| This paper relies on the typical engineering problems encountered in the construction process of tunnels in horizontal strata on several highlands of the Menghua Railway and the successful application of the resistance-limiting and energy-dissipating supporting structure developed by Professor Qiu Wenge and Dr Wang Gang in the initial support optimization of tunnels in horizontal strata on several highlands.The purpose of this paper is to study the surrounding rock stability of tunnels built in multi-jointed sand-mudstone interbeds with high geostress level.And based on the analysis of surrounding rock pressure composition and energy-consuming support,the nursing ideas and countermeasures are put forward.The main contents are as follows:(1)Based on the in-situ stress test data of Yangshan Tunnel,the stability of surrounding rock of tunnels with sandstone as the main component and mudstone as the main component is analyzed by using transverse isotropic constitutive model and multi-joint elastic-plastic constitutive model respectively,and the distribution law of stratum stress along the path is analyzed.(2)Stratigraphic division based on geological prospecting and stratum distribution revealed by palm face,stability of surrounding rock based only on Mohr-Coulomb constitutive model is analyzed,and the "loading" effect exists in excavation of soft and hard rock interbeds by step method.The tunnel loosening zone is divided by the limit analysis based on the ultimate shear strain.(3)The strain softening constitutive model is used to simulate the strain softening of mudstone and the brittle failure characteristics of sandstone.The multi-joint constitutive model is used to simulate the fine jointed rock mass.The stability of surrounding rock based on the actual working conditions in the field is analyzed and the loosening zone is divided.(4)Based on the above calculation and analysis results,it is shown that rock burst and large deformation are not mutually exclusive events,and both of them occur under certain conditions.Two formation mechanisms of rock burst after large deformation are proposed,which can occur under the condition of soft-hard rock interbedding and in jointed rock mass with different integrity of single lithology.The case of rock burst collapse in mountain tunnel is analyzed concretely.(5)The influence of horizontal weak interlayer on the stability of surrounding rock is analyzed,and the reasonable boundary of numerical calculation model and the influence of the shape of cavern on the stress redistribution range are discussed.Based on the volume of the loosened zone as the criterion,the reasonable shape of the tunnel in high geostress horizontal strata is analyzed,which does not consider the specific stratum division and is based on the working condition of Yangshan tunnel.The difference between the optimum axle ratio of a cavern considering plasticity,plasticity and horizontal joints and the optimum axle ratio of a "harmonic cavern" based on elasticity is compared.(6)A method for calculating and analyzing the relationship between the pressure composition of surrounding rock is proposed.Taking Ruyi tunnel as an example,an idea and method for determining the allowable deformation of supporting structure considering the minimum surrounding rock pressure and engineering economy are proposed.Based on the results of case analysis,it is shown that the surrounding rock pressure is mainly deformation pressure.(7)A design calculation and analysis method of rock burst resistance-limiting and energydissipating support structure is presented.The solution method of the sum of strain energy and gravity potential energy released from rock mass is given,and the value and calculation method of design parameters of rock burst energy-limiting and energy-dissipating support structure based on Calculation of rock burst energy are given.(8)The idea of supporting tunnel in high geostress level is to transform the high impact pressure caused by rock burst energy into the limited surrounding rock pressure lower than the bearing capacity of lining support through constant resistance or low resistance energy dissipation support;release part of deformation pressure through rigid-flexible-rigid coupling energy dissipation support;and make loose pressure through reasonable design value of deformation amount of energy dissipation support.The loose pressure will not be too great. |
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