平面变形超固结软黏土蠕变特征

Plane strain tests on creep characteristics of over-consolidated clay

通过对原状软土进行平面变形蠕变试验,研究超固结软土平面变形条件下的蠕变特征。研究表明,正常固结软土平面变形蠕变的体变过程,和一维变形条件下正常固结软土的次固结过程具有相同的规律,在主应力比与K0状态相同时,相对于一维变形平面变形情况具有较小的轴向变形;平面变形条件下,采用土体受到的不同时期的体积球应力定义超固结比,能够全面地反映超固结软土的超固结特征;平面变形条件下,超固结软土蠕变的体积变形较正常固结状态明显减小,超固结比越大减小程度越明显,由超固结比确定体积蠕变系数具有合理性;平面变形在主应力比为K0的状态下,超固结软土蠕变的轴向蠕变系数与超固结比负相关,由超固结比直接确定轴向蠕变系数是可行的;平面变形条件下土体的超固结应力历史,使超固结软土相对于正常固结状态具有较大的泊松比,在限制水平变形方向具有较大的主应力。

It is more realistic that the clay unit cell of road embankment is in the state of plane strain. The creep characteristics of over-consolidated soils are studied through plane strain tests for the undisturbed soft clay. Four creep tests are carried out by using the plane strain creep apparatus, one is conducted on normally consolidated clay and three are on over-consolidated clay. The studies show that for the normally consolidated soils, the volumetric strain of creep in plane strain tests varies in the same way with the secondary consolidation under one-dimension condition, and that the clay presents less axial strain in plane strain tests than that in one-dimension tests when the principal stress ratio equals the ratio in K0 state. The definition of plane strain over-consolidation ratio (OCRp) is given, and it is used to describe the characteristics of over-consolidated soils. It is found that it is reasonable to determine the volumetric creep coefficient as well as axial creep coefficient directly by using OCRp. Compared with normally consolidated clay, under plane strain state, the over-consolidated clay has a lager Poisson's ratio and larger principal stress in the direction of limited deformation.