Durability Effect Of Strength Characteristics Of Lime-metakaolin Modified Silty Sand

Existing earthen sites in their storage areas affected by the meteorological environment and geological environment will produce diseases of different degrees,and even lead to the collapse of earthen sites.Therefore,it is necessary to reasonably formulate the protection and reinforcement work for the earthen sites,and after years of practice,it has been shown that the rational selection of restoration materials is the key to the protection of the earthen sites.Therefore,it is of great significance to carry out research on the protection and restoration materials of earthen sites.In the early stage,the author conducted a study on the mechanical properties of silty soil in the synergistic lime improvement site of the partial kaolin,and found that the lime kaolin(L-MK)has the possibility of replacing water hard lime(NHL),but its durability characteristics are unknown.The indoor freeze-thaw/dry-wet cycle test was carried out with L-MK improved soil as the main research object,and the mechanical strength,mass loss and microscopic mechanism of the sample under the 0/5/15/30 freeze-thaw cycle and the0/5/10/15 dry-wet cycle cycle were compared with NHL.The main research contents and conclusions are as follows:(1)The quality of L-MK and NHL specimens showed a decreasing trend after freeze-thaw cycle and dry-wet cycle.The mass loss of L-MK and NHL specimens in the first 5freeze-thaw cycles was close to linear reduction,and after 5 cycles,the mass loss became more and more gentle,which was caused by the dispersion loss of soil water during the initial freeze-thaw process,and after 30 freeze-thaw cycles,the overall reduction in quality was12.19%to 13.37%;Compared with NHL,L-MK has a slightly weaker effect on maintaining the integrity of pore structure after soil undergoes dry-cycle.(2)After 30 freeze-thaw cycles,the L-MK compressive strength decrease is 74.96%-77.88%,which is slightly better than NHL(about 95%),and the L-MK compressive strength value is about 5-8 times that of NHL;After 15 dry-wet cycle,the attenuation amplitude of L-MK compressive strength is between 22.62%and 41.34%,which is about 2-3 times the strength of NHL.Multiple water-soil interactions damage the native structure of the soil and the inherent cementation between particles,resulting in a decrease in the compressive strength of the soil.However,the increase in the amount of kaolin soil improves the freeze resistance of the soil and improves the water stability of the soil.(3)The tensile strength of L-MK and NHL is reduced to varying degrees by the effects of wet and dry and freeze-thaw cycles,and the attenuation of soil strength is mainly concentrated in the first 5 freeze-thaw cycles,after which the soil strength loss is significantly reduced.(4)The L-MK stress-strain curve has obvious peak strength when it has not undergone freeze-thaw and wet-dry cycle,which belongs to the strain softening type,and the peak strain?_f decreases with the increase of the number of freeze-thaw and dry and wet cycles.Under the action of dry-wet cycle,the softening of the L-MK stress-strain curve did not change significantly,but the softening of the curve weakened under the action of freeze-thaw cycle,and the sample failure form gradually approached the plastic damage from brittle destruction,which was the increase of the amount of kaolin blending to enhance the brittleness of the specimen and the weakening of granularity(plasticity).Since the more brittle the soil,the greater the probability of sudden brittle damage when subjected to force,so in the restoration of earthen sites,it is necessary to reasonably determine the amount of MK,that is,on the basis of meeting the requirements of force and deformation,a lower dosage is selected.(5)The hydration products Ca(OH)₂,CSH and C₄AH₁₃ generated by the L-MK reaction were filled with the main skeleton of the structural pores of the L-MK modified soil;After the freeze-thaw cycle and the wet and dry cycle,the content of CSH and C₄AH₁₃ decreased,but a little Ca(OH)₂ was produced during the freeze-thaw process,but Ca(OH)₂ did not change before and after the dry-wet cycle.(6)Combining the exponential decay function with the linear regression method,it is obtained that the change of the strength of the improved silty soil with the number of freeze-thaw cycles basically follows the function q_u=abⁿ+c attenuation,so as to establish the strength attenuation model of L-MK and NHL modified silty soil under freeze-thaw and dry-wet conditions b?n=(q_u-q_uln)/(q_o-q_uln),and the goodness of fit R² is above 0.99,and the correlation is high.(7)Combined with the quality loss,mechanical strength and microscopic mechanism of the specimen,from the perspective of durability,the use of 6%L+4%MK can effectively replace 8%and 10%NHL for earthen site protection.