The closed section of the inverted arch, formed by the surrounding rock, acts as a bearing ring. Combined with the upper initial support, it ensures stable initial support. However, excavating the inverted arch can disturb the original balance, significantly affecting the tunnel’s stability. To determine the optimal exposure length and excavation length of the elevation arches at different rock levels, numerical analyses were conducted. These analyses used the classical Burgers creep intrinsic structure model for the three-step excavation mode. Various closure distances and exposure distances of the elevation arch were considered. The study aimed to investigate the influence of these factors on the stability of the primary lining, comparing it with the maximum displacement of the vault. The results indicate that the strength of the surrounding rock primarily affects the displacement of the arch crown. Lower rock strength corresponds to greater arch crown displacement. Additionally, increasing the closure distance of the inverted arch leads to increased arch displacement. On the other hand, the exposure distance of the inverted arch has minimal impact on arch displacement. Longer exposure distances result in greater arch displacement. These findings can serve as a basis for improving current standards and adapting them to meet the spatial requirements of large-scale mechanized operations.
The interaction rule between rockmass and water under underground pressure is a difficult problem that needed solving by geotechnical experts.One the base of coupling theory of solid and fluid and the influence of water to constitute model,a coupling mathematical model of solid and fluid for water is present.Later the numerical calculation to simulate the fluid rule of water in saturated rockmass is made.The given results provide a thoretical basis and scientific data for the water extraction from the excaved rockmass.3figs.,5refs.
Abstract The surrounding rock in the closed section of the inverted arch creates a bearing ring that, when combined with the upper initial support, provides stable initial support. However, excavation of the inverted arch can disrupt the original balance and significantly impact the tunnel’s stability. Using the classic Burgers creep constitutive model, we conducted numerical analyses of the construction process for tunnels with different closure and exposure distances of the inverted arch under varying levels of surrounding rock, using the three-step excavation method. We compared the maximum displacement of the arch crown to study the influence of the closure and exposure distances of the inverted arch on the stability of the initial support lining. Our results show that the displacement of the arch crown is primarily influenced by the strength of the surrounding rock; the lower the strength of the rock, the greater the displacement of the arch crown. Furthermore, the displacement of the arch crown increases as the closure distance of the inverted arch increases. Conversely, the exposure distance of the inverted arch has a minimal impact on arch displacement, and the longer the exposure distance, the greater the arch displacement. These findings can serve as a foundation for improving existing standards and adapting them to the spatial requirements of large-scale mechanized operations.
Scholars often consider the deformation of a foundation pit retaining structure as a significant indicator of its stability. However, the current theoretical prediction formula for pit with pile–anchorretaining structure deformation is not yet perfect. This study utilizes a simplified spatial deformation model of a pile–anchorretaining structure and the principle of minimum potential energy to derive a prediction formula for the retaining structure’s spatial deformation. Afterwards, a numerical simulation model is developed based on actual engineering practices. On-site monitoring data is compared with the results of theoretical calculation formulas and numerical simulation models to validate their applicability. The research findings reveal minimal discrepancies between the theoretical calculation results, numerical simulation outcomes, and on-site monitoring data, indicating a high level of accuracy. Those three results follow consistent rules. The horizontal deformation curve of the crown beam exhibits a ‘V’-shaped distribution, and as the distance from the calculation point to the centerline of the foundation pit decreases, the horizontal deformation of the crown beam increases. The horizontal deformation curve of the pile displays a ‘V’-shaped distribution, and the pile’s horizontal deformation increases as the distance to the centerline of the foundation pit decreases. The research findings indicate that increasing the size and material strength of the crown beam and waist beam has only a limited effect on controlling the retaining structure’s deformation. However, by increasing the size and material strength of the pile, the deformation of the retaining structure can be significantly reduced.
Tunnel stability is influenced by the rheological properties of the surrounding rock. This study, based on the Ganshen high-speed railway tunnel project, examines the rheological characteristics of siltstone and sandstone through laboratory tests and theoretical analysis. Rheological curves and parameters are derived, revealing the time-dependent deformation mechanisms of the surrounding rocks. A numerical simulation model is created using these parameters to analyze deformation and stress characteristics based on different rock levels and inverted arch closure distances. Results indicate that sandstone follows the Cvisc model, with the Maxwell elastic modulus increasing under higher loads while the viscous coefficient decreases. The vault displacement is mainly affected by the surrounding rock strength; lower strength leads to greater displacement, which also increases with the closure distance of the inverted arch. These findings are crucial for determining the optimal closure distance of inverted arches in sandstone conditions.
In order to study the creep characteristics and failure mechanism of argillous red sandstone in a water‐bearing state, uniaxial creep tests of argillous red sandstone under dry and saturated states are carried out under fractional loading. Burgers model is used to fit the test results and identify the parameters, and scanning electron microscopy is carried out on the cross section of the damaged sample. The mechanism of creep difference of argillaceous red sandstone with different water content is studied from the microscopic point of view. The results show that the uniaxial compressive strength of the saturated clay red sandstone is 46% of that of the dry clay red sandstone. The deformation level of the saturated clay red sandstone is lower than that of the dry clay red sandstone. The limit deformation of the creep failure of the water‐bearing clay red sandstone is much smaller than that of the dry clay red sandstone. The long‐term strength of the muddy red sandstone is 46.4 MPa in the dry state and only 14.1 MPa in the saturated state, as calculated at the steady‐state creep rate. It is found that the Burgers model can describe the attenuation and stable creep of muddy red sandstone well. Through macro‐ and microanalysis, it is found that the compression failure form of argillaceous red sandstone belongs to x‐shaped conjugate inclined plane shear failure. After saturation, the internal pores of argillaceous red sandstone become larger, and the cementation ability decreases, resulting in the decrease of rock sample strength.
Abstract For the mined land section of the river-crossing tunnel with small clearance, the study should be carried out for excavation method and safe spacing before the tunnel construction, for engineering properties of surrounding rock is poor and the distance between two tunnel tubes is small. In this paper, in combination with the mined land section works of the river-crossing tunnel on Rongjiang Fourth Road, the finite difference numerical simulation software was adopted to calculate mechanical behaviors of three construction methods: three-bench method, CD method and CRD method under different excavation spacing (10 m, 20 m, 30 m and 40 m) on the basis of grouting and pre-reinforcement of surrounding rock in the early stage. The calculation results indicate that vault displacement and ground settlement can notmeet the specification requirements when the three-bench method is adopted for construction, even if the excavation spacing between the former and latter tunnels is 40m; When the CD method is adopted for construction, vault displacement and ground settlement meet the specification requirements when the excavation spacing between the former and latter tunnels is 40m; When the CRD method is adopted for construction, vault displacement and ground settlement meet the specification requirements when the excavation spacing between the former and latter tunnels is 30m; The control effect of initial support deformation and surrounding rock displacement is in the following sequence: CRD method > CD method > three-bench method. Considering various factors, it is found that the CD method is more reasonable and efficient. Therefore, the CD method is recommended for tunnel excavation and the tunnelling spacing should be controlled to 40m.
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