水平循环荷载下非连接式桩筏受力特性分析
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摘要
为了研究非连接式桩筏基础在水平静力及循环加载作用下的受力机理,在可视化水平循环加载装置中进行了室内模型试验,分析了加载方式、垫层厚度、循环幅值及次数对其水平刚度、土体位移及桩身内力的影响,并利用数字图像量测技术获取了土体的位移场。试验结果表明:非连接式桩筏基础的水平刚度随着循环次数的增加而增大,而滞回圈面积逐渐减小并趋于稳定;与水平静载试验相比,群桩中各基桩分担的水平荷载比例随循环加载发生重分配,后排桩的作用逐步得到更多发挥;当循环幅值较小时,前、中排桩所承担的弯矩值较为接近,随着循环幅值的增加,前排桩的作用得到加强;较桩筏基础相比,在水平静载及循环加载时,设置垫层均可显著减小桩身弯矩;前、中排桩的桩顶剪力分担比随着循环幅值的增加而增大,后排桩则呈现逐级减小的趋势。非连接式桩筏基础在水平及循环加载下受力特性的揭示可为今后的研究及工程应用提供参考。
To investigate the stress mechanism of disconnected piled raft( DPR) foundation under lateral static and cyclic loads,we conducted laboratory model tests through a visualizing lateral cyclic loading device. Effects on lateral stiffness,soil displacement,and pile internal force were analyzed,including loading mode,cushion thickness,cyclic amplitude,and time. The displacement field of soil was obtained by digital image correlation technique. Results show that lateral stiffness of DPR increased with cycling,and the hysteresis loop area decreased gradually and stabilized. Compared with the lateral static loading test,the lateral load carried by each pile was redistributed during repeated loading,and the role of the back pile was strengthened step by step. When the cyclic amplitude was small,the bending moments of the front and middle piles were fairly close,while the role of the front pile was strengthened with the increment of cyclic amplitude. Compared with the piled raft,the cushion could significantly reduce the pile bending moment in the lateral static and cyclic loading. The sharing proportion of shear force at the head of the front and middle piles increased with the increment of cyclic amplitude,whereas the back pile presented a decreasing trend. The revealed mechanical characteristics of the DPR foundation under lateral static and cyclic loads could provide a reference for future research and engineering applications.
To investigate the stress mechanism of disconnected piled raft( DPR) foundation under lateral static and cyclic loads,we conducted laboratory model tests through a visualizing lateral cyclic loading device. Effects on lateral stiffness,soil displacement,and pile internal force were analyzed,including loading mode,cushion thickness,cyclic amplitude,and time. The displacement field of soil was obtained by digital image correlation technique. Results show that lateral stiffness of DPR increased with cycling,and the hysteresis loop area decreased gradually and stabilized. Compared with the lateral static loading test,the lateral load carried by each pile was redistributed during repeated loading,and the role of the back pile was strengthened step by step. When the cyclic amplitude was small,the bending moments of the front and middle piles were fairly close,while the role of the front pile was strengthened with the increment of cyclic amplitude. Compared with the piled raft,the cushion could significantly reduce the pile bending moment in the lateral static and cyclic loading. The sharing proportion of shear force at the head of the front and middle piles increased with the increment of cyclic amplitude,whereas the back pile presented a decreasing trend. The revealed mechanical characteristics of the DPR foundation under lateral static and cyclic loads could provide a reference for future research and engineering applications.
引文
[1]王磊,过超,穆保岗,等.带桩沉箱复合基础水平向承载性状模型试验研究[J].岩土力学,2015,36(11):3150-3156,3234.WANG Lei,GUO Chao,MU Baogang,et al.Experimental research on horizontal bearing behavior of caisson-pile composite foundation[J].Rock and soil mechanics,2015,36(11):3150-3156,3234.
[2]过超,付佰勇,龚维明.粉质黏土中沉箱-桩复合基础水平向承载性能试验研究[J].岩土力学,2016,37(S1):350-358.GUO Chao,FU Baiyong,GONG Weiming.Experimental study of horizontal bearing capacity of caisson-pile composite foundation in silty clay[J].Rock and soil mechanics,2016,37(S1):350-358.
[3]LAEFER D F,MANKE J P,TUCKER J E,et al.Challenges and solutions to model-scale testing for composite deep foudations and existing foudation enhancement[J].Contemporary issues in deep foudations(GSP 158).Part of GeoDenver,2007:1261-1277.
[4]ALI JAWAID S M,MADHAV M R.Analysis of axially loaded short rigid composite caisson foundation based on continuum approach[J].International journal of geomechanics,2013,13(5):636-644.
[5]ZHANG X Y,LEE F H,LEUNG C F.Response of caisson breakwater subjected to repeated impulsive loading[J].Géotechnique,2009,59(1):3-16.
[6]REESE L C,COX W R,KOOP F D.Analysis of laterally loaded piles in sand[C]//Proceedings of the 6th Offshore Technology Conference.Houston:OTC,1974:473-485.
[7]BASACK S,PURKAYASTHA R D.Behavior of single pile under lateral cyclic load in marine clay[J].Asian journal of civil engineering,2007,8:443-458.
[8]BROWN D A,REESE L C,O'NEILL M W.Cyclic lateral loading of a large-scale pile group[J].Journal of geotechnical engineering,1987,113(11):1326-1343.
[9]BROWN D A,MORRISON C,REESE L C.Lateral load behavior of pile group in sand[J].Journal of geotechnical engineering,1988,114(11):1261-1276.
[10]唐永胜,张鸿文,黄小明,等.水平循环荷载下饱和砂土中桩-土相互作用机理的试验研究[J].中国港湾建设,2010(4):26-29.TANG Yongsheng,ZHANG Hongwen,HUANG Xiaoming,et al.Experimental research on pile-soil interaction mechanism under lateral cyclic load in saturated sandy soil[J].China harbour engineering,2010(4):26-29.
[11]陈仁朋,顾明,孔令刚,等.水平循环荷载下高桩基础受力性状模型试验研究[J].岩土工程学报,2012,34(11):1990-1996.CHEN Renpeng,GU Ming,KONG Linggang,et al.Large-scale model tests on high-rise platform pile groups under cyclic lateral loads[J].Chinese journal of geotechnical engineering,2012,34(11):1990-1996.
[12]朱斌,杨永垚,余振刚,等.海洋高桩基础水平单调及循环加载现场试验[J].岩土工程学报,2012,34(6):1028-1037.ZHU Bin,YANG Yongyao,YU Zhengang,et al.Field tests on lateral monotonic and cyclic loadings of offshore elevated piles[J].Chinese journal of geotechnical engineering,2012,34(6):1028-1037.
[13]张勋,黄茂松.砂土中沉井加桩复合基础水平静力及循环模型试验[J].岩土工程学报,2015,37(S2):121-124.ZHANG Xun,HUANG Maosong.Model tests on a caisson-pile composite foundation in sand subjected to lateral static and cyclic loadings[J].Chinese journal of geotechnical engineering,2015,37(S2):121-124.
[14]李元海,朱合华,上野胜利,等.基于图像相关分析的砂土模型试验变形场量测[J].岩土工程学报,2004,26(1):36-41.LI Yuanhai,ZHU Hehua,KATSUTOSHI UENO,et al.Deformation field measurement for granular soil model using image analysis[J].Chinese journal of geotechnical engineering,2004,26(1):36-41.
[2]过超,付佰勇,龚维明.粉质黏土中沉箱-桩复合基础水平向承载性能试验研究[J].岩土力学,2016,37(S1):350-358.GUO Chao,FU Baiyong,GONG Weiming.Experimental study of horizontal bearing capacity of caisson-pile composite foundation in silty clay[J].Rock and soil mechanics,2016,37(S1):350-358.
[3]LAEFER D F,MANKE J P,TUCKER J E,et al.Challenges and solutions to model-scale testing for composite deep foudations and existing foudation enhancement[J].Contemporary issues in deep foudations(GSP 158).Part of GeoDenver,2007:1261-1277.
[4]ALI JAWAID S M,MADHAV M R.Analysis of axially loaded short rigid composite caisson foundation based on continuum approach[J].International journal of geomechanics,2013,13(5):636-644.
[5]ZHANG X Y,LEE F H,LEUNG C F.Response of caisson breakwater subjected to repeated impulsive loading[J].Géotechnique,2009,59(1):3-16.
[6]REESE L C,COX W R,KOOP F D.Analysis of laterally loaded piles in sand[C]//Proceedings of the 6th Offshore Technology Conference.Houston:OTC,1974:473-485.
[7]BASACK S,PURKAYASTHA R D.Behavior of single pile under lateral cyclic load in marine clay[J].Asian journal of civil engineering,2007,8:443-458.
[8]BROWN D A,REESE L C,O'NEILL M W.Cyclic lateral loading of a large-scale pile group[J].Journal of geotechnical engineering,1987,113(11):1326-1343.
[9]BROWN D A,MORRISON C,REESE L C.Lateral load behavior of pile group in sand[J].Journal of geotechnical engineering,1988,114(11):1261-1276.
[10]唐永胜,张鸿文,黄小明,等.水平循环荷载下饱和砂土中桩-土相互作用机理的试验研究[J].中国港湾建设,2010(4):26-29.TANG Yongsheng,ZHANG Hongwen,HUANG Xiaoming,et al.Experimental research on pile-soil interaction mechanism under lateral cyclic load in saturated sandy soil[J].China harbour engineering,2010(4):26-29.
[11]陈仁朋,顾明,孔令刚,等.水平循环荷载下高桩基础受力性状模型试验研究[J].岩土工程学报,2012,34(11):1990-1996.CHEN Renpeng,GU Ming,KONG Linggang,et al.Large-scale model tests on high-rise platform pile groups under cyclic lateral loads[J].Chinese journal of geotechnical engineering,2012,34(11):1990-1996.
[12]朱斌,杨永垚,余振刚,等.海洋高桩基础水平单调及循环加载现场试验[J].岩土工程学报,2012,34(6):1028-1037.ZHU Bin,YANG Yongyao,YU Zhengang,et al.Field tests on lateral monotonic and cyclic loadings of offshore elevated piles[J].Chinese journal of geotechnical engineering,2012,34(6):1028-1037.
[13]张勋,黄茂松.砂土中沉井加桩复合基础水平静力及循环模型试验[J].岩土工程学报,2015,37(S2):121-124.ZHANG Xun,HUANG Maosong.Model tests on a caisson-pile composite foundation in sand subjected to lateral static and cyclic loadings[J].Chinese journal of geotechnical engineering,2015,37(S2):121-124.
[14]李元海,朱合华,上野胜利,等.基于图像相关分析的砂土模型试验变形场量测[J].岩土工程学报,2004,26(1):36-41.LI Yuanhai,ZHU Hehua,KATSUTOSHI UENO,et al.Deformation field measurement for granular soil model using image analysis[J].Chinese journal of geotechnical engineering,2004,26(1):36-41.