Culvert lining, a trenchless culvert rehabilitation method, allows culverts to be restored instead of replaced. Culvert lining eliminates the traffic disruption, increased cost, and permitting difficulty that comes with conventional replacement. There are a few different methods of culvert lining including slip lining with InfraSteel, a smooth wall carbon steel liner.
Hydraulic engineers struggle with the concept of culvert lining because the process shrinks the inside diameter of the existing culvert. Improved inlet devices improve the flow characteristics and often remedy that problem.
In this article we go over; what a culvert is, why culverts fail, what culvert lining prevents, whether you should repair or replace a culvert, the culvert lining methods, and a few temporary culvert repair methods.
You may notice these small or large pipes underneath roads and railways that allow water or streams to pass through. Culverts come in a variety of shapes, but they are usually round, arched, elliptical, or rectangular in shape. They are meant to allow water to continue its flow uninterrupted. Road and railway embankments cannot be allowed to obstruct the water flow. Culverts prevent flooding and erosion, making their job extremely important.
Culverts also act as a bridge for traffic to pass over them it, meaning that tons of weight from cars, trucks, trains, or other vehicles continually put traffic load pressure on them.
All over the country, traditional corrugated metal culverts are failing. Large debris can block the mouth of the culvert and cause flooding and embankment erosion. Corrugated metal culvert pipes can lose their integrity due to corrosion over time.
Poor material can also be to blame. Culverts should be built with long-term use in mind, lasting 70 to 100 years or more. The lack of adequate funding combined with the impediment on public transportation, oftendelay repairs to these structures, creating safety issues for the traveling public.
Often, the repairs needed for culverts are minor, like paving the existingculvert’s invert. Even if a culvert is structurally sound, rehabilitation methods such as relining can still be helpful and increase the life-use of the culvert. Most culverts that need repair have been in service for 30-50 years.
What does culvert lining prevent?
Culvert lining prevents culvert failure. A failed culvert is a huge threat to human safety. A collapsed culvert can bring down an entire roadway, detouring traffic and costing taxpayers money in emergency repairs.
Culvert lining(and other repair methods) or replacement?
Once the culvert has been identified as needing attention, the decision of whether the structure should be totally replaced or repaired needs to be made. Factors affecting this decision include;
The extent of damage and distress to the structural integrity of the culvert
Effect on traveling public
The relative cost of either method
Availability of funding
Estimation of the remaining life-use of the existing culvert
Needed flow capacity
Culvert rehabilitation or relining is significantly less expensive, less time-consuming, and less disruptive to the traveling public than what is involved with total replacement of the culvert. Safety issues and cost will be key advantages to a repair-or-replacedecision.
Some variables need to be considered regarding lining vs replacement, primary considerations are often the traffic count, size of the existing culvert, and how deep the culvert is buried. For example, a 24” diameter culvert under a gravel rural county road that is buried 2’ deep, should typically be replaced; it is the least expensive way to remedy that failure. Whereas a large culvert that is buried several feet under a heavily traveled road or railway should be relined or rehabilitated because of the expense of construction, the expense of detouring traffic and emergency vehicles. or loss of railway revenue
When doing a cost analysis for culvert repair under a road, each mile for each detoured vehicle should be calculated at $.55 per mile, and added back to the total cost of replacement. The cost to the public for detoured emergency vehicles should also be considered. Generally, it is clear to DOT’s that culverts under heavily traveled roads need to be rehabilitated.
Culvert lining methods
1. Culvert Slip Lining – Slip lining involves installing a new liner or pipe inside of the old culvert. Culvert slip lining solutions are designedto pass through the tightest obstructions and shape change locations, providing the maximum flow capacity. The space between the liner and the old culvert is normally filled with grout, slurry cement, or similar flowable fill material. The liner is braced to support the structure to reduce the possibility of displacement or distortion.
Some culvert slip lining materials include;
InfraSteel – A smooth wall carbon steel liner with a design life calculated to meet the owners requirements, provides increased structural integrity, and maximized flow capacity, with low environmental impact. Each liner is designed to match the shape of the existing structure.
HDPE – A round, smooth–wall high-density polyethylene with a design life of 75 years, moderate increased structural integrity, low environmental impact, ideal when host pipe is also round.
Round Smooth Wall Steel Pipe – Increased structural integrity, low community disruption, ideal for round culverts. Round slip liners can reduce the flow capacity in arched, elliptical, or box culverts.
RCP – A reinforced concrete pipe with a design life of 50 years, high increased structural integrity, and low environmental impact.
2. Culvert Spray Lining – Spray lining is when the structure of the culvert is sprayed with a variety of different liquid products. Culvert spray lining typically is not going to provide the structural support of slip lining. Some spray lining materials include polyurethane and cementitious materials.
3. CulvertCIPP(Cured-in-place pipe lining) – Flexible, resin-saturated tubes are pulled into existing pipes, expanded with water or air pressure, and exposed to heat or ultraviolet light to stiffen. Curing takes five to 30 hours, depending on diameter.
4. CMPPlate Liner – A corrugated metal(CMP) plate liner provides corrugations extending through the lapped longitudinal joint. When assembled, this liner functions as a corrugated pipe with continuous circumferential corrugations.
5. CulvertReplacement – Total replacement of the culvert is usually extreme in community disruption, environmental impact, high costs to the traveling public, and permitting difficulty and is only used in areas where disruption is kept to a minimum.
The following methods are temporary fixes/repair methods. A structural engineer will have to determine whether any of the repair methods listed below will be structurally sound.
Reinforced Concrete Invert – Sometimes, the damage to a culvert is limited to the invert. If the remainder of the culvert in is good shape, then the rest can be salvaged by adding a new invert through the installation of a reinforced concrete invert pavement section.
Spot Patch and Repair – Small local repairs can be made to the culvert wall, or steel plates in the invert, and coatings using spot patching. The section of damaged culvert is cleaned, repaired, and then coated or painted.
Repair/Modification to Culvert End Treatment – This may take the form of a reinforced concrete cut-off wall combined with slope collars or slope paving to restore integrity to the fill slopes at the culvert ends.
Internal Bands to Problem Joints – Joint problems can be addressed using an internal band with gaskets and sealing materials that help restore uniformity of flow across the joints. Also sealing the area against significant infiltration and exfiltration.
Shotcrete or Gunnite Lining – Cement plaster or concrete is applied using compressed air on the surface of the culvert wall. Reinforcement can be added to improve the strength and durability of such a lining.
Sandblast & Repaint or Recoat – Rust, corrosion, or similar coating damage is removed and the wall is restored where the damage is superficial. The same material the culvert is made of will be used again.
Stabilize Fill or Fill Isolated Voids – Using controlled injections or pressure grouting, distortion or overstress to the culvert can be avoided.
Culverts are an important part of our daily life, even though they lay under our feet. InfraSteel can help you evaluate culvert lining products and find the best fit for your project. Follow the link to also view some frequently asked questions about InfraSteel and slip lining or contact us here.