Section II – Structure Excavation and Backfill For Pump Station
PART I – GENERAL
1.01 WORK INCLUDED
A. The work included under this Section consists of clearing, excavating, backfilling and grading required for the con- struction of the pumping station dry well and wet well as shown on the Drawings and as specified herein.
B. Plan For Excavation: The Contractor shall be responsible for having determined to his satisfaction, prior to the submission of his bid, the conformation of the ground, the character and quality of the substrata, the types and quantities of materials to be encountered, the nature of the groundwater conditions, the prosecution of the work, the general and local conditions and all other matters which can in any way affect the work under this Contract. Prior to commencing the excavation, the Contractor shall submit a plan of his proposed operations to the Engineer for approval. The Contractor shall consider, and his plan for excavation shall reflect, the equipment and methods to be employed in the excavation. The prices established in the Proposal for the work to be done will reflect all costs pertaining to the work. No claims for extras based on substrata or groundwater table conditions will be allowed.
1.02 QUALITY ASSURANCE
A. A Testing Laboratory retained by the Contractor will make such tests as are deemed advisable. The Contractor shall schedule his work so as to permit a reasonable time for testing before placing succeeding lifts and shall keep the laboratory informed of his progress.
PART 2 – PRODUCTS
2.01 MATERIALS
A. Suitable: Suitable materials for backfill shall be classified as A-1, A-3, or A-2-4 in accordance with AASHTO Designation M 145 and shall be free from vegetation and organic material. Not more than 12 percent shall pass the No.200 sieve.
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B. Unsuitable: Unsuitable materials are classified as A-2-5, A-2-6, A-2-7, A-4, A-5. A-6, A-7 and A-8 in accordance with AASHTO Designation M 145.
C. Graded Limerock: Material for backfill below precast structures shall be 3/4-inch graded limerock or gravel.
PART 3 – EXECUTION
3.01 PREPARATION
A. Clearing:
1. The construction site shall be cleared of all obstructions and vegetation, including large roots and undergrowth, within 10-feet of the structure lines.
2. Strip and stockpile topsoil.
B. Removals: Complete all removals within the lines of excavation prior to beginning excavation.
3.02 INSTALLATION
A. Excavation:
1. The Contractor shall perform all excavation of every description and of whatever substances encountered, to the dimensions required for construction and as specified herein. All excavations shall be made by open cut.
2. Walls of the excavation shall be kept vertical and, if required to protect the safety of workmen, the general public, this or other work or structures, or excavation walls, the excavation shall be properly sheeted and braced.
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Excavation for the structures shall be sufficient to provide a clearance between their outer surfaces and the face of the excavation, sheeting, or bracing, of not less than 2-feet. Materials encountered in the excavation which have a tendency to slough or flow into the excavation, undermine the banks, weaken the overlying strata, or are otherwise rendered unstable by the excavation operation shall be retained by sheeting, stabilization, grouting or other approved methods. Excavation for structures shall be required to be dewatered.
3. Excavation for the precast or prefabricated structures shall be carried to an elevation 1-foot lower than the proposed outside bottom of the structure to provide space for the select backfill material.
4. Excavation for structures constructed or cast in place shall be carried down to the bottom of the structure where dewatering methods are such that a dry excavation bottom is exposed and the naturally occurring material at this elevation leveled and left ready to receive construction.
Material disturbed below the foundation elevation shall be replaced with Class B concrete. (See Section III.)
B. Dewatering (When Required): Any water which accumulates in the excavation for structures shall be removed promptly by well point system or by other means satisfactory to the Engineer in such a manner as to not create a nuisance to adjacent property or public thoroughfare. Pumps and engines for well point systems shall be operated with mufflers and at a minimum noise level suitable to a residential area. The Contractor shall be responsible for any nuisance created due to the disposal of water from his drainage system.
C. Stockpiled Materials: Materials removed from the excavation shall be stored and disposed of in a manner which will not interfere with traffic at the site. Material suitable for backfill not needed for backfill at the structure, but needed elsewhere shall be stockpiled until moved and used elsewhere. Material unsuitable for use in backfill and surplus suitable material not required elsewhere shall remain the property of the Owner and shall be removed and disposed of by the Contractor at the Contractor’s expense as directed by the Engineer.
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D. Backfill:
1. Below Precast or Prefabricated Structures: The space between the proposed outside bottom of the structure, and the bottom of the excavation shall be backfilled with graded limerock and screened level to receive the proposed structure.
2. Remainder Of Backfill: Selected material from the excavation shall be used for backfilling around the structure. Trash shall not be allowed to accumulate in spaces to be backfilled. Backfill around the structure shall be placed in uniform layers to the level of the water table. Above the water table, backfill material shall be placed in 8-inch layers and compacted to a minimum of 95 percent of maximum density as determined by AASHTO Designation T 180. Backfilling shall be carried to the finished grades shown on the Drawings.
3.Backfill For Structures Constructed Or Cast-In-Place: Backfill shall not be placed until the structure has been completed above the natural water table, is stable against hydrostatic uplift, exterior from work has been removed and any necessary patching and grouting has been completed. Dewatering operations may then be stopped and backfill shall be placed as specified in Subparagraph D.2. above. Backfilling shall not commence until concrete to be covered has been inspected and approved.
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