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软土地区桩基施工群孔效应作用机理研究 预览

Mechanism of Borehole Group Effect Induced by Pile Foundation Construction in Soft Soils
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摘要 本研究利用 Plaxis 3D 有限元软件对群孔效应引发周边地层显著变形的原因进行了探索分析,通过孔周应力变化及孔周土体变形分析揭示了群孔效应的内在机理.结果表明,单孔情况下周围土体中会出现水平环向应力拱和竖向应力转移,有效限制孔壁内缩变形.而群孔之间的相互作用主要包括以下 3 方面:一是孔与孔之间对彼此应力拱的影响,具体表现为对环向应力拱的分布范围和拱强度的削弱作用;二是孔与孔之间对彼此竖向应力转移的影响,由于群孔之间距离有限,孔间应力转移同样受到削弱和破坏;三是在已有空孔附近再次成孔的卸荷效应,会使得周围土体有向该孔变形的趋势.群孔效应对周边环境的较大影响是以上 3 种因素共同作用的结果.当大量空孔存在且孔间距较小时,孔周边土体水平和竖向应力拱相互影响削弱导致每个空孔的内缩变形均大于单孔时的变形值,这是群孔效应中孔与孔相互作用的内在机理,也是其引发周边土体变形严重的主要原因. The level of groundwater in soft soils is high and the soils are weak;hence,they are sensitive to engineering activities.After the construction of bored and cement fly-ash gravel(CFG)piles that are used as foundations of buildings,a large number of hollow boreholes remain between the top of the piles and the ground surface.Engineering cases show that the presence of many hollow boreholes considerably influence the surrounding environment,and this is also called the borehole group effect.However,the reason for as well as the mechanism of the borehole group effect are still unclear.In this investigation,we used the software Plaxis 3D to investigate the reasons for the significant deformation of the surrounding soil that was caused by the borehole group effect.By analyzing the stress change around the boreholes and the deformation of the surrounding soil,we identified the intrinsic mechanism of the borehole group effect.The simulation results show that stress changes within the horizontal stress arch and vertical stress transfer occur when only one borehole was created,effectively limiting the shrinkage of the hole.The interaction between boreholes mainly involves the following three aspects:a)the influence of the hole on each other's stress arches,which is exhibited by a weakening effect on the distribution and strength of the hoop stress arches;b)the influence of the vertical stress transfer between the holes and the stress transfer between the holes is weakened and destroyed owing to the limited distance between the holes;c)the unloading caused by re-drilling near existing holes will cause the surrounding soil to tend to deform toward the holes.The combination of the above three factors means that a large number of hollow boreholes will considerably influence the surrounding environment.When there are a large number of hollow boreholes with limited spacing between them,the interaction of these holes disturbs the horizontal and vertical stress arches around the holes.As a result,in the presence of many hollow bore
作者 郑刚 王若展 程雪松 张涛 王凡俊 Zheng Gang;Wang Ruozhan;Cheng Xuesong;Zhang Tao;Wang Fanjun(Key Laboratory of Coast Civil Structure Safety of Ministry of Education,Tianjin University,Tianjin 300072,China;School of Civil Engineering,Tianjin University,Tianjin 300072,China)
出处 《天津大学学报:自然科学与工程技术版》 CSCD 北大核心 2019年第A01期1-8,共8页
基金 国家自然科学基金资助项目(51508382) 天津市自然科学基金资助项目(18JCQNJC07900).
关键词 软土 桩基施工 群孔效应 土拱效应 应力转移 soft clay pile foundation construction borehole group effect soil arching stress transfer
作者简介 郑刚(1967-),男,博士,教授,zhenggang1967@163.com;通信作者:程雪松,cheng_xuesong@163.com.
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