Study On Strength Of Red Clay By Rubber Powder Under Freeze-thaw Cycles

Red clay is often used as subgrade filling material of expressway,which has special engineering characteristics such as high moisture content,high plasticity and high void ratio.In order to improve the strength characteristics of red clay as subgrade filler and increase the stability of subgrade engineering.Through the triaxial test,over depth of field test and physical adsorption test,the improvement effect of different content and mesh of rubber powder on red clay was studied,and the appropriate mesh and dosage of rubber powder to improve red clay were determined.The strength characteristics of rubber powder to improve red clay under the freeze-thaw cycle were further explored.With the help of triaxial test,over depth of field test and physical adsorption test,the strength,appearance and The law of pore volume change.The main conclusions are as follows:1.Under the same confining pressure,the peak strength increases first and then decreases with the increase of the content.When the content of rubber powder is between 3%and 5%,the shear strength of red clay can be greatly improved.Under the same content,compared with 4 mesh,12 mesh and 100 mesh rubber powder,60 mesh rubber powder has better improvement effect on red clay.2.The surface morphology of plain red clay and rubber powder modified red clay was analyzed by the ultra depth of field microscope.The 3D Surface comparison shows that the addition of rubber powder makes the area of relatively flat area expand obviously,the area of holes decreases,and the surface becomes relatively smooth.The addition of rubber powder fills the pores between particles and the pores on the surface of red clay to a certain extent.The contact area becomes larger,the friction between particles increases,and the shear strength increases.3.The shear strength of the rubber powder improved soil is significantly higher than that of the red clay plain soil,and with the increase of freeze-thaw cycles,the shear strength of the rubber soil generally keeps constant first and then decreases rapidly.When the number of freeze-thaw cycles is less than or equal to 3,the peak shear strength of the improved red clay changes obviously,but with the increase of the number of freeze-thaw cycles,the peak shear strength changes little.4.Comparing the histogram of soil pore volume distribution,it is found that the pore size distribution curve of the sample is approximately similar,the peak value appears at about 2-5nm before freezing and thawing,and the pore volume occupied by large pore is larger after the pore size is greater than 10nm.With the increase of freeze-thaw cycles,the characteristics of the pores in the soil also changed.After the first and third freeze-thaw cycles,the content of the pores in the soil decreased significantly,and the content of the macropores increased greatly.After the seventh freeze-thaw cycles,the changes of the pores tended to be stable.