摘要
对考虑桩径因素的Mindlin解群桩应力场剖析表明:端阻应力在桩端下2d范围呈现明显的应力集中现象,在竖向和水平向衰减迅速;侧阻应力在桩端平面分布明显不均,至桩端下1d平面趋于均匀,沿深度和水平向衰减较慢。按半无限体表面荷载下的Boussinesq解计算的群桩应力显著偏大,致使按实体深基法计算的桩基沉降需乘以0.25~0.5经验系数折减。桩基沉降计算采用Mindlin解计算附加应力的合理性是明显的,但按习用的自由荷载下应力叠加法计算将导致中点沉降偏大、边角点偏小。基于群桩Mindlin解附加应力场和群桩基础变形特征,考虑承台和上部结构刚度对沉降变形的均化效应,提出Mindlin解均化应力分层总和法计算群桩基础沉降。该方法具有如下特点:一是可反映桩端应力集中贯入变形;二是可近似反映承台和上部结构刚度的影响;三是可查表或采用程序进行计算,操作简便;四是计算值与实测值、规范统计值接近,初步预计无需修正。
Based on the Mindlin stress solution with the pile-diameter effect considered,it is seen that pile-tip stress concentration may appear within the range of two pile diameters below the pile tip,but the pile-tip stress attenuates in the horizontal and vertical directions. The side resistance of the pile group is not uniformly distributed at the pile tip,but it is well distributed at one pile diameter above the pile tip,and the side resistance attenuates slightly along the vertical and horizontal directions. Since the settlement calculation results based on the Boussinesq stress theory are larger than the realistic ones,an empirical coefficient of 0. 25 ~ 0. 5 should be multiplied to the pile-group settlement calculated from solid foundation approach. It is reasonable to apply the Mindlin stress theory to calculate the additional stress of the pilegroup foundation. However, calculating the additional stress of pile-group foundation with the traditional stress superposition method under free loads may lead to the larger settlement at the center and the smaller settlement at the corners. Based on the stress field calculated by the Mindlin stress theory with the pile diameter effect considered,the deformation behavior of the pile-group foundation as well as the homogenization effect of pile cap and the superstructure stiffness on the settlement deformation,a layerwise summation method for settlement calculation of pile group is presented based on the Mindlin stress theory. The advantages of this method are summarized as follows:( 1) the penetration deformation due to stress concentration at the pile tip may be reflected;( 2) the stiffness effect of pile cap and superstructure may be approximately modeled;( 3) table look-up and computer program may be utilized and the processes can be readily done;( 4) the calculation results have good agreements with the measured ones and statistical ones without the necessity of revisions.
出处
《土木工程学报》
EI
CSCD
北大核心
2014年第5期118-127,共10页
China Civil Engineering Journal
基金
"十二五"国家科技支撑计划项目(2012BAJ07B01)
关键词
MINDLIN解
群桩
应力场
均化应力
沉降计算
Mindlin stress solution
pile group
stress field
homogenized stress
settlement calculation
