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

Table 3. Results from pre-production load tests.Net Movement (1) for Maximum Load at Bond Zone atPile Design Max Test PileTest LoadMaximum Test Load (2)LoadingDiameter Load Load Location Top of Pile Telltale atAllowable Actual Min Req'd= Butt Pile Tipin kips kips in in in kips kipsComp 12 430 1002 North 0.22 0.09 0.27 800 645Comp 12 430 859 South 0.53 0.23 0.27 700 645Tension 12 150 300 South 0.03 NA 0.5 NA NA1. Mass. Building Code (MBC) requires that top of pile movement be less than theoretical compression (assuming all theload applied to the butt is transmitted to the tip) + 0.15 in + 0.01 * pile diameter (similar to Davisson, except that 0.01 is0.008 for Davisson). Conservatively this is a net movement of 0.15 inch + 0.01 * pile diameter. MBC also requires that netsettlement at two times design load be less than 0.5 inch for both tension and compression tests.2. MBC requires that at least 150% of the design load reaches the "bearing stratum" at maximum test load.Production Pile InstallationProduction piles were installed from inside and outside the structure ranging between 90and 140 ft in length. The approach used on the interior of the structure was to make anexcavation for the pile cap and to install the piles from within these excavations as shownin Figures 4 and 5. The Comacchio CM1200s and Casagrande M9 rigs employed werespecially outfitted with short masts. Casing lengths were limited to 5-ft for this work.There were as many as four rigs working simultaneously under the low headroomconditions. Pile installation times varied significantly with an average of 1.5 piles per rigshift except when the diabase dikes were encountered unexpectedly. Within the diabaseit took three to five days per pile with as much as 8 hrs to drill one foot.Figure 4. Interior Drilling within Footing Excavation7