Test and Analysis of the Effect of the Freezing Construction of Subway Cross Passage on Adjacent Shield Tunnel Segment
In order to ascertain how the freezing method used for construction of subway cross passage will affect the adjacent segments,a site test has been conducted at the 2#cross passage of the Yaohu East Station—Maqiu Station section of Nanchang Metro Line 1 East Extension project,and the water&earth pressure of adjacent segments,structural internal force,vertical displacement,clearance convergence and ground settlement have been monitored in long term.As the results indicate:(1)Before excavation of the cross passage,the frost heave force will cause the water&earth pressure outside the adjacent shield tunnel segment rings to increase.The maximum values of the pressure are 170 kPa and 150 kPa,which are increased by 11.1%and 15.4%as compared with the values before freezing.After stabilization of the soil mass,the maximum values of the water&earth pressure are 173 kPa and 148 kPa,which are increased by 12.4%and 13.8%as compared with the values before freezing.(2)Under the effect of stratum freezing,the maximum bending moment and axial force of the adjacent segment are-103.1 kN·m and 2 314 kN,which are increased by 28.09%and 19.8%as compared with the values before freezing.(3)Under the effect of the frost heave force,the safety factor of the segment at the frozen side is reduced,and the safety factor near the arch bot-tom is reduced by the greatest margin,which is 22.9%.After unfreezing and stabilization of the soil mass,the safety factor of each segment is increased,but still less than the value before freezing.(4)In the construction period,the maximum heave on the surface is 2.18 mm and the maximum settlement 1 mm.The maximum upward displacement of the segment is 2.3 mm and its maximum settlement 0.9 mm.The maximum value of convergence deformation of segment is no more than 3.4 mm.These results indicate that the freezing method used for construction of subway cross passage is highly feasible.
Shield tunnelFreezing methodCross passageSurrounding rock pressureDeformation by forceSite test
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