Experimental Study On Mechanical Properties Of Fiber Loess Under Freeze-thaw Cycles

The fiber reinforced soil is a kind of composite soil,and the fiber and the soil are uniformly mixed in proportion to improve the physical and mechanical properties.The western part of China is in seasonal frozen soil areas,and the freeze-thaw cycle poses a threat to the stability of build-ings,which will affect the normal use and safe operation of the proj ect.In this paper,Xi'an loess was taken as the research object,and the polypropylene fiber was used as the reinforced material to improve the loess.The effects of fiber blending ratio,fiber length and number of freeze-thaw cycles on the strength and stress-strain relationship of fiber loess were investigated through la-boratory tests.The actual project construction in the land area has certain theoretical guiding sig-nificance.For the fiber loess with different fiber blending ratios(0%,0.2%,0.4%,0.6%)and different fiber lengths(6mm,9mm,12mm),after 0,1,3,and 6 times in the freeze-thaw cycle,The labor-atory tests of conventional triaxial shearing,direct shearing and unconfined compressive strength were carried out to study the mechanical,strength and deformation laws of fiber loess after un-dergoing freeze-thaw cycles under different factors.Get the following conclusions:(1)In the triaxial shear test of consolidated drainage,after the number of different freeze-thaw cycles,the generalized shear stress increases with the increase of confining pressure,and the stress-strain curve is hardened;the fiber incorporation ratio is 0,6%.When the fiber length is 9mm,the reinforcement effect is optimal.After the freeze-thaw cycle,the cohesive force of the fiber loess decreases,while the internal friction angle increases.Under each factor,the coefficient of reinforcement effect of fiber loess is greater than 1,indicating that the fiber increases the strength of the soil and constrains the deformation.(2)Through the direct shear test,after varying the number of freeze-thaw cycles,the shear strength and cohesion were the largest at the fiber blending ratio of 0.6%and the fiber length was 9 mm,and the internal friction angle was not obvious.With the increase of water content(15%,1 8%,2 1%),the shear strength parameter decreases;as the number of freeze-thaw cycles increases,the cohesive force decreases and the internal friction angle increases slightly,but the amplitude is small.(3)Combined with the unconfined compressive strength test,it is found that the strength and deformation of the fiber loess is better than that of the plain soil after the freeze-thaw cycle,indicating that the fiber can resist the freezing and thawing cycle and deformation.The stress-strain relationship curve exhibits a softening type,and the compressive strength value is the larg-est when the fiber blending ratio is 0.4%and the fiber length is 9 mm.(4)Based on the results obtained by the conventional triaxial shear test,the specific param-eters of the Duncan-Chang model were obtained.The variation of the parameters with the fiber blending ratio and the number of freeze-thaw cycles showed that K,n,G,F,Kb,The change law of m is obvious.The deformation trend model of the Duncan-Chang model parameters under the freeze-thaw cycle is established,which further confirms that the fiber enhances the strength and overall deformation stability of the loess,and the fitted equation provides theoretical support for numerical simulation.