为分析膨胀土特殊地层对双洞地铁隧道结构的影响，并对浅埋双洞地铁隧道施工参数进行优化研究，提出运用FLAC3D热力场-应力场耦合方法,利用标定设置热膨胀系数等效模拟膨胀土地层吸水膨胀、失水收缩过程。研究结果表明： 1）数值模拟结果经与现场实测值对比验证，该方法正确、合理； 2）当两隧道净距大于1.5倍洞径时，最大地表沉降值为28.82 mm，衬砌结构内力增量小于20%，双洞中柱围岩塑性区不贯通； 3）当双洞掌子面距离大于40 m时，最大地表沉降值小于30 mm，拱顶沉降增量小于10%； 当双洞掌子面距离大于30 m时，双洞隧道中柱围岩塑性区不贯通； 4）建议双洞地铁隧道净距大于1.5倍洞径、双洞掌子面距离大于40 m。

In this paper, the processes of water absorption expansion and water loss contraction of expansive soil are equivalently simulated by FLAC3D thermal fieldstress field coupling method and expansive coefficients setting, so as to analyze the influence of the expansive soil on the shallowburied twintube metro tunnel structure in expansive soil and optimize the construction parameters. Some conclusions are drawn as follows: 1) The comparison results between simulation method and field test show the rationality and feasibility of the simulation method. 2) When the clear distance between two tunnels is larger than 1.5 times tunnel diameter, the maximum ground surface settlement is 28.82 mm and the internal force of lining structure increases by less than 20%; the plastic zones of the central column of the two tunnels are not connected. 3) When the distance between two tunnel working faces is larger than 40 m, the maximum ground surface settlement is 30 mm and the crown top settlement increases by 10%; when the distance between two tunnel working faces is larger than 30 m, the plastic zones of the central column of the two tunnels are not connected. 4) It is suggested that the clear distance between two tunnels of the twintube tunnel should be larger than 1.5 times tunnel diameter; and the distance between two tunnel working faces should be larger than 40 m.