Experimentation And Study In Fly Ash Soil Reinforced By Randomly Distributed Fibers

Foundation soil liquefaction is one of the main causes that lead to the foundation's instability. When the foundation soil contains too much water, the pore water pressure will occur in the cyclic loading. The pore water pressure is gradually increasing, making effective stress reduction to disappear and soil liquefaction phenomenon occurs. The resistance of liquefaction strength can be tested through dynamic triaxial testing by measuring dynamic strength. Through research, it was found that fiber can improve the strength of concrete, reduce the formation of cracks, increase its resistance performance of freeze-thaw. So polypropylene fiber in the application of civil engineering is studied more and more, and some scholars will use it in soil fiber reinforcement projects. Through research it can be found that the fiber can significantly improve the soil compressive strength, tensile strength and the resistance of liquefaction strength. In this paper, the dynamic strength of polypropylene fiber reinforcement with fly ash soil is studied.Currently, randomly distributed fibers reinforcement fly ash soil test is not too much. The paper shows the polypropylene fiber on the impact of fly ash soil mainly through unconfined compressive strength test, dynamic triaxial tests and so on, by contrast the dynamic strength, dynamic modulus and the resistance of soil liquefaction strength before and after the fiber is added.In order to study the dynamic characteristics of fly ash soil, it is necessary to understand the dynamics of soil and soil liquefaction mechanism. The second chapter describes the basic content of dynamics, the liquefied soil conditions and intensity formula. This paper uses the dynamic load test of tension and compression symmetrical sinusoidal frequency of 1 Hz. We need to study the momentum indicators such as dynamic modulus, dynamic strength, silty clay cohesion and internal friction angle. This paper uses the hyperbolic curve as the dynamic strain - dynamic stress curve described by the equation . By Coulomb's law, we can see that the ability of silty clay to resist reciprocating movement under cyclic loading largely depends on the effective internal friction angle and effective cohesion, as well as the growth of the pore water pressure. When the cohesion completely disappeared as well as effective stress is zero, soil liquefaction occurs.Chapter third introduces the fiber reinforcement mechanism on the soil. "bending mechanism"and"cutting mechanism" gived by Liu Xu-dong said that: the distribution of the fiber in soil is composed of numerous bending turning point, when the soil bears outside force the fiber is in tension. The fiber will have particles pressure and friction on the soil on the first curved concave side. At the same time, the disorder fiber in the distribution of soil has countless intersection. If the intersection suffered force, thereby shift the trend will encounter. But other fibers prevent such displacement .Any section of the fiber deformation will affect all intertwined with the direction of fibers, creating space by the district. Above all aspects reinforce the soil. As through the fiber reinforced soil triaxial test Equivalent additional stress method advanced by Li Guang-xin, we can see that in the axial pressure, adhesive force will occur between fiber and soil, and the greater the pressure, the more closely fiber and soil contact. So if increase the lateral pressure, with the result that the soil compression as well as shear strength will increase.Chapter four is the emphasis of the paper. We had a dynamic characteristics test on randomly distributed fibers reinforcement fly ash soil. Fly ash and soil will be carried out by 1:2, then produce the specimen which contains 19% water. We can get the following conclusions:First determine the polypropylene fiber content of 1% through the unconfined compressive strength test. The results showed that, when the polypropylene fiber content is 1%, the unconfined compressive strength of the fiber enforcement fly ash soil is 74% higher than non-doped fiber fly ash soil. When the polypropylene fiber content continues to increase as well as pulverized coal - lime achieves the same strain conditions, the unconfined compressive strength has declined.Followed by a dynamic triaxial testing, at first determine the dynamic modulus of the fly ash before and after the fiber is added. When the polypropylene fiber content is 1%, the reinforcement fly ash soil dynamic modulus increases 25.64% while fly-ash soil cohesion increased 37.11%, and dynamic strength increased 28.37%. The dynamic strength of fly ash soil increases when the surround pressure increases. When the number of the damaged week of surround pressure increases, the dynamic strength of fly ash soil decreases. The resistance of liquefaction strength of randomly distributed fibers reinforcement fly ash soil has been increased greatly. When N f=5it increases by above 40%; when it increases by above 30%; whenThe main reasons that the strength of polypropylene fiber reinforcement fly ash soil is increased after analysis are that: on one hand, the cohesion of the fly ash soil is increased in the polypropylene fiber reinforcement fly ash soil, according to the formulaτ=σtan ?+c the fly ash soil can withstand more shear stress after the fiber is added, that is to say the dynamic shear strength is improved, thereby enhancing the resistance of liquefaction strength. On the other hand, polypropylene fiber in the random distribution of soil prevents the rise of pore water pressure, making the soil liquefaction more difficult and therefore enhances its resistance of liquefaction strength.After analysis of the research, we found that the unconfined compressive strength, dynamic shear strength, dynamic modulus and the resistance of liquefaction strength of polypropylene fiber reinforcement the fly ash soil have been substantially improved .So randomly distributed polypropylene fibers reinforcement fly ash soil is an effective measure to increase the strength of the fly ash soil. But we still don't have perfect formula to refer to so further study and improvement is needed.