1993 SPECIFICATIONS CSJ SPECIAL SPECIFICATION ITEM 4110 CONCRETE ENCASED DUCT BANK

Transcription

1 1993 SPECIFICATIONS CSJ SPECIAL SPECIFICATION ITEM 4110 CONCRETE ENCASED DUCT BANK 1. DESCRIPTION. This Item shall govern for the furnishing and installation of all materials and equipment for construction of an underground, multiple conduit, electrical duct system of the materials indicated and to the lines, grades, and dimensions shown on the plans and as specified herein. During construction, the electrical duct bank system shall be subject to required inspections by Dallas Area Rapid Transit (DART) representatives. Inspectors shall be given a minimum of two (2) days notice prior to beginning each phase of the construction. To schedule inspections, call 214/ MATERIALS. The Contractor shall furnish all materials and equipment necessary for the safe, efficient construction of the duct system including, but not limited to, conduit, conduit fittings and accessories, bends, couplings, adapters, conduit spacers and concrete. Only materials and equipment which are new, adequate, and suitable shall be used for construction. The Contractor shall be responsible for all hauling, unloading, inspecting, handling, storing, and installation of duct system materials. All PVC conduit shall be stored on flat surfaces to avoid warping or deterioration and protected from direct rays of the sun. (1) Concrete. All concrete shall be Class A and conform to the requirements of Item 421, "Portland Cement Concrete" except as modified herein. Only Type I Portland cement shall be used. Coarse aggregate shall be one and one half (1 1/2) inches or smaller, including pea gravel. Concrete mix designs shall be made by an independent testing laboratory in accordance with Item 6, "Control of Materials", and submitted for approval in accordance with Item 5, "Control of Work". Mix design data shall include, but not be limited to, the following: Aggregate characteristics Water source Cement manufacturer and type Design factors Batch factor Design proportions Test results

2

3 Grout for the duct bank casings shall be a mix of the materials and proportions outlined below: Sand and Grout: 3,100 lb. Fly Ash: 282 lb. (3.0 sacks) Water: 310 lb. Portland Cement, Type II: 423 lb. (4.5 sacks) (2) Conduit. Conduit shall be new and free from blisters, cracks, or other injurious defects. It shall be of six (6) inches nominal diameter and conform to the requirements of Item 618, "Conduit". 3. CONSTRUCTION. (1) Excavation. Trenches for the duct system construction shall be excavated in accordance with the plans and specifications. Variation from the line and grade shown on the Plans will be permitted only to the extent of one (1) inch in 10 feet. The Contractor shall conduct the work to ensure protection of existing structures and utilities. Caution must be exercised to avoid the cutting or breaking of existing underground pipelines, utilities, and cables. Adequacy of sheathing and bracing shall be the responsibility of the Contractor and must meet the requirements of Item 402, "Trench Excavation Protection". Trenches shall be sheeted or braced adequately for stability of excavation to provide full safety for workers throughout the construction period. Trenches shall be kept drained of water prior to and throughout placement of duct systems. All water removed from trenches shall be disposed of into natural drainage ways or into storm sewers to prevent damage to property or inconvenience to the public. (2) Duct Bank Installation. All underground electrical conduits shall be installed in a duct bank conforming to the detailed configurations, alignment, and grade using spacers, reinforcing, and accessories, as detailed and as required. All spacers shall be of the proper sizes and configurations to construct the duct bank as shown on the plans and as specified herein. The conduits shall be installed to slope uniformly over the full length of the duct bank from the crown to the incomplete duct bank line temporary terminations except at cross section transitions due to duct bank rotation or between a trench and a bore and jack installation. No low pockets will be allowed at any point along the duct bank. Wherever possible, all changes of direction made shall be made with long sweep bends of at least 100 feet radius. Smaller radius sweeps shall be made only with the written permission of the Engineer, unless noted otherwise on the plans. Long sweep bends shall be made with one or more curved or straight sections of conduit. Manufactured bends, where permitted, shall have a minimum radius of not less than ten (10) times

4

5 the nominal conduit diameter. Where manufactured bends fifteen degrees (15) and larger are required, they shall be made with galvanized rigid steel conduit bends. The interior of conduit and fittings shall be inspected, and all moisture, oil, grease, or other foreign matter removed prior to assembly and installation. Conduit joints shall be assembled with a solvent cement of the specified type and applied in accordance with the written directions of the conduit manufacturer. All adjacent conduit joints shall be staggered at least six (6) inches so that no two lie in the same vertical plane. Joints may be placed side by side horizontally. All partially completed duct bank conduits shall be protected from the entrance of dirt and debris by means of suitable factory-made conduit plugs. Upon completion of the duct bank installation, ends of conduit intended for future extension shall be sealed by means of caps cemented into place. After the duct bank assembly has been completed and before placement of the concrete encasement, each conduit shall be checked for alignment and clear passage, in the presence of the Engineer, by the following method: (a) A stiff-bristled brush, of the same diameter as the conduit, shall be pulled through each conduit until it is clear of all particles of earth, sand, gravel or other debris. (b) A metallic mandrel with a diameter one (1) inch less than the bore of the conduits and a length equal to the conduit diameter shall be pulled through each conduit. The mandrel shall have a stiff leather or rubber gasket(s) near each end with an outside diameter 1/4 inch less than the bore of the conduits. Each gasket shall have a thickness 1/4 inch. The mandrel details shall be submitted for approval in accordance with Item 5, "Control of Work". (c) Once conduit alignment and clear passage have been assured, a 500 pound test nylon pull line (with the ends doubled back into the conduit) shall be installed in each conduit and the conduit ends plugged or capped, as directed by the Engineer. (3) Concrete Encasement. Upon approval of the duct bank installation by the Engineer, the Contractor shall erect concrete encasement forms. Forming shall conform to the requirements of Item 420, "Concrete Structures". Forming plans shall be submitted in accordance with Item 5, "Control of the Work". (4) Concrete Placement. Concrete transportation and placement shall conform to the requirements of Item 420, "Concrete Structures", except as otherwise specified herein. Construction joints will be permitted only at locations of conduit spacers. Pumping of concrete for grouting duct bank casings shall not proceed until the Engineer is satisfied that the available equipment and manpower is sufficient to place the concrete at the rate and in the

6

7 quantities required to complete the required placement without cold joints. Pumping or pneumatic conveying equipment shall be of a suitable type with adequate pumping capacity to place the concrete mixture throughout the length of the duct bank casing as outlined below. The loss of slump in pumping equipment shall not exceed one (1) inch. Grout mortar pumped into the line to act as a lubricant shall not be used in the casing. No salt or other chemicals shall be used for the prevention of freezing. Forms, coverings, or other concrete protection used during cold weather curing shall remain in place for a minimum period of twentyfour (24) hours after any artificial heating has been discontinued. In hot weather, suitable precautions shall be taken to avoid drying of the concrete prior to finishing operations. Use of windbreaks, sunshades, fog sprays, or other devices shall be provided as required. Concrete deposited in hot weather shall not have a placing temperature that will cause difficulty from loss of slump, flash set, or cold joints. The concrete temperature shall be less than 90 F unless otherwise directed by the Engineer. Concrete shall be kept moist for at least five (5) days after placement. Longer periods of curing, as directed by the Engineer, shall be required when temperatures are below 50 F. (5) Patching. Immediately after stripping of forms, minor defects and honeycombed areas on concrete surfaces shall be patched. Areas to be patched will be chipped to at least one (1) inch depth with regular edges perpendicular to the surface. Patched areas and a six (6) inch area surrounding each patch shall be thoroughly wetted just prior to placing patching mortar. Patching mortar shall be prepared from the same materials and in the same proportions as those used for the concrete except that coarse aggregate shall be omitted. Water in the mix shall be kept to a minimum. Mortar shall be allowed to stand for one (1) hour prior to its use, during which time it shall be periodically mixed to prevent setting. It shall then be placed and compacted to leave patch slightly higher than the surrounding surface. After two (2) hours, the patch surface shall be finished flush to adjoining work. Patches shall be kept wet for at least five (5) days in conjunction with other curing procedures. (6) Backfill. Upon completion of concrete curing and patching, and with the approval of the Engineer, excavations for the duct bank shall be filled and compacted to the level of the finished ground line. Selected material excavated from the trench may be used for backfilling excavations around the duct bank encasement. No rock larger than two (2) inches shall be used in the backfill. Non-selective pushing of excavated material into the trenches will not be permitted. Backfill material shall be placed and spread in layers not to exceed eight (8)

8

9 inches, loose depth, and compacted to the required density using mechanical tampers or other approved compaction methods. Fill material shall be compacted to a minimum of ninety percent (90%) of maximum dry density in accordance with ASTM D 698, Standard Proctor Test. 4. MEASUREMENT. Duct bank will be measured by the linear foot, complete in place. Such measurement shall be made between the extreme ends of the conduit, of the type specified, along the grade of the duct bank as installed. 5. PAYMENT. The work performed and the materials furnished as prescribed by this Item and measured as provided under "Measurement" will be paid for at the unit price bid per linear foot for "Concrete Encased Duct Bank", of the type specified, this price shall be full compensation for all excavation and backfill; for furnishing and placing all electrical conduit, conduit fittings and accessories, conduit mounting brackets and hardware, spacers, accessories, casings, and other required duct bank assembly materials; for furnishing and placing all concrete for duct bank encasement; for all cleanup, removal, and disposal of spoils; and for all labor, tools, equipment, transportation, services and incidentals necessary to complete the Work.

10