| In recent years, with traffic operating of a large number of cold region tunnels, frost damage in tunnel is becoming increasingly outstanding. How to take effective prevention measures on frost damage, this issue urgently needs to be solved in engineering.In thermal insulation method, one of damage prevention technologies in cold region tunnels, the paper uses the glazed hollow beads insulation mortar as insulation layer to reach antifreeze design goals, instead of original organic insulation materials. And, glazed hollow beads insulation concrete is used in secondary lining of tunnel to achieve the integration between load-bearing and thermal insulation, reducing of construction process and energy conservation. Based on these insulation ideas, this paper has given three kinds of thermal insulation structure system in cold tunnels, which are intermediate insulation layer structure with glazed hollow beads mortar, insulation concrete secondary lining structure with glazed hollow beads insulation concrete, intermediate insulation layer structure + insulation concrete secondary lining structure. The paper has implemented theoretical and experimental research around three insulation structure systems and will provide new materials and new technologies for frost prevention of the cold region tunnels. Main research work and results are as follows:(1) Under the actual tunnel temperature, humidity and groundwater conditions, the mix ratio test about glazed hollow beads (GHB) insulation mortar has been completed by orthogonal test.18 different groups of test-pieces have been measured in the test. The test results show that:The amount of GHB and cement are the key factors that affect the compressive strength and thermal conductivity of insulation mortar; When GHB account for 40% of the mortar quality and the amount of cement is 100kg per cubic meter, the ideal mechanical and insulation performance can be obtained. Then, the thermal conductivity of insulation mortar is 0.0553W/(m-K), and compressive strength is 0.483 MPa. Glazed hollow beads insulation mortar layer is more suitable for the intermediate insulation layer method of tunnel antifreeze technology.(2)On the basis of preliminary studies, our task force conducts experimental research on the mechanical properties and durability of the GHB insulation impermeability concrete. Results concluded:On the selection of concrete materials, chemical additives and fine mineral admixtures must be used. On the mixture ratio of concrete, the amount of water and cementitious material should be tried to reduce. In this test, when the strength grade of GHB insulation concrete is C40, its thermal conductivity coefficient is 0.68W/(m-K) and cement consumption is 410kg per cubic meter. Compared with the previous insulation concrete test, cement consumption per cubic meter bas been significantly reduced.(3) Through the elastic-plastic theory, the paper analyzes the mechanical properties of the insulation structure system in tunnel and has derived theoretical formula about plastic zone radius. After tunnel excavation, stress and deformation of tunnel rock in elastic zone and plastic zone have been analyzed. After application of the insulation layer in tunnel, the elastic stress expression and displacement one of the insulation layer structure and the secondary lining have been derived. These works provide a theoretical basis for practical engineering.(4) According to actual tunnel engineering, mechanics numerical simulation analysis on the insulation structure system has been carried out by the stratum-structure model. Analysis shows that:After application of the insulation layer in tunnel, the initial support layer and the surrounding bolt can meet the strength design requirements and the surrounding rock has good stability. For the secondary lining, either C30 common concrete or C40 insulation concrete, lining structure strength can meet all design requirements in the case of configuration reinforcement by the norms. The long-term safety of this tunnel structure is controlled by strength of the arch in secondary lining.(5)After circular cross-section simplification of the actual tunnel cavern, the thermal conductivity mathematical model of the circular tunnel has been established and its differential equations and Bessel characteristic function have been solved by mathematical methods. The approximate analytical solutions of radial and axial temperature field have been obtained in cold region tunnel with the surrounding rock, the initial support, the insulation layer and the secondary lining.(6) The thermal analysis of steady-state and transient on tunnel structure has been carried out by ANSYS software. The insulation effect of each insulation structure system has been calculated through six cases. Numerical analysis shows that:For insulation concrete secondary lining structure, its insulation effect value increases by 1.22 times, compared with tunnel structure without antifreeze measures. For intermediate insulation .layer structural system, its insulation effect value increases by 3.91 times if thickness of insulation mortar layer is 60 mm. So the intermediate insulation layer structure system has better insulation effect. For the tunnel of seasonally frozen zone, this kind of insulation structure system, ordinary support with common concrete+waterproof layer+glazed hollow beads mortar insulation layer (60mm)+insulation concrete secondary lining, is the most economical and reasonable.(7) In 2010, the insulation structure design and field test have been done about actual tunnel. The field test is temperature monitoring test about intermediate insulation layer structure with GHB insulation mortar. The data indicates that:After the application of the insulation layer with 60mm thickness, the measured insulation effect value is 80% of the theoretical value. There is a good fit between the measured value and the theoretical value in this test and its data can be used as a reference basis for temperature design and projection in other tunnel engineering. At the same time, in the field test, the construction process and the possible problems on the insulation layer have been analyzed and solved, which will provide technical guidance for its further promotion. |
PDF Full Text Request