黄土地区新建地铁隧道下穿时既有地铁线路沉降控制标准
Settlement control standard of existing metro line undercrossed by new metro tunnel in loess area

针对西安地铁5号线近距离下穿地铁2号线的工程实际情况,分析了既有地铁线路的安全判断准则、正常使用要求和服役状态,选取弯矩、曲率半径、容许应力、容许切应变与轨道变形作为新建地铁隧道下穿时既有地铁线路沉降标准的控制因素,构建了既有地铁线路的力学模型,推导了既有地铁线路允许沉降计算公式,确定了黄土地区新建地铁隧道下穿时既有地铁线路的沉降控制标准。分析结果表明:以既有地铁线路的弯矩、曲率半径、容许应力、轨道变形与容许切应变依次作为控制因素时既有地铁线路允许沉降分别为22.40、20.85、48.14、20.23、21.06 mm,其他地区下穿工程经验允许沉降与国内相关规范允许沉降为20 mm,因此,最不利控制因素即轨道变形的允许沉降接近既有相关允许沉降,建议黄土地区新建地铁隧道下穿时既有地铁线路沉降控制基准为20 mm; 对既有地铁线路沉降控制标准进行了分级管理,选取沉降控制基准的100%、80%和60%分别作为既有地铁线路的控制值(20 mm)、报警值(16 mm)与预警值(12 mm),提出了下穿时既有地铁线路的预警体系; 评价了新建地铁隧道下穿时既有地铁线路沉降的安全级别,并给出了相应的处置措施,安全级别为Ⅰ级,即沉降不大于12 mm时,新建隧道正常施工并做好监测,安全级别为Ⅱ级,即沉降为(12,16] mm时,加强监测并实时反馈,安全级别为Ⅲ级,即沉降为(16,20] mm时,停止施工,并启动应急预案,安全级别为Ⅳ级,即沉降大于20 mm时,达到破坏级别,不允许施工。
Based on the actual condition of metro line 5 undercrossing metro line 2 at close range in Xi'an, China, the safety judgment criteria, normal-use requirement and service status of existing metroline undercrossed by new metro tunnel in the loess area were analyzed, the bending moment, radius of curvature, allowable stress, allowable shear strain and track deformation were taken as the control factors of the settlement of existing metro line, the mechanical model of existing metro line was constructed, the settlement computation formula was deduced, and the settlement control standard was determined. Analysis result shows the corresponding allowable settlements of the existing metro line are 22.40, 20.85, 48.14, 20.23 and 21.06 mm under the control factors of bending moment, radius of curvature, allowable stress, allowable shear strain and track deformation, respectively, and the empirical allowable settlements of other regional undercrossing projects and the standard allowable settlements of relevant domestic regulations are 20 mm. The most unfavorable control factor is the track deformation, and the corresponding allowable settlement is close to the existing relevant allowable settlements, so, it is suggested that the settlement control standard is 20 mm for the existing metro line undercrossed by new metro tunnel in the loess area. The level-to-level administration of settlement control standard of existing metro line is performed, the 100%, 80% and 60% of the settlement control standard are taken as thecontrol value(20 mm), alarm value(16 mm)and warning value(12 mm), respectively, and an early warning system of undercrossed existing metro line is proposed. The safety level of existing metro line undercrossed by new metro line is evaluated, and the corresponding treatment measures are given. When the safety level is Class Ⅰ and the corresponding settlement is no more than 12 mm, the new metro tunnel should be