c ty commercial
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CASE STUDY Commercial
©2013 Foundation Supportworks®, Inc. All Rights Reserved. Case Number 071913
Project: Location:
Date:
FSU Conradi Building DemolitionTallahassee, FLApril 2013
Challenge:The aged and outdated Conradi Building, constructed in 1956, was planned to be demolished to provide space for additional on-campus parking. The existing three-story structure with a basement was located adjacent to a major thoroughfare. In order to allow demolition of the building, yet still provide support to the road, it was proposed that sections of the north basement wall would remain where grade elevation of the retained soils matched the roadway. An anchoring system would be required to provide the overturning resistance for the wall. The basement wall would then receive aesthetic improvements and remain as a permanent retaining structure.
10-inch diameter holes cored for tieback installation
Helical anchors installed from inside basement prior to demolition
Post demolition basement wall with three helical tiebacks and one Geo-Lock® anchor
through a pilaster
View from roadway showing the distance from the road to the basement wall
Project SummaryArchitect:
Geotechnical Engineer:Structural Engineer:General Contractor:
Certified Installer:Products Installed:
Hicks NationArdaman & AssociatesDavid H. MelvinChilders ConstructionAlpha Foundation Specialists, Inc.(24) Foundation Supportworks® Model 150 Helical Tiebacks, 8”-10” Lead Section, Installed to Lengths of 21 feet, Design Working Tension Load of 12 kips; (3) Geo-Lock® Wall Anchors, Installed to Lengths of 15 feet, Design Working Tension Load of 12 kips
Solution:Both Geo-Lock® wall anchors and helical tiebacks were used to transform the existing simple span foundation wall to a “tied-back” cantilevered earth retaining wall. Helical tiebacks were an ideal system to support the wall and extend beneath the existing roadway without causing disruption to traffic flow. Twenty-four (24) Model 150 (1.5-inch round corner square bar) helical tiebacks with an 8”-10” double-helix lead section were advanced through ten-inch diameter core holes using a Bobcat 323 compact excavator. Standard extensions advanced the helical tiebacks to lengths on the order of 21 feet to achieve final installation torques corresponding to ultimate capacities of at least twice the design working tension load of 12 kips (FOS ≥ 2). The core holes through the wall were filled with concrete prior to placement of the 12-inch by 28-inch wall plates.
Three (3) Geo-Lock® Wall Anchors, one at each of three pilasters, were installed in foundation wall sections not parallel to the roadway. The Geo-Lock® system was selected over helical tiebacks at these locations to prevent cutting of the densely-spaced reinforcing steel. The ¾-inch anchor rods were driven through 1 1/8-inch holes drilled through the wall. The rods were advanced to lengths of approximately 15 feet and into four feet deep excavations where they were connected to 16-inch by 26-inch earth anchor plates. The anchor rod was connected to channel steel at the inside wall face. The channel spanned from the anchor rod to a bolted connection at the basement floor. The wall anchors and tiebacks were installed approximately three feet down from the top of the wall and at a typical spacing of about five feet. All tiebacks and anchors were pretensioned following installation.
Helical Tiebacks and Geo-Lock® Wall Anchors