锚杆工法控制对桩锚支护结构稳定性的影响
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摘要
通过廊坊某广场基坑支护施工过程,分析了锚杆钻孔施工两种工法对桩锚支护结构的稳定性影响。现场锚杆施工使用了两种钻机,分别采用"套管护壁钻进成孔"及"压浆护壁钻进成孔"工法。通过分步开挖变形监测,采用第一种锚杆成孔工法的护坡桩—锚杆结构变形数据比较平稳,边坡稳定;采用第二种锚杆成孔工法的护坡桩—锚杆结构变形剧烈,边坡稳定性差。表现在几个方面:护坡桩后侧土体流失,桩顶外侧出现塌陷沟槽(宽度×深度=1.0m×1.5m);锚杆拉拔效应后移,锚杆长度范围内地表出现多条裂缝;锚杆应力松弛,实测锚头拉力降低30%～50%;坡顶位移巨大,影响边坡安全。针对边坡出现的不稳定险情,采取了综合处理措施:桩顶后侧设置卸载沟;坡脚回填土方,设置反压土方;锚杆二次补张拉;增补一排锚杆。最终边坡恢复了稳定。
In Langfang Square foundation pit engineering,the influence of two anchor hole-boring methods which are called casing hole-boring method and slurry hole-boring method on PARS' stability is studied.Through monitoring,small deformation of the pile is gotten by the first boring-hole method,too large deformation of the pile has been gotten by the second boring-hole method,and the excavation slope becomes unstable.Instability manifested in four aspects:(a)Earth subsidence occurs behind the piles,width and depth of the collapsed trench is 1.5m and 1.0m.(b)Surface cracks appear behind the piles,drawing effect of anchor moves towards far areas.(c)Stress relaxation of the anchors happens,measured bolt tension reduced by 30%～50%.(d)Large top displacements take place behind the piles.Finally treatment measures including the top soil unloading,anchorage reconstruction etc.are proposed and successfully applied on the field,which ensure for the deep foundation pit excavating safety and the slope final stabilization.
In Langfang Square foundation pit engineering,the influence of two anchor hole-boring methods which are called casing hole-boring method and slurry hole-boring method on PARS' stability is studied.Through monitoring,small deformation of the pile is gotten by the first boring-hole method,too large deformation of the pile has been gotten by the second boring-hole method,and the excavation slope becomes unstable.Instability manifested in four aspects:(a)Earth subsidence occurs behind the piles,width and depth of the collapsed trench is 1.5m and 1.0m.(b)Surface cracks appear behind the piles,drawing effect of anchor moves towards far areas.(c)Stress relaxation of the anchors happens,measured bolt tension reduced by 30%～50%.(d)Large top displacements take place behind the piles.Finally treatment measures including the top soil unloading,anchorage reconstruction etc.are proposed and successfully applied on the field,which ensure for the deep foundation pit excavating safety and the slope final stabilization.
引文
[1]丁勇春.软土地区深基坑施工引起的变形及控制研究[D].上海:上海交通大学博士论文,2009.
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[2]程良奎,张作楣,杨志银.岩土加固实用技术[M].北京:地震出版社,1998.
[3]中华人民共和国国家标准.建筑基坑工程监测技术规范(GB50497-2009)[S].北京:中国计划出版社,2009.
[4]中华人民共和国行业标准.混凝土泵送施工技术规程(JGJ-T10-95)[S].北京:中国建筑工业出版社,1995.
[5]张怀文,高全臣,杨文莉.某深基坑工程边坡变形失稳致因及处理对策[J].岩土工程技术,2010,(3).
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