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The work covered by this section consists of the excavation of any material whose removal is necessary for the construction of foundations, end bent caps, and pile encasements for bridges, retaining walls of reinforced concrete or reinforced masonry, arch culverts, and box culverts without floor slabs, in accordance with the plans and these specifications or as directed by the Engineer. Excavation shall include the construction and subsequent removal of all necessary bracing, shoring, sheeting, cribbing, and cofferdams; and all pumping, bailing, and draining. The work shall also include the placing of suitable excavated material as backfill, and the disposal of surplus or unsuitable excavated material as permitted by the Engineer.
Excavated materials shall not be deposited, nor shall earth dikes or other temporary earth structures be constructed, in rivers, streams, or impoundments or so near to such waters that they will be carried into any river, stream, or impoundment by stream flow or surface runoff. As an exception to the above, confined earth materials in cofferdams for structure foundations will be permitted when approved in writing by the Engineer.
All materials shall meet the requirements of Division 10 shown below:
Subdrain fine aggregate Article 10441
Stone, No. 78M Section 1005
Prior to starting excavation operations at any structure site, all necessary clearing and grubbing at the site shall have been performed in accordance with Articles 2003 and 2004.
The Contractor shall clear and grub where excavation for foundations is to be performed. At bridge sites, the Contractor shall also clear the entire width of the right of way beginning at a station 3 feet back of the beginning extremity of the structure and ending at a station 3 feet beyond the ending extremity of the structure. As an exception to the above, clearing and grubbing shall not be done in areas where excavation is to be performed under another contract in accordance with Section 225 or where embankment is to be constructed in accordance with Section 235.
All timber, stumps, and debris shall be disposed of by the Contractor in accordance with Article 2005.
The Contractor shall notify the Engineer a sufficient time before beginning the excavation so that measurements may be taken of the undisturbed ground.
Where necessary for safety, the foundation openings shall be sloped, shored, braced, or protected by cofferdams in accordance with local and State safety standards. Foundation excavation and related work shall be done in such sequence that no portion of the structure will be endangered by subsequent operations. Completed portions of a structure shall be adequately protected during blasting operations.
In addition to the above requirements, shoring will be required for excavation adjacent to a travelway when a theoretical 2:1 slope from the bottom of the excavation on the roadway side intersects the existing ground line closer than five feet to the existing edge of pavement. Where excavation for foundations or footings is required adjacent to a traveled way, the method of shoring, sheeting, or bracing the foundation opening shall have been submitted to the Engineer for review and comment before beginning the excavation. The Contractor shall submit one set of design calculations and 7 copies of drawings showing details of his proposed method of excavation protection including step by step installation procedure. Shoring shall be designed and detailed by a North Carolina Registered Professional Engineer. The provisions of Subarticle 4105(D) will be applicable to such drawings.
The dimensions and elevations of footings, as shown on the plans, shall be considered as approximate only and the Engineer may order, in writing, such changes in dimensions or elevations of footings as may be necessary to secure a satisfactory foundation.
After each foundation has been excavated, the Contractor shall notify the Engineer. No concrete shall be placed until the Engineer has approved the depth of the excavation and the character of the foundation material and has given permission to proceed.
If the Engineer determines it is necessary to drill in order to obtain information as to the depth to which the rock or other hard foundation material extends below the bottom of the footing, the Contractor shall perform such drilling as may be required.
All rock or other hard foundation material shall be cleaned of all loose material and cut to a firm surface, either level, stepped, or serrated, as directed by the Engineer. All seams shall be cleaned out and filled with concrete, mortar, or grout. All loose and disintegrated rock and thin strata shall be removed. The rock surface shall be left in a rough condition so as to form an adequate key against lateral movement of the footing.
When the footing is to rest on an excavated surface other than rock, special care shall be taken not to disturb the bottom of the excavation until immediately before placing reinforcing steel and concrete. Foundation material which has been softened and weakened by exposure and inundation shall be removed to sound, solid material before placing steel and concrete.
When foundation piles are used, the excavation of each pit shall be completed before driving piles is begun.
When pile driving liquifies the soil, or the bed is otherwise unsuitable as determined by the Engineer, the Contractor shall remove the material as required and backfill with an approved granular material to the required elevation. Such work will be paid for as extra work in accordance with Article 1047.
(A) General:
The term cofferdam designates any temporary or removable structure which is constructed to hold the surrounding earth, water, or both, out of the excavation. It includes timber cribs, any type of sheet piling, removable steel shells, or similar structures, and all necessary bracing; and it shall be understood to also include the use of pumping wells or well points for the same purpose. Cofferdams located in bodies of water shall be designed and detailed by a North Carolina Registered Professional Engineer when the distance from the water surface to the bottom of the excavation is 5 feet or greater.
(B) Construction:
Cofferdams shall be carried to adequate depths and heights, be safely designed and constructed, and be as water-tight as is necessary for the proper performance of the work. The interior dimensions of cofferdams shall be such as to give sufficient clearance for the construction and inspection of forms and to permit pumping outside the forms. Where a foundation seal is not required by the plans, clearance between the proposed edge of footing and inside face of cofferdam shall be at least 5 feet when a keyed footing is required and at least 3 feet when a keyed footing is not required. Cofferdams which are tilted or moved laterally during the process of sinking shall be righted, and rest or enlarged so as to provide the necessary clearance.
Cofferdams shall be constructed so as to protect plastic concrete against damage from a sudden rising of the stream and to prevent damage to the foundation by erosion. No timber or bracing shall be left in cofferdams in such a way as to extend into the substructure concrete without permission of the Engineer.
(C) Foundation Seals:
The Contractor shall take reasonable measures to dewater cofferdams without the use of a foundation seal unless a foundation seal is shown in the plans for the substructure unit involved.
If in the opinion of the Engineer the Contractor has used all reasonable measures to provide a dewaterable enclosure and the cofferdam cannot be dewatered, the Engineer may allow construction of a foundation seal of such dimensions and elevations as deemed necessary by the Engineer. Reasonable measures shall include, but not be limited to, the driving of all sheeting to a sufficient depth below plan bottom of footing elevation or else providing a double walled cofferdam lined with clay or other reasonably impervious material. The seal shall be constructed in accordance with Article 4208 or as required by the Engineer. After dewatering, the remaining concrete shall be placed in the dry.
When a foundation seal is not shown in the plans, but a seal is allowed by the Engineer, the seal shall be constructed at no cost to the Department, except for the pier column concrete allowance provided for in Subarticle 42021(C).
(D) Drawings:
The Contractor shall submit to the Engineer for review and comment when required by the plans, special provisions, Article 4104, or Article 4105(A), one copy of design calculations and 7 sets of drawings showing his proposed method of cofferdam construction and other details left open to his choice or not fully shown on the plans. The type and clearance of cofferdams, insofar as such details affect the character of the finished work, will be subject to the review of the Engineer, but other details of design will be left to the Contractor, who will be responsible for the adequacy of the work.
(E) Removal:
Unless otherwise provided on the plans or in the special provisions, cofferdams with all sheeting and bracing shall be removed to the stream bed or 1 foot below existing ground after the completion of the substructure. Care shall be taken not to disturb or otherwise injure the finished concrete.
Pumping from the interior of any foundation enclosure shall be done in such a manner as to preclude the possibility of the movement of water over or through any fresh concrete. No pumping will be permitted during the placing of concrete, or for a period of at least 24 hours thereafter, unless it be done from a suitable sump separated from the concrete work by a substantially water-tight wall.
Pumping to dewater a sealed cofferdam shall not begin until the seal has set sufficiently to withstand the hydrostatic pressure, and in no case less than 7 days after placing or such additional length of time as the Engineer may direct.
410-7 PRESERVATION OF CHANNEL.
Unless otherwise required by the plans or special provisions or permitted by the Engineer no excavation in stream channels shall be made outside of cofferdams. The natural stream bed adjacent to the structure shall not be disturbed without permission from the Engineer. If any excavation or dredging is made at the site of the structure outside of the cofferdam limits, the Contractor shall backfill all such excavation to the original ground surface or river bed with material approved by the Engineer.
Materials placed within the stream area shall be removed and the stream left in its original condition, unless otherwise permitted by the Engineer.
410-8 UTILIZATION OF EXCAVATED MATERIAL.
Suitable excavated material shall be utilized as backfill. Suitable material that is not required for backfill shall be used in the formation of embankments, subgrades, or shoulders. When so utilized, no additional payment will be made for utilization of the material under other pay items or for stockpiling the material for use under other pay items. The Contractor shall furnish disposal areas for excavated materials determined to be unsuitable by the Engineer and for suitable materials not required for use in connection with other work included in the contract. In no case shall excavated material be placed in a stream or other body of water.
No excavated material shall be deposited at any time so as to endanger the partly finished structure, either by direct pressure or indirectly by overloading banks adjacent to the operations, or in any other manner.
410-9 BACKFILLING AND FILLING.
All material used for backfill shall have been approved by the Engineer and shall be free from large or frozen lumps, wood, or other undesirable material. Where there is not an adequate quantity of suitable backfill material available from the excavation, the Contractor will be responsible for providing suitable backfill material and will be compensated for such backfill material as provided for in Subarticle 41014(C).
All excavated spaces not filled with permanent work shall be refilled with earth up to the ground surface existing before the excavation was made. Backfill shall be placed to provide adequate drainage as soon as concrete surfaces have been finished in accordance with Subarticle 42018(B) and the concrete has been inspected and approved by the Engineer. The Engineer will have the authority to suspend all operations until such backfilling has been acceptably completed.
Any slope adjacent to the excavation for abutments, wingwalls, and retaining walls shall be eliminated by stepping or serrating to prevent wedge action.
All portions of the backfill that become a part of roadway typical sections or their foundations shall be compacted in accordance with Subarticle 2354(C). All other portions of the backfill shall be placed in layers not more than 6 inches in depth loose measure and shall be compacted to a density comparable to the adjacent undisturbed material.
In placing backfill or embankment, the material shall be placed simultaneously insofar as possible to approximately the same elevation on both sides of an abutment, pier, or wall. If conditions require placing backfill or embankment higher on one side, the additional material on the higher side shall not be placed until the concrete has developed the minimum specified strength for the class of concrete required for the structure.
Backfill or embankment shall not be placed behind the walls of concrete culverts or abutments of rigid frame structures until the top slab is placed and has developed the minimum compressive strength required by Article 42020. The backfill and embankment shall be carried up simultaneously behind opposite abutments of rigid frames or sidewalls of culverts.
Backfill or embankment shall not be placed behind the abutments of bridges other than rigid frames until the concrete has developed the compressive strength required by Article 42020. This backfill shall be placed to a minimum elevation of 1 foot below the bridge seats before beams or girders are set.
Backfill shall be done so as not to cause excess lateral forces against the structure by heavy equipment or from earth masses transmitting pressures caused by earth moving equipment. Backfill immediately adjacent to the structure shall be done by hand operated mechanical tampers. Heavy earth moving equipment shall not operate within 10 feet of the structure in backfilling operations.
410-10 SUBSURFACE DRAINAGE AT WEEP HOLES.
A stone drain consisting of 1 cubic foot of No. 78M stone contained in a bag of porous fabric shall be placed at each weep hole. Weep holes shall be covered on the fill face side with hardware cloth of commercial quality, approximately 4 mesh, of aluminum or galvanized steel wire. Subdrain fine aggregate shall be placed beneath, around, and over the stone drain so that the stone drain is covered by a layer of subdrain fine aggregate at least 1 foot thick. A horizontal drain of subdrain fine aggregate at least 1 foot square in cross section shall then be placed to connect all stone drains. In the case of abutments and retaining walls, in addition to the above requirements a vertical drain of subdrain fine aggregate at least 1 foot square in cross section shall be placed at each weep hole to an elevation 2 feet below the subgrade or surface of the embankment.
When embankment around the structure is to be placed as part of another contract, the portion of the subsurface drainage system described above which is located in such embankment will not be considered part of the work of this section.
410-11 SUBSTRUCTURE SCOUR PROTECTION.
Substructure scour protection shall be provided as indicated in the plans. The two to six inch size stone shall be placed after footing formwork has been removed and while the excavation is dewatered. The rip rap stone shall be placed before the cofferdam sheeting is removed, either before or after the excavation is allowed to flood. When no sheeting is used, each stone type shall be placed to the required thickness and shall extend horizontally to the undisturbed material.
The two to six inch size Scour Protection Stone shall be hard and durable in nature. While no specific gradation is required the various sizes of stone shall be reasonably equally distributed within the required size range. The stone shall be essentially cubical in shape.
410-12 BLASTING ADJACENT TO HIGHWAY STRUCTURES.
Blasting operations adjacent to highway structures shall be conducted in accordance with the following requirements.
No blasting operation shall be conducted within 60 feet of any structure until the concrete strength has reached 2400 PSI. After the concrete has achieved a strength of 2400 PSI, the maximum peak particle velocity shall be limited to four (4) in./sec. as measured at the closest structure extremity.
For multi-column bents with column heights up to 40 feet and a combined span length for the two adjacent spans of 160 feet or less, the following criteria shall apply:
1. Blasting within 6 feet will not be permitted without obtaining prior written approval from the Engineer.
2. At distance of 6 to 10 feet, a quantity of explosives equivalent to 1/2 pound per delay period is the maximum charge weight allowed.
3. From 11 to 60 feet, a maximum charge weight per delay of 1/2 pound + 1/2 pound of explosives per foot of distance over 10 feet is allowed as a safe charge weight.
If the criteria mentioned above cannot be met, the structure shall be monitored with an engineering seismograph to determine true ground vibration levels at the structure.
For single column bents (hammerheads), or multi-column bents outside the range of column height or span length listed above, the Contractor will be required
to submit a blasting plan to the Engineer prior to conducting any blasting operation.
On all projects, the Contractor shall evaluate each proposed blast and if he deems necessary, more restrictive controls than those listed in the provision shall be used to prevent damage.
Payment of blasting operations shall be included in the bid price for Foundation Excavation at the affected substructure unit.
(A) Cubic Yard Basis:
Where the contract calls for foundation excavation to be paid for on a cubic yard basis, the quantity of foundation excavation to be paid for will be the actual number of cubic yards of materials, measured in their original position within the limits described below and computed by the average end area method, which have been acceptably excavated in accordance with the plans and specifications, or as directed by the Engineer.
The upper limits for measurement will be the actual ground surface at the time of starting work, except that where the excavation is to be performed in cut areas excavated under Section 225 the upper limits will be the roadway plan typical section. For keyed footings the upper limits of the keyed section shall be as shown on the plans. A keyed footing is a footing which has been placed without forms for the keyed depth in an excavation whose sides, as near as practicable, are located at the neat line dimensions of the footing and are vertical.
When the foundation material is other than rock, the lower limits for measurement will be the elevation of the bottom of footing as established by the plans or as directed by the Engineer. When the foundation material is rock, the lower limits for measurement will be the actual rock elevations after the foundation has been approved by the Engineer.
As an exception to the lower limits established above, when in the opinion of the Engineer excess excavation has been performed due to carelessness or negligence on the part of the Contractor, the Engineer shall notify the Contractor of that portion of the excavation which will not be measured for payment.
Horizontal limits for measurement will be established by vertical planes located 18 inches outside of the neat line dimensions of the footing as established by the plans or directed in writing by the Engineer. For keyed footings the horizontal limits for measurement of the keyed section will be established by vertical planes located at the neat line dimensions of the footing as established by the plans or directed in writing by the Engineer.
Measurement will include mud, muck, or similar semi-solid material within the limits described above provided such material was present at the time excavation was begun and further provided that such material cannot be drained away or pumped without the use of a jet or nozzle.
No measurement will be made of the following excavation, as such excavation will be considered as incidental to the work covered by this section:
1. Excavation necessary to construct end bent caps and the berm adjacent to the cap.
2. Excavation necessary to construct pile encasement.
3. Excavation outside of the limits described in this subarticle.
4. Excavation made necessary by the heaving of a foundation due to the driving of piles.
5. Excavation made necessary by overbreaks or slides.
6. Mud, muck, or similar semi-solid material which can be drained away or pumped without the use of a jet or nozzle.
7. Excavation made before the Engineer has made measurements of the undisturbed ground.
8. Excavation made necessary due to exposure or inundation allowed by the Contractor, or carelessness on the part of the Contractor.
(B) Lump Sum Basis:
Where the contract calls for foundation excavation to be paid for on a lump sum basis, no measurement will be made of any foundation excavation made at such locations.
(A) Cubic Yard Basis:
The quantity of foundation excavation, measured as provided in Subarticle 41013(A), will be paid for at the contract unit price per cubic yard for "Foundation Excavation" except as otherwise provided below.
Where the Engineer directs the Contractor in writing to excavate below the original plan elevation of the bottom of the footing, payment for such excavation will be made as follows:
1. For excavation made below the original plan elevation of the bottom of the footing to an elevation 3 feet below such plan elevation, payment will be made at the contract unit price per cubic yard for "Foundation Excavation".
2. For excavation made below an elevation 3 feet below the original plan elevation of the bottom of the footing but not more than 6 feet below such plan elevation, payment will be made at 150 percent of the contract unit price per cubic yard for "Foundation Excavation".
3. For excavation made below an elevation 6 feet below the original plan elevation of the bottom of the footing, payment will be made as provided in Article 1047 for extra work.
4. In areas where piles have been driven, removal of material and backfilling with approved granular material, in accordance with Article 4104, will be paid for as extra work as provided in Article 1047.
(B) Lump Sum Basis:
Payment for the work of all foundation excavation at locations where the contract calls for payment on a lump sum basis will be made at the contract lump sum price for "Foundation Excavation for Bent No. __________ at Station ________________", except as otherwise provided below.
Where the Engineer directs the Contractor to excavate below the original plan elevation of the bottom of the footing by a distance which is less than 3 feet, the character of the work will not be considered to be materially changed and no additional compensation will be allowed for the foundation excavation at such location.
Where the Engineer directs the Contractor in writing to excavate more than 3 feet below the original plan elevation of the bottom of the footing, payment for such excavation will be made as provided in Article 1047 for extra work.
(C) Furnishing and Hauling Backfill Material:
Where it has been necessary for the Contractor to provide backfill material from sources other than excavated areas or borrow sources being used in connection with other work included in the contract, payment for furnishing and hauling such backfill material will be made as provided in Article 1047 for extra work. Placing and compacting such backfill material will not be considered as extra work, but will be considered incidental to the work covered by this section.
(D) Compensation:
When the Contractor has been directed by the Engineer to drill in the vicinity of a footing to obtain subsurface information, such drilling in excess of a 5 foot depth will be paid for as provided in Article 1047 for extra work.
The above prices and payments will be full compensation for all work covered by this section including but not limited to clearing and grubbing, excavation, exploratory drilling at footings to a depth not to exceed 5 feet, blasting, draining, diversion of water, bailing, pumping, bracing, shoring, sheeting, cribbing, cofferdams, concrete foundation seals when a foundation seal is not shown in the plans, drawings, backfilling, substructure scour protection, subsurface drainage, hauling, and disposal of materials.
(E) Pay Items:
Payment will be made under:
Foundation Excavation Cubic Yard
Foundation Excavation for Bent No. ____________
at Station __________ Lump Sum