Study On Statics And Dynamic Characteristics Of Fiber Reinforced Soil

The study of the strength properties of soils is one of the important topics in the field of geotechnical engineering.In engineering practice,soils generally cannot directly meet engineering needs and often need to be treated with reinforcement techniques to improve the mechanical properties of soils and ensure the safety of construction projects.At this stage,soil improvement techniques usually use cement and artificial reinforcing materials mixed into the soil,but few scholars use natural plant fibres as the improvement material for soil strength.Compared with cement and artificial reinforcing materials,natural plant fibres have the advantages of being green,low cost and widely available,but there is still a lack of research on the mechanical properties of natural plant fibre reinforced soil.Therefore,in this thesis,three natural plant fibres,namely straw,palm and ramie,were selected as the soil strength improvement materials,and the static and dynamic properties of fibre-reinforced soil were investigated.The optimum reinforcement lengths and rates for different fibre-reinforced soils were obtained,and the microscopic reinforcement mechanisms of different fibre-reinforced soils were further explained by SEM scanning.The main research and conclusions of this thesis are as follows:(1)The magnitude of compressive strength of straw,palm and ramie fibre reinforced soils was investigated using the unconfined compressive strength test.The optimum reinforcement length of 20 mm and the optimum reinforcement rate of 0.2% for straw fibre reinforced soil,20 mm and 0.3% for palm fibre reinforced soil,and 16 mm and 0.4% for ramie fibre reinforced soil were found at an optimum moisture content of 18%.(2)The shear strength of straw,palm and ramie reinforced soils was investigated using the direct shear test.The test showed that the shape of the shear stress-shear displacement relationship curve of the reinforced soil specimens was strain-softening type,and the optimum reinforcement ratios of the three fibre reinforced soils were obtained by comparing the cohesion and internal friction angle of the three reinforced soils under different reinforcement conditions.(3)The static strength properties of the three types of reinforced soils,namely straw,palm and ramie,were compared under the optimum reinforcement rate and reinforcement length,and the results showed that the palm fibre reinforced soil had the best mechanical properties.(4)SEM was used to study the surface structural properties of the three plant fibres and the mechanism of reinforced soil tendon-soil interaction.It was found that the tendon-soil combination of the three fibres conformed to the bending mechanism and interweaving mechanism of fibre-reinforced soil,and formed a tight framework structure in the soil,which could provide compressive and shear resistance to the soil.(5)The dynamic properties of fibre-reinforced soils were investigated using resonant column tests.It was found that the dynamic shear modulus of fibre-reinforced soil specimens decreased with increasing dynamic shear strain and the damping ratio decreased with increasing dynamic shear modulus.The normalized curves of the dynamic shear modulus ratio and damping ratio of fibre-reinforced soils in the range of 10-7 to 10-3 were quantified by fitting the Hardin-Drnevich hyperbolic model and averaging,which showed that plant fibre-reinforced materials can improve the dynamic response of soils.