低应变法判定PHC管桩接头拉脱缺陷效果研究及拉脱成因分析

Analysis of the Effect of Judging Pull-off Defect of the PHC Pipe Pile Joint with Low Strain Method and the Reason of Pull-off

基于南京某PHC管桩工程存在大量基桩接头拉脱的低应变反射波判定结果,采用孔内摄像法、高应变法、静载法对初判拉脱桩与未拉脱桩进行分组对比试验,以验证低应变法判定接头拉脱的有效性和可靠性。比对试验结果表明,孔内摄像法发现初判为拉脱桩的接头拉脱最大达125 mm,高应变法锤击作用下桩顶沉降量剧增,静载法获取的单桩竖向抗压承载力大幅下降,表明采用低应变反射波法可以有效分析判定接头拉脱类缺陷。通过与同一区域多个无接头拉脱缺陷的类似桩基工程对比分析,发现该工程桩身中浅部土层的可压缩性明显小于其它工程,分析认为该工程的接头拉脱是打桩引起的强烈挤土效应下土层上隆的结果,并提出了对类似土层工程场地桩型和施工工艺选择的建议。

In order to verify the effectiveness and reliability of the low strain method,We push forward the group contrast experiment based on the results of existing plentiful problems of pulling of foundation pile joint in the engineering in Nanjing.The group comparison tests were conducted between the initial judging pull out pile and the unpullout pile by in-hole camera method,high strain method and static load method.The comparison test results show that the maximum pull-out of the joint initially judged as pull-out pile is 125 mm by the in-hole camera method,the settlement of the pile top increases sharply under the hammer action of the high strain method,and the vertical compressive bearing capacity of the single pile obtained by the static load method decreases significantly.All this shows the low-strain reflected wave method can be used to effectively analyze and judge the pull-out defects of the joint.Contrast with other similar pile foundation engineering which without joint defects in the same area,we found that the compressibility of the shallow soil layers in the pile body in this project is lower than other engineering obviously.We analyzed that the pull off of joint may be caused by pile driving strong compaction effect of soil on the result of the lung.Then we can offer a proposal about the similar soil engineering site pile type and construction technology of choice.