Load Transfer Calculation and Analysis of Large-Diameter Bored Piles According to Rules Based on Test Pile Measurement

Abstract

This study aims to establish an appropriate method to calculate the bearing deformation of large-diameter bored piles in alluvial deposits with soils characterized mainly by medium-dense to dense silt, fine sand, and plastic to hard plastic silty clay in the middle and lower reaches of the Yellow River. According to the field measurement results of 18 large-diameter bored piles in six sites of the third-ring expressway project in Zhengzhou, this study discusses the action laws of pile shaft friction with pile-soil shear displacements and pile tip resistances with pile end displacements. A pile shaft load transfer model and pile tip bearing model are then established for large-diameter bored piles. The calculation parameter values are also given. The feasibility and rationality of the calculation method are verified by an engineering example. According to the engineering example and by changing the parameters of the pile diameter and pile length, the properties of bearing capacities and deformations of the large-diameter bored piles under this site condition are further analyzed. Results show that the inflection point of the pile Q~s curve is obvious for large pile diameters. The pile bearing capacity and deformation property are significantly improved by increasing the pile diameter under a small load. The increase amplitude of the pile bearing capacity and deformation property obviously decreases with the increase in pile length. This result indicates that the improvement of the pile bearing capacity and deformation property by increasing the pile length is not effective. The pile without grouting shows an obvious puncture damage model. Moreover, the settlement of the pile without grouting is small with a large pile diameter or short pile length. The effective length and bearing capacity of a large-diameter bored pile can be greatly increased by pile tip post grouting. The increased value of the pile bearing capacity is high with a large pile diameter and pile length under pile tip post grouting conditions.