基于静力触探试验的基坑开挖卸荷单桩水平承载力损失预测研究
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摘要
选取典型成层地基场地并设计试坑开挖卸荷试验,开展了基于静力触探(CPT)测试的基坑开挖卸荷单桩水平承载力损失程度预测研究。通过在试坑开挖卸荷前后进行CPT原位测试,得到了试坑开挖卸荷前后的CPT贯入锥尖参数变化规律。进而基于CPT测试p–y模型研究了基坑开挖卸荷前后邻近既有单桩的水平承载力损失及桩身弯矩分布特征。分别考察了基坑开挖卸荷后邻近桩基试桩加载模式下的残余水平承载力和桩顶加载联合土体位移共同作用下的卸荷桩基水平承载特性。研究表明,依据真实卸荷土体CPT参数更能准确预测桩基水平承载力损失程度及损失特征,卸荷桩设计阶段须同时考虑卸荷桩较自由场地桩基的水平承载力损失及土体运动位移对桩基水平承载的影响。以上研究为合理确定基坑开挖引起的既有桩基水平承载力损失提供了一种技术思路,同时对卸荷桩水平承载性能评价具有参考意义。
The prediction of lateral capacity losses of a single pile adjacent to the excavation of foundation pits is made, by designing the excavation of a test pit in multi-layer soils based on CPT tests. The CPT-qc curves before and after the excavation of the test pit are obtained and compared, and the lateral capacity losses of the single pile adjacent to the excavation of the test pit and its bending moment characteristics are analyzed using CPT-based p-y curve models. The residual lateral capacity of the test pile after exaction unloading and the lateral bearing rules facing the combined loadings from horizontal forces on pile head and soil movement forces are evaluated. The results show that using the actual CPT parameters of unloading soils is more reasonable than that of free-ground soils for the prediction of lateral capacity losses of a single pile adjacent to the excavation of foundation pits. The lateral capacity reduction after adjacent excavation unloading and the influences of lateral soil movement on piles must be taken into account in the design of engineering pile foundations. The study about CPT tests on unloading soils gives a technical approach for estimating the lateral capacity losses of the single pile adjacent to the excavation of foundation pits and has referential meanings for the evaluation of excavation unloading piles.
The prediction of lateral capacity losses of a single pile adjacent to the excavation of foundation pits is made, by designing the excavation of a test pit in multi-layer soils based on CPT tests. The CPT-qc curves before and after the excavation of the test pit are obtained and compared, and the lateral capacity losses of the single pile adjacent to the excavation of the test pit and its bending moment characteristics are analyzed using CPT-based p-y curve models. The residual lateral capacity of the test pile after exaction unloading and the lateral bearing rules facing the combined loadings from horizontal forces on pile head and soil movement forces are evaluated. The results show that using the actual CPT parameters of unloading soils is more reasonable than that of free-ground soils for the prediction of lateral capacity losses of a single pile adjacent to the excavation of foundation pits. The lateral capacity reduction after adjacent excavation unloading and the influences of lateral soil movement on piles must be taken into account in the design of engineering pile foundations. The study about CPT tests on unloading soils gives a technical approach for estimating the lateral capacity losses of the single pile adjacent to the excavation of foundation pits and has referential meanings for the evaluation of excavation unloading piles.
引文
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[2]韩爱民,肖军华,梅国雄.横向流动土体作用下的群桩反应性状[J].岩土工程学报,2005,27(12):1463-1467.(HAN Ai-min,XIAO Jun-hua,MEI Guo-xiong.Behavior of pile groups subjected to excavation-induced lateral soil movement[J].Chinese Journal of Geotechnical Engineering,2005,27(12):1463-1467.(in Chinese))
[3]ROSCOE K H,SCHOFIELD A N,THURAIRAJAH A.Yielding of clays in states wetter than critical[J].Géotechnique,1963,13(3):211-240.
[4]YIN Z Y,CHANG C S.Stress-dilatancy behavior for sand under loading and unloading conditions[J].International Journal for Numerical and Analytical Methods in Geomechanics,2013,37(8):855-870.
[5]刘国彬,贾付波.基坑回弹时间效应的试验研究[J].岩石力学与工程学报,2007,26(增刊1):3040-3044.(LIUGuo-bin,JIA Fu-bo.Test research on time effect of foundation pit rebound[J].Chinese Journal of Rock Mechanics and Engineering,2007,26(S1):3040-3044.(in Chinese))
[6]POULOS H G,CHEN L T.Pile response due to excavation-induced lateral soil movement[J].Journal of Geotechnical and Geoenvironmental Engineering,1997,123(2):94-99.
[7]GOH A,WONG K S,TEH C I,et al.Pile response adjacent to braced excavation[J].Journal of Geotechnical and Geoenvironmental Engineering,2003,129(4):383-386.
[8]ONG D E,LEUNG C E,CHOW Y K.Pile behavior due to excavation-induced soil movement in clay:I stable wall[J].Journal of Geotechnical and Geoenvironmental Engineering,2006,132(1):36-44.
[9]黄茂松,王卫东,郑刚.软土地下工程与深基坑研究进展[J].土木工程学报,2012,45(6):146-161.(HUANGMao-song,WANG Wei-dong,ZHENG Gang.A review of recent advances in the underground engineering and deep excavations in soft soils[J].China Civil Engineering Journal,2012,45(6):146-161.(in Chinese))
[10]LEE J,KIM M,KYUNG D.Estimation of lateral load capacity of rigid short piles in sands using CPT results[J].Journal of Geotechnical and Geoenvironmental Engineering,2009,136(1):48-56.
[11]DYSON G J,RANDOLPH M F.Monotonic lateral loading of piles in calcareous sand[J].Journal of Geotechnical Geoenvironmental Engineering,2001,127(4):346-352.
[12]HALDAR S,SIVAKUMAR BABU G L.Design of laterally loaded piles in clays based on cone penetration test data:a reliability-based approach[J].Géotechnique,2009,59(7):593-607.
[13]SURYASENTANA S K,LEHANE B M.Numerical derivation of CPT-based p-y curves for piles in sand[J].Géotechnique,2014,64(3):186-194.
[14]李洪江,刘松玉,童立元.基于CPTU测试p-y曲线法及其在桩基水平承载中的应用[J].岩石力学与工程学报,2017,36(2):513-520.(LI Hong-jiang,LIU Song-yu,TONGLi-yuan.A p-y curve method for determining the horizontal bearing capacity of single pile based on CPTU test and its application[J].Chinese Journal of Rock Mechanics and Engineering,2017,36(2):513-520.(in Chinese))
[15]STEWART D P.Program PYGMY version 2.31,p-y analysis of laterally loaded piles under general loading-user manual[J].University of Western Australia,2000.
[16]JGJ106-2014建筑基桩检测技术规范[S].2014.(JGJ106-2014 Technical code for testing of building foundation piles[S].2014.(in Chinese))
[17]JGJ 94-2008建筑桩基技术规范[S].2008.(JGJ 94-2008Technical code for building pile foundations[S].2008.(in Chinese))
[18]李洪江,童立元,刘松玉,等.后注浆超长灌注桩水平承载特性现场试验研究[J].建筑结构学报,2016,37(6):204-211.(LI Hong-jiang,TONG Li-yuan,LIU Song-yu,et al.Experimental study on lateral bearing behavior of post-grouting super-long bored pile[J].Chinese Journal of Building Structures,2016,37(6):204-211.(in Chinese))