| With the continuous improvement of infrastructure technology in China,many medium and long tunnel projects have been built in western China,especially in Gansu Province,and most of these tunnel projects are located in the overlapping area of saline-alkali soil and frozen soil.In order to improve the stability and frost resistance and heat preservation performance of tunnel structure in alpine saline-alkali area of western China,this paper takes the construction of Muzhailing tunnel project as the background,and explores the stability and frost resistance and heat preservation performance of tunnel structure in alpine saline-alkali area by combining the method of adding silica fume to tunnel structure concrete and laying Fulikai insulation material to tunnel structure.Through freeze-thaw and saline-alkali erosion test,and tunnel frost heave numerical simulation study concluded.(1)Under the action of freeze-thaw cycles and saline-alkali corrosion,the compressive strength,splitting tensile strength and frost elastic modulus of single silica fume concrete showed a downward trend.The mechanical properties of freeze-thaw and saline-alkali erosion decreased slightly in the early stage,increased in the middle stage,and slowed down in the later stage.The mass loss rate decreased first to a negative value and then increased.Under the action of freeze-thaw and saline-alkali erosion,the mechanical properties of concrete specimens in LN(sodium sulfate)decreased the most,followed by concrete specimens in LG(calcium chloride),and the mechanical properties of concrete specimens in S(water)changed the least.(2)Through the crushing test,the S(water)concrete specimen is crushed and presents a top-down penetrating crack.The LG(calcium chloride)concrete specimen is dominated by penetrating cracks in the early stage of freeze-thaw and saline-alkali erosion,followed by a small amount of transverse cracks and collapse.The concrete specimens of LN(sodium sulfate)are mainly transverse cracks and collapses throughout the test,indicating that LN solution has a stronger erosion on concrete.At the same time,the concrete specimens of freeze-thaw cycles and saline-alkali erosion show sanding,gas shell,spalling and other phenomena.Single-doped silica fume concrete has better frost resistance and saline-alkali corrosion resistance in the early stage of freeze-thaw and saline-alkali corrosion,but the effect is not good in the middle and late stages.(3)When the thickness of the freeze-thaw circle and the lining thickness are constant,the frost heave force of the tunnel structure and the overall displacement of the tunnel structure increase with the increase of the frost heave rate of the surrounding rock.When the thickness of frost heave ring is constant,the thickness of frozen surrounding rock decreases with the increase of lining thickness,and the frost heave force and the overall displacement of tunnel structure decrease continuously.When the thickness of frost heave ring is 3m,the thickness of lining is 0.5m and the frost heave rate is 0.08 %,the maximum frost heave force and overall displacement of tunnel structure are 4.64 MPa and 0.042 m respectively.The maximum frost heave force of the tunnel is concentrated in the arch waist and arch bottom of the tunnel,and the maximum displacement of the whole is concentrated in the vault of the tunnel.(4)When the thickness of the expansion ring is 3m,the frost heave rate is 0.08 %,and the lining thickness is 0.05 m,the frost heave force and the overall displacement of the tunnel structure show a continuous decline with the increase of the length from the tunnel entrance.When the thickness of the expansion ring is 3m,the frost heave rate is0.08 %,the lining thickness is 0.05 m and the length of the tunnel entrance is the same,the frost heave force and the maximum displacement of the tunnel decrease first and then increase with the increase of the thickness of the insulation layer.When the thickness of insulation layer is 0.03 m,the frost heaving force and displacement of tunnel appear minimum.When the thickness of the expansion ring is 3m,the frost heaving rate is 0.08 %,the lining thickness is 0.05 m and the distance from the hole is100 m,the frost heaving force and the overall displacement are reduced by 45.21 % and47.61 % respectively compared with the unlaid insulation layer and the 0.03 m Fulikai insulation board.(5)When the thermal insulation layer is laid,the temperature rise near the tunnel wall is more obvious in the radial direction of the tunnel,and the temperature is basically unchanged in the position away from the tunnel wall.As the length of the tunnel increases,the radial temperature change of the tunnel is less obvious.When the distance from the tunnel entrance is 100 m and the thickness of insulation layer is0.03 m,the axial displacement of tunnel in X-axis direction is reduced by 50.37 % and in Y-axis direction is reduced by 50.68 %.The single-doped silica fume concrete is used as the tunnel lining structure material,and the laying of 0.03 m Fulikai insulation board can effectively improve the temperature field distribution of the tunnel wall position,reduce the structural damage caused by frost heaving force and overall displacement,and improve the stability of the tunnel structure.Figure [ 70 ],Table [ 21 ],References [ 72 ]... |
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