Study On Bearing Characteristics And Corrosivity Of Soda Residue Soil Foundation In Complex Environment

The soda residue produced in the process of soda production by ammonia-soda method can be used as foundation soil,which can effectively solve the problems of land occupation and environmental pollution caused by soda residue accumulation.As a kind of foundation soil,the bearing characteristics and corrosivity of soda residue soil are two key factors to be considered in the design of engineering safety and durability.Previous studies have shown that the microstructure of soda residue soil is completely different from the general natural sedimentary soil,and its water content is higher,its void ratio is larger,and the bearing mechanism of soda residue soil is more complex.In the field of geotechnical engineering,at present,the research on the engineering properties of soda residue soil mostly focuses on the basic physical and mechanical properties.However,there is still a lack of systematic research on the bearing characteristics of soda residue soil under complex stress states,such as the static characteristics under different initial bias consolidation and over consolidation,the dynamic characteristics under cyclic load and the creep characteristics under long-term load.In addition,the high concentration of chloride ion rich in soda residue soil can lead to the durability damage of reinforced concrete structures,and no research work has been carried out on this problem at present.To sum up,the bearing characteristics and corrosivity of soda residue soil in complex environment still need to be further studied.Therefore,the basic physical and mechanical properties,the static,dynamic and creep properties of soda residue soil under complex stress conditions were studied by the combination of geotechnical test and numerical simulation;At the same time,the physical model test was carried out to preliminarily study the corrosion mechanism of soda residue soil on concrete structure.The specific work and conclusions are as follows:(1)Taking the undisturbed soda residue soil of Tianjin Port area as the test sample,a series of geotechnical tests such as moisture content measurement,density measurement,consolidation test and direct shear test were carried out.The results showed that the soda residue soil had low density,small specific gravity,poor permeability and high compressibility,and the void ratio and moisture content were much higher than those of general natural sedimentary soil.Through the indoor static triaxial test,the effects of complex stress states such as different consolidation confining pressure,overconsolidation ratio and biased consolidation on the static characteristics of soda residue soil were analyzed.Based on the statistical analysis of test data,the calculation formula of shear strength index of soda residue soil considering the the coupling effect of over consolidation ratio and bias consolidation ratio was proposed.(2)A series of dynamic triaxial tests of soda residue soil were carried out with overconsolidation ratio,cyclic dynamic stress,cycle times and cycle frequency as test variables.The dynamic characteristics of soda residue soil under cyclic load were studied.It was found that the cyclic cumulative pore pressure of over consolidated soda residue soil did not change monotonically with the increase of dynamic stress level.By analyzing the coupling effect of cyclic compression and shear dilation on cyclic pore pressure of soda residue soil,a cyclic pore pressure model of soda residue soil considering the influence of over consolidation ratio and cyclic dynamic stress was established.On this basis,based on Yasuhara equivalent overconsolidation model,a cyclic strength evolution model of soda residue soil considering the coupling effect of overconsolidation ratio and cyclic dynamic stress was proposed.(3)Through the triaxial creep test of soda residue soil,the creep characteristics of soda residue soil under different consolidation confining pressure,drainage conditions and load levels were deeply studied.The results showed that the consolidation confining pressure,drainage conditions and load level had significant effects on the creep deformation of soda residue soil,and when the load level was high,the creep curve of soda residue soil would not have obvious attenuation stability characteristics.Through the statistical analysis of creep test data,the creep prediction model of soda residue soil under drainage condition was established based on Mesri creep model.(4)Through the secondary development of ABAQUS,the strength index calculation formula of soda residue soil,the strength evolution model of soda residue soil under cyclic load and the creep prediction model of soda residue soil fitted in this paper were embedded into the numerical model,and a relatively complete finite element numerical simulation method of soda residue soil foundation bearing characteristics was established.In addition,taking the soda residue soil foundation project in Tianjin Port as an example,the effects of over consolidation effect,initial bias consolidation and cyclic loading on soda residue soil foundation bearing capacity were analyzed by using the loading coefficient method,and the settlement of soda residue foundation was predicted by numerical simulation.(5)Through the indoor test of chloride ion intrusion into concrete in soda residue soil foundation,the structural durability caused by chloride ion intrusion into reinforced concrete in soda residue soil base was preliminarily studied,and the distribution and diffusion law of chloride ion concentration in concrete adsorption area with the most serious erosion under soda residue soil foundation environment were revealed.Based on Fick’s second law,the chloride diffusion model of concrete adsorption zone in soda residue soil foundation environment was established.On this basis,the durability service life of reinforced concrete structure in soda residue soil foundation was predicted based on soda residue soil foundation project in Tianjin port area,and compared with that in marine environment.The results show that the durability problem of reinforced concrete structure in soda residue soil environment was more serious than that in marine environment.