Surrounding Rock Pressure Analysis of Underground Station with Extra-large Section and Small Spacing

The design and construction of underground station with extra-large section and small spacing is one of the difficult issues of concern of the civil engineering sector. Since the time is short, the theoretical research of underground station with extra-large section and small spacing is far behind the engineering practice. There has not been a unified understanding of the distribution rule of the station surrounding rock pressure, only with the means of numerical simulation study. In this paper, a small distance station of Chongqing rail transit is taken as the background, using the large finite element software MIDAS/GTS, a two-dimensional numerical model is established for analysis and calculation. Through respectively changing the different buried depth and spacing, the influence of the surrounding rock pressure from buried deep and spacing is studied and the basis is provided for the design and parameter optimization of the station lining structure. Introduction With the rapid development of urban rail transit, the large span and small distance tunnel has gradually increased. However, because of its short time, there is no unified understanding of the distribution of pressure and deformation of surrounding rock. At present, there are three main methods for solving geotechnical materials: exact solutions, numerical methods and test methods. The interaction between underground stations and surrounding geotechnical media under various dynamic and static loads is very complicated, and because geomaterials are mostly non-continuous and nonlinear materials, they cannot be accurately solved by a single function or equation. Only linear elastic systems with simple geometric shapes and material properties, and simple load patterns and boundary conditions can obtain more accurate answers. For an underground station with any geometric shape in a complex nonlinear rock mass, the mechanical analysis must be performed by means of computer numerical simulation[1]. The finite element method has become a powerful tool for geotechnical engineering applications. It is also a very effective numerical analysis method for the discretization of more complex continuum structures and the use of mechanical theory and computer technology to solve complex problems. Due to the complexity of the extra-large section and small spacing underground station, the relative theoretical research is lagging behind. At present, there are many researches on the construction methods of small-section tunnels with extra large sections[2-5]. Qihang Zhang studied the construction stability factors of small-section tunnels with extra large sections under complex conditions[6,7]. Zhang Li studied the stability control technology of surrounding rock of small clearance tunnel[8]. Some scholars have carried out research on the confining pressure of small clearance tunnels[9-11], but there are few studies on the surrounding rock pressure of small-section tunnels with extra large sections. At present, it is mainly to use large finite element software to establish a numerical analysis model to study.In the aspect of surrounding rock pressure analysis, Zhen Wang used large finite element software MIDAS/GTS to simulate the surrounding rock pressure of single tunnel, small spacing tunnel and double arch tunnel, and compared with the commonly used theoretical calculation, and drew some conclusions[12]. Zhu Zhengguo used finite