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

The final pile drilling depths were determined in the field by the Owner’s engineer usingthe information summarized in Table 2 based on drilling rates and the design loads. TheGroup C materials were added during project construction when the diabase material wasencountered unexpectedly.Table 2. Bond Parameters for Each Idealized GroupingLoadingConditionC/C Allowable Skin Allowable Skin Allowable Skin Allowable SkinPile Ø Spacing Friction Group A Friction Group B Friction Group C Friction Clay(in) (ft) kip/sq. ft. kip/lft kip/sq. ft. kip/lft kip/sq. ft. kip/lft psf plfComp.Ten.Comp.Ten.121299>= 5 2.4 7.54 6.0 18.85 14.0 43.984 2.0 6.28 6.0 18.85 14.0 43.983 1.8 5.65 6.0 18.85 14.0 43.98>= 5 1.9 5.97 6.0 18.85 14.0 43.98 350.0 1099.004 1.6 5.02 6.0 18.85 14.0 43.98 300.0 942.003 1.4 4.40 6.0 18.85 14.0 43.98 260.0 816.40>= 4 2.4 5.65 6.0 14.14 14.0 32.993 2.0 4.71 6.0 14.14 14.0 32.99>= 4 1.9 4.48 6.0 14.14 14.0 32.99 350.00 824.673 1.6 3.77 6.0 14.14 14.0 32.99 300.0 706.86Load Test ProgramPile load tests are used routinely on micropile projects to confirm the relatively largedesign loads. The micropile test program consisted of three pile load tests; two incompression and one in tension. All tests were on non-production 12-in piles. Tworeaction piles were installed for each test pile.Test piles were installed at two locations, one on the north side of the structure and oneon the south side. Compression tests were conducted at both locations with the northcompression test pile founded in rock and the south compression test pile founded inglacial till. A second test pile was installed at the north location within the glacial till forthe tension test.Figure 2 shows thelocations of the testpiles as well as thegeneral layout of thesite. A typical loadtest set-up is shownin Figure 3.A center holehydraulic jack,reacting against a testframe supported bytwo adjacent reactionpiles, was used toapply the test load."Sister bars",installed adjacent tothe steel reinforcingNORTHTESTPILE SITENORTHEASTSTAIRTOWERFigure 2 Test Pile LocationsCENTERCOREVEHICLE BRIDGESOUTHEASTSTAIRTOWERSOUTHTESTPILE SITE5