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Montana Demonstration Project: Innovative Culvert Rehabilitation Using Trenchless Technologies
Using trenchless technologies to rehabilitate deteriorated culverts is gaining popularity because it provides transportation agencies with a versatile, cost-effective alternative to traditional culvert rehabilitation methods. By incorporating culvert liners, these technologies allow an agency to repair aging concrete or metal culverts cost effectively in hours instead of days, without excavating the roadway, and with little or no disruption to traffic flow. Generally speaking, there are five trenchless methods of rehabilitating culverts:
As part of the HfL demonstration project, MDT used two methods—sliplining and CIPP lining systems—to rehabilitate deteriorated culverts on U.S. 12 near Helena. For the sliplining method MDT used seam-welded HDPEP, and for the CIPP lining it used resin-impregnated polyester felt.
The project involved rehabilitating 10 24-in (609.6-mm) CSP culverts along a 10-m (16-km) stretch of U.S. 12 in Powell and Lewis and Clark Counties over MacDonald Pass near Helena (see figure 1). U.S. 12 at this location is a mountainous, undivided four-lane National Highway System (NHS) roadway with an ADT of 2,670 and 12.1 percent trucks.
The poor structural condition of the culverts at this location prompted MDT to rehabilitate them in a manner that did not interfere with the flow of traffic. MDT used two innovative methods, CIPP and HDPEP liners, to achieve this goal. Five culverts were rehabilitated using the CIPP lining system, and the other five were rehabilitated using HDPEP liners. The locations of these culverts and the treatments they received are shown in table 1.
Sliplining is a simple technique consisting of inserting a new pipe, normally made of a polymeric, thermoplastic-type material, into a deteriorated culvert. Liners are inserted into the existing culverts either by pulling or pushing. After insertion, the annular space between the existing pipe and the new liner is filled with a relatively slow flow rate cementitious grout material. This method of rehabilitating culverts provides a versatile and cost-effective alternative to traditional excavation and replacement. If installed properly, the sliplined pipe functions like a new installation. Several different lining materials can be used in sliplining, including high-density polyethylene, polyethylene, polypropylene, polyvinyl chloride (PVC), and ethylene propylene diene monomer. For this project, MDT used 18-in (457-mm) outside diameter HDPEP with a smooth interior and exterior and a wall thickness of about 0.75 in (19 mm). Before the pipes were inserted, debris was removed from the existing pipes (figure 2) using a high-pressure jet wash and a truck-mounted vacuum, as shown in figure 3.
The HDPEP sections were delivered to the job site in 25-foot (ft) (7.6-meter (m)) segments. The pipe sections were welded together to a proper length using a device called a plastic pipe fuser (figure 4). Before the fusing phase, the ends of the pipes were trimmed with a special rotary cutting tool equipped with three razors to remove any imperfections, dirt, or grease and ensure a good-quality weld.
Next, a preheated round electric iron with an average temperature of 425 degrees Fahrenheit (°F) (218 degrees Celsius (°C)) was placed between the two pipe sections (figure 5). The pipes were compressed against the heated iron for about 2 to 3 minutes until the pipes started to melt and form a circular bead (figure 6).
The size of the bead indicates when the HDPEP is at the temperature required to fuse the pipe sections. The ends are allowed to cool in place and, depending on the ambient temperature, the average time to complete the weld ranges from 15 to 20 minutes. According to the manufacturer's specifications, a properly fused seam is structurally stronger that the pipe itself.
After all the sections were fused together to a proper length, spacers were attached along the pipe at intervals of 8 to 10 ft (2.4 to 3 m). The primary purpose of the spacers is to facilitate efficient insertion of the new pipe and placement of the cementitious grout, which was pumped between the existing CSP and the new liner. Figure 6 shows the formed bead after fusion and the spacers. Figure 7 shows the welded pipe liner ready for installation.
Before the liner was inserted, a PVC tube was attached along the entire length of the pipe to allow pumping of the cementitious grout material from the pumping station. As the grout was pumped, completely filling the space between the liner and the existing pipe, the PVC tube was pulled back slowly until the grouting was complete. Figure 8, 9, and 10 illustrate the operation.
The grout, which was made of a low-density cellular material had a compressive strength specified between 100 and 300 psi. The primary purpose of the lining was to restore the structural integrity of the pipes. However, it was also important to maintain the hydraulic capacity of the pipes. According to the Montana DOT's Research Project Manager, two of the pipes were completely clogged and several were filled with debris reducing the capacity anywhere from 30 to 40 percent.
The CIPP lining system is used to restore the structural integrity of deteriorated pipes with a seamless, jointless liner. Similar to sliplining, CIPP does not interfere with the flow of traffic because it does not require work zone traffic control. The lining does not come in standard sizes, but is designed specifically for the individual pipe to be rehabilitated, with variable diameters and shapes (e.g., round, elliptical, oval) and wall thicknesses.
When necessary, a minimum liner thickness is specified to provide resistance in abrasive conditions and to improve the longevity of the liner. Unlike sliplining, no grouting is required because there is no annular space between the existing culvert and the liner. The CIPP liner system creates a close-fit "pipe within a pipe" that conforms to the contour of the inside surface of the existing culvert and, for the most part, retains the original culvert's capacity.
The CIPP liner installation at MacDonald Pass involved inserting resin-impregnated polyester felt into the existing pipes through an inversion process. The resin impregnation was done offsite at the installer's facility, and the liner was placed in a refrigerated truck for delivery to the job site (figure 11).
Since curing begins as soon as the resin is applied, it is imperative to keep the resin-impregnated polyester at temperatures below 20 °F (6.6 °C ). This retards the setting process until the liner is ready for insertion and final curing. Inversion is achieved using either compressed air or pressurized water. For this project, compressed air was used in installing all CIPP liners.
The following procedures and materials were used in relining the culverts for this project:
The access ramp shoulders of the new interchange were paved with RCC. The finished color of the RCC is slightly different from the portland cement concrete (PCC) ramp travel lane, enhancing delineation and increasing roadway safety.
Using RCC was good for quick installation of the shoulders and was demonstrated on this project to be a timesaver. However, a smooth surface profile was difficult to obtain with RCC. As constructed, it was suitable for shoulder–type work, but not necessarily for high–speed traffic lanes.
This page last modified on 04/04/11