Laboratory Study On Shear Strength And Permeability Characteristics Of Red Mud-Lime Soil

Red mud is slurry residue produced during alumina extraction from bauxite,the increasing aluminum output correspondingly increase the red mud generated.Red mud is disposed in landfills and stored for long term in large lagoon-type impoundments,and the large stockpiling of red mud generate the disposal problem,which not only bring about land occupation,but also wreak havoc on soil,ground water and air.The economic utilization of red mud could solve the above problems.Red mud appear reddish brown due to the presence of SiO₂,Al₂O₃ and other components.It has characteristics of adsorption,gelling,condensation and accumulation in water.While,the disadvantages of thermal shrinkage and drying shrinkage of lime soil are liable to produce crack in construction and lead to destructive damage.The addition of red mud as a substitutive material in lime soil can improve the strength and engineering performance of lime soil and simultaneously solve the resource utilization of red mud.Hence,the aim of this research is to investigate the shear strength and permeability characteristics of red mud-lime soil through laboratory tests.The impact of the addition of red mud on the shear strength,complex resistivity parameters and permeability coefficient were studied through direct shear test and permeability test.Moreover,the solidification effect and solidification mechanism were investigated.Through the direct shear test and nondestructive resistivity testing,the relationship between shear stress and displacement,shear stress and strain of modified soil were obtained.The red mud content,vertical pressure and curing age were deemed as variable on shear test,and the variation of complex resistivity parameters were recorded during the test.Consequently,the correlation between shear strength and complex resistivity were established.Through the permeability test,the impacts of red mud content,initial moisture content,void ratio and curing age on permeability coefficient were revealed,the conclusions are as follows:?1?In the direct shear test,with the increase of shear displacement,the shear stress increased,the growth rate in the process appeared slow-fast-slow trend.During the rapid growth of shear stress,the shear stress-displacement curve increased linearly.As the strain increases,the shear stress increased gradually.The optimal red mud content for shear strength is 42%⁴8%.With the increase of vertical pressure,the shear strength increased linearly.The curing process of specimens contributed to the improvement on the shear strength and solidification performance.?2?The current frequency affect the amplitude and phase angle of specimens.As the current frequency increases,the complex resistivity amplitude declined rapidly and followed by a tardiness reduction.The trend of phase angle exhibited"U"shape.The data under 50kHz current frequency were opted for further study.The complex resistivity amplitude increases with the slide of the shear plane.?3?As increase in the red mud content and vertical pressure indicated a negative impact on the complex resistivity amplitude,and the amount of movable ions and pore structure transformed.The amplitude of complex resistivity increased logarithmically over time,and the growth rate fell off at the later stage of curing.The non-destructively measurement of the variation of complex resistivity parameters in shear process manifested the shear deformation of soil.The variation of complex resistivity amplitude-curing age reflected the completion degree of internal reaction.?4?The incorporation of red mud can prevent the abrupt disruption of lime soil as well as improve its impermeability.Increasing the weight percentage of red mud reduced the permeability coefficient of the solidified soil gradually.The stabilized soil shows optimum impermeability with higher compactness at the optimum moisture content condition.It was noted that the increase of void ratio greatly affected the permeability coefficient.The permeability coefficient of the specimens decreases over time.?5?According to the results of the direct shear test and permeability test,the large-scale utilization of red mud is feasible,the optimum red mud content is 42%.