BG28 with CSM tool installing a CSM panel Installation Following the successful load test program on the ACIP piles, production was scheduled for an immediate start. Due to the aggressive schedule of the project, two BG- 28 rigs were utilized for the pile production. Installation of the initial piles proved difficult in some areas of the site, particularly along the west side of the site nearest the Gulf of Mexico. During the installation of these piles, initial attempts to maintain a positive head of grout resulted in grout overages exceeding 400% of the pile volume. The excessive grout overages were mostly attributed to the lenses of shell and gravel in the upper soils, which provided a nearly direct connection to the Gulf of Mexico. Grout return was never achieved, and collapses at the ground surface were experienced on multiple piles during auger extraction. Collapses at the ground surface present a major safety issue when drilling with large and heavy drilling equipment, as the tracks sit within a few feet of the pile being installed. Following the initial attempts on multiple piles in the area of concern, and after multiple collapses of the pile and ground surface, a different approach to grouting was considered in an effort to reduce safety risks, time and costs related to the grouting of the piles. Following discussions with the client and geotechnical engineer, it was agreed that the best approach to mitigating the time and cost risk to the project was to establish, at the beginning of grouting, a theoretical minimum head of grout of about 10 ft (3.0 m) Partially excavated wall and site at the south side with internal and external dewatering above the auger tip, and to extract the auger at a continuous rate such that a minimum volume of 110% of theoretical volume was achieved per lineal foot of pile. While this approach did not reduce the risk of ground collapse, BFC felt that there was no additional risk to the crew or equipment. To try and mitigate the large grout takes, BFC focused on installing the piles along the perimeter of the site nearest the Gulf of Mexico, subsequently improving the ground around the entire site, and therefore creating a barrier that would help reduce excessive grout overages. Following the completion of the line of piles closest to the Gulf of Mexico, it was immediately observed that the grout takes for the inner piles were significantly reduced and were in the average range of about 150% of the theoretical volume. At this stage, no further ground collapse issues were encountered for the remainder of the installation of the ACIP piles. In total, 1,562 piles were installed following the required design changes during production. Quality Control and Results In the original design provided to the contractor, there were 50 different cage elevations utilizing two different cage designs, with some top of rebar cage elevations set as deep as 14 ft (4.3 m) below the working grade. Installation depths well below the top of the pile, cages that did not extend to the bottom of the pile, and multiple cage and elevation configurations created numerous opportunities for errors and confusion. To reduce confusion and increase the speed of installation of the rebar cages, BFC provided a design that reduced the type and lengths of cages to three different options. To accomplish this, a single cage design was used and the reinforcement cages were extended in certain piles to allow a more efficient means of tracking and installing the cages. This solution required an additional expense for BFC because of the additional steel required, but the time saved and the assurance of installing the reinforcement to the proper elevation more than made up for the additional material costs. As the general contractor was already providing pile cutoffs, there was little-to-no impact to their costs, and the majority of the upper portion of the pile was cutoff, as opposed to chipped down to expose the rebar. Conclusion A combination of in-service facilities, unforeseen existing foundations, proxi- mity to the Gulf of Mexico, and challenging Ground collapse at pile locations DEEP FOUNDATIONS • MAR/APR 2018 • 79
