Cofferdams
The following was from a Georgia manual on construction requirements for Cofferdams:
[SIZE=14pt]525.3.05 Construction[/SIZE]
A. Designing Cofferdams
Cofferdams shall be structurally adequate to withstand external and internal forces including the following:
1. Forces and pressures from an excavation depth of not less than 6 ft (2 m) below the elevation of the bottom of the footing
2. Forces and pressures from surcharge loads from adjacent structures, roadbeds, tracks, slopes, and equipment.
Design the cofferdam to meet these conditions:
· Cofferdams shall permit placing pumping equipment outside the footing forms.
· Cofferdams shall permit driving piling between braces.
· Cofferdams shall be watertight to permit the construction of the footings, seals, or substructure.
B. Correcting Cofferdams
Correct to the Engineer’s satisfaction cofferdams that tilt or move laterally during construction.
C. Lowering Cofferdams
Substructure elevations shown on the Plans are approximate; therefore, the Engineer may require that both substructures and cofferdams be lowered by a specified amount.
D. Dewatering Cofferdams
Try to dewater cofferdams without using seal concrete unless the Plans require seals.
1. Dewatering Cofferdams Without Seal Concrete
Use all reasonable methods to provide a dewaterable enclosure, including the following:
a. Drive all sheeting within the cofferdam to a depth of at least 1 ft (300 mm) below the bottom of the excavation.
b. Provide a double-walled cofferdam lined with clay or other reasonably impervious material.
The Engineer decides if the Contractor has used all reasonable methods to provide watertight cofferdams.
If the enclosures are not dewaterable, and the Engineer decides the Contractor has not used all reasonable methods to provide watertight cofferdams, the Engineer may do either of the following:
· Require the Contractor to place Seal Concrete at the Contractor’s expense.
· Permit the Contractor to place Seal Concrete at the Contractor’s expense instead of trying further dewatering methods without a seal.
2. Dewatering Cofferdams with Seal Concrete
If all reasonable methods to provide a dewaterable enclosure have been used and the Engineer determines that seal concrete is necessary, place the concrete as outlined in Subsection 500.3.05.V, “Place Seal Concrete.”
When using seal concrete, dewater the cofferdam no earlier than 24 hours after the concrete is placed unless the Engineer determines that a longer period is necessary.
E. Removing Cofferdams
Unless otherwise specified, completely remove all cofferdam material. This material shall remain the property of the Contractor.
525.3.06 Quality Acceptance
General Provisions 101 through 150.
525.3.07 Contractor Warranty and Maintenance
General Provisions 101 through 150.
