W911WN21SSMSWC - Montgomery Secant Wall.pdf

Contract Synopsis

Upper Ohio – Secant Wall Montgomery Locks and Dam, Ohio River, Pennsylvania

The U.S. Army Corps of Engineers, Pittsburgh District, plans to award a contract for construction of a secant pile wall at Montgomery Locks and Dam, Ohio River, PA. The secant pile wall will be constructed downstream of Gate Bay 1, through the concrete apron. The major features of the contract are identified below:

1) Installation of a bulkhead system on top of the fixed crest dam, commonly referred to as

“flashboards”;

2) Installation of instrumentation and monitoring devices including on top of the apron underwater;

3) Drilling of exploratory test borings at the center of piles shown on the contract drawings;

a) If extensive voids are present, as directed in specifications, grouting under the apron may be required, prior to drilling the Primary/Secondary piles;

4) Construction of demonstration secant piles;

5) Demolition of existing concrete baffles, as required;

6) Layout of secant wall;

7) Removal and disposal of limited portions of concrete apron;

8) Drilling and placement of primary piles;

9) Drilling and placement of secondary piles;

10) Pressure grouting at both ends of secant wall;

11) Under the apron grouting may be required to fill voids created by construction.

The work is to be performed downstream of Gate Bay 1, with the centerline of the secant wall 14’ riverward off of the centerline of Pier 1. Water elevations shown below may vary and all elevations shown are for information purposes only. Typical downstream pool elevation at Montgomery Locks and Dam is 664.5’, with the top of apron elevation of 647.5’. Top of alluvium, which is just under the concrete apron, is elevation 642.5’ and the top of rock elevation is elevation 620.0’+/-. Pool elevations will not be adjusted for this contract, though altered Gate Schedules will be followed in order to aid the Contractor with reduced turbulence. Construction of the secant wall will involve drilling through the 5’ thick concrete apron, alluvium, and an estimated 18’ into rock for the secondary piles. Each pile is approximately 4’-0” in diameter, and will be filled with tremie concrete, or a steel wide flange reinforcement beam and tremie concrete. There are 17 piles that are shown on the contract drawings, 10 secondary piles (tremie concrete with steel wide flange reinforcement beam) and 7 Primary Piles (tremie concrete alone).

All work will be performed from the Contractor’s floating plant located downstream of Gate Bay 1 and the fixed crest dam. Dive work is to be expected for this project. This project shall be completed, including final submittals, by 31 December 2022.

Off-site disposal of concrete, alluvium, and rock will be required. Debris and rubbish shall be disposed of at a properly permitted facility licensed to accept waste or recyclable materials as applicable.

Construction work will occur in close proximity to waterway traffic and operating lock and dam gates. The existing lock chambers are currently operated 24 hours a day, 7 days a week.