Model Test Study On Soil Nailing Wall Retaining Structure In Loess Foundation Pit

Excavation engineering is innovated and improved with the development of subwayengineering,urban underground space applications,and foundation engineering of building asa branch of geotechnical engineering.With the accelerating process of China’s large-scaledevelopment of the western region,high-rise buildings and structures in loess area areemerging,the excav ation and support technology of excavation engineering will also continueto improve and standardize.With the excavation of foundation pit engineering becoming moreand more difficult,during the design,theoretical calculations,monitoring and control,andindoor model test of excavation and support of foundation pit,higher requirements areattached,on the basis of meeting the practical requirements of supporting foundationpit,engineering requirements of advanced technology,simple construction,economic andreasonable,small impact on the surrounding environment are strived to achieve.Although many scholars at home and abroad have done a lot of research and calculationwork in foundation support,rely the foundation pit support only on theoretical calculationsand analysis is not enough.The complexity,uncertainties and external disturbances will affectthe excavation and support of pit,so there are still a lot of problems in the field of researchneed to be improved.Soil nail wall support,compared with the other supporting structures,is a technicallyfeasible and economically reasonable support technology with simple construction,which nowis widely used in foundation support.But so far, the theoretical calculation and analysis of soilnailing wall technology is not perfect, and further research on this field is needed,thefollowing two phenomena often appear in the practical application of the soil nail wallsupporting:(1)due to the problems of engineering investment,in order to save costs,the designers ofthe pit would be too aggressive in the design,resulting in large deformation of the soil nailingwall pit,which can give rise to major engineering accident.(2)In the design of soil nailing wall structure,in order to ensure the security and stabilityof the pit during excavation,the designers improve the safety factor of the pit too much,resulting in the waste of the project investment.Based on the present researching situation on soil nailing wall supporting,the authordesigns and develops a whole set of model test device,and simulate the process of excavationand even overloading on slope top in engineering,change in soil pressure,force act on the nails,and displacement of the surface layer is tested, the internal law is obtained by summarizationand analysis,and some valuable results are included as follows: (1)When soil in lower layer is excavated,topsoil will continue to experience lateraldeformation.However,the lateral displacement resulted from the excavating subsoil does notmake the upper layer soil produce the same displacement,but it is certain that the subsoilexcavation will cause the increase the internal force of the upper layer of soil nails.(2)According to the surface displacement values measured in model test,it can beanalyzed that the amount of displacement of the nail wall slope support is presented as big onupper layer,small on sub layer,deformation mode is shown as belly drum surface.(3)The following conclusions can be obtained by analyzing experimental data measuredin different conditions:The supporting effects when horizontal and vertical spacing of soil nailis10x15cm is better than that is12x15cm.The supporting effects when nails are insertedinto the soil with a angel of9°is better than that of5°,and there will be a smaller degree ofdeformation and failure compared with5°.Comparing the measured data of the fifth kind ofworking condition in which the nail is long on top and short on bottom,it is concluded that theeffects of controlling stability,deformation and failure is not as good as the previous fourconditions.Sum up and compare the five conditions,the effect of excavation support of thethird condition is the best,and the amount of excavation deformation is the smallest.Finally,the paper summarizes the comprehensive work put forward,based on this topicremains to be further studied some problems.