Project Details

Background

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:

• Sliplining
• Close-fit lining
• Spirally wound lining
• CIPP lining system
• Spray-on lining

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.

Project Description

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.

Figure 1. View of the project site.

Sliplining

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.

Figure 2. Existing condition of a typical culvert at the project site.

Figure 3. Cleaning and removal of debris from the existing CSP.

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.

Figure 4. View of the pipe fuser apparatus.

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.

Figure 5. View of the preheated iron during the fusion process.

Figure 6. View of the welded pipes and spacers.

Figure 7. View of the welded HDPEP liner ready for installation.

Figure 8. Pulling the liner and PVC tube into the existing pipe.

Figure 9. View of the pumping apparatus.

Figure 10. Fully installed HDPEP and the cementitious materials.

Cured-In-Place Pipe

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).

Figure 11. View of the refrigerated truck and the liner.

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 CIPP liners, specified to proper length and diameter by MDT, were delivered to the jobsite in a refrigerated truck. Several layers of ice bags were placed on the truck bed to ensure the temperature of the liner was kept low enough to impede setting until the steam curing phase.
• The nonresin-impregnated liner system has three separate layers, with the outer layer having a denser weave than the two inner layers. Once cured, all layers are bonded together, forming a monolithic layer that becomes the new interior surface of the existing culvert. Figure 12 shows a close-up of the three layers of the nonresin-impregnated polyester.

Figure 12. Close-up of the nonimpregnated polyester liner.

• A propane heated core was used to place a 3-in (76.2-mm) diameter hole in the liner, for attaching a bracket and an air hose to the liner (figure 13). In preparation for installation, the contractor cut slots in the liner layers to be hooked onto the inversion apparatus, facilitating the inversion of the liner. All five CIPP liners were inserted at the intake or upstream ends of the culverts.

Figure 13. Inserting a circular hole into the liner using a heated core.

• The inversion apparatus is equipped with two rows of hooks to hold the liner in place while the liner is pressurized for its travel through the existing CSP culvert. Figure 14 shows the process of attaching the liner to the hooks of the inversion apparatus.

Figure 14. View of the inversion apparatus.

• To invert and force the liner through the CSP culvert, compressed air at an average pressure of 12 pounds per square inch (psi) (82.7 kilopascals (kPa)) was applied through the bracket into the liner. Figure 15 shows application of the compressed air and a completely inverted liner at the culvert's intake.
• Figure 16 shows a fully exited liner at the culvert's outlet releasing the air pressure, which had forced it through the culvert (see the yellow arrow). Since the liner was inverted at the culvert's intake, it provided a natural plug through the entire inversion process.
• Once fully deflated, as shown in figure 17, the liner was ready for the curing phase. On average, for a 130-ft (39.6-m) CSP culvert like the ones at MacDonald Pass, it takes about 30 minutes to invert the liner from the intake to the outlet of the culvert.

Figure 15. Close-up view of compressed air application and fully inverted liner.

Figure 16. Fully exited liner at the outlet end.

Figure 17. Fully deflated liner at the outlet.

• The next step in the operation, the curing phase, entails the application of air and steam. A large-diameter rubber plug was placed inside the liner at the outlet. The plug was equipped with two connections, which allowed attachment of an air line (red arrow) and steam line (yellow line). Figure 18 shows the rubber plug attached to the air and steam lines.
• Air was applied to inflate the liner to conform to the interior of the existing CSP culvert. Once fully expanded, steam was applied at an average temperature of 235 °F (112.7 °C ) and at a rate of about 5 psi (34.4 kPa).
• Figure 19 shows steam exiting at the intake end of the culvert. Curing can take place at ambient temperature, but using steam can accelerate the curing time. Applying steam reduces the curing time from several weeks to 1.5 hours.
• A close-up view of a fully cured CIPP liner is shown in figure 20. All three polyester layers of the liner are bonded, forming a composite monolithic rigid layer with an average thickness of 0.625 in (15.8-mm).

Figure 18. View of the rubber plug with air and steam line connections.

Figure 19. View of steam exiting at the intake end of the culvert.

Figure 20. View of a fully cured CIPP.

• After the application of the steam, the CIPP was allowed to cool. The rubber plug was removed, and the excess CIPP at the intake and outlet was trimmed to a proper length.
• Fiber meshed grout was used to seal the interface of the CIPP liner and the existing culvert at its intake and the outlet ends (figure 21).
• As shown in figure 22, the installation of the CIPP liner was monitored and inspected remotely by a tractor-mounted closed-circuit television camera to ensure proper placement.

Figure 21. View of a fully installed CIPP liner ( Note intimate contact of the liner with the pipe).

Figure 22. Remote monitoring and inspection.

Roller–Compacted Concrete

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.