Micropile Installation with Spoil Control at Logan Airport - Nicholson ...

Project ChallengesThe Logan Airport job provided many challenges that can be divided into two groups: i)coordination of trades working within difficult access and while trying to maintain garageoperations; and ii) unexpected surprises.The Construction Manager made significant effort to facilitate the work activities of thevarious trades by having daily coordination meetings. These meetings were very helpful,however, inevitably there were conflicts related to scheduling access to various portionsof the site such that trades could not work optimally. As is generally the case during thenegotiation stages of a project, concerns for these types of conflicts and inefficiencies fallon deaf ears and there is over-optimism regarding the coordination that is possible.A significant challenge encountered was the presence of diabase dikes that were notidentified in the subsurface exploration. These dikes were especially troublesomebecause of the external flush "lost bit" drilling technique employed. The lost bits are infact used roller bits from the oil industry. The use of these used bits is necessary becauseof the very high cost of new bits when considering a single use application. For thefounding materials expected to be encountered, namely argillite and glacial till, the usedbits were more than adequate. However, when the diabase was encountered installationoperations slowed dramatically wherein pile installation went from taking about six hoursper pile, to taking 3 to 5 days per pile. The use of down-hole percussion hammers wouldhave penetrated much faster, but the confined space conditions, existing site layout, theuncertainty of the number of piles possibly effected by the diabase, and changes neededto support operations made this option a last resort.Another impediment to production was the presence of utilities at unknown locations,which is a very common occurrence on urban construction sites. The time necessary toidentify the extent of the utilities, their owner, and to negotiate a plan for their movementor development of a foundation retrofit is often substantial. Importantly, money for theseactivities is never budgeted and therefore there is always haggling over what constitutesfair compensation; with ultimately no one feeling like they were treated fairly.SummaryThis paper provided an overview of micropile installation operations to support anexpansion to the Central Parking Garage at Logan Airport. Topics discussed included:1. The re-design of the foundation system to make use of micropiles in place ofdrilled shafts. The redesign allowed the work to be completed at the lowest levelof the garage and thereby minimize disruption of the parking operations. Thedrilled shaft approach was to be completed by drilling through the top floor andwould have required substantial bracing of the structure to accommodate thecrane loads.2. The external flush method was used to install the piles and the specific selectionof bond length was based on drilling response. The drilling penetration rate wascorrelated with specific founding materials and appropriate bond stresses.12