| Expansive soil is widely distributed in China.Under the continuous action of rainfall-evaporation process in nature,it shows water swelling,water loss and shrinkage,and its properties are extremely unstable,which will cause many impacts on foundation construction projects such as foundation pits and slopes.Due to its special composition,state and structural characteristics,expansive soil is still not perfect in the mechanism of soil and water.Therefore,it is necessary to study the properties of expansive soil under drying and wetting cycles.The expansive soil in Shijiazhuang area was selected as the research object.The expansion test,consolidation test,direct shear test and static triaxial test before and after the drying and wetting cycles were used to study the changes of soil properties before and after the drying and wetting cycles,and the expansion was established by using Midas GTS software.The solid model of the soil foundation pit is analyzed during the construction phase.The main research contents and results are as follows:(1)Through the expansion rate test,the relationship between the expansion force and expansion ratio of expansive soil and various influencing factors is explored.The fitting relationship between expansion force and expansion ratio and water content and dry density is obtained,as well as the variation law under the action of drying and wetting cycles.The test results show that the expansion process of expansive soil is divided into three stages: severe expansion stage,deceleration expansion stage,and gentle expansion stage.(2)Based on the consolidation test,the influence mechanism of drying and wetting cycles in the consolidation process of expansive soil is revealed.The functional relationship is used to analyze the compression process,and the relationship between the overlying load and the compressive deformation under arbitrary loads is obtained.(3)Through the direct shear test under the drying and wetting cycles with overlying load,the effects of drying and wetting cycles under different overburden pressures on the strength of expansive soils were investigated.The strength decay law and strength parameters of expansive soils were obtained.The results show that the overburden load has an inhibitory effect on the intensity decay in the drying and wetting cycles.Based on the static triaxial test of samples with different moisture content,the constitutive relation expression of expansive soil related to moisture content is constructed based on the logarithmic relationship between secant modulus and strain.(4)Combined with the dynamic triaxial test of expansive soil under drying and wetting cycles,the effects of confining pressure,drying and wetting cycles and vibration times on dynamic elastic modulus and damping ratio of expansive soil were obtained.The stability and failure accumulation of expansive soil were qualitatively analyzed.According to the deformation characteristics,the relationship between the cumulative deformation of the expansive soil and the number of vibrations is derived.The cumulative deformation prediction model of expansive soil is established,which can be used to analyze the variation of the cumulative deformation of the soil with the number of vibrations.Based on the stress-strain curve under cyclic loading,the effects of dynamic stress and drying and wetting cycles on the hysteresis loop are discussed,and the variation of the shape,size and density of the hysteresis loop is obtained.(5)The three-dimensional solid model of a foundation pit engineering was established by using finite element software.The deformation of the soil inside the foundation pit and the variation law of the internal force of the supporting structure system at each construction stage were studied to verify the safety of the expansive soil foundation pit under normal construction conditions.Sexuality and design rationality.It has certain guiding significance for the design and construction of expansive soil foundation pit. |
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