- Critical Repairs Assessment
The U.S. Army Corps of Engineers (USACE) identified concrete distress on the chute slab and walls of the emergency spillway for Fort Peck Dam in Montanta. Burns & McDonnell evaluated the entire chute floor slab and walls for physical damage. The work included an extensive field investigation, inventory and documentation of both observable damage and suspected damage.
Non-destructive testing (NDT) of the spillway floor slab was conducted to identify anomalous responses caused by suspected concrete distress, concrete delaminations, sub-slab and inter-slab voids, and physical damage related to the observed slab uplift and slab damage. The methods used included geophysical ground-penetrating radar (GPR) and geophysical impact echo (IE). NDT data was compiled and a geophysical data report was prepared.
NDT of seven vertical lift gates was also completed using ultrasonic and magnetic particle examinations. Gates 3, 6, 7, 12, 13, 14 and 16 were tested as part of this project. Results of the NDT were provided to the USACE for interpretation.
Using the NDT results of the spillway floor slab, 15 locations were selected for destructive testing. Corings were made through the concrete slab. Each coring was examined for delaminate, condition of rebar and the presence of voids below the slab. A video record of each coring was used to document the findings.
Burns & McDonnell prepared plans and specifications to remove delaminated, detoriated and damaged concrete on the chute slab floor and walls of the emergency spillway. Based on the results of the field inspection and testing work, Burns & McDonnell developed recommendations and opinions of cost for short-term and long-term remedial measures to improve the reliability of the strucuture.
The USACE set a schedule of 19 weeks for development of plans and specifications. Final plans and specifications were delivered three weeks ahead of schedule.
- Field investigation
- Field testing
- Structural analysis and design
- Opinion of cost
- Long-term repair alternatives
The distress was prevalent through the 5,030-foot long spillway and is comprised of cracking, spalling, freeze-thaw damage and sulfate attack.
Considerable rebound of the chute slab was experienced following the unloading of the shale foundation material. Uplift has created domes along the chute slab as much as 3.5 feet above design grades. It was suspected that the uplift has resulted in the formation of voids below the slabs, which would induce bending and/or shear stresses that were not accounted for in design.
Burns & McDonnell was employed to evaluate the entire chute floor slab and walls for physical damage. The work included an extensive field investigation, inventory and documentation of both observable damage and suspected damage. Burns & McDonnell also prepared plans and specifications to repair distress and developed long-term alternatives to address uplift.
- Non-destructive testing of verticle lift gates
- Non-destructive testing of concrete spillway
- Destructive testing of concrete spillway
- Development and analysis of alternatives
- Plans and specifications for structural repairs