摘要
综合考虑有效内摩擦角、有效黏聚力、基质吸力等非饱和土强度参数以及基底以下基质吸力随埋深增加而变化的工程实际(以水土特征曲线表征),采用多刚性块上限分析法对非饱和土条形基础竖向极限承载力进行研究。假定非饱和土抗剪强度公式是Mohr-Coulomb饱和土抗剪强度公式的延伸,根据线性破坏准则和相关联流动法则,构建一个承受竖向荷载的非饱和土地基承载力二维机动破坏模式。根据外力功率与内部耗能相等原理获得非饱和土地基极限承载力的目标表达式,并把其转化成一个求含有非线性约束的极限承载力上限解最小值计算模型。对建立的计算模型采用序列二次规划法进行优化求解。研究结果表明:非饱和土抗剪强度参数取值对极限承载力量值具有非线性影响;土中基质吸力存在所引起的附加抗剪强度使非饱和土地基承载力较饱和土得到提高;土体内基质吸力分布方式和地下水位高低对条形基础极限承载力影响也较大,地下水位升高导致基质吸力降低,极限承载力减小;非饱和土过渡为饱和土时,同类方法相比本解答是较优上限解。
The bearing capacity of shallow foundations obtained by the conventional approaches, which assume fully saturated conditions ignoring the influence of the matric suction, may not be reliable and lead to uneconomical designs. On the assumption that the shear strength formula of unsaturated soils is the extension and expansion of the shear strength formula of saturated soils, and based on the linear failure criterion and associated flow rule, the bearing capacity of strip footing on unsaturated soils under the action of ultimate loads is studied by means of the kinematical approach of limit analysis theory. A planar knematically admissible failure mechanism is proposed for the calculation schemes. The objective functions of bearing capacity are obtained by equating the work rate of external force to internal dissipation along the velocity discontinuities, and then the objective function is transformed as a upper-bound mathematic optimization model for bearing capacity as low as possible. The objective functions are obtained by use of the sequential quadratic programming. The bearing capacity of unsaturated soil is predicted by using the approach presented above, in which not only the effective internal friction angle, effective cohesion and matric suction, but also the soil-water characteristic curve and the engineering practice are analyzed synthetically. Numerical results show that the existence of matric suction, the distribution mode of matric suction and under water level in unsaturated soils have significant effects on the ultimate bearing capacity. The parametric analysis indicats that preferences possessing nonlinear effect on the bearing capacity. If the yield criterion of unsaturated soils turns into the yield criterion of saturated soils, the presented solution provides better upper-bound result.
出处
《岩石力学与工程学报》
EI
CAS
CSCD
北大核心
2009年第A01期3021-3028,共8页
Chinese Journal of Rock Mechanics and Engineering
基金
西部交通建设科技项目(2006318802111)
铁道部科技研究开发计划重点资助项目(2008G032-3)
关键词
基础工程
非饱和土
基质吸力
条形基础
地基承载力
线性破坏准则
foundation engineering
unsaturated soils
matric suction
strip footing
bearing capacity of foundation
linear failure criterion
