浸水饱和条件下黄土微型桩抗压和抗拔承载力试验  

Field compression and uplift tests on micropiles in collapsible loess under completely-soaked and saturated conditions

作　　者：盛明强 乾增珍[2] 杨文智[2,3] 鲁先龙 SHENG Ming-qiang;QIAN Zeng-zhen;YANG Wen-zhi;LU Xian-long(Nanchang University,Nanchang 330031,China;China University of Geosciences,Beijing 100083,China;China Electric Power Research Institute,Beijing 100192,China)

机构地区：[1]南昌大学,江西南昌330031 [2]中国地质大学(北京),北京100083 [3]中国电力科学研究院有限公司,北京100192

出　　处：《岩土工程学报》2021年第12期2258-2264,共7页Chinese Journal of Geotechnical Engineering

基　　金：国家自然科学基金项目(52069013);国家电网公司科技项目(GC17201100065)。

摘　　要：为开展浸水饱和条件下黄土微型桩基础抗压和抗拔承载性能试验,设计了一种桩周土体浸水饱和方案,并在甘肃地区2个湿陷性黄土场地分别完成了浸水饱和与天然含水率状态下微型桩单桩抗压抗拔和群桩抗压对比试验。结果表明:浸水饱和条件下黄土地基微型桩单桩抗压抗拔与群桩抗压荷载–位移曲线均呈"陡变型"变化规律,而天然状态下相应微型桩桩荷载–位移曲线则呈初始弹性段、弹塑性曲线过渡段和破坏直线段的三阶段"缓变型"变化规律。浸水饱和条件与天然状态下黄土抗压微型桩桩端阻力分担桩顶下压荷载的10%~15%,而相应黄土抗拔微型桩呈摩擦桩性状。天然状态下黄土微型桩单桩抗拔极限承载力为抗压极限承载力的66%~87%。当黄土浸水饱和后,相同微型桩单桩下压极限承载力平均下降70%,抗拔极限承载力平均下降50%,相同群桩基础下压极限承载力降低约75%。浸水饱和后黄土微型桩单桩和群桩基础下压极限承载力损失远高于相应基础的上拔极限承载力损失,相关试验研究成果可为今后黄土地区工程建设参考。In order to investigate the compression and uplift bearing capacity of micropiles in collapsible loess,a method for loess prewetting under completely soaked and saturated conditions is firstly designed.Consequently,the comparative field compression and uplift load tests on single micropile and group micropiles are respectively carried out in the two collapsible loess sites in Gansu Province.Both the site conditions and the load tests are documented comprehensively.The compression and uplift load-displacement curves of the single micropile and group micropiles in completely soaked and saturated loess generally follow a typical two-phase steep change pattern,which is quite different from those in-situ moisture content loess because they can be simplified into three distinct regions:initially linear,curvilinear transition and finally linear regions.Both in the in-situ moisture content loess and the completely soaked and saturated loess,the compression or uplift loaded single micropiles should be considered as the frictional pile foundations,and the tip resistances are only about 10%to 15%of the applied compression loads.For the micropiles in loess under in-situ moisture content,the ultimate uplift load capacities are 66%to 87%of those under compression.However,the loess under completely soaked and saturated condition will lead to a reduction of 70%in compressive bearing capacity and 50%in uplift bearing capacity for single micropile,and that for group micropiles is about 75%in compressive bearing capacity.These experimental results may provide a reference for the designers in loess in the future.

关 键 词：完全浸水 湿陷性黄土 微型桩 抗压 抗拔 现场试验 

分 类 号：TU43[建筑科学—岩土工程]