INSERTION LINING OF PIPE CULVERTS By WILLIAM T. SUNLEY, Engineer of Local Roads and Streets

There are numerous pipe culverts located under local highway systems in Illinois that have deteriorated and need restored or replaced due to loose joints, corrosion, or a variety of other causes.

The usual solution to this problem is to replace the pipe culvert. Pipe culverts used on entrances or low volume roads can usually be excavated and replaced at a minimal cost. However, replacing culverts under high volume roads, in urban areas, and under high fills is often costly, time-consuming, and a traffic control problem. An effective solution to the problems incurred with replacing these culverts is the use of insertion liners.

Insertion lining is the insertion of a prefabricated pipe inside an existing pipe culvert. The Illinois Department of Transportation's Standard Specifications Manual allows the use of liners made of polyethylene or reinforced plastic mortar. Insertion liners are readily available in diameter sizes from ten inches to eight feet. Some typical insertion liner material costs are $13 per lineal foot for twelve inch diameter and $42 per lineal foot for 36 inch diameter.

The extent of deterioration to the existing culvert must be taken into consideration before deciding to use insertion liners. Partial culvert failures or extensive protrusions of broken culvert walls may prohibit their use.

There are a number of ways the liner can be inserted into the existing pipe culvert. The most common construction method consists of, first, cleaning out debris from the existing culvert. Then the liner should be inserted into the culvert by pushing, pulling, or a combination of both. The equipment most commonly used to push the liner into the culvert consists of a backhoe, chain, and pushing plate. The backhoe sits over the end of the culvert. A pushing plate is used at the end of the liner to protect the liner end and is attached to the backhoe bucket by a chain. The backhoe operator then slides the liner into the culvert by retracting the bucket. Once the liner is inspected to assure proper placement, the space between the culvert and the liner must be grouted.

One advantage of insertion lining is that it provides a virtually new pipe culvert that is comparable to replacement without the problems incurred with replacing the culvert. A second advantage is cost savings. It is easy to see that the cost of insertion lining an existing pipe culvert under a high volume road compared to the cost of open cut trenching, with resultant increased construction time, increased manpower, and traffic control problems will yield a savings. The amount of savings realized is dependent on the depth of fill over the culvert, length of the culvert, volume of traffic on the road over the culvert, and a number of other factors.

One possible disadvantage of using insertion lining is that the cross-sectional area of the pipe will be reduced, possibly reducing the hydraulic capacity. However, the hydraulic capacity may not be reduced when lining an existing corrugated metal pipe (CMP). Because the inside of the insertion liner is much smoother than the CMP, the effect of the reduced cross-sectional area caused by the insertion liner is usually offset and results in a comparable hydraulic capacity.

Based on each individual situation, insertion lining can be a viable alternative to replacing existing deteriorated pipe culverts.

June 1994 / Illinois Municipal Review / Page 7