Experimental Study And Numerical Simulation On Physical And Mechanical Properties Of Stabilized Expansive Soil

Expansive soil refers to a type of clay with repeated expansion and shrinkage properties for its moisture variations,it is primarily composed of montmorillonite and illite.As common methods,fly ash and lime are used to stabilizing expansive soil for the purpose of reducing the expansibility and improving the strength.Huainan belongs to the typical Jianghuai undulating plain and expansive soil is widely distributed in this area.Meanwhile,as an important coal-fired power generation area in China,the rational utilization of fly ash has also become a problem need to be solved.Therefore,two group comparative tests were set in this study,the use amounts of modifiers are 0,5%,10%,15%,20%,25%,30%fly ash and 5%lime on the basis content of fly ash above.The comparison was drawn between the variation laws of swelling characteristics of expansive soil stabilized by pure fly ash and fly ash-lime with different mixing ratios first;Then,the static and dynamic mechanical properties of the stabilized soil were studied by using a universal testing machine,a direct shear test device and a Hopkinson pressure bar device with a diameter of 50mm.Combined with scanning electron microscope(SEM)and X-ray diffraction(XRD)tests,the microscopic mechanism of expansive soil stabilized by fly ash and lime was further revealed;Finally,the finite element software ABAQUS was used to explore the influence of additional expansion force on the deformation of the foundation pit support system from the perspective of thermal and mechanical coupling.The relevant research results are as follows:(1)The tests for liquid and plastic limit,free swelling ratio,and unloading swelling ratio were adopted on pure fly ash stabilized soil and fly ash-lime combined stabilized soil and the variation laws of the parameters above with different mixing ratios were analyzed.The datas show that when the content of pure fly ash exceeds 25%,the soil sample does not belong to expansive soil.Under the conditions of fly ash-lime combined stabilization,10%fly ash and 5%lime stabilized soil are no longer swellable.(2)The tests for static unconfined compression,split tensile,direct shear and impact compression were conducted on pure fly ash stabilized soil and fly ash-lime combined stabilized soil.The stress-strain relationship of the modified expansive soil under static and dynamic loads was explored,and the change laws of the strength and final fracture shapes under different test conditions were observed and analyzed.The fragmentation process of the stabilized soil under impact load was analyzed from the perspective of energy,and the relationship between the dynamic compressive strength and the absorbed energy with different mixing ratios was established.The test results show that the strength change laws of the stabilized soil under dynamic and static loads is consistent.Under the pure fly ash content,the dynamic and static strength of the stabilized soil first rises and then decreases with the upregulation of the fly ash content.The strength reaches the peak value when the fly ash content is 10%,and the strengths for split tensile and dynamic compression were maximum when the fly ash content was 20%.Under the combined effect of fly ash-lime,the unconfined compressive and splitting tensile strength reach the highest value at 10%fly ash-5%lime content,and the dynamic compressive strength reaches the maximum at 20%fly ash-5%lime content.The test confirmed that the adding of 5%lime to fly ash can significantly enhance the mechanical properties of the stabilized soil,and there is an optimal ratio of fly ash content between 10%and 20%.(3)Micro-analysis of plain soil,10%fly ash modified soil,10%fly ash-5%lime combined modified soil on SEM images show that the plain soil is exhibited obvious pores and cracks,thereby forming water passages.There is obvious flocculent substance between the fissure passages;The pores and cracks of the soil modified by fly ash are filled with fly ash particles to a certain extent,and the soil modified by fly ash and lime shows a blocky structure.By binarizing the SEM image,it can be seen that the porosity of plain soil is more similar to round,while the porosity of modified soil is irregularly cracked.This is because the hydration products of the modifier are filled into the pores and cracks randomly,which greatly improve the compactness of the soil.These changes further explain the microscopic mechanism of fly ash and lime stabilized expansive soil.(4)From the similar principle of temperature field and humidity field,the ABAQUS thermal coupling unit was used to simulate the expansion force from the perspective of thermal expansion and deformation.The results show that the horizontal displacement on the top of the foundation pit is reduced to a certain extent after the addition of fly ash and lime,and the horizontal displacement of foundation pit is minimal under the combined effect of lime and fly ash.This study analyzes the dynamic and static mechanical properties and microstructures of pure fly ash stabilized soil and fly ash-lime combined stabilized soil with different mixing ratios,and the optimal ratio of modifiers under experimental conditions was obtained;The deformation laws of the foundation pit is obtained under the consideration of the expansion force,which provides further reference for the actual projects.Figure 60 Table 10 References 99...