湿陷性黄土地基中桩基负摩阻力计算新方法OA北大核心CSTPCD

The negative skin friction(NSF)has important influence on the bearing and deformation behavior of piles in collapsible loess soils.The current calculating method of NSF recommended by the Standard for Building Construction in Collapsible Loess Regions(Standard Ⅰ)and the Technical Code for Building Pile Foundations(Standard Ⅱ)cannot reflect the actual behavior of the NSF.This paper conducted a statistical analysis on the field flooding test datum of reinforced concrete piles in the loess area of China during the past 30 years.The relationship between the depth of the neutral plane,the depth of the maximum NSF as well as the coefficient of NSF with the pile length diameter ratio was analyzed,and the empirical expressions of the three parameters above with the pile length diameter ratio were obtained linear fitting,then a new approach for calculating NSF of piles in loess soils was established.According to the proposed method,the distribution of the NSF along pile shaft is represented by a triangle,i.e.,the NSF increases with the depth and reaches a maximum value at a certain depth,then decreases to zero at the neutral plane depth,which perfectly reflects the actual distribution characteristics of the NSF along pile shaft.The calculated NSF by using the new method presented herein,Standard Ⅰ and Standard Ⅱ were compared with the field test datum.The results show that the neutral plane depth ratio predicted by Standard Ⅱ is better than that by Standard Ⅰ,and the maximum drag load predicted by Standard Ⅰ is better,while the NSF calculated by the new approach are in good agreement with the measured.