Study On Deformation Mechanism And Stability Controlling Of Tunnel In Rich Aquifer Erosed Granite Area By Similar Model Test

Granite altered rock refers to the rock mass formed by hydrothermal alteration on the late intrusive original granite rock, the strength of granite altered rock mass is low, which has the characteristics of expansibility after absorbing water, and it’s easy to loosen and disintegrate, there are many joints and fissures in the granite altered rock, it is broken and loose with mostly gravel and silt like soil, whose stability is poor. At present,this geological phenomenon is relatively rare in domestic and international engineering construction,the experience of the costruction of similar projects and the relevant research on stability and deformation law of altered granite rock tunnel is rare,there are no rules to follow about the construction and design of altered granite rock tunnel currently, therefore,the research of this thesis carried out with great significance.This thesis based on project of Beigang tunnel of Luoyang-Zhanjiang railway,the tunnel exists in a thick weathered altered granite zone,where is rich in groundwater,thus in the process of tunnel construction when the tunnel through the section of the water-rich soft rock mass, the surrounding rock of the tunnel dramatically deformed and collapsed repeatedly,many other problems such as sudden mud,water burst,falling water tables,dried up springs,ground subsidence,cracking also happened again and again,which eventually led to the construction of the tunnel was forced to comprehensively stop and the design of the tunnel was changed.To solve above problems,three types of mechanical model was established in this paper according to geometric similarity ratio CL=100and density similar ratio Cy-1which was considered as basic similarity ratio,the models were respectively used to study the impacts on deformation of the tunnel caused by engineering properties of the rock,seepage effects and location of rock interface these three factors,and the deformation mechanism of altered tunnel was gained finally;To study the effects on deformation of the tunnel by supporting structure and its supporting effect,the mechanical model was established according to the similarity ratio CL=30,which was used to evaluate the supporting effect of the supporting structure and provide a meaningful reference for the design of the supporting structure; meanwhile,numerical simulation was considered as the auxiliary method to further validate and complement the results of the model tests, these two methods can complement and confirm each other,the mainly achevements about altered rock tunnel of this thesis as followed:1. Altered rock tunnel converge obviously and quickly during excavation,and this will lead to crack within a larger area on the ground surface or even partial collapse,and if it is not supported,the settlement law of cross-section of the stratum in line with the theoretical curve proposed by Peck;2. Groundwater seepage will result in the sudden mud and gushing water,and the mechanical properties of the surrounding rock will be damaged,which is the most fundamental cause of the severe collapse of the Beigang tunnel;3. The collapse mainly began from the vault of the tunnel,it is called the arch-failure mode,which is the typical failure mode of loose non-cohesive soil;4. When the rock interface exist in or near the excavation surface,the surrounding rock is easy to dislocate or destroy partly along the rock interface, meanwhile,the existence of the rock interface will also lead to surface subsidence and geotechnical pressure become asymmetric,the combined effects of this asymmetry is most obvious while the angle of the interface is about45,but with the increase of the distance between the interface and the excavation face,this impact will be significantly smaller and smaller. In short, the more part of tunnel surrounding rock is the weak rock, the more unfavorable the deformation and the stability of the tunnel will be;5. After excavating Beigang tunnel,we shoule focus on preventing seepage and applying the invert in time,the design strength of the supporting structure should be higher than the general provisions in the standard of railway tunnel design,and the constitutive model which consider the damage should be used in design and calculation;...