Study On The Heave Deformation Of The Bottom Of Railway Tunnel And Engineering Countermeasures

Most of China’s new railway tunnel adopts ballastless track,so it’s very strict with the heave deformation at the bottom of tunnel.It’s an urgent problem to solve the heave deformation,because the heave deformation at the bottom of tunnel which is operated or constructed brings great difficulties to traffic safety and construction. But,the mechanism of the heave deformation at the bottom of tunnel is very complicated, so we are still short of proper foundation of mechanical analysis and engineering countermeasure at present.Firstly, through the survey of railway tunnel’s heave deformation case in China and overseas and experimental study on rock strength, the influence factors and the mechanism of heave deformation is analyzed; Then, the heave deformation phenomenon in sedimentary rock is researched by numerical simulation based on Fuchuan tunnel of Lanzhou Xinjiang Railway. Finally, the engineering countermeasures are made. The main results obtained are as follows:(1) Through literature survey and data collection, this paper analyzes and summarizes the main influence factors of heave deformation at the bottom of tunnel: groundwater, expansive clay and high ground stress in soft surrounding rock. It is clear that there are two main types of heave deformation mechanism at the bottom of the tunnel,namely squeezing deformation and water swelling.(2) It shows that the water content has great influence of rock strength especially in mudstone, sandstone, tuff and other sedimentary rocks, in other words, the strength of rock mass will be significantly increased with the increase of water content.(3) Based on elasto-visco-plastic theory, mechanics mechanism of heave deformation at the bottom of the tunnel in the sedimentary rock containing swelling clay minerals is funded that uses the deterioration of Strength model. At the bottom of the tunnel, because of the increase of water content, the strength of surrounding rock can be increased, and the squeezing deformation of the surrounding rock is increased, which causes the heave deformation of the bottom structure.(4) In this paper, taking Fuchuan tunnel of Lanzhou Xinjiang Railway as an example, in the case of two different inverted arch thickness, it’s concluded that the heave deformation, tensile stress value and range at the bottom of the tunnel gradually increase and the structure of inverted arch and surrounding rock’s plastic zone are also gradually increase; the decrease of inverted arch thickness leads to the deterioration of surrounding rock strength and heave deformation, stress and plastic zone are more significant. It’s approximately consistent with the field monitoring results,including the result of the heave deformation and the cracking of the filling layer of the inverted arch.(5) Taking Fuchuan tunnel of Lanzhou Xinjiang Railway as an example, through numerical simulation study, it’s concluded that the increase of the inverted arch’s curvature can effectively reduce the heave deformation of the bottom in tunnel caused by the deterioration of surrounding rock strength.