| With the deployment of the national "14th Five-Year Plan" and the "dual carbon" strategy,promoting green and low-carbon development and promoting the construction of ecological civilization have become the theme of current social development.Under the encouragement and guidance of national policies,modern transportation facilities represented by expressways and high-speed railways will be built in large quantities.Loess is widely distributed in Northwest,North China and Northeast China,and its unique porosity,weak cementation,undercompression and other structural forms lead to collapsibility,disintegration and dissolution,which poses problems to engineering construction.The fiber reinforcement method has the characteristics of economy,environmental protection and durability.This method mainly forms a composite material by adding a certain quality of fiber to the soil,and the fiber is used to limit the deformation of the soil by virtue of its good tensile properties and friction and bite cooperation with soil particles.In this thesis,the influence of moisture content,fiber length,fiber content,confining pressure and cyclic stress ratio on the shear strength of basalt fiber reinforced soil was analyzed by carrying out triaxial consolidation undrained shear tests under static and dynamic loading.Combined with the microstructure of reinforced soil tested by scanning electron microscopy,the mechanism of basalt fiber reinforcement was revealed.Based on the results of static triaxial test,by analyzing the influence of basalt fiber on the cohesion force and internal friction angle of reinforced soil,a shear strength model of basalt fiber reinforced loess considering the correlation of fiber length,fiber content and fiber diameter was established.The main findings are as follows:(1)Under static loading,the stress-strain curve of the plain soil showed the strain weakening and softening type,while the stress-strain curve of the fiber reinforced soil showed the strain hardening type,and the shear strength of the reinforced soil was significantly higher than that of the plain soil.The peak strength of fiber reinforced soil increases with the increase of fiber length,fiber content and confining pressure,and decreases with the increase of moisture content.(2)Under dynamic loading,the dynamic strength of plain soil and reinforced soil decreases with the increase of vibration order,and increases with the increase of confining pressure,fiber length and fiber content,and the dynamic strength of reinforced soil is significantly higher than that of raw soil.The dynamic strain of plain soil and reinforced soil showed a trend of first increasing and then stabilizing with the increase of the amplitude,while it increased with the increase of cyclic stress ratio,and the dynamic strain of reinforced soil was significantly lower than that of primitive soil.(3)The comprehensive test results show that the optimal reinforcement conditions for basalt fiber reinforced loess under static loading and dynamic loading are fiber length of 16 mm and fiber content of 0.8%.(4)The mechanism of fiber reinforcement is divided into one-dimensional rib action and three-dimensional space grid action.The force deformation of reinforced soil will cause misalignment between the fiber and the soil particles,and promote the interfacial friction and adhesion of a single fiber.A large number of randomly distributed fibers are intertwined into a network,and when one fiber is pulled,other fibers will be pulled together to form a three-dimensional force network,thereby transmitting the local loading to a wide area.(5)The cohesion and shear strength data of fiber reinforced soil were evenly distributed on both sides of the predicted and measured bisecting line,which confirmed that the calculation results of the shear strength model were in good agreement with the test results,verified the reliability of the model,and showed that the model was suitable for predicting the shear strength of basalt fiber reinforced loess. |
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