东天山隧道穿越断层破碎带初期支护变形分阶段控制标准研究

Phased Control Standards of Primary Support Deformation of East Tianshan Tunnel Crossing Fault Fracture Zone

为解决东天山特长公路隧道穿越F2断层破碎带软岩大变形问题,综合采用理论分析、数值模拟、现场监测与统计分析等手段,开展隧道两台阶预留核心土法和三台阶法施工初期支护变形控制标准研究,并提出隧道初期支护变形分级预警方法。研究结果表明:1)东天山隧道穿越F2断层破碎带的预留变形量选取60~80 cm能够满足施工要求。2)对于两台阶预留核心土法,上、下台阶开挖产生的初期支护变形占其总变形量的比例建议为60%、40%;对于三台阶法,上、中、下台阶开挖产生的初期支护变形占比建议为20%、65%、15%。3)当初期支护变形未超过预留变形量、超过预留变形量但未超过5%二次衬砌设计厚度、未超过10%二次衬砌设计厚度时,分别启动Ⅰ、Ⅱ、Ⅲ级预警。Ⅰ级预警时正常施工,Ⅱ级预警时采取控制开挖进尺和台阶长度、及时设立护拱、尽快封闭初期支护等处治措施,Ⅲ级预警时则进一步采用短台阶或微台阶法施工。

Soft rock large deformation occurred in East Tianshan extra-long highway tunnel crossing F2 fault fracture zone.Accordingly,the theoretical analysis,numerical simulation,on-site monitoring,and statistical analysis are employed to investigate the control standards of primary support deformation of tunnel constructed by two-bench reserved core soil method and three-bench method.Then the phased early warning method of primary support deformation is proposed.The results reveal the following:(1)The reserved deformation of East Tianshan tunnel crossing F2 fault fracture zone is recommended to be 60~80 cm,which can meet the construction requirements.(2)The primary support deformations induced by top heading and lower bench excavation using two-bench reserved core soil method are recommended to be 60%and 40%in total deformation,respectively,whereas those induced by top heading,middle bench,and lower bench excavation using three-bench method are recommended to be 20%,65%,and 15%in total deformation,respectively.(3)GradesⅠ,Ⅱ,andⅢearly warning should be started respectively when the primary support deformation not exceed reserved deformation,exceeds the reserved deformation but not exceed 5%of the secondary lining design thickness,and not exceed 10%of the secondary lining design thickness.Normal construction can be operated in case of gradeⅠearly warning,treatment measures such as controlling excavation advance and bench length,setting up retaining arch in time,and closing primary support as soon as possible shall be undertaken in case of gradeⅡearly warning,and short bench or micro bench method shall be further used in case of gradeⅢearly warning.