Experimental Study On Static-Dynamic Mechanical Properties And Microstructure Of Stabilized Expansive Soil

Expansive soil often brings many inevitable hazards and serious economic losses to practical engineering construction because of its particular properties of expansion when absorbing water and shrinkage when losing water.Therefore,it is necessary to improve the behaviors of expansive soil before it can be used in practical engineering of expansive soil areas.At present,the investigations of expansive soil mainly focus on the physical properties,microstructural analysis and static mechanical properties of stabilized expansive soil.However,the researches on the dynamic mechanical performances of stabilized soil under impact loading are relatively rare.In practical engineering,the stabilized soil is often subjected to impact loading,so it is essential to study the dynamic mechanical properties of stabilized soil.Firstly,cement and fly ash were used together to improve the behaviors of expansive soil,and a series of physical and mechanical properties tests were performed to obtain the optimum mixed percentages of cement and fly ash.On the basis of the optimum mixed percentages of cement and fly ash,the unconfined compression test,SHPB test and SEM test were conducted on cement-fly ash stabilized soil with different basalt fiber contents and different sand contents.The main contents of this research are exhibited as follows:Firstly,the original expansive soil was treated "with cement or cement-fly ash mixtures,and a series of physical and mechanical properties tests were carried out on cement stabilized soil and cement-fly ash stabilized soil,which include the free swelling rate test,shrinkage test,limit moisture content test,no-load swelling rate test and compression strength test.The change law of the swelling-shrinkage characteristic and mechanical property of stabilized soil was analyzed.The results show that the cement content of 5%and fly ash content of 10%are regarded as the optimum mixed percentages of cement-fly ash stabilized soil in this study.Secondly,based on the optimum mixed percentages of cement and fly ash,the basalt fiber and natural sand were selected to further optimize and improve the behaviors of cement-fly ash stabilized soil.The unconfined compression tests were carried out for cement-fly ash stabilized soil with different fiber contents of 0%,0.3%,0.6%,0.9%and 1.2%and different sand contents of 0%.8%?16%and 24%.The stress-strain curves,unconfined compressive strength and failure modes of stabilized soil under static loading were analyzed.In addition,it is concluded that the optimum fiber content is 0.6%and the optimum sand content is 8%,respectively.The comparative analysis indicates that the addition of fiber has a better effect on the enhancement of unconfined compressive strength of cement-fly ash stabilized soil.Thirdly,based on the optimum mixed percentages of cement and fly ash,the dynamic compression tests for cement-fly ash stabilized soil with different fiber coltents of 0%.0.3%.0.6%,0.9%and 1.2%and different sand contents of 0%9 8%,16%and 24%were performed by SHPB apparatus.The dynamic stress-strain curves and dynamic compressive strength of cement-fly ash stabilized soil under impact loading were analyzed.Besides,the energy dissipation of stabilized soil during the impact fragmentation process was also analyzed and discussed.Based on the fractal theory,the change rule of fractal dimension of stabilized soil fragments was obtained by statistical analysis,and the relationship between fractal dimension and energy dissipation density was established.The relationship between energy dissipation density,dynamic compressive strength and fractal dimension of fragments under impact loading was also obtained.According to the analysis of dynamic strength and energy dissipation,it can be concluded that the optimal content of fiber is 0.6%and the optimal content of sand is 8%in SHPB tests.The comparative analysis shows that ’with the addition of fiber,the energy absorption ability of cement-fly ash stabilized soil has been improved obviously.Finally,the analysis of the formation of hydration products and the change of xnicrostructure inside cement-fly ash stabilized 5oil was performed by SEM test.The internal microstructure morphology of stabilized soil with different fiber contents and different sand contents was observed and analyzed.Moreover,the intermal mechanism of the enhancement on the strength of cement-fly ash stabilized soil with fiber or sand was further explained according to the macroscopic mechanical properties.Figure 61 table 13 references 95...