Based on the field destructive test of six rock-socketed piles with shallow overburden,three prediction models are used to quantitatively analyze and predict the intact load−displacement curve.The predicted values of ...Based on the field destructive test of six rock-socketed piles with shallow overburden,three prediction models are used to quantitatively analyze and predict the intact load−displacement curve.The predicted values of ultimate uplift capacity were further determined by four methods(displacement controlling method(DCM),reduction coefficient method(RCM),maximum curvature method(MCM),and critical stiffness method(CSM))and compared with the measured value.Through the analysis of the relationship between the change rate of pullout stiffness and displacement,a method used to determine the ultimate uplift capacity via non-intact load−displacement curve was proposed.The results show that the predicted value determined by DCM is more conservative,while the predicted value determined by MCM is larger than the measured value.This suggests that RCM and CSM in engineering applications can be preferentially applied.Moreover,the development law of the change rate of pullout stiffness with displacement agrees well with the attenuation form of power function.The theoretical predicted results of ultimate uplift capacity based on the change rate of pullout stiffness will not be affected by the integrity of the curve.The method is simple and applicable for the piles that are not loaded to failure state,and thus provides new insights into ultimate uplift capacity determination of test piles.展开更多
A footing may get an eccentric load caused by earthquake or wind, thus the bearing capacity of footing subjected to eccentric load become a fundamental geotechnical problem. The conventional limit equilibrium method u...A footing may get an eccentric load caused by earthquake or wind, thus the bearing capacity of footing subjected to eccentric load become a fundamental geotechnical problem. The conventional limit equilibrium method used for this problem usually evaluates the material properties only by its final strength. But the classical finite element method(FEM) does not necessarily provide a clear collapse mechanism associated with the yield condition of elements. To overcome these defects, a numerical procedure is proposed to create an explicit collapse mode combining a modified smeared shear band approach with a modified initial stress method. To understand the practical performance of sand foundation and verify the performance of the proposed procedure applied to the practical problems, the computing results were compared with the laboratory model tests results and some conventional solutions. Furthermore, because the proposed numerical procedure employs a simple elasto-plastic model which requires a small number of soil parameters, it may be applied directly to practical design works.展开更多
随着城市化进程中地下空间开发及抗浮问题的凸显,抗拔桩在东南沿海等高水位黏性土地区的应用日益广泛,然而常规钻孔施工工艺面临诸多挑战,如泥皮效应导致桩侧阻力难以达标、扩底成孔困难等。为此,提出考虑扰动效应的束浆挤扩桩抗拔承载...随着城市化进程中地下空间开发及抗浮问题的凸显,抗拔桩在东南沿海等高水位黏性土地区的应用日益广泛,然而常规钻孔施工工艺面临诸多挑战,如泥皮效应导致桩侧阻力难以达标、扩底成孔困难等。为此,提出考虑扰动效应的束浆挤扩桩抗拔承载力计算方法。以上海第(5)1层灰色黏土为对象,建立黏土和砂的弹塑性扰动状态(clay and sand elastic-plastic-disturbed state concept,简称CASM-DSC)模型,精确模拟桩周地基土力学特性。通过用户自定义材料本构(user-defined material mechanical behavior,简称UMAT)子程序,开展数值模拟,分析桩周地基土及挤扩尺寸的扰动效应。修正前期研究的束浆挤扩钢管桩抗拔简化计算方法。结果表明,钻孔开挖显著削弱黏性土的侧阻力,影响桩-土界面的力学性能,扰动系数和范围对地基土应力状态呈二次曲线和线性折减关系。在不同的挤扩长度下,模型桩的极限抗拔承载力随长度增加呈“V”字型特点,且挤扩工艺可改变桩侧受力面积与轴力分布。通过上海徐汇滨江地块的现场试验,验证了简化计算方法的有效性与适用性,其计算误差控制在15%以内,为桩基础工程设计提供了可靠的理论支持与实用计算方法。展开更多
基金Project(2016YFC0802203)supported by the National Key R&D Program of ChinaProject(2013G001-A-2)supported by the Science and Technology Research and Development Program of China Railway CorporationProject(SKLGDUEK2011)supported by the State Key Laboratory for GeoMechanics and Deep Underground Engineering,China University of Mining&Technology。
文摘Based on the field destructive test of six rock-socketed piles with shallow overburden,three prediction models are used to quantitatively analyze and predict the intact load−displacement curve.The predicted values of ultimate uplift capacity were further determined by four methods(displacement controlling method(DCM),reduction coefficient method(RCM),maximum curvature method(MCM),and critical stiffness method(CSM))and compared with the measured value.Through the analysis of the relationship between the change rate of pullout stiffness and displacement,a method used to determine the ultimate uplift capacity via non-intact load−displacement curve was proposed.The results show that the predicted value determined by DCM is more conservative,while the predicted value determined by MCM is larger than the measured value.This suggests that RCM and CSM in engineering applications can be preferentially applied.Moreover,the development law of the change rate of pullout stiffness with displacement agrees well with the attenuation form of power function.The theoretical predicted results of ultimate uplift capacity based on the change rate of pullout stiffness will not be affected by the integrity of the curve.The method is simple and applicable for the piles that are not loaded to failure state,and thus provides new insights into ultimate uplift capacity determination of test piles.
基金Projects(cstc2012jjA0510,cstc2013jcyjA30014)supported by Chongqing Natural Science Foundation in ChinaProject(CDJZR12200011)supported by the Fundamental Research Funds for the Central Universities in China+1 种基金Project(KJTD201305)supported by the Innovation Team Building Programs of Chongqing Universities in ChinaProject supported by the Scientific Research Foundation for the Returned Oversea Chinese Scholars
文摘A footing may get an eccentric load caused by earthquake or wind, thus the bearing capacity of footing subjected to eccentric load become a fundamental geotechnical problem. The conventional limit equilibrium method used for this problem usually evaluates the material properties only by its final strength. But the classical finite element method(FEM) does not necessarily provide a clear collapse mechanism associated with the yield condition of elements. To overcome these defects, a numerical procedure is proposed to create an explicit collapse mode combining a modified smeared shear band approach with a modified initial stress method. To understand the practical performance of sand foundation and verify the performance of the proposed procedure applied to the practical problems, the computing results were compared with the laboratory model tests results and some conventional solutions. Furthermore, because the proposed numerical procedure employs a simple elasto-plastic model which requires a small number of soil parameters, it may be applied directly to practical design works.
文摘随着城市化进程中地下空间开发及抗浮问题的凸显,抗拔桩在东南沿海等高水位黏性土地区的应用日益广泛,然而常规钻孔施工工艺面临诸多挑战,如泥皮效应导致桩侧阻力难以达标、扩底成孔困难等。为此,提出考虑扰动效应的束浆挤扩桩抗拔承载力计算方法。以上海第(5)1层灰色黏土为对象,建立黏土和砂的弹塑性扰动状态(clay and sand elastic-plastic-disturbed state concept,简称CASM-DSC)模型,精确模拟桩周地基土力学特性。通过用户自定义材料本构(user-defined material mechanical behavior,简称UMAT)子程序,开展数值模拟,分析桩周地基土及挤扩尺寸的扰动效应。修正前期研究的束浆挤扩钢管桩抗拔简化计算方法。结果表明,钻孔开挖显著削弱黏性土的侧阻力,影响桩-土界面的力学性能,扰动系数和范围对地基土应力状态呈二次曲线和线性折减关系。在不同的挤扩长度下,模型桩的极限抗拔承载力随长度增加呈“V”字型特点,且挤扩工艺可改变桩侧受力面积与轴力分布。通过上海徐汇滨江地块的现场试验,验证了简化计算方法的有效性与适用性,其计算误差控制在15%以内,为桩基础工程设计提供了可靠的理论支持与实用计算方法。
