底部刚性层限制条件下条形基础地基承载力系数Nc与破坏模式  

Bearing capacity coefficient N_(c) and failure mode of strip foundation restricted by bottom rigid layer

作　　者：杨峰[1] 慈新航 高益康 赵炼恒[1] YANG Feng;CI Xinhang;GAO Yikang;ZHAO Lianheng(Civil Engineering School,Central South University,Changsha,Hunan 410075,China)

机构地区：[1]中南大学土木工程学院,湖南长沙410075

出　　处：《岩石力学与工程学报》2023年第4期1031-1040,共10页Chinese Journal of Rock Mechanics and Engineering

基　　金：国家自然科学基金资助项目(51478477);湖南省自然科学基金资助项目(2021JJ10063);湖南省交通运输厅科技进步与创新项目资助(202017)。

摘　　要：存在底部刚性层限制时,极限荷载作用下的条形基础地基破坏模式会变得异常复杂。此时,应用极限分析、滑移线或数值分析等方法求解地基极限承载力,难以获取明确的定量破坏形态。为此,本文应用刚体平动运动单元上限有限元,通过多次网格更新方式进行系统地分析研究,重点揭示与黏聚力相关的地基极限承载力系数Nc的上限解曲线及其滑移线网破坏模式,探讨地基土层厚度、土体内摩擦角和基础与地基界面有限摩擦等关联因素的影响规律。研究结果表明:当刚性层上方地基土较厚时,Nc和刚性层影响的修正因子Kc随土体内摩擦角和土层厚度的变化不明显;而当土层厚度变薄时,Nc和Kc伴随土体内摩擦角增大和土层厚度变小而急剧增长;土层厚度较小时,基础与地基土接触面摩擦条件对地基破坏模式影响显著,表现为接触面粗糙程度的下降使得Nc大幅减小,与无底部刚性层限制时的规律差异显著。最后,应用运动单元上限有限元分析,验证了底部刚性层限制条件下地基极限承载力系数Nc与Nq之间的转换关系。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 N_(c) 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 N_(c) and K_(c) 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 N_(c) 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 N_(c) and N_(q) is verified through the analysis using the finite element upper bound method with rigid translational motion element.

关 键 词：基础工程 条形基础 极限承载力系数 地基破坏模式 底部刚性层限制 上限分析 刚体运动单元 

分 类 号：TU47[建筑科学—结构工程]