Abstract:High-strength layer at the bottom of foundation is treated as rigid layer to determine ultimate bearing capacity of strip foundation. Failure modes of strip foundation under the action of ultimate load become extremely complex when it is restricted by the rigid layer at the bottom of foundation. Under this scenario,ultimate bearing capacity of foundation is derived using limit analysis,slip line or other numerical methods,which is less likely to obtain quantitative failure modes. In this paper,the finite element upper bound method with rigid translational motion element is adopted to conduct systematic analysis. The upper bound solution reflected by curves and the slip line failure modes for bearing capacity factor Nc related to the cohesion is mainly discussed. The related factors such as the thickness of soil layer,the internal friction angle of soil mass and the finite friction of foundation at the interface are studied. The results show that the changes in Nc and the correction Kc influenced by rigid layer are not prominent with varying friction angle and thickness of the soil layer when the thick foundation is above the rigid layer. However,for thinner soil layer,the Nc and Kc increase sharply with the increase of internal friction angle of soil mass and the decrease of soil thickness. Furthermore,for the thinner soil layer,the friction conditions of contact surface between strip footing and foundation has a significant influence on the failure modes. In other words,the decreasing roughness of the bottom of the foundation makes the Nc smaller. It is significantly different from the one free from the restriction of the bottom rigid layer. Finally,the conversion relationship between the ultimate bearing capacity coefficient of the foundation Nc and Nq is verified through the analysis using the finite element upper bound method with rigid translational motion element.
CHEN W F. Limit analysis and soil plasticity[M]. Amsterdam:Elsevier Science,1975:211-294.
[1]
TERZAGHI K,PECK R B. Soil mechanics in engineering practice[M]. 3rd ed. New York:John Wiley and Sons,1996:258-262.
[10]
仲淑姮,张 军. 露天矿排土场软弱基底极限承载力分析[J]. 煤炭工程,2017,49(12):145-148.(ZHONG Shuheng,ZHANG Jun. Analysis on ultimate bearing capacity of weak foundation in open pit mine[J]. Coal Engineering,2017,49(12):145-148.(in Chinese))
[6]
王昌兴,刘明辉,陈春材. 软弱夹层地基的极限承载力分析[J]. 建筑结构,2016,46(16):83-87.(WANG Changxing,LIU Minghui,CHEN Chuncai. Ultimate bearing capacity analysis of soft interlayer foundation[J]. Building Structure,2016,46(16):83-87.(in Chinese))
[17]
孔垂烛,邓安福. 刚性下卧层对上部土层变形的影响[J]. 岩土工程技术,2005,19(6):303-306.(KONG Chuizhu,DENG Anfu. Influence of rigid substratum on upper soil's displacement[J]. Geotechnical Engineering Technique,2005,19(6):303-306.(in Chinese))
[18]
殷 勇,周国庆. 软弱夹层的极限荷载分析[J]. 岩土力学,2015,36(4):1 035-1 040.(YIN Yong,ZHOU Guoqing. Ultimate load analysis of soft interlayer[J]. Rock and Soil Mechanics,2015,36(4):1 035-1 040.(in Chinese))
[3]
MARTIN C M. Exact bearing capacity calculations using the method of characteristics[C]// Proceedings of the 11th international conference of IACMAG. Turin:[s. n.],2005:441-450.
[5]
宋二祥,付 浩,李贤杰. 地基承载力机制及新计算方法[J]. 岩土工程学报,2022,44(1):37-44.(SONG Erxiang,FU Hao,LI Xianjie. Mechanism and new calculation method for bearing capacity of foundations[J]. Chinese Journal of Geotechnical Engineering,2022,44(1):37-44.(in Chinese))
[7]
张凤文,陈广刚,赵国忠. 振冲碎石桩法在土岩组合地基中的应用[J]. 岩石力学与工程学报,2000,19(2):242-245.(ZHANG Fengwen,CHEN Guanggang,ZHAO Guozhong. Application of vibroflotation for improving ground base composed of soil and weathered rock stratum[J]. Chinese Journal of Rock Mechanics and Engineering,2000,19(2):242-245.(in Chinese))
[4]
HJIAJ M,LYAMIN A V,SLOAN S W. Numerical limit analysis solutions for the bearing capacity factor Nγ[J]. International Journal of Solids and Structures,2005,42(5/6):1 681-1 704.
[8]
吴旭平,杨新安,李亚翠,等. 含软弱夹层浅埋隧道变形特性及控制指标研究[J]. 岩石力学与工程学报,2014,33(增1):2 685-2 691. (WU Xuping,YANG Xinan,LI Yacui,et al. Research on control indices and deformation characteristic of shallow tunnel with weak interlayer[J]. Chinese Journal of Rock Mechanics and Engineering,2014,33(Supp.1):2 685-2 691.(in Chinese))
[11]
秦会来,黄茂松. 双层地基极限承载力的极限分析上限法[J]. 岩土工程学报,2008,30(4):611-616.(QIN Huilai,HUANG Maosong. Upper-bound method for calculating bearing capacity of strip footings on two-layer soils[J]. Chinese Journal of Geotechnical Engineering,2008,30(4):611-616.(in Chinese))
[13]
钱家欢,殷宗泽. 土工原理与计算[M]. 北京:中国水利水电出版社,1996:380-381.(QIAN Jiahuan,YIN Zongze. Geotechnical principles and calculations[M]. Beijing:China Water Power Press,1996:380-381.(in Chinese))
[15]
ZHAO L H,YANG F,DAN H C. The influence of horizontal confinement on the bearing capacity factor Nγ of smooth strip footings[J]. Computers and Geotechnics,2014,61(9):127-131.
[19]
殷 勇,乔来军,周国庆. 考虑层面滑移条件的软弱夹层极限荷载分析[J]. 建筑科学与工程学报,2016,33(4):36-43.(YIN Yong,QIAO Laijun,ZHOU Guoqing. Ultimate load analysis of soft interlayer considering slip plane conditions[J]. Journal of Architecture and Civil Engineering,2016,33(4):36-43.(in Chinese))
[9]
祝方才,曹 平,王文星. 土岩组合边坡浅层滑动稳定分析[J]. 矿山压力与顶板管理,2004,(4):98-99.(ZHU Fangcai,CAO Ping,WANG Wenxing. Research on control indices and deformation characteristic of shallow tunnel with weak interlayer[J]. Ground Pressure and Strata Control,2004,(4):98-99.(in Chinese))
[14]
SALENÇON J. Bearing capacity of strip footings with horizontal confinement[J]. Comptes Rendus Mécanique,2003,331(5):319-324.
[16]
AZAM G,HSIEH C W,WANG M C. Performance of strip footing on stratified soil deposit with void[J]. Journal of Geotechnical Engineering,1991,117(5):753-772.
[20]
YANG F,ZHENG X C,ZHAO L H,et al. Ultimate bearing capacity of a strip footing placed on sand with a rigid basement[J]. Computers and Geotechnics,2016,77(7):115-119.
[12]
MANDEL J,SALENÇON J. Force portante d?un sol sur une assise rigide(étude théorique)[J]. Géotechnique,1972,22(1):79-93.
[21]
YANG F,ZHANG J,YANG J S,et al. Stability analysis of unlined elliptical tunnel using finite element upper- bound method with rigid translatory moving elements[J]. Tunnelling and Underground Space Technology,2015,50(8):13-22.