| Loess is a Quaternary loose deposit mainly composed of silt particles,which is widely distributed in the Loess Plateau of western China.Due to the the particularity of loess property and the rapid development of infrastructure construction in recent years,loess geological disasters or geotechnical engineering problems become more and more prominent especially loess deformation and stability problems closely related to time effect.Under the constant action of a certain stress,the process of soil deformation continuing to grow with time is called creep.Although there have been some researches on the creep behavior of soils from both theoretical and experimental aspects,many useful results have been obtained,but due to the complexity of soil creep problems,the diversity of natural conditions,under certain conditions.The exploration of soil creep behavior is still worthy of advancement,especially for the creep behavior and mesoscopic mechanism of loess,which is widely distributed in western China.Based on data collection and domestic and foreign literature research,this paper takes Yan’an Malan loess as the research object through field investigation.Firstly,the basic physical index of the original loess using soil mechanics is obtained,and the particle separation test of Malan loess is carried out.Conventional pressure consolidation-creep test and microstructure test in the original and remodeled soil samples,the initial moisture content,initial compaction degree,clay content,structure and consolidation pressure affect the consolidation-creep characteristics,and the deformation mechanism is discussed,and the relationship between porosity,consolidation pressure and secondary consolidation coefficient is established.Secondly,with the discrete element analysis software particle flow program PFC2 D as the technical means,the key problems to be solved in the process of creep simulation of loess creep are introduced.Finally,the discrete element method is used to carry out one-dimensional consolidation-creep and biaxial creep numerical tests.The experimental results are analyzed and discussed.The application of discrete element method to study the creep properties of loess is demonstrated.Finally,based on the evolution of the model meso-structure and state parameters in the creep process,the meso-mechanism of loess creep is further explored.The results show that Yan’an Malan loess has obvious secondary consolidation phenomenon.Initial moisture content,initial compaction degree,clay content,structure and consolidation pressure have certain influence on the consolidation-creep characteristics.The ratio of the secondary consolidation coefficient and the initial porosity of the remolded loess shows a linear relationship with the initial porosity,reflecting the relationship between the secondary consolidation coefficient and the initial porosity,which is a hyperbolic form.It provides a convenient method for estimating the secondary consolidation coefficient of soil in engineering.PFC2 D can be used to simulate the creep behavior of loess,which can truly reproduce the staged characteristics and creep constitutive characteristics of loess creep indoor curve.The creep of loess is inseparable from the relative motion,rotation and alignment of the internal mesoscopic particle unit.The most intuitive mesoscopic evolution of the particle unit is the change in the average contact number of the particles,ie,the coordination number.The mesoscopic parameters and the evolutionary characteristics of the structure can well reveal the mesoscopic mechanism behind the macroscopic creep phenomenon.As creep progresses,the creep stress is gradually assumed by the normal contact force rather than the tangential contact force and has an anisotropic character.As a result of the creep,the contact points of the particles increase,and the skeleton particles are transferred from the point contact to the agglomerates,and the mutual restraint is enhanced,and the skeleton tends to be more stable and can withstand a larger load.The relevant research results in this paper have important theoretical and practical significance in understanding the creep characteristics and mechanism of loess,effectively controlling the factors affecting creep,preventing and reducing landslides and other disasters,guiding engineering construction in loess region and ensuring the long-term safety and stability of engineering foundation. |
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