Charleston Water System Chooses Sliplining with 8" Fusible C-900® Pipe to Replace Corroded Wappoo Road Iron Water Main

When Arcadis was assigned the task of designing a replacement pipeline for a 12" water main in Charleston, South Carolina, several installation options were explored including direct bury in the same ditch, open cutting a new right-of-way, and trenchless options such as pipe bursting or lining. Replacing the line with ductile iron pipe would have required special coatings and protection due to the corrosive nature of the salt marsh soils in the area. As a result, the design team turned to plastic pipe options. The direct bury option was also quickly discarded as too expensive and disruptive to a neighborhood where the alignment was bordered on one side by homes and the other by the Stono River.

During the preliminary design phase, Charleston Water System (CWS) suggested that a 12" diameter line along a section of Wappoo Road might be oversized due to system improvements completed over the previous decade. Arcadis further examined this possibility and concluded that an 8" replacement water main would indeed be sufficient to achieve the required flow rates. The owner and engineer then examined the pros and cons of sliplining the 12" main with 8" Fusible C-900® pipe. Ultimately, the benefits of improved performance, lower project cost, and reduced disturbance to the surrounding neighborhood made sliplining the preferred installation approach.

General Site Conditions

Pipeline Details and Project Summary
Owner: Charleston Water System
Project: Wappoo Road Water Main Slipline
Engineer: Arcadis
General Contractor: B & C Utilities, Johns Island, SC
Host Pipe: 12" Cast Iron
Replacement Pipe: 4,940 LF of 8" DR18 Fusible C-900®
Slipline & Fusion Sub: Carroll Enterprises LLC, Walterboro, SC
UGSI Contact: Gary Shepherd (804) 677-8950

Construction began with the above-ground installation of a 4" polyethylene bypass line to maintain potable water service to the residents on Wappoo Road. Shortly thereafter, access pits were dug to expose the existing host pipe to allow sliplining operations to begin. A directional drill rig was used to push rods through the host pipe to connect to the pre-fused pipe lengths for sliplining pullback. Known services and connection locations on the existing pipe were precut prior to pull-in of the Fusible C-900® pipe. Valves and fittings were then cut into the line and service taps were completed. Up to 800 LF of pipe was pulled in at one time, including sections through a curved alignment with a radius of approximately 500 feet. Following installation, the line was pressure tested to 150 psi and disinfected to prepare for transfer of services back to the new pipeline. Finally, the annular space was grouted with a low strength flowable fill to stabilize the system against both thermal and external load.

Both owner and consultant were pleased enough with the resulting installation that a change order was issued to slipline an additional 1,200 LF. In total, over 4,900 LF of 12" DIP was rehabilitated with an equal length of 8" Fusible C-900® pipe between March and June 2010.

The following page illustrates the sequence of construction tasks completed by the contractors that performed the work.

Wappoo Road Slipline Project: Sequence of Construction Operations

1) Installation of Temporary Bypass Line

2) Cutting Host Pipe for Access

3) Preparation for Curved Section Pull-In

4) Fusible C-900® Pipe Enters Host Pipe

5) Installation of MJ Fittings for Connections

6) Grouting Operations