强膨胀土——桩基相互作用及隔胀效果数值模拟
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摘要
黑棉土是一种强膨胀土,其受湿度变化影响呈现很强的胀缩特性,对桩基的承载力和变形不利,易导致断桩等多种问题。本文建立了强膨胀土桩基有限元模型,分析了胀缩条件下桩基内力和位移的变化规律,与桩土共同作用解析解对比,验证了数值模型的有效性并解释离心机试验现象。利用该模型进行参数分析,指出黑棉土胀缩对桩的不利影响及工程中采用隔胀措施的必要性,进而模拟局部换填和界面隔胀措施。结果表明:浅表层黑棉土适合采用局部换填隔胀,换填宽度宜不小于膨胀土厚度;深厚层黑棉土适合采用双层分离式隔胀,隔胀套管应保证界面折减程度达到土体参数的30%且布置至黑棉土和普通土分界面附近;桩基承台底部宜增加柔性垫层,预留胀缩空间。
Black cotton soil is a kind of strong expansive soil. It presents obvious swelling-shrinkage characteristics and has negative effects on bearing capacity and deformation of piles which would cause serious problems such as broken piles. This paper built a finite element analysis model which contains black cotton soil and pile foundation and analyzed the force and displacement in swell-shrink process. The results were verified by the analytical solutions of pile-soil interaction and the findings in the centrifuge test were explained. Parameter study showed the negative effects and the necessity of adopting expansion isolation measures. Furthermore,part-replacing and filling measure and interface isolation measure were simulated. The calculation results indicated that,partreplacing and filling should be used in shallow surface black cotton soil layer and the width of replacing and filling earth should be not less than the thickness of expansive soil. As for thick black cotton soil layer,interface isolation measure should be applied and the isolation pipe should be extended to the interface between the black cotton soil and ordinary soil with more than 30% shear stiffness reduction. For pile foundation with cap,flexible cushions should be installed under the caps,leaving space for soil expansion.
Black cotton soil is a kind of strong expansive soil. It presents obvious swelling-shrinkage characteristics and has negative effects on bearing capacity and deformation of piles which would cause serious problems such as broken piles. This paper built a finite element analysis model which contains black cotton soil and pile foundation and analyzed the force and displacement in swell-shrink process. The results were verified by the analytical solutions of pile-soil interaction and the findings in the centrifuge test were explained. Parameter study showed the negative effects and the necessity of adopting expansion isolation measures. Furthermore,part-replacing and filling measure and interface isolation measure were simulated. The calculation results indicated that,partreplacing and filling should be used in shallow surface black cotton soil layer and the width of replacing and filling earth should be not less than the thickness of expansive soil. As for thick black cotton soil layer,interface isolation measure should be applied and the isolation pipe should be extended to the interface between the black cotton soil and ordinary soil with more than 30% shear stiffness reduction. For pile foundation with cap,flexible cushions should be installed under the caps,leaving space for soil expansion.
引文
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[9]杨长青,董东,谭波,等.重塑膨胀土三向膨胀变形试验研究[J].工程地质学报,2014,22(2):188-195.(Yang Changqing,Dong Dong,Tan Bo,et al.Laboratory tests on three-directional swelling deformation of remolded expansive soil[J].Journal of Engineering Geology,2014,22(2):188-195.(in Chinese))
[10]Xiao H,Zhang C,Wang Y,et al.Pile-soil interaction in expansive soil foundation:Analytical solution and numerical simulation[J].International Journal of Geomechanics,2011,11(3):159-166.
[11]李雄威,刘涛,王勇,等.吸湿环境下膨胀土与桩接触面强度特性试验研究[J].岩土工程学报,2015,37(增1):161-166.(Liu Tao,Wang Yong,Sun Jizhu,et al.Experimental study on pile-soil interface strength of expansive soil under environment of moisture absorption[J].Chinese Journal of Geotechnical Engineering,2015,37(Supp.1):161-166.(in Chinese))
[2]Oriola F,Moses G.Groundnut shell ash stabilization of black cotton soil[J].Electronic Journal of Geotechnical Engineering,2010,15:415-428.
[3]Nelson J D,Miller D J.Expansive soils-problems and practice in foundation and pavement engineering[M].Wiley-Inter Science,1992.
[4]李冬,岳大昌,唐延贵,等.微型桩复合土钉墙在膨胀土基坑中的应用研究[J].地下空间与工程学报,2016,12(6):1645-1652.(Li Dong,Yue Dachang,Tang Yangui,et al.Application Research of Micro Piles Composite Soil Nailing Wall in Expansive Soil Foundation Excavation[J].Chinese Journal of Underground Space and Engineering,2016,12(6):1645-1652.(in Chinese))
[5]陈正汉.非饱和土与特殊土力学的基本理论研究[J].岩土工程学报,2014,36(2):201-272.(Chen Zhenghan.On basic theories of unsaturated soils and special soils[J].Chinese Journal of Geotechnical Engineering,2014,36(2):201-272.(in Chinese))
[6]张大峰,杨军,李连友,等.考虑膨胀土地基膨胀率和刚度沿深度变化的桩-土共同作用解析解[J].工程力学,2016,33(12):86-93.(Zhang Dafeng,Yang Jun,Li Lianyou,et al.Analytical solutions of pile-soil interaction in expansive soil foundation with expansion rate and stiffness variation along the depth[J].Engineering Mechanics,2016,33(12):86-93.(in Chinese))
[7]杨军,张大峰,李连友,等.高液限膨胀性黏土基桩工作性状的离心机试验研究[J].岩土工程学报,2017,39(10):1770-1776.(Yang Jun,Zhang Dafeng,Li Lianyou,et al.Centrifuge modelling of working performance of foundation pile embedded in high liquid limit expansive clay[J].Chinese Journal of Geotechnical Engineering,2017,39(10):1770-1776.(in Chinese))
[8]张颖钧.裂土三向胀缩性的室内研究[J].水电自动化与大坝监测,1990(1):13-22.(Zhang Yingjun.Laboratory investigations of three-dimensional swellshrinking characteristics of expansive soils[J].Hydropower Automation and Dam Monitoring,1990(1):13-22.(in Chinese))
[9]杨长青,董东,谭波,等.重塑膨胀土三向膨胀变形试验研究[J].工程地质学报,2014,22(2):188-195.(Yang Changqing,Dong Dong,Tan Bo,et al.Laboratory tests on three-directional swelling deformation of remolded expansive soil[J].Journal of Engineering Geology,2014,22(2):188-195.(in Chinese))
[10]Xiao H,Zhang C,Wang Y,et al.Pile-soil interaction in expansive soil foundation:Analytical solution and numerical simulation[J].International Journal of Geomechanics,2011,11(3):159-166.
[11]李雄威,刘涛,王勇,等.吸湿环境下膨胀土与桩接触面强度特性试验研究[J].岩土工程学报,2015,37(增1):161-166.(Liu Tao,Wang Yong,Sun Jizhu,et al.Experimental study on pile-soil interface strength of expansive soil under environment of moisture absorption[J].Chinese Journal of Geotechnical Engineering,2015,37(Supp.1):161-166.(in Chinese))