Study On Creep Characteristics Of Loess

With rapid advance in western development, more and more geotechnical problems arise from the northwestern inland area. It is of great significance for the western development in solving these problems, such as the deformation and collapse of building caused by foundation settlement, collapse of slope and landslide, which have severely adverse influence on engineering in western part of China.The creep characteristic of loess is an important factor, which cannot be ignored for the calculation of consolidation settlement of foundation and analysis in the stability of slope. The thick layer of loess is widely distributed in northwestern China and large numbers of researches on the geotechnical problems above were conducted by domestic and overseas scholars and many beneficial achievements which showed the close relationship between the problems and the creep characteristics of loess were obtained. Thus, it is of great theoretical and pratical significance to conducting researches in creep property of loess for modification of creep theory and prediction and treatment of geotechnical problems by investigating the main factors affecting creep property.In this paper, the progress in laws of creep deformation, creep model and its application in pratical engineering is concluded by reading massive research papers and reports. Based on the laboratory test, the creep properties of loess samples taken from a loess slope in Yangling District are studied in order to better understand the mechanism and deformation character of loess. A series of creep models are proposed by the experimental data and further analysis in characteristic parameters of creep is conducted.In general, some development for loess is involved in this dissertation as below:(1) According to the uniaxial and triaixal laboratory shear creep test on loess samples with different original requirement, the shear creep properties and influencing factors and creep deformation merchanisms are analysized. The experimental results indicate that under a certain stress, the higher water content is, the more obvious creep deformation of loess becomes; with a given water content, the strain-time relations all show a strain-hardening tendency and decay-creep morphology and the creep deformation tends to be stable; with improvement in stress, the creep process gradually transit to non-decaying period. The intact loess, the disturbed loess and saturated loess all have creep characteristics; under the same experimental conditions, the creep strain rate of saturated loess is the fastest and the creep strain is the biggest among the three kind of loess. The creep characteristic of disturbed loess is less obvious than saturated loess; and it is least obvious in intact loess. In the treatment of loess slope, enhancing the drainage ability of loess slope can reduce the probability of creep rupture.(2) Based on the expermental data of shear creep test, the creep curves under different stress are obtained by Boltzmann principle. According to the characteristics of creep curves, a new empirical logarithmic creep model is suggested. By the comparison between different rheological models, a one-dimensional shear creep property is simulated by fraction- linearity creep model. The relationship between shear modulus and normal stress and time is fitted by mathematical statisitics, which suggests a new method to determine shear modulus. Besides, under triaxial shear creep condition, the influence of time and deviatoric stress on strain rate is analyzed, a new empirical creep model for Yangling District is concluded, and by comparison with familiar empirical model and Burgers model, it shows higher accuracy, better applicability and easier way to obtain parameters. The empirical relation between viscous coefficient and deviatoric stress and time under triaxial conditon is obtained.(3) The influence of original water content and consolidation pressure on the coupled behaviors of consolidation and creep is analyzed based on unaxial consolidation data. The results show that the influence of original water content and consolidation pressure on coupled behaviors of consolidation and creep is obvious. According to strain-time curves, the stress-strain-time relation is proposed. After validation, the model shows a good correlation with experimental data. Based on experimental data and secondary consolidation coefficient proposed by Buisman, the relation between secondary consolidation coefficients with time is fitted.