限界计算是地铁工程设计过程中较为繁琐的一项工作，直接关系到车辆运行安全。针对天津地铁6号线工程中应用9号曲尖轨道岔的情况，综合考虑车辆在道岔侧股运行时的几何偏移量、欠超高引起的动态偏移量、曲线轨道参数及车辆参数变化引起的车体横向位移量，计算并拟合B型车道岔区建筑限界加宽量图，为道岔区土建、结构设计提供理论依据。计算结果表明：B型车道岔外侧建筑限界加宽始于岔心前端25.75 m处，最大加宽量为166 mm；道岔内侧加宽始于岔心前端22.55 m处，最大加宽量为429 mm。
Calculation of metro gauges is tedious in the design process of metro engineering. The design of metro gauges is directly related to the safety of vehicle operation. In view of the application of the No. 9 curved switch turnout on Tianjin metro line 6, the widening of structure gauge in the turnout zone is calculated and the diagram of widening is fitted in this paper. The quantity of throw, dynamic offset caused by deficient superelevation, transverse displacement of the car body caused by changes in curved track, and vehicle parameters are considered. The theoretical basis for the civil and structural design of the turnout zone is provided. The calculation results show that the widening of the structure gauge of a type-B vehicle outside the turnout starts at 25.75 m at the front of the turnout, and the maximum widening is 166 mm. The widening of the inner side of the turnout starts at 22.55 m at the front of the turnout, and the maximum widening is 429 mm.