Study On The Deformation Mechanism Of Invert Heave In Mudstone Tunnel Of High-Speed Railway

With the increase of traffic demand and the development of infrastructure construction technology,the construction of high-speed railway mountain tunnels has increased significantly.Mudstone is widely distributed in China,so it is necessary to solve the engineering problems caused by the special geological properties of mudstone.Invert heave is one of the common diseases of mudstone tunnel,which seriously affects the tunnel construction safety and late operation and maintenance.Invert heave is also an extremely complex process.It is of great scientific value and practical significance to correctly understand the mechanism of floor heave for dealing with tunnel diseases and maintaining line stability.In this paper,the mudstone tunnel of high-speed railway was taken as the research object.The lithology,occurrence conditions,main influencing factors and failure characteristics of surrounding rock of invert floor heave in typical tunnels in China were statistically analyzed.The mineral composition analysis and related mechanical tests of mudstone samples were carried out.The similar materials for simulating tunnel structure were developed,and the expansion model test of basement surrounding rock was carried out.The stress characteristics and deformation characteristics of tunnel structure under different expansion ranges were compared.The main work and the research results are as follows:(1)Through statistical analysis,it is found that invert floor heave is more likely to occur in mudstone tunnel.Invert heave is the result of many factors,such as surrounding rock expansion,high ground stress,uneven settlement of basement,complex geological structure and groundwater erosion.The main factor of invert heave in mudstone tunnel is the expansion of mudstone in water.The invert heave has the greatest influence on the bottom structure of the tunnel,and the side wall and vault also have some influence.(2)By analyzing the mineral composition of the undisturbed mudstone,it was concluded that the clay minerals content in mudstone accounts for 30% of the total mineral content,and the hydrophilic clay minerals are mostly,which determines that mudstone is easy to expand,disintegrate and soften when it encounters water.Through different mechanical tests,the uniaxial compressive strength,elastic modulus,internal friction angle,cohesion and tensile strength of mudstone were obtained respectively.(3)Based on the similarity theory,the invert heave model test was designed,and a similar material of particulate concrete was prepared to simulate the tunnel lining and filling layer,and its basic mechanical properties were determined by mechanical tests.The mechanical response and deformation characteristics of rock and tunnel structure around the tunnel under the action of basement expansion were obtained by monitoring elements.(4)Numerical simulation method was used to simulate the hygroscopic expansion of surrounding rock by thermodynamic module.The deformation of the rock around the tunnel and the stress distribution of the tunnel structure were analyzed with the expansion degree under different ranges of surrounding rock(sidewall surrounding rock,basement rock,sidewall rock + basement rock).The comparative analysis showed that when the surrounding rock of the tunnel sidewall expanded,tunnel sidewall was prone to tensile failure.When the basement surrounding rock expanded,the filling layer was prone to tensile cracks.When the surrounding rock of tunnel sidewall and tunnel basement swelled,the influence on the tunnel structure was less than that when the surrounding rock of the side wall or the basement swell alone.Through the above research on the inverted arch floor heave phenomenon of mudstone tunnel of high-speed railway,this paper aims to provide reference for tunnel construction and tunnel damage control under similar engineering conditions.