Chance Technical Design Manual

DESIGN EXAMPLE 5: HELICAL PULLDOWN MICROPILES FOR NEW CONSTRUCTION

PROBLEM Determine the capacity of the following Chance® Helical Pulldown® micropile (HPM) installed into the soil described in Figure 8-4.

REVIEW OF COMPRESSION TEST Figure 8-3 is a load deflection plot from the actual compression test on the HPM installed into the soil described in Figure 8-4. From the plotted data, the ultimate capacity (based on 0.08D h + PL/AE) was 80 kip, compared to the calculated total capacity of 66.8 kip. This calculated value provides a conservative ap proach to determining the ultimate capacity of an HPM.

SS5 1-1/2” x 1-1/2” square shaft Helix configuration: 8”-10”-12” Total depth: 40 ft Grout column: 5” dia x 31 ft

CALCULATIONS End bearing calculations from the HeliCAP® engineering soft ware. See Table 8-3 below for the ultimate end bearing capac ity of the proposed 8”-10”-12” lead configuration. Summary: Compression Capacity ( ∑ Q h ) = 44.7 kip Summary: Friction Capacity (Q f ) = 22.1 kip (see Table 8-4) Total Capacity (Q t ) = ∑ Q h + Q f = 44.7 + 22.1 = 66.8 kip

DESIGN EXAMPLES

HELICAP SOFTWARE SUMMARY REPORT, TABLE 8-3

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