Experimental Study On Mechanical Properties Of Fiber Bubble Lightweight Mixed Soil

When fiber bubble lightweight mixed soil is used as engineering soil such as filling,its fluidity and lightness should be considered in addition to its good mechanical properties such as strength and deformation.After a comprehensive exploration of many test groups,some representative test groups are selected to further analyze their durability and micro mechanism.In the research process,the practical application is fully considered,and the research is mainly carried out for different admixtures.The research contents include the following aspects:(1)Determine and analyze the physical properties of various raw materials(raw material soil,cement,fiber,foaming agent,fly ash and mineral powder)in fiber bubble lightweight mixed soil,carry out the test proportion design and test scheme design,and elaborate and analyze the process and scheme flow of convection value test,density test,unconfined compressive strength test,triaxial test,cyclic loading and unloading consolidation test,flexural strength test and durability test.(2)The fluidity and lightness of soil samples are studied through flow value test and density test.The test results show that when exploring the influence of raw material content on fluidity,the flow value decreases with the increase of cement,fiber,bubble,fly ash and mineral powder,and increases with the increase of water content.Among them,water and bubble have a great influence on fluidity,and the fluidity evaluation is given.The density of soil samples in the same test group increases with the increase of curing age.At each age,when the content of cement,fiber,fly ash and mineral powder increases,the density of soil samples increases,and when the content of water and bubble increases,the density decreases.(3)The strength of soil samples is studied through unconfined compressive strength test and consolidated undrained test.The test results show that the peak compressive strength increases with the increase of the content of cement and mineral powder at the same age;The peak compressive strength decreases continuously with the increase of the content of water,bubble and fly ash;With the increase of fiber content,the peak compressive strength first increases and then decreases.When exploring the influence of the content of raw materials on the shear strength,when the content of cement and mineral powder increases,the cohesion and internal friction angle continue to increase;When the content of water and bubble increases,the cohesion and internal friction angle continue to decrease;With the increase of fly ash content,the cohesion and internal friction angle change little;With the increase of fiber content,the cohesion first increases and then decreases,and the internal friction angle is almost unchanged.It is better to choose single mineral powder when adding external admixtures(fly ash and mineral powder).The mathematical model of peak compressive strength,age and material content is established by selecting appropriate function.(4)The deformation characteristics of soil samples are studied by cyclic loading and unloading compression deformation test.The test results show that when the cement content increases,the initial void ratio and the reduction of void ratio decrease continuously;When the content of water and bubble increases,the initial void ratio and the decrease of void ratio continue to increase;When the total content of fly ash and mineral powder is certain,when the content of mineral powder increases,the initial void ratio and the reduction of void ratio increase.The soil samples without bubbles showed low compressibility,and the soil samples of other test groups showed medium compressibility.In the unloading process,the unloading rebound deformation decreases with the increase of cement content;With the increase of fiber content,the unloading rebound deformation first decreases and then increases;With the increase of water and bubble content,the unloading rebound deformation increases continuously;The higher the relative content of mineral powder in the admixture,the smaller the unloading rebound deformation.The results of unconfined compressive deformation study show that with the increase of cement content,the failure strain decreases,the failure of soil sample changes from ductility to brittleness,the failure strain increases with the increase of fiber,water and bubble content,the failure of soil sample changes from brittleness to ductility,and there is a good linear relationship between peak compressive strength and secant modulus.The results of the deformation study of the consolidated undrained test show that the soil sample under low confining pressure(cement,fiber and bubble)shows strain softening,and changes to strain hardening with the increase of confining pressure.The higher the cement content is,the soil sample is easy to show softening type under high confining pressure,and the higher the fiber and bubble content is,the soil sample is easy to show hardening type under high confining pressure.(5)The durability of soil samples is studied through dry wet cycle and freeze-thaw cycle tests.The results show that the peak compressive strength first increases and then decreases with the increase of dry wet cycles;With the increase of freeze-thaw cycles,the peak compressive strength of the samples decreases.Through the flexural strength test,the fatigue resistance of soil sample is analyzed.The research shows that the sample with only15% mineral powder has better flexural strength.The microscopic mechanism of soil samples was analyzed by SEM,EDS and X ray diffraction.The results showed that the addition of fly ash and mineral powder could effectively reduce the calcium hydroxide in products,and produced more hydrated calcium silicate gel and ettringite,resulting in better mechanical properties of soil samples.