非连接式桩筏基础水平特性试验
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摘要
为了给非连接式桩筏的设计与施工提供参考,针对大型桥梁工程采用的减隔震基础形式——非连接式桩筏,考虑竖向荷载、垫层厚度等因素的影响,进行了非连接式桩筏水平承载性能的室内模型试验研究。采用粒子图像测速法跟踪了土体水平位移路径,利用数字图像关联技术获得了土体位移场与剪切带,分析了竖向荷载、垫层厚度等因素对筏板水平位移、桩身弯矩和剪力分布的影响规律,提出了非连接式桩筏基础水平承载力的简化模型及计算方法,并用试验数据进行了验证。研究结果表明:竖向荷载可有效限制筏板水平位移,设置垫层可显著减小桩身弯矩及剪力,并且桩身弯矩和剪力随垫层厚度的增加而减小;土体在垫层顶部形成位移集中区,产生局部塑性变形并不断扩大,最后局部塑性变形区贯通形成完整的剪切带;非连接式桩筏基础水平承载力与竖向荷载相关,当竖向荷载较小时,其水平承载力由筏板与垫层界面摩擦力控制,当竖向荷载较大时,其水平承载力取决于垫层的水平承载力,这与图像分析获得的垫层破坏结论一致。因此,对于非连接式桩筏基础的设计及具体工程应用,可以通过调整垫层的厚度来减小桩身弯矩及剪力;所揭示的非连接式桩筏基础水平承载力变化规律可为今后大型桥梁隔震基础的设计与研究提供参考。
To provide reference for the design and construction of disconnected piled rafts(DPRs), specifically aiming at the seismic isolation foundation of DPRs, which has been widely adopted in large scale bridge construction, by considering the influences of vertical load and cushion thickness, the horizontal bearing characteristics of DPRs were studied by conducting a laboratory test. Particle image velocimetry was used to track the horizontal soil displacement path, and the displacement field and shear zone were obtained using the digital image correlation(DIC) technique. The influences of vertical load and cushion thickness on the horizontal displacement of the raft, pile bending moment, and shear force were analyzed. A simplified model and calculation method for obtaining the lateral bearing capacity of DPRs were proposed and verified with the test data. Results demonstrate that the vertical load on raft could limit the horizontal displacement of the rafts, whereas the pile bending moment and the shear force reduced with a reduction in the thickness of the cushion, which was positioned between the raft and the pile head. The soil concentration zone formed at the top of the cushion and the local plastic deformation zone then appeared and expanded continuously. Toward the end, the local plastic deformation zones penetrated to form an overall shear zone. The lateral bearing capacity of DPRs was dependent on the friction between the raft and the cushion or the horizontal bearing capacity of the cushion, which was related to the vertical load on the raft. This conclusion corresponds to the cushion failure mode obtained by the DIC technique. Therefore, the bending moment and the shear force can be reduced by adjusting the cushion thickness during the design and engineering applications of the DPRs. The revelation of the failure mode of the cushion under a horizontal load can be used as the reference for the design and research of vibration isolation foundation in large-scale bridge.
To provide reference for the design and construction of disconnected piled rafts(DPRs), specifically aiming at the seismic isolation foundation of DPRs, which has been widely adopted in large scale bridge construction, by considering the influences of vertical load and cushion thickness, the horizontal bearing characteristics of DPRs were studied by conducting a laboratory test. Particle image velocimetry was used to track the horizontal soil displacement path, and the displacement field and shear zone were obtained using the digital image correlation(DIC) technique. The influences of vertical load and cushion thickness on the horizontal displacement of the raft, pile bending moment, and shear force were analyzed. A simplified model and calculation method for obtaining the lateral bearing capacity of DPRs were proposed and verified with the test data. Results demonstrate that the vertical load on raft could limit the horizontal displacement of the rafts, whereas the pile bending moment and the shear force reduced with a reduction in the thickness of the cushion, which was positioned between the raft and the pile head. The soil concentration zone formed at the top of the cushion and the local plastic deformation zone then appeared and expanded continuously. Toward the end, the local plastic deformation zones penetrated to form an overall shear zone. The lateral bearing capacity of DPRs was dependent on the friction between the raft and the cushion or the horizontal bearing capacity of the cushion, which was related to the vertical load on the raft. This conclusion corresponds to the cushion failure mode obtained by the DIC technique. Therefore, the bending moment and the shear force can be reduced by adjusting the cushion thickness during the design and engineering applications of the DPRs. The revelation of the failure mode of the cushion under a horizontal load can be used as the reference for the design and research of vibration isolation foundation in large-scale bridge.
引文
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[12] 郑刚,刘双菊,伍止超,等.刚性桩复合地基在水平荷载作用下工作性状的模型试验[J].岩土工程学报,2005,27(8):865-868. ZHENG Gang, LIU Shuang-ju, WU Zhi-chao, et al. Experimental Study on Behavior of Rigid Pile Composite Ground Under Horizontal Load [J]. Chinese Journal of Geotechnical Engineering, 2005, 27 (8): 865-868.
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[14] 吴春林,闫明礼,杨军,等.CFG桩及其复合地基水平荷载作用下的性状[J].工程勘察,1996(4):18-21. WU Chun-lin, YAN Ming-li, YANG Jun, et al. Behavior of CFG Pile Composite Foundation Under Lateral Load [J]. Geotechnical Investigation and Surveying, 1996 (4): 18-21.
[15] 戚科骏,宰金珉,梅国雄,等.群桩复合地基褥垫层效用的数值分析[J].岩石力学与工程学报,2004,23(1):4590-4593. QI Ke-jun, ZAI Jin-min, MEI Guo-xiong, et al. Numerical Analysis on Effects of Cushion of Composite Found with Pile Group [J]. Chinese Journal of Rock Mechanics and Engineering Mechanics, 2004, 23 (1): 4590-4593.
[16] 宰金珉,凌华,王旭东.桩筏基础非线性共同作用数值分析[J].南京工业大学学报,2002,24(5):1-7. ZAI Jin-min, LIN Hua, WANG Xu-dong. Numerical Analysis of Nonlinear Interaction of Piled Raft Foundation [J]. Journal of Nanjing University of Technology, 2002, 24 (5): 1-7.
[17] 刘汉龙,陶学俊,张建伟,等.水平荷载作用下PCC桩复合地基工作性状[J].岩土力学,2010,31(9):2716-2722. LIU Han-long, TAO Xue-jun, ZHANG Jian-wei, et al. Behavior of PCC Pile Composite Foundation Under Lateral Load [J]. Rock and Soil Mechanics, 2010, 31 (9): 2716-2722.
[18] 孔纲强,杨庆,郑鹏一,等.考虑时间效应的群桩负摩阻力模型试验研究[J].岩土工程学报,2009,31(12):1913-1919. KONG Gang-qiang, YANG Qing, ZHENG Peng-yi, et al. Model Test on Negative Skin Friction for Pile Groups Considering Time Effect [J]. Chinese Journal of Geotechnical Engineering, 2009, 31 (12): 1913-1919.
[19] 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 Yuan-hai, ZHU He-hua, KATSUTOSHI U, et al. Deformation Field Measurement for Granular Soil Model Using Image Analysis [J]. Chinese Journal of Geotechnical Engineering, 2004, 26 (1): 36-41.
[2] MALI S, SINGH B. Behavior of Large Piled-raft Foundation on Clay Soil [J]. Ocean Engineering, 2018, 149: 205-216.
[3] CAO X D, WONG I H, CHANG M F. Behavior of Model Rafts Resting on Pile-reinforced Sand [J]. Journal of Geotechnical and Geoenvironmental Engineering, 2004, 130 (2): 129-138.
[4] LIANG F Y, CHEN L Z, SHI X G. Numerical Analysis of Composite Piled Raft with Cushion Subjected to Vertical Load [J]. Computers and Geotechnics, 2003, 30 (6): 443-453.
[5] 陈龙珠,梁发云,黄大治,等.高层建筑应用长-短桩复合地基的现场试验研究[J].岩土工程学报,2004,26(2):167-171. CHEN Long-zhu, LIANG Fa-yun, HUANG Da-zhi, et al. Field Study on Behavior of Composite Piled Raft Foundation for High-rise Buildings [J]. Chinese Journal of Geotechnical Engineering, 2004, 26 (2): 167-171.
[6] SINHA A, HANNA A M. 3D Numerical Model for Piled Raft Foundation [J]. International Journal of Geomechanics, 2017, 17 (2): 04016055.
[7] TRADIGO F, PISANO F, DI PRISCO C, et al. Non-linear Soil-structure Interaction in Disconnected Piled Raft Foundations [J]. Computers and Geotechnics, 2015, 63: 121-134.
[8] TRADIGO F, PISANO F, DI PRISCO C. On the Use of Embedded Pile Elements for the Numerical Analysis of Disconnected Piled Rafts [J]. Computers and Geotechnics, 2016, 72: 89-99.
[9] ZHOU F, LIN C, WANG X D, et al. Application of Deformation Adjustors in Piled Raft Foundations [J]. Proceedings of the Institution of Civil Engineerings: Geotechnical Engineering, 2016, 169 (6): 1-14.
[10] HAMADA J, TSUCHIVA T, TANIKAWA T, et al. Lateral Loading Tests on Piled Rafts and Simplified Method to Evaluate Sectional Forces of Piles [J]. Geotechnical Engineering Journal of the SEAGS & AGSSEA, 2015, 46 (2): 29-42.
[11] SAWADA K, TAKEMURA J. Centrifuge Model Tests on Piled Raft Foundation in Sand Subjected to Lateral and Moment Loads [J]. Soils and Foundations, 2014, 54 (2): 126-140.
[12] 郑刚,刘双菊,伍止超,等.刚性桩复合地基在水平荷载作用下工作性状的模型试验[J].岩土工程学报,2005,27(8):865-868. ZHENG Gang, LIU Shuang-ju, WU Zhi-chao, et al. Experimental Study on Behavior of Rigid Pile Composite Ground Under Horizontal Load [J]. Chinese Journal of Geotechnical Engineering, 2005, 27 (8): 865-868.
[13] 朱世哲,徐日庆,杨晓军,等.带垫层刚性桩复合地基桩土应力比的计算与分析[J].岩土力学,2004,25(5):814-818. ZHU Shi-zhe, XU Ri-qing, YANG Xiao-jun, et al. Computation and Analysis of Ratio of Pile Stress to Soil Stress of Rigid Pile Composite Foundation with Cushion [J]. Rock and Soil Mechanics, 2004, 25 (5): 814-818.
[14] 吴春林,闫明礼,杨军,等.CFG桩及其复合地基水平荷载作用下的性状[J].工程勘察,1996(4):18-21. WU Chun-lin, YAN Ming-li, YANG Jun, et al. Behavior of CFG Pile Composite Foundation Under Lateral Load [J]. Geotechnical Investigation and Surveying, 1996 (4): 18-21.
[15] 戚科骏,宰金珉,梅国雄,等.群桩复合地基褥垫层效用的数值分析[J].岩石力学与工程学报,2004,23(1):4590-4593. QI Ke-jun, ZAI Jin-min, MEI Guo-xiong, et al. Numerical Analysis on Effects of Cushion of Composite Found with Pile Group [J]. Chinese Journal of Rock Mechanics and Engineering Mechanics, 2004, 23 (1): 4590-4593.
[16] 宰金珉,凌华,王旭东.桩筏基础非线性共同作用数值分析[J].南京工业大学学报,2002,24(5):1-7. ZAI Jin-min, LIN Hua, WANG Xu-dong. Numerical Analysis of Nonlinear Interaction of Piled Raft Foundation [J]. Journal of Nanjing University of Technology, 2002, 24 (5): 1-7.
[17] 刘汉龙,陶学俊,张建伟,等.水平荷载作用下PCC桩复合地基工作性状[J].岩土力学,2010,31(9):2716-2722. LIU Han-long, TAO Xue-jun, ZHANG Jian-wei, et al. Behavior of PCC Pile Composite Foundation Under Lateral Load [J]. Rock and Soil Mechanics, 2010, 31 (9): 2716-2722.
[18] 孔纲强,杨庆,郑鹏一,等.考虑时间效应的群桩负摩阻力模型试验研究[J].岩土工程学报,2009,31(12):1913-1919. KONG Gang-qiang, YANG Qing, ZHENG Peng-yi, et al. Model Test on Negative Skin Friction for Pile Groups Considering Time Effect [J]. Chinese Journal of Geotechnical Engineering, 2009, 31 (12): 1913-1919.
[19] 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 Yuan-hai, ZHU He-hua, KATSUTOSHI U, et al. Deformation Field Measurement for Granular Soil Model Using Image Analysis [J]. Chinese Journal of Geotechnical Engineering, 2004, 26 (1): 36-41.