G G Goble

Pile Design and Installation Specification Based on Load-Factor Concept

The use of load-factor procedures for the design of bridge superstructures is expanding rapidly. However, substructure design is still based exclusively on allowable stress methods. This paper presents an approach to load-factor design for pile foundations. The load factors suggested follow the current American Association of State Highway and Transportation Officials recommendations, while the resistance factors recommended are based on the capacity-determination methods and the construction control procedures used. Actual values are selected to be consistent with currently used procedures where they are available. The proposed specification can provide a framework for the use of more-appropriate resistance factors as they become available from ongoing research. (Author)

Construction Control for Augercast Piling

Where soil conditions are favorable, augercast piles have significant economic advantages, but they also have some uncertainty due to the construction methods. To confirm bearing capacity and structural integrity, static testing can be performed on a small sample of piles. However, the load test piles are not necessarily constructed in a manner representative of production piling. Additional assessment methods must be used on more piles to increase confidence in augercast piling foundations. Non-destructive Evaluation (NDE) methods like Pulse Echo are frequently specified for a large percentage of the production piles. However, such NDE methods require testing the pile after the grout or concrete has hardened. If problems are found, then the repair or replacement can be relatively expensive. The confidence in the quality of augercast piles can be improved by automatically monitoring the grout volume pumped as a function of depth. If a low grout volume is measured for any depth increment, the pile can be repaired immediately while the grout is still fluid. Such installation monitoring equipment can be of great help to the installation crews and may reduce the need for subsequent NDE tests. While Pulse Echo tests and monitoring during installation can assess the pile structural integrity, the bearing capacity cannot be assessed by these methods. Bearing capacity of augercast piles can be evaluated by the same high strain Dynamic Pile Testing methods used to test driven piles if a suitable drop weight is available, or by conventional static load testing. This paper describes the background and benefits of various construction control and pile evaluation methods for augercast piles. Case studies demonstrate application of these methods.