Study On The Mechanical Properties Of Composite Soda Residue Mixed With Fly Ash And Soft Clay

Soda residue is the industrial waste produced when producing soda ash by the ammonia-alkali process,the use of soda residues for engineering padding can not only solve the problems of land occupation and environmental pollution,but also effectively reduce engineering costs.However,the properties of soda residue soils directly used as engineering soil are poor,and many scholars have carried out a lot of research to obtain soda residue soils with excellent bearing performance.A variety of improved schemes for mixing fly ash,cement and other materials with soda residue soils were proposed.However,most of the previous studies have the following problems:the improvement plan lacks consideration of economic factors,resulting in high cost and difficult to implement;when the soda residue soils is mixed,the moisture content of the caustic slag is not clear,and the same scheme will lead to the addition of different soda residue soils moisture content.The dry mass of the soda residue soils is different,resulting in different test results,which makes it difficult to generalize the conclusion;the influence of complex stress conditions such as stress history and cyclic action on the mechanical properties of soil is not considered,resulting in limited soil application scenarios.For the above problems,24 kinds of composite soda residue soils mixed with fly ash and soft clay were designed.The optimum moisture content and maximum dry density of each mix ratio were determined by compaction test.According to the optimal moisture content and maximum dry density of each mix ratio,composite soda residue was prepared,and its unconfined compressive strength was measured.Synthesize unconfined compressive strength and economic indicators,and determine the optimal proportion by fuzzy evaluation method.The fuzzy evaluation method gives weights to economic factors,and considers the reinforcement cost while ensuring the mechanical properties.According to the optimal proportion of composite soda residue,the static test,dynamic test and triaxial creep test were further carried out,to explore the static shear properties,dynamic properties and creep properties of composite soda residue.And established relevant prediction models.In order to provide reference for the use of soda residues for foundation engineering padding.The main conclusions are as follows:(1)Soft clay and fly ash have obvious reinforcement effect on soda residue,the addition of soft clay can reduce the amount of fly ash,reduce the cost of reinforcement,and has good economic applicability.The optimal proportion of the composite soda residue is determined by the fuzzy evaluation method,which is the scheme that the fly ash is mixed with 10%,and the soft clay and alkali slag are mixed with 45%,its optimum moisture content is 33.95%and its maximum dry density is 1.253g/cm~3,and the unconfined compressive strength of the composite soda residue with the optimal proportion is about 140k Pa higher than that of the soda ash slag sample.(2)Static triaxial tests were carried out for the composite soda residue with the optimal proportion to explore its shear resistance under different confining pressure,over-consolidation ratio and eccentric pressure consolidation ratio.The effective strength index of composite soda residue is c’=48.02k Pa,φ’=21~°.Confining pressure,over-consolidation ratio and consolidation ratio have significant effects on the mechanical properties of composite soda residue.When the confining pressureσ_cincreases from 100k Pa to 200k Pa,the undrained strength of the composite soda residue increases by about 75%;when the overconsolidation ratio OCR increases from 1 to 6,the undrained strength decreases by about 50%;the consolidation ratio K increases from1 to 1.8,its undrained strength increases by about 30%。(3)Dynamic triaxial tests were carried out for the composite soda residue with the optimal proportion to explore its dynamic characteristics under the conditions of different confining pressure,dynamic stress ratio,over-consolidation ratio,bias consolidation ratio and cycle times.The cyclic cumulative plastic strain development model,cyclic cumulative pore pressure development model and cyclic strength weakening model of composite soda residue were established,and the reliability verification of the above models was completed.(4)Triaxial creep tests were carried out for the composite soda residue with the optimal proportion to explore its creep characteristics under different confining pressure and drainage conditions.By modifying the Singh-Mitchell creep model,the creep prediction model of the composite alkaline slag was obtained and verified.