The Test Study On The Collapsible And Strength Deformation Of Unsaturated Loess In Qingyang

As the main building and engineering site in Northwest China, loess has always been the important object of study for the researchers in the field of geotechnical engineering because of its special engineering properties. Qingyang City is located in the Dongzhiyuan hinterland of Longdong Loess Plateau, and loess layer thickness is large and well developed. Groundwater is located in the depths of underground in Qingyang, so loess exist as unsaturated state. The loess of Qingyang City has a significant research value why have continuous distribution and more complete history of development. In the past, the research of loess mainly focused on Lanzhou, Xi’an and other places, but there are few studies on the loess in Qingyang.For the above reasons, this paper is supported by the building science and technology key project from Gansu province "Super large thickness characteristic loess structure and basic optimization resear ch"(Grant No. JK2014-34). Based on the investigation and study on formation environment and its basic properties of loess in Qingyang, the thesis carry out the experimental research and theoretical analysis for moistening collapsibility characteristics and strength-deformation characteristics of Q3 loess in Qingyang, and provide a test reference and theoretic basis for the follow-up basic optimization research of Qingyang. The strength deformation characteristics of unsaturated loess in Qingyang is core content of this paper. This paper analysed the deformation law of undisturbed loess and remolded loess of three dry density(ρd=1.5 g/cm3, ρd=1.6 g/cm3, ρd=1.7 g/cm3) based on the consolidated drained shear tests under controlled cell pressure and suction using triaxial test apparatus for unsaturated soils. In the past, most researchers only consider the influence of matrix suction on the shear strength of unsaturated remolded-loess, but the study on the joint influence of dry density and matrix suction on the strength characteristics of remolded-loess is still rare. Therefore, this paper studies the deformation law of the remolded-loess with different dry density under the control of suction force, and analyses the effect of dry density and matrix suction on the strength-deformation of the remolded-loess. The results show that the influence of matrix suction and dry density on the strength of the unsaturated remolded-loes is mainly reflected in the cohesion, and they have no influence on the friction angle, sunction friction angle has a linear increase with the increasing of dry density. The shear strength formula of Qingyang unsaturated remodeling Q3 loess considering dry density and matrix suction was proposed, which can be used for reference in practical engineering. At last, the non-linear constitutive model and its calculation parameters about undisturbed unsaturated loess were analyzed based on the Duncan-Chang model and the data of triaxial shear test.