Innovative Secant Pile Excavation Support: Weapons Storage and Maintainance Facility – Malmstrom Air Force Base-PPT Presentation

PPT Presentation

Pdf Summary

The Weapons Storage and Maintenance Facility at Malmstrom Air Force Base required excavation support for a basement on a congested site with nearby drilled shafts, a constrained construction sequence, and strict limits on movement. Interior work also had to be completed before the top slab was built.<br /><br />The project team evaluated grouted tiebacks, tie-rods with deadman anchors, external wale and anchor shafts, internal temporary wale frames, and top-down construction. Tiebacks and tie-rods were impractical given the site geometry, while internal frames obstructed an opening. Rather than use top-down construction, the selected design combined elements of several options: deadman anchor piles supported the east and west walls; the permanent mat slab and drilled shafts provided lateral resistance on the south side; and shallow basement secant piles acted as cantilevers. An integrated concrete wale connected the system.<br /><br />The design used 1 m diameter secant piles, with spacing and overlap varying by basement depth. The deadman piles were 6 ft in diameter and 50 ft long, with reinforcement tailored to structural demand and steel sleeves and bearing plates for the tie-rods.<br /><br />Construction included guide walls for pile alignment, open-hole drilling in stiff soils, and sectional casing for secondary piles. The team coordinated work around two tower cranes. Tie-rods were installed through the concrete wale and locked off at 250 kips, below their 400-kip maximum design load. They were later de-tensioned after the slab over the opening was completed.<br /><br />The combined support solution enabled an unimpeded construction sequence while limiting deflection and ground movement. The presentation emphasizes that considering multiple options and coordinating stakeholders helped produce an effective design.

Keywords

excavation support

basement construction

secant piles

deadman anchors

tie-rods

congested site

lateral earth support

construction sequencing

drilled shafts

Malmstrom Air Force Base