Study On Deformation And Stability Of Improved Loess Foundation In Filling Area Under Strong Earthquake

With the gradual implementation of the The Belt and Road and the rural revitalization strategy,the construction of towns and cities in the loess areas of northwest China has been developing rapidly.In order to ensure economic construction for the benefit of the people of the land,the project builders have long been using means such as cutting mountains and filling ditches to transform the unique beam,mount and loess landform types in the loess area.However,due to the characteristics of loess itself such as collapsible and vulnerability,and the loess area is China's high frequency and high intensity earthquake area,some construction sites in the loess area also gradually show some problems.Loess slope fill site due to fill area soil by construction time,construction equipment and other factors,part of the building located on the fill foundation has appeared successively due to the failure of the fill foundation soil and foundation deformation,foundation cracking and other safety hazards,coupled with the high-frequency susceptibility to earthquakes in loess areas,which has seriously threatened the economic construction of loess areas and the safety of people's lives and property.This paper is based on a site investigation of loess slopes,study of loess fill sites in seismic areas as the target.A series of indoor tests were conducted with fly ash reinforced composite improvement method to investigate the improvement effect of fly ash reinforced composite improvement method on the properties of loess from the perspective of improving the physical parameters of loess.Using the indoor test results,shaking table model tests were conducted to investigate the deformation and seismic resistance of different slope treatment methods of the fill slope model with fly ash reinforced composite improved fill foundation under strong seismic effects.Combined with numerical simulation methods,a multi-parameter discrepancy model is established to explore the relationship between different parameters on model deformation and seismic resistance.The research methods and conclusions used in this paper provide new ideas for the study of seismic resistance of foundation treatment in the fill area,and the research results achieve the purpose of seismic mitigation and disaster prevention,which can provide reference and basis for the seismic protection in northwest China.The main conclusions of this paper are as follows:(1)The maximum dry density of loess after improvement with fly ash showed a trend of increasing and then decreasing with the increase of fly ash incorporation ratio,in which a better improvement effect was obtained when the fly ash incorporation ratio was between 15% and 20%.The straight shear test on the specimens modified with fly ash shows that the shear strength and friction angle are greatly improved,and the shear stress is enhanced by a minimum of 4% and a maximum of 42%.Thus,the use of fly ash for improvement can significantly improve the seismic performance of the soil itself and reduce the deformation and damage of the soil.(2)Soil specimens after fly ash reinforced composite improvement are affected by the size effect and test method in the test,the cohesive force of the reinforced improved soil is smaller than that of the improved soil in the unreinforced state,and the friction angle of the reinforced improved soil is larger than that of the unreinforced state specimens,and the increase of the friction angle is up to 13%-17%.(3)The deformation and damage of the large shaking table model of the filler foundation after using fly ash reinforcement mainly occurred in the junction area between the original slope site and the filler,and the test results showed that the crack width at the junction of the treated slope and the filler area was about 1-2 mm,while the crack width on the untreated side was up to 6 mm,and the foundation on the untreated side sank about 8 mm.Therefore,the stepped treatment implemented for the filler slope can effectively reduce the surface damage and foundation sinking caused by The step treatment for the fill slope can effectively reduce the surface damage and foundation subsidence at the junction caused by the earthquake.(4)The peak acceleration measured by the accelerometers placed from low to high in the shaking table model test shows a more obvious elevation amplification effect,which increases with the increase of earthquake intensity,and the amplification factor is about 3.The peak acceleration of the stepped side can be reduced by about25% compared with the untreated side at the same height and under the same working condition of earthquake.(5)The average PGA amplification factor for the model with stepped treatment side is about 2.24 at seismic intensities of ?,?,and ?.The average amplification factor for the treated side using ordinary slope is 3.68,and the recommended height-to-width ratio of the steps is 1:2.