Mechanical Properties And Reinforcement Mechanism Of Lignin-modified Loess

Loess is a special quaternary unconsolidated sediment with overhead pore,weak cementation and rich soluble salt.It has a strong disaster risk under the external stress.The improvement of the mechanical properties of loess is an important way for foundation treatment,tunnel protection and slope treatment in loess area.In this paper,lignin with good adhesion,chelation,corrosion resistance and environmental protection is used as the modified material.This paper aims at the mechanical properties and reinforcement mechanism of lignin-modified loess.Based on the basic physical and mechanical property tests,scanning electron microscope(SEM)and X-ray diffraction(XRD).The basic physical properties,compressive strength,shear strength,dynamic modulus,damping ratio,dynamic residual strain,microstructure and mineral components of lignin-modified loess were studied.The main research results:(1)The influence of lignin content on the basic physical properties of modified loess was revealed.With the increase of lignin content,the specific gravity and plastic index decrease obviously and the content of clay and sand increase,while the content of powder decreases.After the addition of lignin,the water stability of the modified loess is significantly improved,which reached the optimum when the lignin content is 1%-2%.Under the same matric suction,the modified loess with lignin content of 1%-2% has better water-holding capacity.(2)The change of compressive strength and shear strength of modified loess with the lignin content was studied.The unconfined compressive strength of the lignin-modified loess increase first and then decrease with the increase of lignin content.It increases gradually with the increase of curing age.The compressive strength of the modified loess with curing age of 28 days and lignin content of 1% was significantly higher than that of the modified loess with other curing ages and lignin contents.The shear strength of the modified loess with lignin content of 1% is the greatest under each confining pressures.Cohesion plays a major role in the shear strength of lignin-modified loess,but internal friction angle has little effect.(3)The dynamic characteristics of the lignin-modified loess were systematically analyzed,and the optimal seismic ratio of the lignin-modified loess was proposed.When the lignin content is 1%,the maximum dynamic elastic modulus of the modified loess reaches the maximum.Under the same dynamic strain,the modified loess with lignin content of 1% has the smallest damping ratio,the slowest increase in dynamic residual strain,and the smallest residual strain under the same dynamic stress,showing the best dynamic stiffness characteristics and seismic collapse resistance.(4)The reinforcement mechanism of lignin-modified loess was discussed.Lignin can effectively fill the pores and enhance the cementation strength of the loess.The porosity and average pore area of modified loess decreased significantly.The lignin-modified loess does not produce new mineral components.The reinforcement mechanism of lignin-modified loess includes the intercalation of lignin,the cementation effect,the network structure reinforcement,the mineral strengthening effect.