2-61 SECTIO N 208 – COFFERDAMS 208.0 1 DESCRIPTION . This work shall consist of the construction, material excavation within, dewatering, maintenance , and removal of cofferdams in accordance with the Contract. The work will be classified as follows:
a.Cofferdam . This item shall consist of providing a method for constructing, in the dry, a specific foundation or other component of a structure in accord ance with Contract requirements. This may involve the design, construction, maintenance, and removal of a watertight structure or may involve alternate methods of dewatering and stabilizing the specific site. Construction of foundation seals as specified i n the Contract or as required by Contractor plans and schedule of operations is also within the scope of work for the cofferdam item. The Contractor shall obtain any and all necessary permits or clearances for alternate methods.
b.Cofferdam Excavation, E arth. This item shall consist of all material excavated within the pay limits as set forth in these specification s or indicated on the Plans except solid rock, mortared stone masonry, concrete, and boulders measuring 0.5 cubic yards or more.
c.Cofferdam Excavation, Rock . This item shall consist of all solid rock material excavated within the pay limits as set forth in these specification s or indicated on the Plans, including all solid rock, mortared stone masonry, concrete, and boulders measuring 0.5 cubi c yards or more. 208.0 2 MATERIALS . Concrete used in a cofferdam foundation seal or for replacing overbreakage shall have a minimum 28 -day compressive strength of 3,000 psi and shall conform to the requirements of Section 541 . 208.0 3 GENERA L CONSTRUCTIO N REQUIREMENTS . The locations and ele vations for excavation shall be as indicated on the Plans. The Engineer may order removal of poor foundation material below the normal designated elevation and replacement with an approved material. All suitable excess excavated material shall be used in t he formation of embankment s as indicated on the Plans, or as directed by the Engineer. Unsuitable material shall be hauled and disposed of with no additional compensation to the Contractor. 2-62 208.0 4 PRESERVATIO N OF CHANNEL . Unless otherwise indicated o n the Plans or ordered by the Engineer, the Contractor, in performing the excavation, shall confine excavating operations to the site of the proposed structure and to the limits of the cofferdam. The natural stream bed shall not be disturbed without permis sion of the Engineer. 208.0 5 PREPARATIO N OF FOUNDATION . The foundation pits shall be excavated so that the footings will be the full lengths and widths indicated on the Plans. The footings shall be constructed with full horizontal beds. Unless otherwise s pecified or authorized by written order , foundations shall be constructed in the dry. In the dry means foundations and other structural components being constructed are not in or under water. The site shall be dewatered to, or below, the bottom of footing elevation or lowest elevation of a structural component. The excavation shall continue to either bedrock or the elevation specified for footings on soil. All loose material shall be removed and all seams in the rock shall be cleaned out and filled with con crete or as directed by the Engineer. No excavation shall be done below the elevations indicated on the Plans unless directed by the Engineer in writing. Any material so excavated without authority shall be replaced with concrete or as directed by the Engineer at the Contractor’s expense. When the footing is to be constructed on an excavated surface other than rock, particular care shall be taken not to disturb the bottom of the excavation. No excavation shall be performed below the elevations indicated on the Plans unless directed by the Engineer in writing. Any material excavated without authority shall be replaced with approved backfill, which shall be thoroughly compacted in accordance with Section 204, at the Contractor’s expense. When poor foundati on material is encountered at the foundation design elevation, it shall be removed as cofferdam excavation of the appropriate type and replaced with granular backfill for structures or other suitable material, as indicated on the Plans or as directed by th e Engineer, and thoroughly compacted in accordance with Section 204 . 208.0 6 COFFERDAMS . The Contractor shall prepare detailed plans and a schedule of operations for each cofferdam specified in the Contract. Construction drawings shall be submitted in acco rdance with Subsection 105.06 .
a.The professional engineer is responsible for ensuring that the proposed cofferdam meets the following criteria: 2-63 (1) The design is structurally stable for all conditions to be encountered (e.g., soils, water, forces, and loadings)
2.The design and details conform with the Contract and the applicable requirements in the AASHTO Standard Specifications for Highway Bridges or the AASHTO LRFD Bridge Design Specifications
3.The design and details are in conformance with applicable safety codes
4.Adequate size and shape to construct the foundation and structural components specifi ed
5.The cofferdam is adequately watertight for proper performance of the work
6.The foundation seals are adequate to achieve their design function
b.The submittal shall include plan, elevation , and section details indicating the following:
1.The w aterway
2.Information regarding the cofferdam and any indication that a foundation seal is required to ensure the structural integrity of the cofferdam during dewatering and foundation construction and inspection
3.Substructure location
4.Dimensions of any temporary restrictions that are to be placed in the waterway (e.g., barges, lines, earth dams, causeways, temporary diversion channels, and access bridging)
5.The location, dimensions, clearances, and other relevant information for any temporary scaffolding or netting
6.Dewatered heads, taking into consideration water level fluctuations
7.Details for screening, pumping, and filtering discharges from the cofferdam
8.Details of siltation control and sediment isolation measures
9.A statement stipulating whether any equipment will be removed at night
10.A schedule or sequence of operations that includes placement of the foundation seal, time from placement to dewatering, and foundation construction and inspection 2-64 The Contractor shall be responsible for performing the work in accordance with the submitted details and schedule of operations. All welding shall be performed per Subsection 506.10 . Cofferdam construction shall conform to the AASHTO LRFD Bridge Constructi on Specifications . Cofferdams shall be constructed so as to protect freshly placed concrete against damage from sudden rising of the water level and to prevent damage to the foundation or other structural component by erosion. The cofferdam shall be constr ucted so that no timber, bracing, or forms will extend into the foundation or other structural component. In the event the Contractor elects to place fill material in the stream to facilitate access to, or be part of, a cofferdam operation, it shall be cle an stone fill. The Contractor shall take measures to prevent all sediments and pollutants from entering waters of the state during installation, use, and removal of the cofferdam. The sediment isolation measures used shall completely enclose the portion of the work area that will be under water. The Contractor shall design and construct the measures to deflect and withstand existing current or wave action, to be anchored continuously along the bottom, and to be effective at the anticipated water levels. The Contractor shall maintain the sediment isolation measures while in use and shall repair or replace damaged or otherwise ineffective measures as ordered by the Engineer. 208.0 7 PUMPING . Pumping from or dewatering of the interior of any cofferdam enclosure shall be performed so that disturbance of the subsoil or freshly placed concrete will not occur. Dewatering of a sealed cofferdam will be in conformance with the Contractor’s sequence or schedule of operations. Pumping during the construction of a foundation or other structural component shall be from a suitable sump separated from the concrete work . The discharge from any pumping operation, filtration system, or settling basin shall conform to the requirements of Section 105 and the Contract.
208.08 INSPECTIO N OF FOUNDATIO N PIT. Immediately following the completion of each
foundation pit, the Contractor shall notify the Engineer, who shall approve the depth of the pit and the nature of the bearing surface before the placement of the concrete.
208.09 BEDDIN G FOR STRUCTURES . Excavation and preparation of the bed for a structure shall
conform to the specification s for the specific structure being installed. 2-65 208.1 0 METHO D OF MEASUREMENT .
a.Cofferdam . The quantity to be measured for payment wil l be on a lump sum basis for each cofferdam specified on the Plans or in the Contract.
b.Cofferdam Excavation , Earth. The quantity to be measured for payment will be the number of cubic yards of earth excavated from within the pay limits of the cofferdam as set forth in these specification s or as shown on the Plans. The removal of earth excavation authorized by the Engine er below the elevation of the bottom of the excavation, as indicated on the Plans, will be factored in accordance with Table 208.10A . TABLE 208.10A – COFFERDAM EXCAVATION MULTIPLIERS Vertical Depth (D) Below Bottom of Excavation Indicated on the Plans (feet) Volume of Cofferdam Excavation Multiplied By 0 ≤ D < 1 100% 1 ≤ D < 5 150% 5 ≤ D < 10 450% 10 ≤ D < 15 750% 15 ≤ D Paid as extra work
c.Cofferdam Excavation , Rock. The quantity to be measured for payment will be the number of cubic yards of rock excavated from within the pay limits of the cofferdam as set forth in these specification s or as shown on the Plans. The removal of rock excavation authorized by the Engineer below the elevation of the bottom of the excavation, as indicated on the Plans, will be factored in accordance with the list shown above. Where a foundation or component of a structure is designed or directed to be placed on bedrock, a maximum of 6 inches average allowance for overbreakage will be allowed. Additional overbreakage will be at the Contractor’s expense.
d.Bottom of Excavation . The bottom of excavation shall be as indicated on the Plans. When a foundation seal is specified in the Contract, the bottom of excavation shall be considered to be the bottom of the excavation required for the foundation seal. For a seal proposed by the Contractor, no excavation shall be measured for payment below the bottom of excavation as indicated on th e Plans. 2-66 208.1 1 BASIS OF PAYMENT . The accepted quantity of Cofferdam will be paid for at the Contract lump sum price . Payment will be full compensation for the preparation of detailed plans and schedule of operations, performing the work specified, and furnishing of all labor, tools, equipment, materials, and incidentals necessary to complete the work. Payment will include the cost o f altering the cofferdam; foundation seals; sheeting; bracing; dewatering; installation, maintenance, repair, and replacement of siltation and sedimentation control measures; incidentals necessary for properly constructing the foundation or structural comp onent; maintaining the cofferdam in a dewatered condition; and removing the cofferdam and associated siltation and sediment control measures when no longer required. The accepted quantities of Cofferdam Excavation, Earth and Cofferdam Excavation, Rock will be paid for at the Contract unit price per cubic yard for each of the pay item s in the Contract . Payment will be full compensation for performing the work specified and the furnishing of all labor, material s, tools, equipment , disposal of surplus material , and any other incidentals necessary to complete the work . Partial p ayment s for Cofferdam will be made as follows:
a.A payment of 75% of the lump sum bid price will be made when excavation within the limits of the structural unit is completed and the cofferdam has been successfully dewatered.
b.The remaining 25% of the lump sum price will be paid when the cofferdam is completely removed , or, if the Contract require s the cofferdam to be left in place, when the associated foundation or other component of a structure is completed. If the Engineer , by written order , requires that the cofferdam be left in place and this requirement is not specified in the Contract, a change order will be processed in accordance with Section 109 . Payment will be made under: Pay Item Pay Unit
208.30 00 Cofferdam Excavation, Earth ................................ ................................ ....Cubic Yard
208.35 00 Cofferdam Excavation, Rock ................................ ................................ ....Cubic Yard
208.40 00 Cofferdam ................................ ................................ ................................ .Lump Sum
2-67 SECTION 209 – TRENCHLESS CONSTRUCTION
209.01 DESCRIPTION . This work shall consist of performing trenchless construction as specified in the
Contract and in accordance with standard industry practice.
209.02 SUBMITTALS . The Contractor shall submit a detailed work plan that encap sulates a wide range
of procedural precautions necessary to ensure a proper trenchless installation. The work plan shall be submitted to the Engineer for acceptance in accordance with Subsection 105.0 6(c)(2) prior to the beginning of any work associated wi th the trenchless work. The work plan shall contain, at a minimum, entry and exit points, entry and exit angles, any horizontal bend radii, a profile showing points of tangency and curvature, vertical radii, the depth of the bore along the proposed alignm ent, equipment details and specifications, anticipated duration of the drill and assembly, and the Contractor’s qualifications. The qualifications, at a minimum, shall be three projects in the last 5 years where the Contractor or subcontractor performing t he work has successfully used the trenchless construction method for projects of similar diameter, length, and difficulty as required for this project. The work plan shall also indicate if the Contractor intends to do any preliminary subsurface investigati on.
209.03 Equipment Requirements .
a.Horizontal Directional Drilling . Horizontal directional drilling equipment shall consist of a directional drilling rig of sufficient capacity to perform the bore and pull -back, a drilling fluid mixing and delivery sy stem of sufficient capacity to successfully complete the work, and a guidance system to accurately guide drilling operations. Equipment shall include a vacuum trailer to withdraw excess drilling fluid and a drilling fluid cleaning system truck for mixing a nd recycling bentonite. All equipment shall be in good and safe operating condition with sufficient supplies, materials, and spare parts on hand to maintain the system in good working order for the duration of the work.
1.Drilling System .
a.Drilling Rig . The directional drilling machine shall consist of a hydraulically powered system to rotate, push, and pull hollow drill pipe into the ground at a variable angle while delivering a pressurized fluid mixture to a guidable drill head. The machin e shall be anchored to the ground to withstand the pulling, pushing, and rotating pressure required to complete the work. The hydraulic power system shall be self -contained with sufficient pressure and volume to power drilling operations. The hydraulic sys tem shall be free of leaks. The drill rig shall have a system to monitor and record maximum pull back pressure.
Source: Vermont Standard Specifications for Construction, 2024 Edition. Pages 201–206 of 1,380.