Study On Temporal And Spatial Effect In Construction Of Large Span And Shallow-Buried Tunnel

With the modern transportation rapid development, tunnel construction quantity increases day by day.my country have many mountains, especially in western regions .In the design and construction of the tunnel , soft rock appears frequently, rheology is the intrinsic characteristic of the soft rock. For the rheological phenomena exist in various soft rock projects, the influence of rheological phenomena has been recognized by many people, If the rheological characteristics of surrounding rock are taken into account, theory must be more consistent with practice, this has great practical significance.In this paper, temporal and spatial effect in construction of large span and shallow-buried tunnel is studied preliminarily and some useful conclusions are got.Rheological model theory is introduced at first.the characteristic of combination model is summarized.Then characteristics and solving thoughts of FLAC^3d are analyzed, description of Cvisc creep constitutive model and methods of solving creep problem are introduced.Finally the paper taken the Jiang Xiang Gou tunnel as the project background, choosed the ideal elastoplasticity model, simulated the effect of excavation face by Lagrange method, studied the deformation of surrounding rock with the process of tunnel excavation, for the large span and shallow-buried tunnel,under the the benching tunnel construction method , the excavation face plays the hypothesized support role. its area of effect apart from the face is about two times of hole diameter, the arch settlement is mainly influenced by upper bench cutting.the lower bench cutting makes the lateral movement of the middle wall increase quickly, and little effect on the arch settlement,with the distance apart from excavation face increasing,the spatial effect gradually weakened,the deformation of surrounding rock tends to be stable.Since the surrounding rock takes significant time-varying effects, and the mechanical response of the tunnel is closely related to the process of construction,so the paper choosed the H-K body rheology model, studied the rheological characteristics in the construction process of the large span and shallow-buried tunnel ,after analyzing the computed results,nearby the excavation face is the coupling function by spatial effect and temporal effect, the effect of excavation face is primary in the advancing face zone, Rheological effect plays a key role out of the influence range of the spatial effect of excavation face.the deformation of surrounding rock will continue to increase.the surface settlemen,arch settlement,and the lateral movement of the middle wall in the tunnel construction will increase with timeand will increase quickly in the early excavation, one month later will change slowly. Compared to the elastoplastic results, if considering the time effect, the deformation of surrounding will increase much, it shows that taking the rock creep into account is essential in the construction of the tunnel.