Drainage systems are essential in conveying storm water runoff and minimizing flooding hazards. In general, these drainage systems are an extensive underground network of culverts and pipes within dense residential neighborhoods and metropolitan regions.
The drainage system in Orange County, Fla. is not an exception. Most of the pipes are in dense urban areas and along high volume roads. Even though the roads and drainage (R&D) division periodically maintains these drainage systems to ensure their reliable operation, there is always the need to rehabilitate extremely deteriorated pipes.
Whenever a pipe needs to be repaired, the R&D division faces the challenge of choosing the best rehabilitation method according to the physical constraints of the location, while at the same time causing minimum disturbance to the citizens.
For example, for many years the county has used a pipe sealing crew to literally go inside the drainage pipes to grout and seal every crack and leak found. This is a proactive solution that has certainly contributed to improve the operation of the drainage system. However, factors such as pipe length, size, material, joint failure, age and degree of deterioration affect the grouting crew effectiveness, especially because it is a time-consuming task.
Since 1999, the R&D division has been trying other pipe retrofitting methods, such as sliplining, cured-in-place pipe (CIPP) lining, internal joint sealing, and more recently, 3S segment paneling (channel lining). These trenchless methods have proven to be effective tools to rehabilitate pipes without the need for excavation, causing minimum disturbance to citizens.
Sliplining
Sliplining involves pulling or pushing a smaller diameter pipe inside an existing deteriorated pipe and sealing the annular void between the liner and the host pipe with watertight grout. The R&D division has sliplined pipes that range between 15 and 24 in. in diameter by using PVC or HDPE liner pipes. Depending on the length and size of the pipe to be repaired, the liner pipe is formed by several segments, typically 8 to 20 ft long, which are screwed in together while being inserted inside the host pipe.
The R&D division has also used the sliplining method to retrofit flat arch pipes crossing under roads. The significance of these projects is that the sliplining process was modified according to the physical constraints of the site and the shape of the pipes. Traditional sliplining was not feasible because it was impossible to screw in several segments of elliptical liner pipes together. It was also not practical to use CIPP lining because of water channels at both ends of the pipes that did not permit the equipment setup. In the end, these flat arch pipes were sliplined with several 8-ft long sections of elliptical liner, weighing 300 to 400 lb each, and joined together through a bell and spigot system.
As a trenchless method, the key advantage of sliplining is that it requires little or no excavation. Generally, the liner pipes are installed inside the existing pipeline through manholes. Even though sometimes it might be required to excavate small pits to access longer sections of pipeline, the excavation is minimal compared to traditional open trench pipe rehabilitation. Sliplining has proven to be a cost-effective method of pipe rehabilitation because long lengths of pipes can be repaired with minimal disruption and in a short period of time. The method is also effective in solving structural problems in the pipeline.
In terms of disadvantages, the insertion of a smaller diameter pipe into an existing pipe creates a slight reduction in the pipe interior diameter. In addition, bends or elbows in the pipeline interrupt the insertion of the new liner pipe.
For instance, in cases of extreme pipe deterioration, the sliplining method cannot be used because it is impossible to fit a rigid pipe through bends and sags in the deteriorated pipeline.
CIPP lining
The CIPP lining process involves inserting a resin-impregnated flexible tube into a faulty pipe and curing it with hot water. Due to its sensitivity to temperature, this liner is delivered and kept in the field inside refrigerated trucks to avoid the premature curing of the resin.
The CIPP lining process begins by diverting the flow and cleaning the pipeline of all debris, roots and silt deposits. Once the remote TV inspection ensures the pipe interior is clean, the resin-impregnated tube is inserted into the pipe from a single entry point.
The liner is turned inside out, expanded against the pipe wall, and cured in place by using water pressure. The curing of the liner is done by recirculating hot water through the pipe. In the end, the hardened resin forms a durable new pipe inside the existing one. The pipe is TV-inspected a second time to determine the success of the rehabilitation process, and the ends of the liner are trimmed.
The CIPP lining process has been used successfully in Orange County during the past six years to rehabilitate storm water drainage pipes that generally range between 24 and 36 in. in diameter. Larger diameter culverts have also been lined in sections up to 2,000 linear ft by “over-the-hole wet outs,” a procedure in which the production equipment is temporarily set up at the job site.
This technique is typically used for large diameter pipe segments when conventional CIPP lining is not feasible due to the weight of a liner of such large size. During this process, the liner is brought to the job site and the resin is impregnated (“wetted out”) prior to insertion in the pipe. The wet-out equipment basically consists of a roller bed system that uniformly distributes the resin throughout the liner tube. A mixer blends the resin with a catalyst before being pumped into the liner, and a vacuum pump removes any trapped air during the liner saturation. The liner is passed through a roller frame to set the resin thickness, and is later turned inside out and hanged from a frame high above the pipe opening. Then, the pressure of pumped water extends the liner along the pipeline until the end point. After the insertion is completed, a hot water recirculation system is used to deliver uniform heat throughout the section for a consistent cure of the resin.
A recent “over-the-hole” wet-out was completed in March 2006 to repair approximately 550 ft of a 42- x 54-in. concrete pipe running behind residences within the Montpelier Village Subdivision. The temporary CIPP manufacturing facility was set up within an easement between two residences, without obstructing the street. No excavation was required because the liner could be inserted through an existing manhole. The entire process took two days.
Examining CIPP
According to the experience of the R&D division, the main advantage of CIPP lining has been the elimination of excavation, and the avoidance of conflicts with other buried utilities, caving soils and dewatering issues. In addition, CIPP lining is useful to avoid temporary patches to the roadway that might not endure Florida’s rainy season.
For instance, CIPP lining allowed the rehabilitation of storm water pipes along the Central Florida Parkway, a main hub to International Drive and tourist attractions. This project required a ground penetrating radar survey to locate voids in the most deteriorated areas along the pipeline, and the use of pressure grouting to fill these voids prior to the lining process. The CIPP lining of Central Florida Parkway was completed successfully during Christmas season without disrupting heavy tourist traffic.
In other cases, like the one at Palermo Road, CIPP lining has permitted the repair of pipes that run directly under buildings without damaging or disturbing the structure.
In fact, most of the CIPP lining projects performed by the R&D division include the rehabilitation of drainage pipes that run within residential areas, schools or cross under roads with high traffic volume. The speed and ease of installation of CIPP lining makes it a cost-effective method for projects where open trench rehabilitation would require the costly and time-consuming job of clearing extensive areas.
Unlike sliplining, cured-in-place liners mold to the host pipe, an ability that makes them suitable for relining non-circular cross-sections. The CIPP lining process can negotiate multiple bends of up to 90?. This versatility allows the liner to form a seamless, jointless pipe inside the existing pipe that can increase the flow as it provides an improved friction coefficient.
As with any other method, CIPP lining also has disadvantages and limitations. For example, this method does not correct structural problems of the pipeline. CIPP follows the old pipe alignment without removing sags or curves in the existing pipe. Larger defects, such as offset joints, may continue to present structural problems or affect the flow rates, although they may not leak after the liner is installed.
The liner also has to be handled properly at the time of installation. First, liners must be delivered and kept in the field inside refrigerated trucks to prevent the premature curing of the temperature-sensitive resin. This is particularly important in Florida, where hot weather prevails throughout the year.
In addition, the pipe to be rehabilitated must be cleaned of loose materials and roots so debris cannot damage the liner during installation. This required extensive pipe cleaning might be time consuming.
Internal joint sealing
Internal joint seals are an effective and economical method of repairing underground pipes that leak due to offset, cracked or deflected joints. The internal joint sealing process involves the use of a flexible rubber gasket that is inserted into the pipe, positioned over the center of the joint and held firmly in place against the inner wall of the pipe with stainless steel bands. This method ensures a tight seal around the full inside circumference of the pipe joint area.
The R&D division has used the FDOT-approved internal joint seal method since 2002 to repair leaking storm water pipes that are in good condition but show a slight joint separation that cannot be fixed with grout. These internal joint seals have been installed in pipes with inside diameters ranging from 30 to 84 in.
An advantage of the internal joint seal installation is that it does not require excavation because the pipe can be accessed through manholes or direct man-entry from the pipe ends. As with any other method that requires man-entry repair, special attention must be given to the approved guidelines that ensure safe entry to a confined space.
3S segment paneling
The 3S segment paneling process consists of installing plastic segment panels inside the pipe, assembling the panels into rings that will later be joined together to form an internal pipe and then injecting grout in the space between the existing pipe and the panels.
The method is useful for structural repair of pipes, particularly for cracked large diameter pipes. When the grout cures within approximately four hours, the result is a structurally integrated composite pipe.
One advantage of the 3S segment paneling method is that each panel is light and can be easily handled in the field. In addition, the transparent PVC panels allow visual check of the grouting process to ensure uniform distribution.
A pilot project of 3S segment paneling was completed in February 2006 by the term contractor at Oak Ridge Road to retrofit a 60-in. diameter pipe crossing under an intersection with a school main entrance. Technically, CIPP lining could have been used to rehabilitate this pipe. However, existing overhead electric lines at both sides of the pipe ends did not allow the use of the crane needed to lift, hold and cure a liner of such size. Fortunately, the 3S segment paneling method provided a feasible alternative to repair this cracked pipe without the need for excavation.
Lessons learned
So far, the Orange County R&D division has used all of these methods to rehabilitate the aging storm water drainage pipe system. After weighing the advantages and limitations of each method, CIPP lining is still the most frequently used method in the county for pipe retrofitting.
Since January 2000, the county has spent over $4 million per year in various CIPP lining projects to rehabilitate more than 100,000 linear ft of pipes, at an estimated cost of $120 per linear ft of pipe. The experience acquired from all these projects has encouraged the R&D division to further investigate new trenchless methods of pipe rehabilitation.
A new trenchless technique that involves steam curing, a process that cuts the liner insertion and curing time in half, is being explored in a search for more cost-effective solutions to storm water drainage problems.
Even though there will always be circumstances where excavation is the best method for drainage pipe retrofitting, having several trenchless methods available offers the county the flexibility of selecting the most adequate technique to better serve citizens’ needs.
