Alternate Verification Methods for Augercast Piles

Abstract

Augercast piles have become increasingly common. Engineers are attracted to this pile type as a way to reduce foundation costs. In addition, the applied design loads have increased as the equipment used by the augercast contractors has increased to both larger diameters and longer lengths, allowing augercast piles to be considered on a wider range of project sites. The performance of this pile type requires a shaft with good integrity and sufficient soil resistance. However, inspection for this pile type is difficult. The augercast pile is constructed in situ and at no time during the process can the "hole" or injected concrete along the shaft be inspected visually. By contrast, driven piles can be inspected prior to installation. Closed end steel pipes can be visually inspected after driving and prior to concreting. The integrity of driven piles is further indirectly confirmed by driving the pile to the required blow count, and in many cases dynamic pile testing is used to confirm whether or not a pile has suffered damage, even for solid section piles like H piles or square concrete piles. While pile and shaft performance can be verified by static load tests, the cost and time constraints prevent static testing for all but a few augercast piles on even the largest site. For augercast piles, current typical practice with visual inspection does inspect the pile completion process including installation of reinforcement. However, typical inspection during the critical augercast grouting phase in the United States is often limited to counting the total number of pump strokes (and computing a total volume based on that count). This paper describes automated electronic monitoring during construction to assure proper incremental grout volume versus depth for every augercast pile on site. Dynamic integrity inspection after installation and dynamic pile capacity determination for larger percentages of augercast piles on site are discussed. These alternate inspection methods increase the confidence in augercast pile foundations.

Determining the Pile Bearing Capacity by the Curve Match Method of High Strain Dynamic Testing

“…In recent years, compared with the traditional static load testing, the practice of engineering shows that the error of high strain curve match method is within ±20%, and its low trail-cost, short time for loading, high efficiency etc. In most cases, it can partly replace or reduce the static load testing [1,2]. Therefore, in order to preferably promote and apply the new technology of high strain trail-pile, it is significant to research on measurement accuracy and error source.…”