic mechanics analysis method considering expansion and dilatancy will be applied to the soft rock tunnel-Xiejiapo Tunnel.The analysis results show that under the same rock mass level,the displacement calculation results of the surrounding rock considering the expansion and dilatancy effect based on the viscoelastic plastic theory are significantly greater than those considering only the dilatancy effect;Under different levels of surrounding rock,the displacement of Grade IV surrounding rock is significantly smaller than that of Grade V surrounding rock.(3)Based on the actual design and construction situation of the Xiejiapo Tunnel,a strain softening model considering the expansion and dilatancy effect under the Mohr Coulomb criterion was established using Flac3 d finite analysis software,and the construction process was simulated and analyzed.From the simulation results of surrounding rock deformation,it can be seen that when the surrounding rock around the tunnel undergoes softening and expansion and dilatancy effects at different positions,it will have a significant impact on the deformation of the entire tunnel structure or a certain part.From the analysis of tunnel structural deformation and stress simulation,it can be seen that the deterioration of the mechanical properties of the surrounding rock to a certain extent weakens the impact on structural deformation caused by the expansion and dilatancy effect of the surrounding rock.(4)From the results of theoretical analysis,numerical simulation,and on-site testing,it can be seen that the displacement values of various parts of the tunnel obtained using the theoretical analysis method are closer to the on-site testing results,that is,there is little difference between the theoretical model calculation and on-site measurement results for different levels of surrounding rock.The above analysis indicates that there is an expansion and dilatancy characteristic in the surrounding rock.The theoretical analysis method and model constructed in this paper considering the expansion and dilatancy effect can reflect the expansion expansion impact of the surrounding rock.