球应力往返作用下饱和砂土变形特性的试验研究

TESTING STUDYON DEFORMATION CHARACTERISTICS OF SATURATED SAND UNDER REPEATED SPHERICAL STRESS

在固结排水条件下保持偏应力不变,进行球应力往返变化的三轴试验,对球应力往返作用下饱和砂土的变形随着往返作用次数增大而变化的规律及其受干密度状态和固结应力状态的影响问题给出系统的试验成果与分析。研究结果表明(1)球应力往返作用主要产生体应变,同时出现明显的残余体应变与往返体应变,且往返体应变表现为压缩物态(加荷)与回胀物态(卸荷)的交替变化,而产生偏应变很小,可忽略不计;(2)压缩物态段的体应变与回胀物态段的体应变与作用球应力比的对数值之间均存在良好的线性关系,这些线性关系的参数,视具体情况与固结应力状态和土性状态以及球应力的往返作用次数有关;(3)压缩物态段的线性关系,对固结应力有一定的“记忆性”,这种记忆性在均压固结下表现为线性关系在固结球应力处的转折性(在固结球应力前后有不同的斜率),在偏压固结下表现为转折随固结剪应力出现的衰减性(一般在固结球应力前后可有相同的斜率);(4)在两种物态段,再次与多次的加荷或卸荷主要引起体应变与球应力比关系直线截距的升高,而基本上不改变体应变关系线的斜率;(5)利用所揭示的规律与有关参数,可以跟踪球应力的往返变化,计算相应球应变的变化,计算结果与试验结果吻合较好。

Cyclic triaxial tests are conducted on saturated sand under drained conditions with cyclic loading and unloading of spherical stress, and constant deviator stress. The systematic test results are analyzed for the deformation variation with cyclic number and the influence of dry density and consolidated stress condition. It is shown as follows: (1) cyclic spherical stress mainly causes volumetric strain, apparent residual, and cyclic volumetric strain, and the later presents compressive (loading) and swelling (unloading) physical states. At the same time, the deviator strain is very small and can be omitted; (2) the relationship between volumetric strain and the logarithm of spherical stress ratio is linear both in compressive and swelling physical states. The linear parameters have relationship with cyclic number, dry density as well as consolidated stress condition; (3) the linear relation in compressive physical state has some memory of consolidated stress, which makes the linear relation a turn at a point of spherical stress under isotropic consolidation, and under anisotropic consolidation it disappears; (4) secondary cyclic loading mainly increases the intercept of the linear relation, and its slope scarcely changes in two physical states; (5) using the revealed law and related parameters, the volumetric strain can be calculated by following spherical stress change and the calculation results are preferably consistent with those by experiment.