Study On Liquefaction Resistance Of Basalt Fiber Reinforced Sand Soil

The foundation instability caused by the liquefaction of saturated sand is one of the common earthquake damage phenomena.Large-scale slippage caused by liquefaction seriously threatens the safety of various infrastructure and lifeline projects.In order to reduce various hazards caused by the liquefaction of sandy soil,it is necessary to increase the strength of the site soil.At present,the main reinforcement method is to mix randomly distributed fiber materials into the sand to improve the strength of the sand.Most of the previous studies focused on the static properties of sand after reinforcement,but relatively few studies on the dynamic properties,especially the liquefaction characteristics.In order to systematically study the effect of basalt fiber reinforcement on the liquefaction resistance of sand,this paper uses a vertical-torsional two-way coupled shear instrument to add 0% to Fujian standard sand and fine sand with a relative compactness of 50%.,0.5%,1% and 1.5% basalt fibers were subjected to a series of cyclic torsional shear tests under consolidated undrained conditions to analyze the liquefaction resistance of fiber-reinforced sand and its influencing factors.By analyzing the pore water pressure curve,stress-strain relationship and effective stress path curve of saturated sand under different test conditions,the main research work and conclusions of the thesis are as follows:(1)The incorporation of basalt fibers has a constraining effect on the sandy soil.Under the action of cyclic loads of different amplitudes,the fibers inhibit the liquefaction process of the sandy soil and the strain under the action of cyclic loads.The content of basalt fiber has a significant influence on the dynamic strength of Fujian standard sand,and the selection of a reasonable proportion of fibers can make the fiber reinforcement effect to be optimal.(2)Basalt fiber also has a significant effect on the improvement of the liquefaction resistance of fine sand.Due to its poor particle gradation,fine sand is prone to liquefaction.By adding basalt fiber,the sand particles and fibers are brought into contact and the internal friction is increased.Compared with pure sand,fiber-reinforced fine sand has stronger liquefaction resistance under cyclic loading,but the growth mode of pore water pressure and stress-strain change mode of sand are not affected by the addition of fibers.to change(3)The change of the load frequency will affect the liquefaction mode of the fiber-reinforced sand.Under the high-frequency load,the bearing capacity of the sand decreases significantly,showing a "softening" liquefaction characteristic,and the shear stress and effective stress are stable at "zero".nearby,showing shrinkage.The stress path curve shows a gradually shrinking "butterfly airfoil" after the sand is liquefied,and the incorporation of fibers will still increase the number of fluctuations that the sand needs to experience to reach "zero" effective stress under high-frequency loading.(4)The shear modulus of each stage after liquefaction decreases with the increase of reference shear strain.Under the action of large dynamic shear stress,the attenuation trend of shear modulus of sand is slowed down by the addition of basalt fiber,but this effect is not obvious under the action of small stress.and the effect of fiber is only reflected in the small strain stage of sand sample after liquefaction.The cyclic loading amplitude has no obvious effect on the shear modulus and its attenuation characteristics of the stress-strain curve of basalt fiber reinforced sand in the zero effective stress stage and strength recovery stage under the condition of extra-large deformation after initial liquefaction,but the influence on the shear modulus in the reverse unloading stage is relatively large and the law is obvious.