考虑中主应力及三向应力状态影响的地基承载力分析

Study of bearing capacity of foundations considering both effects of intermediate principal stress and three-dimensional stress state

基于推广的SM P准则,建立了平面应变条件下和三轴压缩条件下土的抗剪强度参数关系的简单解析表达式.基于这一关系,采用各自应力状态下土的强度参数,用滑移线方法分析了条形基础、圆形基础承载力系数及圆形基础承载力形状修正系数.计算结果表明,若忽略应力状态对土的强度参数的影响而简单地用三轴压缩试验下土的强度参数,由此计算得到的条形基础承载力系数具有较大的误差,且这种误差随着土的内摩擦角的增大而增大.针对圆形基础,将计算结果与T erzagh i经验关系对比分析发现,T erzagh i的经验系数在多数情况下是合适的,但当基底光滑时,由土自重所引起的承载力系数所对应的形状修正系数取0.6是偏于不安全的,根据计算结果建议取为0.4.

Based on the extended SMP criterion, analytical formula is presented for expressing the strength parameters of soils under plane-strain condition and under triaxial compression condition. Based on this proposed relationship, the bearing capacity factors of strip foundations and circular foundations are computed according to the solution given by the slip-line method respectively using soil shear strength parameters under plane-strain condition and under triaxial compression condition. The difference between the bearing capacity factors computed based on the strength parameters under different stress states is considerable. The correlation coefficients of bearing capacity factors which allow for the effect of footing shape for circular foundations are determined and then compared with the empirical values proposed by Terzaghi which have been widely used in engineering design. It is found that for most cases, the shape correlation coefficients of bearing capacity proposed by Terzaghi are rational. However, for the shape correlation coefficient of bearing capacity resulting from soil weight for circular foundation under smooth contact condition, the value of 0. 6 which was proposed by Terzaghi is not valid. For this case, it is suggested to use the value of 0. 4.