Study On Plane Creep Characteristics Of Unsaturated Loess

As for the large area of loess in our country, and the further development of the west regions, much engineering activities are closely related to loess. Taking the security of engineering activities in loess district into account, the creep characteristics of loess under the condition of plane strain state were discussed in this paper, which could provide significant theories and guiding for the engineering constructions in loess district. A reformed plane creepmeter was used for the testing of unsaturated loess in Jingyang district in Shaanxi province. The purpose of the consolidation and exhausting-draining tests was to analysis the plain creep characteristics of loess in this area under the influence of different water content, confining pressure, dry density and deviatoric stress, as well as the influence law of axial strain, lateral strain and volume strain by these factors. Meanwhile, a new empirical creep model, which was suitable for simulating the characteristics of loess under the plane strain state in this area, was established. Moreover, the results of plane creep were compared with the ones of triaxial creep tests, and the compared results are as followed.(1) With the certain value of other factors, the influence of water content to axial strain and volume strain of sample are alike to some extent, which is that the strain values and the time for stabilization are climbing with the increasing of water content. When the water content and the confining pressure are low, the samples swell in little lateral side, and when the water content and confining pressure is high, the samples compress in little lateral side. The volume strain value in 20% water content is much closer to, or even over the one in 30% water content.(2) As one of important factors in tests, confining pressure has a similar influence to axial strain and volume strain, which is that the value of axial strain and volume strain, and the time for stabilization are decreasing with the increasing of confining pressure. When the dry density is less, the samples swell in little lateral side. When the dry density is higher, the samples compress in little lateral side. As for the volume strain, the function of confining pressure is relatively higher when the dry density is less.(3) The influence of dry density on axial strain and volume strain of plane creep samples are same, which is that the value of axial strain and volume strain are less when the dry density is higher, and the time for stabilization is shorter. The affection of dry density on lateral strain is low, and the law shows approximately that the value of lateral strain is lower when there is a higher dry density. Meanwhile, the function of dry density on volume strain curves is more significant when the water content and confining pressure is lower, and the function of dry density becomes weaker with the increasing of water content and confining pressure. In some cases, the change law mentioned above might reverse.(4) During the process of tests, the value of axial strain and volume strain is becoming larger with the rising value of deviatoric stress, as well as the time for stabilization. The value of lateral strain under high deviatoric stress is higher than the one under low deviatoric stress, no matter what the change is(swell or compress). As for the change law of volume strain, it is that the influence of deviatoric stress on volume strain is higher under the condition of high confining pressure.(5) A new empirical creep model which was suitable for the loess under plane strain state in this area was established. After verification, it shows that the simulation precision is high, and the less model parameters is easily obtained, which illustrate that the new model can describe the plane creep characteristics of unsaturated loess in this area well. After the comparison results of plane creep tests and triaxial creep tests under same condition, it shows that the regularity of triaxial creep strain curves is more obvious than the one of plane creep strain curves. When the water content is high, the value of plane creep strain is higher than the one of triaxial creep strain. When the water content and confining pressure keep stable, the value of plane creep strain is higher than the one of triaxial creep strain under low deviatoric stress.