Innovative Secant Pile Excavation Support: Weapons Storage and Maintainance Facility

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Video Summary

At Malmstrom Air Force Base in Montana, engineers designed a 40-foot-deep basement within a congested construction site. The secant-pile walls had to support vertical building loads, limit movement to half an inch, and remain accessible for installing heavy mechanical equipment before the roof slab was built.<br /><br />The team evaluated tiebacks, deadman anchors, internal bracing, and top-down construction. Top-down construction was initially selected, but equipment-installation requirements ruled it out. The final solution combined reinforced-concrete wales integrated into the secant-pile walls, tie rods connected to deadman shafts or surrounding foundations, and a cantilevered section where the excavation was shallower.<br /><br />Construction proceeded alongside extensive foundation work and a tight schedule. Crews installed the secant piles, built the wales, placed and tensioned the tie rods, and excavated in stages. Once the basement’s top slab was complete, the tie rods were detensioned, transferring support to the permanent structure.<br /><br />Close coordination among the designers, contractor, general contractor, and mechanical team helped avoid schedule interruptions. Wall movements stayed below the project’s quarter-inch alert threshold, and the project was completed safely and cost-effectively.

Keywords

secant-pile walls

deep basement excavation

tie rods

deadman anchors

top-down construction

foundation support

construction coordination