ITEM 503  EXCAVATION FOR STRUCTURES

503.01   Description
503.02   Classification
503.03   Cofferdams, Cribs, and Sheeting
503.04   Protection for Excavation
503.05   Footings in Rock
503.06   Approval of Foundations
503.07   Culvert Foundations
503.08   Disposal of Excavated Material
503.09   Backfill
503.10   Method of Measurement
503.11   Basis of Payment

503.01  Description.  This work consists of designing cofferdams and shoring, 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 shoring;
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, Cribs, and Sheeting.  This item includes the preparation of a plan; the construction, maintenance, and subsequent removal of all cofferdams, cribs, sheeting, shoring, bracing, or other materials necessary to safely support the sides of excavations, embankments, adjacent buildings, tracks, or other premises; and all pumping necessary to complete required construction.

Construct cofferdams, cribs, and sheeting such that wales and crossbraces, if practical, clear the top of the footings by at least 1 foot (0.3 m).  If this is not practical, construct this bracing using structural steel and leave 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, box back the steel ends at least 6 inches (150 mm) from the concrete face, and burn off the ends at least 3 inches (75 mm) back of the concrete face.  Completely fill the resulting holes with concrete.

Where water is not encountered, the Contractor may place sheeting at the plan dimension of the footing and use it as forms 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.

Design and construct cofferdams, cribs, and sheeting to accommodate a water elevation 5 feet (1.5 m) above the normal water elevation shown on the plans.

Cofferdams may be designed and constructed to accommodate a lower water elevation.  If cofferdam is designed and constructed to accommodate a lower water elevation, do not submit a claim for a changed condition unless the water is over 5 feet (1.5 m) above normal water elevation shown on the plans.

Submit any request citing a changed condition to the Engineer with information substantiating that the water elevation was 5 feet (1.5 m) above the normal water elevation shown on the plans.

503.04  Protection for Excavation.  Cut the sides of all excavations to prevent caving, or protect the excavation 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 503.09.

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  Culvert Foundations.  The Contractor may place cast-in-place box culverts directly on solid rock if the rock exists for the full length of the culvert.  If boulders, unstable material, and rock exist for a portion of the length, remove and replace them with suitable compacted material for a depth the Engineer determines, but in no case less than 6 inches (150 mm) below the bottom of the culvert.  Remove rock and boulders for a width sufficient for placing and proper compaction of the backfill.  Remove unstable material on each side of the culvert for a width generally equal to the span of the culvert, but not less than 2 feet (600 mm).

503.08  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.

503.09  Backfill.  Backfill under this item includes all replaced excavation and new embankment adjacent to structures.  Use backfill embankment materials conforming to 203.02.R.  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.

503.10  Method of Measurement.  After the requirements of Items 201, 202, and 203 have been met, the Department will measure excavation 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 503.10.C.1.
(2)     For the remainder of the excavation, the same as described in 503.10.C.2.a.

3.      For unstable material under culverts, by the limits of removal as specified.

For abutment excavation quantities, the Department will include material removed above the bench (if any), in front of the vertical plane described in 503.10.C.1, and by the finished slope of the cut or embankment.

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 include culvert excavation and backfill between the surface of the original ground, the flow line of the culvert, and 1:1 slopes from the outer face of the culvert with Item 203 quantities.  This item governs the remaining culvert excavation and backfill.

The Department will measure Unclassified Excavation on a lump sum basis when shown on the plans.

The Department will measure Cofferdams, Cribs, and Sheeting on a lump sum basis.

503.11  Basis of Payment.  If Cofferdams, Cribs, and Sheeting is not included in the Contract, the Department will pay for cofferdams, cribs, and sheeting under the contract unit price for excavation.

The elevations shown on the plans for the bottoms of footings and cast-in-place box culverts 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 503.10.C.1 at the unit price bid for the class of excavation.

The Cofferdams, Cribs, and Sheeting 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 109.04.

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: