Calculation of Bearing Capacity of Cast-in-place Piles in Collapsible Loess Site Based on Immersion Environment
Research purposes:When the pile foundation of a railway bridge passes through a large-thickness collapsible loess site,the current specification calculates the negative friction resistance according to the limit value under the most unfavorable state,which leads to the length of the pile body is too long,resulting in a lot of waste of engineering investment.This paper proposed the concept and classification of a site immersion environment.Considering the topography and landforms,focusing on the analysis of the immersion conditions and degree of the site,the flooding environment of the site is divided into four states:complete immersion environment,long-term immersion environment,short-term immersion environment,and comprehensive treatment measures environment.For different immersion environments,when calculating the negative friction resistance,the lower limit depth of the collapsible soil layer is considered to be reduced.Research conclusions:(1)In terms of evaluation of collapsible loess with large thicknesses,the current specification is suitable for industrial and civil construction projects with thin collapsible soil layers,but not for railway projects with large-thickness collapsible soil layers.(2)For a complete immersion environment,negative skin friction is calculated according to the recommended method of current specifications.For a long-term immersion environment,the calculated depth of collapsible soil layer around piles can be considered 10～15 m.For a short-term immersion environment,the calculated depth of collapsible soil layer around piles can be considered as 5～10 m.(3)For comprehensive foundation treatment in large-thickness collapsible loess sites,negative skin friction can be ignored,which can shorten pile length,reduce construction difficulty,and save investment.(4)The research results can provide a reference for pile foundation engineering design in collapsible loess regions.
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维普
