The Research On Shear Creep Characteristics And Long-term Strength Of Expansive Soil Under Drying And Wetting Cycles

Due to drying and wetting cycle effects on the internal structure of expansive soil,a certain degree of damage was caused. In order to establish constitutive model with the parameters fitted that comply with practical engineering and reasonably reflect the creep behavior of expansive soil, and then predict the creep characteristics of expansive soils,the further study was carried out on expansive soil stress-strain law, shear creep model and long-term strength parameters of soil attenuation law under drying and wetting cycle. In this paper, the indoor sheer creep experiments of expansive soil under different normal pressure were carried out respectively after undergoing 0 times, 2 times, 4 times, 6 times drying and wetting cycles, the shear creep mechanism of baise expansive soil were studied by shear creep test curve data analysis and sorting, a semi-emperical and semi-theory shear creep constitutive model was established.the parameters of model is clear physical meaning, not only did it describe the attenuation creep and constant creep stage of the expansive soil, but also describe the accelerated creep stage,and fully reflect the rheological sticky elastic-plastic properties of the soil and the easier parameters identification, its accuracy has been relatively good verification.The following main conclusions was obtained:?1? Under the same stress path, instantaneous deformation and accumulated deformation of soil samples after undergoing drying and wetting cycle are larger than without it, and deformation increases with drying and wetting cycle times increasing. Drying and wetting cycle effects had a significant impact on soil creep characteristics, its instantaneous strength and long-term strength is also greatly reduced compared with the previous cycle.?2? Nonlinear creep of baise expansive soils exhibit elastic, viscoelastic, viscoplastic, viscoelastic plasticity characteristics by shear strain-time curve analysis.?3? Shear creep deformation of expansive soils can be divided into three stages: attenuation creep stage, constant creep stage, accelerated creep stage.Under the low shear stress level of ?_i<?₁, deformation occurs only instantaneous, no creep phenomenon; When shear stress continues to increase to the level of ?₂>?_i??₁, the soil begin to creep, but the creep rate constant decreases, and the final convergence,known as the attenuation creep stage; When shear stress continues to increase to the level of ?₂??_i>?_f, the soil begin to creep at a constant speed, known as the constant creep stage; When shear stress continues to increase to ?_i??_f,the soil enter into accelerated creep stage, the failure quickly.?4? A semi-empirical and semi-theoretical shear creep model with a set of fitted parameters was established.The model proved that its creep test and measured value is consistent, which can provide a reliable basis for calculating soil creep deformation of Baise area for construction.?5? Drying and wetting cycle will cause the instantaneous strength and long-term strength of expansive soil greatly attenuated, and attenuation amplitude of the long-term strength greater than the instantaneous strength.?6? Instantaneous strength and long-term strength magnitude of the sort order: long-term strength of expansive soil after 6 times drying and wetting cycle<Instantaneous strength of the soil after 6 times drying and wetting cycle<long-term strength of the soil without the drying and wetting cycle<instantaneous strength of the soil without the drying and wetting cycle.Drying and wetting cycle cause instantaneous strength and long-term strength of the soil attenuation, the degree of attenuation increases with wet and dry cycle times increases.