SECTION 511- COFFERDAMS
511.01 Description This work shall consist of the complete design, construction,
maintenance and removal of cofferdams and other related work, including dewatering and inspection, required to allow for the excavation of foundation units, to permit and protect the construction of bridge or other structural units and to protect adjacent Roadways, embankments or other structural units, in accordance with the Contract.
511.02 Materials As specified in the cofferdam Working Drawings.
511.03 Cofferdam Construction
A.Working Drawings. The Contractor shall submit Working Drawings, showing the materials to be used and the proposed method of construction of cofferdams to the Department. Construction shall not start on cofferdams until such Working Drawings have been submitted. Any review of or comment on, or any lack of review of or comment on, these Working Drawings by the Department shall not result in any liability upon the Department and it shall not relieve the Contractor of the responsibility for the satisfactory functioning of the cofferdam.
B.Construction. Construct cofferdams in conformance with the submitted Working Drawings. Cofferdams shall, in general, be carried below the elevation of the bottom of footings to adequate depths to ensure stability and adequate heights to seal off water. Cofferdams shall be braced to withstand pressure without buckling, secured in place to prevent tipping or movement and be as watertight as necessary for the safe and proper construction of the substructure Work inside them. With the exception of construction of a 5-115 concrete foundation seal placed under water, the interior dimensions of cofferdams shall provide sufficient clearance for the construction and inspection of forms and to permit pumping outside of forms. The Contractor shall be responsible for the righting and resetting of cofferdams that have tilted or moved laterally, as required for construction. During the placing and curing of seal concrete, maintain the water level inside the cofferdam at the same level as the water outside the cofferdam, to prevent flow through the concrete. No timber or bracing shall be used in cofferdams in such a way as to remain in the substructure Work. Cofferdams shall be constructed to protect fresh concrete against damage from the sudden rising of the water body, to prevent damage by erosion and to prevent damage to adjacent Roadways, embankments or other structural units. Unless otherwise noted, cofferdams, including all sheeting and bracing involved, shall be removed after the completion of the substructure work in a manner that prevents disturbance or injury to the finished Work. Cofferdams shall be constructed, dewatered and removed in accordance with the requirements of Section 656 - Temporary Soil Erosion and Water Pollution Control and related Special Provisions.
C.Inspection of Seal Cofferdams. Seal cofferdam excavations shall initially be inspected and approved by the Contractor. For each seal cofferdam excavation, the Contractor shall submit a written procedure to the Resident for sediment/overburden removal and excavation inspection. For cofferdams where seal concrete is to be placed on bedrock, the inspection procedure shall describe the Contractor’s final cleaning and inspection process for attaining cleanliness of each cofferdam excavation. For cofferdams where seal concrete is not excavated to bedrock, the procedure shall describe the Contractor’s final cleaning and inspection process for attaining the bottom of seal elevation shown on the Plans. The Contractor shall notify the Resident at least 48 hours prior to when each seal cofferdam excavation will be ready for final inspection by the Department. The Contractor shall allow adequate time for each occurrence of cofferdam excavation inspection by the Department. The Contractor shall provide and maintain access and equipment, such as steel probes, for the Resident and/or the Department’s Dive Team to independently inspect each cofferdam excavation. No seal concrete placement shall begin until the Department has approved the cofferdam excavation. 5-116
511.04 Pumping Pumping from the interior of any cofferdam shall be done in such a
manner as to prevent any current of water that would carry away or segregate the concrete. Pumping to dewater a sealed cofferdam shall not commence until the seal concrete has set sufficiently to withstand the hydrostatic pressure and meets the following minimum curing time, after the completion of the installation of the seal concrete:
1.When the temperature of the water body outside the cofferdam is greater than 40 degrees Fahrenheit, a minimum of 5 days.
2.When the temperature of the water body outside the cofferdam is less than 40 degrees Fahrenheit, a minimum of 7 days. Procedures for the removal of all water and materials from cofferdams shall be described in the Soil Erosion and Water Pollution Control Plan as required in Section 656 Temporary Soil Erosion and Water Pollution Control and related Special Provisions.
511.05 Method of Measurement Cofferdams will be measured as one lump sum unit, as
indicated on the Plans or called for in the Contract.
511.06 Basis of Payment The accepted quantity of cofferdam will be paid for at the
Contract lump sum price for the respective cofferdam items, which price shall be full compensation for design, construction, maintenance, inspection and removal. When required, the elevation of the bottom of the footing of any substructure unit may be lowered, without change in the price to be paid for cofferdams. However, if the average elevation of more than 25 percent of the area of the excavation is more than three feet below the elevation shown on the Plans, and if requested by the Contractor, then the additional costs incurred that are included in the cofferdam Pay Item will be paid for in accordance with Section 109.7, Equitable Adjustments to Compensation and Time. The Contractor shall immediately notify the Department when these additional costs commence. Failure of the Contractor to provide this notification will result in undocumented additional work that will be non-reimbursable. The Department will evaluate this additional work to determine an appropriate time extension, if warranted. All costs for sedimentation control practices, including, but not limited to, constructing, maintaining, and removing sedimentation control structures, and pumping or transporting water and other materials for sedimentation control will not be paid for directly, but will be considered incidental to the cofferdam Pay Item(s). All costs for related temporary soil erosion and water pollution controls, including inspection and maintenance, will not be paid for directly, but will be considered incidental to the cofferdam Pay Item(s). All costs associated with preparation of Working Drawings, design calculations, written procedure for sediment/overburden removal and excavation inspection, and the inspection of the seal cofferdam excavation shall be considered incidental to the cofferdam Pay Item(s). 5-117 There shall be no additional payment for repeated inspection by the Department of the same cofferdam excavation. All costs for cofferdams and related temporary soil erosion and water pollution controls, including inspection and maintenance, will be considered incidental to related Pay Items, when a specific Pay Item for cofferdams is not included in the Contract. Seal concrete will be evaluated under Section 502. Payment will be made under: P a y I t e m P a y U n i t
511.07 Cofferdam L u m p S u m
Referenced in this section
Sections that cite this one
Cofferdams in other states
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Source: Standard Specifications — Highways and Bridges, 2020 Edition. Pages 406–409 of 817. View official source ↗