| With the national strategies of "Western Development","One Belt,One Road"and "Sichuan-Tibet Railway",China’s transportation network is gradually extended to high cold and high altitude areas.Under the action of frost-heaving pressure(FHP),a large number of tunnel lining structures under construction and in operation in the cold areas are caused by frost damage such as cracking and ice hanging in the secondary lining,which seriously restricts the construction,operation and maintenance of tunnel engineering facilities in the cold regions.In view of the complexity of frost-heaving in cold zone tunnels,there is no consensus on the study of FHP for the surrounding rocks.In this paper,theoretical analysis,indoor tests,numerical simulations and model tests were used.Based on this,a theoretical solution for the FHP of the frozen circles in surrounding rock under plain strain state was derived considering the influence of water content and proportion index of surrounding rock.A model for calculating the FHP in tunnels considering composite rock layers such as weathered broken rock and fractured rock was established.An improved model of three-dimensional cone constrained local water accumulation in frost heaving was established,and a method for calculating local FHP in cold regions was proposed.A three-dimensional numerical analysis model of reinforced concrete lining structure was established to reveal the mechanical characteristics,random cracking and damage modes of the lining structure under the action of FHP,which was verified in engineering.The research content of this paper provides the theoretical basis and technical support for the mechanism of FHP and lining cracking evolution of water-rich tunnel in cold areas.The following research results are obtained and summarized as follows:(1)The frost-heaving evolution mechanism of frozen circles in surrounding rock around water-rich tunnel is a key scientific problem that affects the operation safety in cold regions.To explore the evolution law of frost-heaving pressure in frozen circles in such surrounding rock,scaled three-dimensional geomechanical model tests were carried out.In these tests,freezing of water-bearing surrounding rock at low temperature was considered.The temperature field distribution characteristics of surrounding rock at the tunnel portal section was simulated by introducing ambient air into the tunnel for cooling.Micro-pressure sensors were employed to dynamically monitor the frost-heaving pressure in real time.The spatial and temporal evolution curves of the frost-heaving pressure were obtained for various water content and thickness in surrounding rock.(2)Frost-heaving of local water accumulation in the surrounding rock of cold mountain tunnels is one of the main causes of lining cracks.Carrying out indoor frozen tests based on self-designed water bladder devices to simulate local water accumulation behind the lining;The frost-heaving response characteristics of tunnel surrounding rock and local water space were studied,and the variation law of temperature field and FHP under the action of frozen was analyzed.The thermal stress method is used to simulate the evolution characteristics of FHP,and the experimental results in this paper are in good agreement with the numerical results.(3)Based on the measured data of laboratory tests,the fitting formulas for parameters such as the frost-heaving rate of surrounding rock,thickness of the frozen circles,and water content were established utilizing multiple regression analysis.Combined with the analytical solution of frost-heaving of fracture surrounding rock in elastic state,the semi-empirical theoretical solution of FHP of frozen circles surrounding rock in plane strain state considering water content and specific gravity of surrounding rock was given.(4)Based on the theoretical research of FHP mentioned above,the improved model of FHP calculation of weathered broken rock and fractured rock was comprehensively considered,and the analytical solution of FHP of composite frozen circles was derived.Coupled multi-parameter analysis method was used to give the equation of FHP of rock mass considering the water-heat transfer effect,and reveal the influence law of frost depth and FHP of multi-parameter coupling.The sensitivity characteristics of different parameters to FHP were studied by system stability analysis.(5)Based on the diversified characteristics of tunnel structure void size and shape,an improved constrained frost heaving model of three-dimensional cone was proposed,and an analytical calculation formula was derived considering the space volume of water,constraint surface,surrounding rock and resistance factor of lining.Based on the experimental results of FHP,the evolution law of FHP considering time effect was established,and the semi-empirical theoretical solution of FHP was obtained.The FHP model proposed in this paper can consider the effect of arbitrary shape and size in three-dimensional local water space,which is in good agreement with the existing theoretical model and experimental results,and has a certain reference value for engineering application.(6)FHP is actually a special form of external additional load.Aiming at the cracking evolution of tunnel lining under external load,a horizontal loading model test device was developed to study the mechanical properties and cracking evolution law of reinforced concrete lining.Based on the extended finite element method and the load-structure model calculation theory,a three-dimensional calculation model for the lining of a horseshoe reinforced concrete tunnel was constructed.The feasibility of the proposed numerical calculation method to simulate the cracking evolution law of the lining was verified by comparing the numerical solution with the experimental values.(7)Based on the above research results,a total of 21 sets of numerical simulation tests with different grade of surrounding rock and local water accumulation in the frozen circles were carried out to reveal the mechanical characteristics of reinforced concrete lining under the action of FHP,the evolution law of cracking and the safety characteristics of the lining section.Based on the distributed strain test results of optical fiber and the calculation model of the lining structure,the FHP of the lining of the tunnel entrance section in the engineering site was predicted.Conclusions of this study provide a theoretical basis and engineering reference for frost heaving mechanism and preventing freezing damage in cold region tunnels. |
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