New Method for Prediction Pile Capacity Executed by Continuous Flight Auger (CFA)

Wael N Abd Elsamee

doi:10.4236/eng.2013.54047

Abstract

A study of piles is quit complex and the estimation of carrying capacity is calculated from theoretical formula and load test results. The design resistance may be calculated using conventional static pile design theory. The pile founding depths should be predetermined before installation from a site geotechnical investigation. To ascertain the field performance and estimate load carrying capacities of piles, in-situ pile load tests should be conducted. In this study, field pile load test data is analyzed to estimate the ultimate load for end bearing piles. The investigated site is about 100 × 110 m located in Alexandria, Egypt. Geotechnical investigations at the site are carried out to a maximum depth of 45 m. Four borings have been done in field. The tests are conducted at the site for two skelton structure buildings to be constructed on raft foundation rested on piles executed by continuous flight auger. Four pile load tests are performed on 600 mmdiameters and 27 mlengths. Ultimate capacities of piles are determined according to different methods. It is concluded that the percentage of friction load carried by the shaft along the pile length is about 46% of total load while the percentage of load carried by the end bearing is 54% of total load. A new proposed method by the author is presented to calculate the ultimate capacity of pile from pile load test. The proposed method depends on the settlement of pile without taken into consideration the elastic deformation. An empirical formula is presented from the relationship between stress and settlement of pile due to friction and end bearing only after deducting the elastic deformation. However, the obtained results for the ultimate capacity of end bearing piles are considered to be more accurate than other methods. The proposed method appears to give bitter results that agrees well with the theoretical predictions. The proposed method is easier, quicker and more reliable.

Highlights

Piles are relatively long and generally slender structural foundation members that transmit superstructure loads to deep soil layers
It can be shown from Equation (3) and Figure 3 that the percentage of friction load carried by the shaft along the pile length is about 46% of total load, while the pile load carried by the end bearing is 54% of total load
CFA method can be summarized as follows: 1) The pile is formed by first drilling into the ground with a continuous flight auger to the required depth; 2) Concrete is injected under pressure through the auger’s hollow stem as it is being withdrawn; 3) The concrete pressure is maintained during the auger withdrawal so that it assists the extraction as well as exerting a lateral pressure on the surrounding soils; 4) Reinforcing cage is placed into the concrete column

Summary

Introduction

Piles are relatively long and generally slender structural foundation members that transmit superstructure loads to deep soil layers. There are numerous types of piles being developed and extensively use in the construction industry. Difference pile system will serve difference purposes in different type of soil and site conditions. Most of the piles are design to meet the requirements of the end bearing capacity which is driven to set on to the hard strata. Pile section can generate certain percentage of resistance through skin friction that produced between the pile and soil. The prediction of the axial capacity of piles has been a challenge since the beginning of the geotechnical engineering profession

Objectives

Methods

Findings

Conclusion