Laserfiche WebLink
4. The Contractor shall use appropriate means such as a clean-out bucket, to clean the <br /> bottom of the excavation such that a minimum of 50 percent of the base of each shaft <br /> will have less than 1 inch of sediment at the time of placement of the concrete. The <br /> maximum depth of sediment or any debris at any place on the base of the shaft shall not <br /> exceed 27 inches. <br /> 5. When unexpected obstructions, which require specialized equipment and/or labor are <br /> encountered, the Contractor shall notify the Engineer promptly and the obstructions shall <br /> be removed and the excavation continued as directed by the Engineer. <br /> Excavation Inspection <br /> 1. The Contractor shall provide equipment for checking the dimensions and alignment of <br /> each permanent shaft excavation. The dimensions and alignment shall be determined by <br /> the Contractor under the direction of the Engineer. <br /> 2. Final shaft depths shall be measured with a suitable weighted tape or other approved <br /> methods after final clean-out. <br /> 3. Shaft cleanliness will be determined by the Engineer, by visual inspection. <br /> 4. The excavated shaft shall be approved by the Engineer prior to placing any steel or <br /> concrete into the shaft. <br /> Reinforcing Steel Cage Construction and Placement <br /> 1. The reinforcing steel cage consisting of longitudinal bars, ties, cage stiffener bars, <br /> spacers, centralizers, and other necessary appurtenance shall be completely assembled <br /> and placed as a unit immediately after the shaft excavation is inspected and accepted <br /> prior to concrete placement. The reinforcing cage shall be rigidly braced to retain its <br /> configuration during handling and when lowered into the shaft, during placement of <br /> concrete and extraction of the casing from the shaft. No loose bars will be permitted. The <br /> reinforcing steel fabricator shall include bracing and any extra reinforcing steel required <br /> to fabricate the cage in the shop drawings. <br /> 2. If the bottom of the constructed shaft elevation is lower than the bottom of the shaft <br /> elevation in the Plans, a minimum of % of the longitudinal bars required in the upper <br /> portion of the shaft shall be extended the additional length. Tie bars shall be continued <br /> for the extra depth, spaced on 2 feet centers, and the stiffener bars shall be extended to <br /> the final depth. These bars may be lap spliced, or unspliced bars of the proper length <br /> may be used. Welding to the planned reinforcing steel will not be permitted unless <br /> specifically shown in either the Plans or Special <br /> Provisions. <br /> 3. The reinforcing steel in the shaft shall be tied and supported so that the reinforcing <br /> steel will remain within allowable tolerances given in this Specification. Concrete spacers <br /> or other approved noncorrosive spacing devices shall be used at sufficient intervals <br /> (near the bottom and at intervals not exceeding 5 feet up the shaft) to insure concentric <br /> spacing for the entire cage length. Spacers shall be constructed of approved material <br /> equal in quality and durability to the concrete specified for the shaft. <br /> 4. The elevation of the top of the steel cage shall be checked before and after the <br /> concrete is placed. If the rebar cage is not maintained within the specified tolerances, <br /> Swift Green Line—Corridor Stations Special Provisions SP121 <br /> May 2017 <br />