浅基础竖向极限承载力的可靠度分析

结合各种地基土的原始载荷板试验资料,用太沙基理论公式、汉森理论公式和魏西克理论公式进行了浅基础极限承载力的计算,对计算模式的不确定性、土性固有的变异性及由其引起的极限承载力的不确定性等进行了研究;根据以上计算结果,计算了各类地基土承载力的可行度指标;结合上部结构的荷载标准及分项系数,计算了各类地基土承载力的分项系数。     

矩形浅基础地基极限承载力的理论解

对于非条形浅基础的承载力的求解,目前国内外学者均采用分步单独考虑地基自重影响的求解方法。为求解矩形浅基础地基极限承载力的理论解,首先假定三维地基滑动面,同时考虑黏聚力、超载和土的自重的耦合影响作用,然后在均布荷载作用下根据极限平衡理论,由塑性体的静力平衡条件得到地基承载力计算公式,最后对影响结果的各参数进行了讨论,得出一些有益的结论;通过算例将文中计算公式与几个典型公式计算结果进行了对比分析。验证了文中公式的实用性。     

Development of partial factor design method on bearing capacity of pile foundations for Japanese Specifications for Highway Bridges

ABSTRACT

This paper shows the development of a partial factor design method on the bearing capacity of pile foundations for Japanese Specifications for Highway Bridges. Firstly, estimation design equations on the bearing capacities of pile foundations are improved by analysis of pile load test results and uncertainties in the bearing capacities are evaluated. Secondly, the reliabilities of pile foundations designed by the former specifications are evaluated based on reliability analysis considering the uncertainties in the bearing capacities and coefficients of subgrade reaction. Finally, a partial factor design method is developed based on the target reliability index obtained based on the conventional pile installation method by the pile installation methods. The factors are different for each pile installation method.     

Seismic bearing capacity of shallow foundations near rock slopes using the generalized Hoek–Brown criterion

The seismic bearing capacity of shallow foundations resting on a modified Hoek–Brown rock mass is investigated within the framework of the kinematic approach of limit analysis theory. The analysis focuses on evaluating the reduction in bearing capacity induced by seismic loading and by the proximity of a rock slope. A pseudo‐static approach is adopted to account for the earthquake effects for the seismic bearing capacity evaluations. At the rock material level, the closed‐form expressions previously obtained for the support functions of the rock failure criterion allow the implementation of different failure mechanisms families, and thus to derive rigorous upper bounds estimates of the load‐bearing capacity in both static and seismic conditions. The effects of geometrical, strength and loading parameters are assessed through a large number of parametric computations. Finally, design tables are presented for practical use in rock engineering. Copyright © 2010 John Wiley & Sons, Ltd.     

基于综合变异系数的地基承载力可靠性分析

采用一次二阶矩法,考虑岩土参量变异系数的试验及历史数据,提出了基于综合变异系数的地基承载力简化可靠性与风险分析方法。利用提出的简化可靠性与风险分析方法,可在传统确定性分析的基础上,采用合理的变异系数,分别得到与地基承载力有关的可靠度、破坏概率和平均期望损失的最可能值及其变化范围,为提出优化的地基基础设计方案和工程决策奠定基础;相对于土重度和黏聚力,地基承载力可靠度对于内摩擦角的变化更加敏感;设计时可以综合考虑所需的安全系数、可靠度和破坏概率,确定合适的基础宽度或基底面积。当地基土的场地勘察统计结果的变异系数权重逐渐增加时,综合变异系数不断减小,其相应的地基承载力的可靠度逐渐增加,而相应的破坏概率逐渐减少。     

地震荷载作用下条形基础地基动承载力统一强度理论解

基于考虑中主应力影响的统一强度理论,通过假定复合型滑动面,利用拟静力和极限平衡分析法得到了条形基础地基静、动承载力解答。对比分析研究发现:在条形基础地基静承载力方面,本文提出的基于统一强度理论地基承载力系数有不同程度的提高,说明现有方法中地基承载力系数比较保守;而在动承载力方面,不同地震荷载下条形地基动承载力系数Ncd变化不大在2%~6%之间,但动承载力系数Nqd、Nγd值均有20%~75%的降低,而地基承载力有15%~40%的下降。