Experimental Study On Physical And Mechanical Properties And Microstructure Of Red Clay Contaminated By NH₃·H₂O In Guilin

After the middle and late 20th century,with the continuous and rapid development of economy and increasingly serious man-made pollution,the problem of contaminated soil has been paid more and more attention by scholars.This research was supported by Guangxi Natural Science Foundation?2017GXNSFAA198213?and Guangxi Key Project of Department?KY2015ZD055?,ammonia?NH₃·H₂O?solution was used to immerse the red clay in Yanshan,Guilin.Taking into account the double factors of ammonia concentration?0?4.5%?9.5%?13.5%?18%?and time?1d?7d?14d?,a series of tests were carried out.The effect of ammonia pollution on the physical and mechanical properties and micromechanism of red clay in Guilin was analyzed.The main research results are as follows:?1?The physical properties test results show that:with the increase of NH₃·H₂O mass fraction and curing time,the mass,moisture content,specific gravity and pore ratio of red clay increase gradually,and the whole performance is mass,moisture content and specific gravity.The increase of porosity ratio was greater than 13.5%to 18%of NH₃·H₂O mass fraction,the rate of increase was the fastest in the first 7 days,and slowed down after 7 days.The liquid limit and plastic limit of red clay increased gradually,and the maximum amount of increase occurred at the mass fraction of NH₃·H₂O 18%and the curing time 14 days respectively.?2?The experimental results of mechanical properties show that:the compressive modulus of contaminated red clay decreases with the increase of NH₃·H₂O mass fraction in curing time.The shear strength of red clay decreases with the increase of mass fraction of NH₃·H₂O,while the shear strength of contaminated red clay increases with the prolongation of curing time when the mass fraction of NH₃·H₂O is in the range of 0%and 18%,respectively.With the increase of the mass fraction of NH₃·H₂O,the curing time is certain.When the mass fraction of NH₃·H₂O is constant,the pollution of red clay is increased with the increase of curing time.?3?The experimental results of microstructure properties show that:with the increase of NH₃·H₂O mass fraction and curing time,he microstructure of the soil changes as follows:the surface of soil particles is smooth,with few pores and compact aggregates,most of which are laminated or laminated?the surface became rough,the pores became larger,and a small number of granular bodies appeared?and the structure of the agglomerate is gradually changed to be loose,the pores are dispersed,and an overhead structure is formed.The changes of physical and mechanical properties of red clay caused by NH₃·H₂O solution invading red clay can be explained by alkali-soil interaction.The cementitious material formed by the reaction of NH₃·H₂O solution eroding red clay is filled with soil particles.The bound water film on the surface of soil particles gradually thickens,and the volume of soil expands,resulting in the mass,specific gravity and pore ratio of soil particles increasing gradually.At the same time,the cements between soil particles are consumed,resulting in the destruction of the original structure of red clay.The plastic limit of red clay is increased;A series of OH^-ionized by hydrolysis and cementitious minerals?SiO₂,Al₂O₃?in red clay The physical and chemical reaction causes the cement between the contaminated red clay soil particles to be dissolved and then to form the flocs again,which leads to the decrease of the cementation ability between the soil particles,the change of the original stable structure state of the soil,and the enhancement of the deformation ability.The compressibility of soil increases.