为提高铁路双线大断面隧道二次衬砌钢筋保护层控制质量，降低拱顶开裂风险，针对隧道二次衬砌钢筋在大跨度时本身具有向下的沉落变形特点，需对钢筋沉落量进行有效控制。二次衬砌环向主筋受力体系与拱的受力方式相同，以郑万高速铁路隧道二次衬砌结构几何参数、钢筋及垫块布置、钢筋的自重为研究对象，按无铰拱结构受力计算方式，采用经典力学原理、拱的挠度理论、挠度叠加设立方程，对钢筋自重下的预留沉落量进行研究，得到环向主筋越小施工沉落量越大，环向主筋越大施工沉落量越小的规律。通过理论公式计算出各种衬砌类型钢筋施工沉落量，提前进行有效预设，并按施工沉落变形对钢筋进行有效限位支撑，提高钢筋安装的准确性，有效控制了二次衬砌钢筋保护层，满足了设计要求。

In order to improve the control quality and reduce the crack risk of the secondary lining reinforced steel of doubleline large crosssection tunnel layer, the amount of sedimentation of reinforced steel is controlled according to deformation characteristics of the secondary lining reinforced steel with large span. The bearing force system of the circumferential reinforcement coincides with that of arch. The geometric parameters, arrangement of reinforced steel and cushion block and selfweight of reinforced steel are studied; the reserved sedimentation of secondary lining reinforced steel under selfweight is studied by classical mechanical theory, deflection theory of arch and the setting equation of deflection superposition under stress calculation of nonhinged arch; and it is obtained that the smaller the circumferential reinforcement, the larger the construction sedimentation, and the larger the circumferential reinforcement, the smaller the construction sedimentation. By calculating the amount of construction sedimentation of each lining reinforced steel by theoretical formula, effective presetting in advance and effective positionlimit supporting for the reinforced steel, the accuracy of the reinforced steel installation is improved, and the secondary lining reinforced steel protection layer is control.