Post-construction Settlement Prediction Of Gully-type Loess High-fill Foundation And Foundation Treatment

In order to solve the shortage of construction land in the Loess Hilly and gully region of Northern Shaanxi,cutting hills to backfill ditches and artificial land creation have been implemented.A lot of loess high fill foundationshave been formed.However,it also have brought a series of geological and geotechnical problems,among which the post construction settlement of high fill is one of the hot topics.Based on loess high fill project in Yan’an new area,this study investigatedthe physical and mechanical properties of compacted loess and its microstructure evolution process,the settlement law of loess high fill,the post construction settlement prediction of loess high fill under self-weight and load,the foundation treatment and planning utilization of high fill site,to provide technical guide for similar projects.The main research contents and results are as follows:(1)The whole process monitoring of the gully loess high fill project with the maximum filling thickness of 90 m in the research area during the construction period and later stage was carried out.The changes of the settlement and water content of the primary foundation and filling body during filling were measured basically.The relationship between the filling thickness and the total settlement and the settlement during the construction period was discussed.And the whole process variation of layered settlement was analyzed.(2)The sdudy on mineral composition,physical and mechanical properties and permeability of compacted loess were carried out.By means of SEM and NMR,the evolution of microstructural parameters of compacted loess with different dry densities and water contents under wetting-drying cycles was investigated.The mechanism of compression deformation of compacted loess and the relationship between its permeability properties and microstructure were explained.(3)Based on the laboratory test and theoretical analysis,research on the post-construction settlement prediction of high loess fill foundation was carried out.The post-construction settlement prediction rheological model in primary state and groundwater level rising was established.The post-construction settlement control standard was put forward,then the stability time and settlement of high loess fill foundation with different compaction coefficient and different filling thickness were obtained.An improved model of growth curve for postconstruction settlement prediction was established by regression analysis of a large amount of settlement monitoring data.The influence of primary topography on the settlement of gully loess high fill was discussed.(4)A study on the prediction of post-construction settlement of loess fill foundations under extreme conditions(saturation + loading)was conducted by means of in situ test pit immersion loading tests.By means of numerical simulation with coupled stress and seepage fields,the whole loading and water infiltration process was reproduced,providing new insights into the prediction of post-construction settlement of loess high-fill foundations under loading.(5)Based on the analysis and summary of the existing foundation treatment technology of loess high fill site,the sensitivity analysis of differential settlement of loess fill foundation with different primary terrain slope and fill thickness was carried out,a sensitivity classification was made,and a recommended foundation treatment plan for loess high fill sites was proposed,providing a scientific basis for the planning and siting of loess high fill sites.