ITEM 503 EXCAVATION FOR STRUCTURES
503.01
Description
503.02
Classification
503.03
Cofferdams and Excavation Bracing
503.04
Protection for Excavation
503.05 Footings
in Rock
503.06 Approval
of Foundations
503.07 Disposal
of Excavated Material
503.08 Backfill
503.09 Method
of Measurement
503.10 Basis of
Payment
503.01
Description.
This
work consists of designing cofferdams and excavation bracing, and excavating
materials not removed under other items of work that must be removed to enable
construction of bridges, and other structures. Included in this work are:
A.
constructing, maintaining, and subsequently removing cofferdams and excavation
bracing;
B.
dewatering and backfilling the excavation;
C.
protecting the excavation against collapse; and
D.
disposing of materials not required or suitable for backfill.
503.02
Classification.
Excavation is classified as unclassified
excavation, unclassified excavation including rock (or shale), or rock (or
shale) excavation.
503.03
Cofferdams
and Excavation Bracing. This item
includes the preparation of a working drawing according to 501.05 for all cofferdams and excavation bracing
and the construction, maintenance, and subsequent removal of all cofferdams and
excavation bracing. A cofferdam is an enclosure within a water environment
constructed to allow dewatering for the purpose of creating a dry work
environment. Excavation bracing is that required to safely support the
sides of excavations, embankments, adjacent buildings, tracks, or other
premises.
Construct
cofferdams and excavation bracing such that support members clear the top of
the footings by at least 1 foot (0.3 m). If this is not practical,
support members shall be structural steel and left it in place. If
bracing is to be left in place and the ends would not be visible when the
structure is completed, burn off the steel ends flush with the concrete
surface. If ends would be visible, form a 6 inch (150 mm) deep recess
around the steel embedment and remove the external portion of the embedment to
provide at least 3 inches (75 mm) of clearance to the finished concrete
face. Completely fill the resulting recess with concrete.
Where
water is not encountered, the Contractor may place excavation bracing at the
plan dimension of the footing and use it as formwork for footing
concrete. Leave this sheeting in place at least to the top of the
footing, or properly separate it from the footing concrete so that it may be
removed without damaging the concrete.
Where
water is encountered, and cofferdams are necessary, construct them practically
watertight before excavating below water level. Make provisions outside
the footing to drain, collect, and remove water. When placing concrete,
keep the excavation dewatered until the concrete is above the prevailing water
level. Effectively protect footing concrete from erosion. If using
a concrete seal to stop the flow upward from the bottom of a cofferdam, place
the seal below the planned footing and consider it as a part of the
cofferdam. The Department will not pay for a seal unless it is shown on
the plans.
Unless
otherwise shown in the plans, design and construct
cofferdams to accommodate a water elevation 3 feet (1.0 m) above the ordinary
high water mark shown on the plans. If the actual water elevation exceeds 3
feet (1.0 m) above the stated ordinary high water mark, the Department will
reimburse the Contractor for any resulting damage to the work protected by the
cofferdam provided the Contractor has exercised normal due diligence. If
the actual water elevation exceeds 3 feet (1.0 m) above the ordinary high water
mark and causes a delay to the project, the Department will grant the
Contractor an excusable, non-compensable delay in accordance with 108.06.B.
Establish
a monument upstream of all proposed cofferdams to visually monitor the water
elevation in the waterway. Maintain the monument throughout the project.
Provide a visual mark on the monument that identifies the required high water
elevation as defined above. Ensure that the monument can be read from the bank
of the waterway. Have this elevation set and certified by an Ohio Registered
Surveyor.
Cofferdams
may be designed and constructed to accommodate a lower water elevation;
however, the Department will not reimburse the Contractor for repairs to work
damaged nor grant additional time unless the water elevation exceeds 3 feet
(1.0 m) above the ordinary high water mark shown on the plan.
Submit
any request for reimbursement for repair to work damaged or for delay to the
Engineer with information substantiating that the water elevation was more than
3 feet (1.0 m) above the ordinary high water mark shown on the plans.
503.04
Protection
for Excavation. Protect all
excavations from caving. Do not disturb the material below the bottom of
footings. Perform blasting in a manner that avoids damage to the material
supporting the structure vertically or laterally and that avoids subsequent
slides that damage the structure, road, or adjacent property. If the
material below the bottom of footings not supported by piles is disturbed,
remove it and fill the entire space with concrete at no expense to the
Department. Under footings supported on piles, replace and compact the
over-excavated or disturbed material as the Engineer directs. If backfilling is necessary to correct caving or slides, backfill
according to 503.08.
Excavation adjacent to railroad tracks
are
subject to the supervision of the involved railway company. Provide sufficient
bracing to ensure the proper support of the roadbed and tracks.
503.05 Footings in Rock.
Where
rock or shale excavation is a separate pay item, fill the portion of the
excavation into rock or shale that is below the top of footing with concrete.
If
removing rock or shale as part of Unclassified Excavation and the footing is
designed to be keyed into the bedrock, confine the excavation into bedrock for
the minimum specified depth of keying within the area bounded by the outer edge
of the footing. Fill excavation outside these limits and within and below
the keyed depth with concrete.
503.06 Approval of Foundations.
Notify
the Engineer when the excavation is to be completed to the depth shown on the
plans. Do not place footings until the Engineer has approved the subfoundation.
503.07 Disposal of Excavated
Material. Dispose of
excavated material not needed or not suitable according to 105.16
and 105.17.
Use other suitable excavation material for backfill.
503.08 Backfill.
Backfill
all excavations made under this item with materials conforming to 203.02.R, except behind abutments and
below the approach slabs use materials conforming to Item 203 Granular Material Type B.
Place
and compact the backfill materials according to 203.06 and 203.07,
except as modified by this subsection.
Do
not place backfill material against any structural element until the Engineer
has approved the element.
In
bridge abutment areas compact backfill material to meet the compaction
requirements in 203.07. Elsewhere,
compact backfill material to 95 percent of the maximum laboratory dry density.
When
a test section method is used for compaction acceptance: Use compaction
equipment with a total weight or a centrifugal force of least 1 ton (0.9 metric
tons). Supply the manufacturers’ information to verify this
information. Use at least six passes to construct the production
areas. Use at least 97 percent of the test section maximum dry density
for acceptance of the production areas.
The
Contractor does not have to place backfill material around piers that are not
within the embankment area or adjacent to a roadway or a railway in thin layers
or compact it, but should leave the backfill material in a neat condition with
a compensating allowance made for settlement.
Backfill in front of abutments and
around piers to the ground lines shown on the plans.
Backfill
all structural foundation units as soon as practical after the required
conditions of this subsection are met to avoid the ponding of surface water and
the accumulation of debris. Simultaneously backfill in
front of and behind abutments, piers, wing walls, and retaining walls.
Carefully backfill against waterproofed
surfaces to avoid damage to the waterproofing material.
503.09 Method of Measurement. After the requirements of Items 201, 202, and 203 have been met, the Department will measure excavation
on a lump sum basis or by the number of cubic yards (cubic meters) as follows:
A.
Bounded on the bottom. Bounded bottom plane of the footing, crossbeam, or wall.
B. Bounded on the top
1.
In cut sections, by the surface of the remaining
ground.
2.
In fill sections:
a.
If excavation is performed before embankment is placed, by the surface of the
original ground.
b.
If excavation is performed after embankment is placed, by the surface of the
embankment.
C. Bounded on the sides
1.
For Unclassified Excavation, 1 foot (0.3 m) outside the outer edge of the
footing, crossbeam, or wall.
2.
For Rock Excavation or Shale Excavation:
a.
If Rock Excavation is included in the Contract, by the outer edge of the footing
or wall.
b.
If rock or shale is removed as part of Unclassified Excavation Including Rock
and/or Shale:
(1)
Above the minimum specified depth of keying, the same as described in 503.09.C.1.
(2)
For the remainder of the excavation, the same as described in 503.09.C.2.a.
For keys below
footings, the Department will determine the volume of keys by the number of
cubic yards (cubic meters) shown on the plans.
The Department will
measure Cofferdams and Excavation Bracing on a lump sum basis.
503.10 Basis of Payment. If an Item for Cofferdams and Excavation
Bracing is not included in the Contract for payment, perform work according to 503.03 and the Department will pay for Cofferdams
and Excavation Bracing under the contract unit price for excavation.
The
elevations shown on the plans for the bottoms of footings are considered as
approximate. When excavation below plan elevation for footings is
required, the Department will pay for the 3 feet (0.9 m) immediately below the
plan elevation within the lateral limits described in 503.09.C.1
at the unit price bid for the class of excavation.
The
Department will consider additional excavation to a maximum depth of 1 foot
(0.3 m) within the lateral limits described in 503.09
as incidental to the lump sum price. Excavation deeper than 1 foot (0.3 m)
below plan elevation may be provided for as Extra Work, as described in 109.05.
If
Cofferdams and Excavation Bracing is a separate pay item, the lump sum price
includes any extra cost involved for cofferdams for additional depth up to 3 feet
(0.9 m) below plan elevation. Excavation deeper than 3 feet (0.9 m) below plan
elevation and the additional cofferdams necessitated by this excavation may be
provided for as Extra Work, as described in 109.05.
The Contractor shall provide additional fill material and subsequent excavation
to provide the minimum cover over culverts to accommodate heavy earth moving
equipment at no expense to the Department.
The
Department will pay for accepted quantities at the contract prices as follows:
Item
Unit
Description
503
Lump
Sum
Cofferdams and Excavation Bracing
503
Cubic
Yard
Unclassified Excavation
(Cubic Meter)
503
Lump
Sum
Unclassified Excavation
503
Cubic
Yard
Unclassified Excavation Including Rock
(Cubic
Meter)
503
Cubic Yard
Unclassified Excavation Including Shale
(Cubic
Meter)
503
Cubic
Yard
Unclassified Excavation
(Cubic
Meter)
Including Rock and/or
Shale
503
Cubic
Yard
Rock Excavation
(Cubic Meter)
503
Cubic
Yard
Shale Excavation
(Cubic Meter)