超期服役深基坑复工时的加固技术措施

张艳芳 蔡忠强 陈佳宇

摘 要：除有特殊要求外，基坑支护结构的设计使用期限通常为一年，然而在实际工程中经常会出现基坑开挖完成后长时间搁置再复工的现象，形成了一批存在安全风险的超期服役深基坑。北京地区某深基坑停工超过5年，历经两次加固，通过对现状基坑支护结构及周边环境进行检测鉴定、变形分析，确定加固设计的关键环节，针对基坑存在的锚杆预应力损失、桩后土体疏松、堆土挖除后将继续变形等问题，制定了加固方案，包括杆锚增设及二次张拉、疏松土体注浆加固、桩间护壁修补及加强复工时的动态监测等，本加固项目在保证施工质量合格的情况下，顺利开挖至槽底，未发生事故，表明加固措施安全可靠，能够为类似工程提供借鉴与参考。

关键词：超期服役基坑;基坑检测鉴定;加固技术措施;动态监测

Abstract： Except for special requirements， the design life of foundation pit support structure is usually one year. However， in practical projects， after the excavation is completed the foundation pit is often put aside for a long time and then resumed for utilization. Such extended service deep foundation pits create a number of safety risks. A deep foundation pit in Beijing area has been stopped for more than 5 years and has undergone reinforcement twice. The key link of reinforcement design is determined through the detection， appraisal and deformation analysis of the present supporting structure of the foundation pit and its surrounding environment. In view of the problems existing in the foundation pit， such as loss of prestress of the anchor rod， loose soil behind the pile， and continued deformation after the pile is excavated， a reinforcement scheme is carefully worked out that includes addition and secondary tensioning of anchor rods， grouting reinforcement of loose soil， repair of wall protection between piles and dynamic monitoring during resumption of the work. With quality qualified， the construction work successfully digs to the bottom of the trench without any accident， indicating that the reinforcement measures are safe and reliable， and can provide reference for similar projects.

Keywords： extended service pit;detection and appraisal of foundation pit; technical measures for strengthening;dynamic monitoring

基坑支护结构通常为临时性结构，设计使用年限为1年，但由于天气、设计修改、资金不足等原因出现超期使用的现象，这对基坑自身及周围建筑、管线等构成了潜在的威胁，为了降低基坑复工时的安全风险，需合理选择加固措施。

近些年来我国超期服役深基坑屡见不鲜，如沈阳的宝能环球金融中心项目深基坑自完工历时2年10个月才完成回填，恢复使用前对基坑进行了检测评估并采取了适当的加固措施，保证了基坑的安全（梁贵才等，2017）。广州某中央商务区地下空间项目基坑开挖使用超过2年，复工时通过锚索加固、分区段素混凝土回填等技术措施保证了基坑再开挖的安全（任斌向，2020）。……