Plan, Special Provision, and Utility Conflict at a Suburban Signal
A plan set for a new traffic signal at a suburban intersection shows 165 ft of 2-in Schedule 40 PVC conduit from the controller cabinet to the northwest strain pole. The general notes require 30 in of cover under pavement, 24 in under unpaved shoulder, and 5 ft of horizontal clearance from water mains. During layout, the utility locate marks an 8-in ductile iron water main crossing the proposed alignment at 3.5 ft horizontal clearance. The plans reference a Standard 5-12 conduit detail, but that standard is not in the specification book provided. The special provisions state that all conduit under pavement must be Schedule 80. The crew has already excavated 40 ft of trench in the shoulder. The quantity table lists 165 ft, but routing around the water main would require about 210 ft. The owner's inspector is on site and asks how you want to proceed.
1. The 2-in Schedule 40 PVC shown on the plan conflicts with the special provision requiring Schedule 80 under pavement. Which document governs, and what should you do before the crew continues?
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The contract's order of precedence controls. In most public works contracts the special provisions outrank the plans, which outrank the standard specifications and standard details; confirm the exact order in the contract's Order of Precedence or Interpretation section. Because the special provision specifically addresses conduit under pavement, the Schedule 80 requirement governs over the plan's Schedule 40 callout. The missing Standard 5-12 is a separate defect and must not be assumed. Stop work on the affected run, measure and photograph the location, and submit an RFI asking for the correct detail and confirmation whether Schedule 80 applies only under pavement or to the entire run. Do not install Schedule 40 in the pavement crossing while the RFI is open. If the owner gives a verbal direction, confirm it in writing before proceeding, otherwise the contractor may bear the removal and replacement cost.
2. The water main leaves only 3.5 ft of horizontal clearance against a 5-ft requirement. Identify at least three resolution options and the approval needed for each.
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The crossing cannot be built as laid out without an approved resolution. Options include: (1) shift the conduit alignment horizontally or vertically to achieve 5 ft, which may require additional fittings or a deeper trench; (2) install a steel casing or concrete encasement around the conduit for the crossing length, with the water utility's written approval; (3) ask the water utility to relocate or lower its main by agreement; (4) directional-drill beneath the main at a verified clearance. Each option needs the water utility owner's approval and usually the design engineer's and owner's approval; a field verbal OK is not enough. First pothole the main to confirm the locate is accurate, then submit the proposed solution with a sketch and clearances. Do not backfill until the inspector signs off.
3. The run may grow from 165 ft to 210 ft. How should the quantity change be processed?
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Use the contract's measurement and payment provisions. If the bid item is a unit-price item measured in linear feet actually installed, the additional 45 ft is measured and paid at the contract unit price, subject to any overrun/underrun clause or change-order threshold. If the quantity table was a stipulated lump sum or the change exceeds the contract threshold, prepare a change order with field measurements, a plan showing the revised route, and the reason for the change. Document the original 165 ft and the as-built 210 ft with measurements witnessed by the inspector. Do not proceed on the assumption of payment without written authorization; many contracts require notification before installing extra work. Keep the RFI, utility approval, and change order in the project file.