Research On Deformation Of Cut-Fill Foundation In Loess Region

In order to research the deformation characteristics of cut-fill foundation,the settlement and horizontal displacement of cut-fill foundation are monitored at a filling project which is located at the Qingbaishi of Lanzhou.The specific work and research results are as follows:From the theoretical point of view,the differences in the pore ratio,saturation,water gravity and soil gravity of the original soil and the backfill soil have led to some differences in the foundation deformation.In addition,due to the age of the original soil,only the foundation deformation of the original soil under additional stress is generally considered,while the deformation of the backfill soil should be considered not only under additional stress but also under self-weight stress.The monitoring data of the post-excavation site deformation shows that,the settlement of the excavation junction foundation is mainly concentrated in the lower area of the backfill,which is more than 75% of the settlement.When the thickness of the backfill increased from 15 m to 20 m,the proportion of settling of the backfill to the total settlement of the foundation increased from 46.7% to 54.4%.The regression analysis method based on part of the actual data can be used to predict more accurately the settlement of the foundation of the excavation junction over time;the maximum horizontal displacement occurs at the top of the excavation junction,for a 30° slope,when the backfill thickness increases from 10 m to 20 m,the maximum horizontal displacement decreases from 135 mm to 65 mm.During the monitoring period,ground level displacement growth began to slow at the earliest at about 158 d,while settlement at the corresponding monitoring point showed no signs of slowing and continued to increase.The influence of different compaction,slope,backfill height,load distribution and load size on the foundation settlement and horizontal displacement at the excavation junction was studied by using FLAC3 D.The results show the horizontal displacement of the foundation is mainly concentrated in the backfill area above the intersection;the deformation of the backfill can be reduced by increasing the compaction of the fill,but when the compaction is increased to 0.93,the settlement and horizontal displacement of the foundation are no longer significantly reduced;the settlement and horizontal displacement of the backfill increases with increasing the slope of the intersection in the range of 30°-55°;the settlement of the foundation and the height of the backfill are roughly linear,but the load size has a weak influence on the horizontal displacement of the foundation;when the load is distributed in the original foundation,the settlement and horizontal displacement of the foundation is the smallest;if load is distributed in both the original foundation and the backfill area,the foundation will have the greatest deformation.Through field monitoring and analysis of numerical simulation results,it is believed that the uneven settlement of the soil along the direction of the slope leads to a certain degree of upward and downward misalignment of the foundation surface,while the horizontal displacement of the foundation is the main factor leading to the cracking of the cut-fill foundation;when the compaction degree increases to 0.93,slope control is below 30°,additional load distribution on the original foundation surface and control the construction quality can effectively reduce the foundation deformation at the fill and excavation junction.