Cigmat01

Sliplining Rehabilitation of Large Diameter Sewers

Richard C. Turkopp, P.E., Technical Director

Hobas Pipe USA, Inc., Houston, TX
(281) 821-2200; rickt@hobaspipeusa.com

Abstract
Much of this nation’s infrastructure is very deteriorated and requires significant updating in order to maintain service levels. Included in this widespread need is the vast network of sanitary sewers. Since these pipelines are almost exclusively underground, direct replacement by open cut methods would likely be cost prohibitive as well as very disruptive to surface activities. For these reasons, several in-place renewal techniques have been developed to rehabilitate sewer lines with minimal excavation. One such method is lining the existing host pipe with a new, factory-made, slightly smaller pipe. This process is called sliplining.

Introduction
Sliplining is a semi-trenchless renewal method since access to the host pipe is gained by excavating a pit above the existing line and removing the top half of that pipe for a distance long enough to insert the new liner pipes. Prior to lining the existing pipe, generally, any debris, sludge or other material that may prevent passage of the liner pipe, must be removed. After lining, typically laterals are reconnected by point excavation. Grouting of the residual annular space to secure the liner position and improve resistance to external loads normally completes the installation. Several different types of pipes are used in sliplining including PVC, HDPE and fiberglass (primarily centrifugal cast fiberglass reinforced polymer mortar, acronym CCFRPM).

Diameters and Joints
Each of the pipe material types is available in specific diameter ranges and generally with one of two joint types; gasket-sealed bell-spigot (segmented system) or fused ends (continuous system).

Pipe Material Diameters Joint / System Installation

PVC </= 54” Gasket-sealed / Segmented Push-in
HDPE-Solid wall </= 54” Fused ends / Continuous Pull-in
HDPE-Profile wall </= 144” Gasket-sealed / Segmented Push-in
CCFRPM </= 102” Gasket-sealed / Segmented Push-in

Advantages
1) All of the joining systems can be leak-free, thereby stopping infiltration and exfiltration.
2) All of the materials are highly corrosion resistant, so further internal deterioration due to chemical attack is prevented.
3) Properly designed and installed, all of these systems provide structural reinforcement and may restore full integrity or more.
4) Depending on pipe thickness and insertion clearance, full flow capacity recovery can typically be achieved and, frequently, it can be increased because of the excellent hydraulic characteristics of these pipes.

Manning’s “n” Pipe diameter for equal flow
0.009 new 13% smaller vs. pipes with “n” = 0.013
0.011 slimed 13% smaller vs. pipes with “n” = 0.016
17% smaller vs. pipes with “n” = 0.018

Typical diameter reduction is 6” to 12”, depending on the pipe wall thickness and desired amount of clearance for insertion. Typical annulus size is +/-5% of the host pipe diameter. Examples:

Liner Type Liner Wall t ID Reduction Flow Capacity
CCFRPM 2 to 3% dia. 10% Increased
PVC 3 to 4% dia. 12% Increased
HDPE-SW 4 to 5% dia. 14% Approx. Equal
HDPE-PW 6 to 8% dia. 19% Decreased

5) Only general cleaning to remove debris, sludge, etc. that would prevent passage of the liner pipe is required. No surface cleaning of the host to create a bond is necessary.
6) Insertion of segmented liner systems can almost always be done in “live” flow without by-pass pumping, flow diversion or plugging. Fused (continuous) systems can only be done in low flow conditions or with flow diversion, by-pass or temporary plug.
7) Insertion pits for segmented systems can be small: slightly longer than the pipe section length. Insertion pits for continuous (fused) systems must be longer to enable bending the liner from the surface into the host sewer.
8) Insertion push or pull distances can be quite long provided that the host pipes’ alignment is suitable (relatively “straight”). Longest single push known to me is 5600 feet of CCFRPM 51” inserted into an existing 57” RCP. Maximum insertion distances for profile wall and hollow pipes are less due to lower push capacities.
9) Insertion of segmented systems can be very quick. Sustained installation rates of 240 feet per hour have been achieved many times with CCFRPM pipes.
10) Sliplining is a very cost effective method of rehabilitation. In fact, many times it is the least expensive of all renewal procedures. Installed costs have been as low as $3 to $4 per diameter inch. Actual cost will depend on many items including local labor rates, number of shafts required, pit requirements, host line cleanliness, cover depth, surface restoration, etc.

Limitations
1) Sliplining is a semi-trenchless method. Access pits for insertion of the liner pipes are required.
2) Passage of the liner pipes through curves or PI’s in the host line may require short sections, fittings or excavation.
3) Reconnection of laterals typically requires a point excavation at the lateral.
4) Sliplining requires that the diameter of the line be reduced. However, this does not necessarily mean a loss of flow capacity. In fact, many times the flow capacity will actually be increased after lining despite the reduction in diameter.

Summary
Sliplining is a very cost effective, performance proven, semi-trenchless (some excavation required) sewer renewal method that is available in most all diameters by installing a new factory-made pipe into an existing line. Sliplining has been used successfully for over 30 years to solve pipeline problems such as severe corrosion, structural deterioration, leakage and poor flow. Sliplining features minimal disruption and frequent live flow insertion with out by-pass pumping or diversion. Several types of liner pipes are available and all have been used successfully.