| Large-thick Ness backfilling loess site is the inevitable product of urban extension in the Loess Plateau region.In recent years,the research on foundation treatment technology of this kind of site has become a key problem in the process of construction and development.The previous studies mostly take the embankment,airport,earth and rock dam as the research object,and have achieved a lot of fruitful results.However,there is still a lack of research on the large-thickNess backfilling loess site,and the understanding of such problems is not profound.On the basis of summarizing the domestic research status and combining with the actual geological conditions of the site,the study takes a typical backfilling loess site in Lanzhou New Area as the background to analyse the application of deep dynamic compaction method(SDDC)and sinking pipe compaction pile method in the foundation treatment of large thickNess backfilling loess site by combining field test with numerical simulation methods.Furthermore,the paper studies the mechanical characteristics of cast-in-place bored piles in the treated site foundation soil,and the results have a strong guiding significance for the treatment of similar sites.Based on the field tests of composite foundation bearing capacity,soil compaction coefficient of pile body,coefficient of soil compaction between piles and collapsibility of loess,this paper makes a detailed comparative analysis of the foundation treatment effects of deep dynamic compaction method(SDDC)and sinking pipe compaction pile method,and discusses the discreteness of the results and deviation from the standard values.Through field test,it is concluded that the pre-leaching method combined with the sinking pipe compaction pile technology is a feasible and effective foundation treatment method for large thickNess backfilling loess site.Through numerical simulation with finite element method,the study obtains the attenuation law of pile displacement,and gives the influence range of two foundation treatment methods.The influence range of SDDC compacted pile is 2 times of pile spacing,and the influence range of immersed tube compacted pile is 5 ~ 6 times of pile spacing.The stress transfer mode of the soil around the pile is given,and the lower part of the soil around the pile is the main stress area when the applied load is small or the pile spacing is large.When the applied load is large or the pile spacing is small,the whole area of the bearing pile and the soil around the pile bear the applied load.The main bearing area of bearing pile under two foundation treatment methods is given.For SDDC method,the main bearing area is more than 1/2 of bearing pile.For the compacted pile with sunken pipe,the main stress area is the upper 1/3 area.Through comprehensive analysis,it is concluded that the method of immersed tube compaction pile in this site is superior to that of SDDC compaction pile.Through the vertical compressive ultimate bearing capacity of single pile test,the study gets 43 m limit bearing capacity of bored piles and discovers the distribution of side friction resistance in recent accumulation of loess,powder sand layer and loess silt layer.Under the combined action of pile self-weight and external load,the variation law of the bearing load proportion of reaction forces of pile end and soil around piles is given. |
