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TRENCHLESS TECHNOLOGIES (By Tom Gillette, P.E.)
I would like to mention a few items about trenchless pipeline technologies because there seems to be a lot of interest and questions these days related to some of the new methods available to replace and restore pipelines. There are two basic types of trenchless technologies that either replace or repair your defective pipe. The end result of methods that replace the defective pipe is brand new pipe. The end result of methods that repair your defective pipe is repaired pipe. Brand new pipe is always superior to repaired pipe. Examples of trenchless methods that replace the defective pipe with brand new pipe are boring/augering, micro-tunneling and pipe bursting. Examples of trenchless methods that repair the defective pipe are cure-in-place, internal spray-on liners, slip lining, internal spiral wound liners and chemical grouting. The costs and benefits of trenching in new pipe, boring/augering, micro-tunneling and pipe bursting can all be compared equally to each other because at the end of the day, you have brand new pipe. The costs and benefits of trenchless repair methods can be compared to each other because at the end of the day, you have repaired pipe. When the cost per foot of repaired pipe equals or exceeds the cost per foot of brand new pipe without a doubt, install the brand new pipe and forget about repairing the defective pipe. If you have a section of defective pipe in a refinery under a processing unit or under railroad tracks and parallel to a freeway in Houston or Dallas paying a premium to use a trenchless repair method may have some benefit although brand new pipe is better for the same cost. If you have a section of defective pipe in an open field behind Wal-Mart it does not make sense to repair the pipe using trenchless methods at any reduced cost, just install brand new pipe in an open cut trench.
Do you know exactly what is defective with your pipeline and how many linear feet are defective? Is it corroded? Are the pipe joints leaking? Where is the pipe located? What diameter is the pipe? What type of material is the pipe composed of? How deep is the pipe buried in the ground? What type of material is being conveyed through the pipe? All of these questions may determine what method of trenchless pipe repair you select or you may determine that new pipe is the best choice.
Cure-in-place pipe is a great repair product that is getting a lot of attention these days and establishing a track record. What about some of the new internal spray-on linings? Could you live with a smaller inside diameter and just slip line your old pipe? What about pipe bursting? There are cutters available now that can slice through ductile and cast iron pipes and pull a larger diameter replacement pipe behind the cutter head! What about an internal spiral wound liner? Augering and boring is less disruptive than open cut and works quite well in soft ground typically found in Houston. Micro-tunneling is less disruptive than augering and boring although usually costs considerably more. And let’s not leave out chemical grouting that repairs the defects by consolidating soil on the outside of the defect?
How do you evaluate all of the trenchless technologies to decide which one will work best in your situation and conditions? How much risk are you willing to take? Installing brand new pipe in an open cut trench has less risk than any other trenchless method because all unknowns are exposed in the open cut trench. Don’t let a salesman sell you his product because it is his product, all trenchless methods have risk and even the best products can become inferior or fail if not installed properly.
TRENCHLESS TECHNOLOGIES SUMMARY
1) Don’t overpay for repaired pipe. If the cost per foot of repaired pipe is the same or close to the cost of new replacement pipe, go with brand new pipe.
2) Know what your pipe defects are. Televise the lines to confirm the defects and condition.
3) Cleaning and televising defective pipelines and then doing nothing has no benefit. Have a plan and the resources available to replace or repair the defective pipelines.
4) Decide which trenchless method if any will apply to the conditions you have.
5) Stay flexible. Quite often, a combination of several different trenchless methods may be the answer.
6) You can compare the benefits and costs of open cut, augering/boring, micro-tunneling and pipe bursting to each other because all methods result in new pipe. New pipe is the benchmark that all other repair methods should be compared to.
7) You can compare the benefits and costs of cure-in-place, spray-on liners, slip line, spiral wound liners and chemical grouting to each other because all methods result in repair of your defective pipe.
8) Get help. Hire a Civil Engineer to get your defective pipes cleaned, televised and help you decide which trenchless technology if any will work best for your situation.
9) If you are still reading, “Thank You” for taking time out to read the information on this website. Now let’s go quietly out and replace and repair some defective pipelines using trenchless technologies.
This failed PVC liner was removed from a 108 inch diameter sanitary sewer trunk line north of downtown Houston, Texas as part of an emergency repair construction contract. Sewage found it's way between the concrete host sewer and the liner and peeled the liner away from the host pipe and balled the liner material up at a downstream junction box.
