North Shore Force Main Emergency Rehabilitation
San Francisco, CA
Due to repeated failures of an existing 36-inch steel force main, the San Francisco Public Utilities Commission (SFPUC) elected to rehabilitate the sewer force main under an emergency procured design-build contract. The existing steel force main was installed along the historic road, The Embarcadero. The shoreline drives along San Francisco Bay adjacent to the Ferry Building. LAN provided technical support for the contractor, Shimmick Construction Company.
Because of the deteriorating state of the existing 36-inch steel force main, the sliplining 28” HDPE pipe was designed to withstand the full internal pressure and external loading which included grouting of the annular space. Due to the obstructions in place during the construction of the original 36” force main, there were multiple double offsets throughout the line (ranging from 5 degrees to 14 degrees). In a few locations, the bends were within a few feet of each other presenting complications in the necessary sliplining process, utilizing 2,550-ft of HDPE pipe as a replacement for the original pipeline.
LAN provided recommendations for annular space-grouting, thrust restraints, and using controlled low strength material (CLSM) as backfill during construction.
At a glance
Design-Build Contract value was $4,141,000
2,600 feet of 36-inch diameter pipe rehabilitated
Emergency Contract: 120 calendar days
Work hours: 8 PM to 5 AM, close 3 lanes to 1. No more than a 24 hour shut down
Traffic count of 40,000 vehicles per day on the Embarcadero
Constant pedestrian traffic
Design Constraints: Pressure class of pipe & fittings; Multiple/sequential bends; Presence of prior repairs; Limited accessible points; Temporary reconnections
Evaluation of grouting options: Cement + bentonite; Injected from low point @ max 30 psi
Determination of allowable pull stresses
Flexibility in design
Method of thrust restraint
Pipeline Design, Assessment & Rehab