Why Trenchless Technology May Be The Best Option For Repairing Underground Pipes:

Three Ways Not To Dig

Alternatives to conventional trench-and-replace methods make lateral repairs
quicker, less costly, and less disruptive

By Gerard Marc-Aurele and Stephane Therrien

According to the U.S. Census Bureau, more than 76 million laterals (house sewers) were connected to public sewers across the United States in 1990. More than 50 million of these laterals are more than 30 years old. Because they are buried shallow, laterals can be vulnerable to structural damage, root intrusion and blockages even after only a few years. Lateral problems fall into four categories:

• Backups caused by roots
• Water infiltration and exfiltration
• Installation of non-durable material, such as tar and cardboard
• Corrosion, open joints, offset joints, dips, pipe deformation and crushed pipes

In 2004, the most common way to repair and replace laterals is still by digging up and replacing the pipe. In act, estimates show that 95 percent of lateral repairs are completed with the most expensive method: conventional trench and replace.

Potential savings
Newer repair technologies that require little or no digging can save taxpayers and consumers billions of dollars every year. So the question is, what are the alternatives to digging? A number of companies offer trenchless or no-dig lateral-repair solutions, but the technologies fall into three basic categories:

• Inversion lining
• Pull-in-place lining
• Pipe bursting

Trench-and-replace remains the best solution for problems such as dips (reverse slopes) and crushed pipes. But for other lateral problems like cracked pipes, root intrusion and infiltration/exfiltration lining and pipe bursting are generally cheaper and faster and have less environmental impact.

Laterals repaired by these methods can last 50 years often longer than the original pipe. That is because the newly installed pipes do not have joints that can fail or admit damaging root growth. The new lateral is also mechanically stable. In addition, with trenchless or no-dig repair, homeowners do not have to worry about the soil settling that can occur after a trench-and-replace repair.

Trenchless and no-dig repairs also prevent root intrusion. Roots invade older pipes through joints and through cracks created by soil movement. Liners and the polyethylene pipe used in pipe bursting have no joints, and they also flex under soil movement instead of cracking.

Knowing the difference
Trenchless repair means exactly what it says there is no trench. Inversion lining and pipe bursting are trenchless methods, even though the repairs require the digging of one or two access pits to provide access to the lateral. Pull- in-place lining requires no digging at all. Typically, these techniques can solve common lateral problems for a fraction of the price of digging.

Quality repairs
Before we examine these solutions in detail, let’s look at what is vital for a high-quality repair. The liner in the lateral must be smooth and thin and must be able to maintain the line’s original hydraulic capacity, or even increase it somewhat if necessary. The liner must be structurally sound it must by itself sustain all soil loads and live loads. Usually, liner thickness calculations are made according to ASTM F 1216.

Because laterals can vary in size, the liner must adapt to different pipe diameters and must be able to line transitions where pipe diameter changes from four to six inches.

The liner must comply with lining standards such as ASTM D 5813, ASTM F 1216, or ASTM F 1743 (the most commonly used is ASTM F 1216). An independent third party such as NSF can certify lining products. Usually, the certification covers mechanical properties such as flexural strength, tensile strength, and water tightness.

The liner must have tapered ends to ensure that toilet paper and other materials do not catch where the liner starts in the lateral. The liner must be jointless (one piece) and flexible (capable of being deformed without breaking) to ensure permanent protection against tree roots.

Because no-dig and trenchless technologies are reliable, durable, environmentally friendly, faster and cheaper than digging, industry professionals are using them more often to replace laterals and other underground piping. Their usage will most likely continue to increase rapidly in the coming years.

Technologies in action
Here are brief descriptions of the three main trenchless and no-dig lateral repair technologies:

• Inversion liner: The liner is made of felt tube and resin. One soft dig is usually required. The liner is inverted with air and is usually cured at ambient temperature. Curing time varies from three to eight hours, depending on the ambient temperature and the amount of catalyst used. It results in a smooth and jointless lateral. The entry pit must be backfilled. 
• Pull-in-place liner: In this process, a fiberglass and resin liner is pulled through the old pipe by a winch. The liner is inserted through the main clean- out, so that no digging is required. The liner can be heat-cured with steam (30 minutes to one hour) or ambient cured (three to eight hours, depending on ambient temperature and amount of catalyst used). The result is a new jointless pipe molded inside the host pipe. 
• Pipe bursting: This lateral repair technique requires one pit at each end of the pipe section. The burst head is pulled by a winch and is followed by a polyethylene pipe. As the burst head is pulled through, the old pipe is burst aside into the surrounding soil, and the new pipe replaces it. Pipe bursting can be used to increase the size of the pipe being replaced. It results in a smooth lateral. The two access pits must be backfilled. 

Comparing performance
The accompanying tables compare these three basic technologies as they relate to technical performance, work planning, and environmental impact. These are general comparisons all repair jobs are different. Furthermore, in most instances, a variety of factors not just one determine which technology is best for a given project.

Choosing the right system
In ideal weather and site conditions, most trenchless and no-dig systems work well, but conditions are often far from ideal. Contractors may encounter complications like cold temperatures, water, pipe diameter transitions, deformed pipes, and other on-site problems. One solution may be more efficient and reliable than the others for solving a site-specific problem.

The first question to ask is: Can the pipe be lined? If so, then lining is an obvious choice, because lining (inversion or pull-in-place) is the cheapest and fastest way to renew most laterals.

If the pipe is severely damaged, or if it is in an unstable condition (pieces are falling down during the cleaning process), then pipe bursting is the alternative. Although it requires more preparation, including the digging of two access pits, pipe bursting solves problems that lining alone cannot.

If the lateral cannot be lined or pipe-burst, then it must be repaired conventionally. However, as technology improves, situations where lining and pipe bursting cannot be used become increasingly rare.

Before going ahead, you must identify your needs carefully including your plans for the next five years. Will you need lateral repairs, point (spot) repair, manhole to manhole lining, or. a combination of these?

Gaining ground
If you choose a pipe lining system for lateral repairs, there are a few more factors to consider. Because most lateral repairs are made for homeowners, it may be desirable to use a process that has no odor and uses no volatile organic compounds (VOCs).

In addition, the curing process should be considered. Some contractors prefer heat-cured lining systems to provide better control over curing and faster repairs. For example, a 70-foot lateral repair with a steam cure system may take 45 minutes, versus several hours in some conditions for ambient systems. On the other hand, ambient curing requires no heating and steam delivery mechanism.

Because no-dig and trenchless technologies are reliable, durable, environmentally friendly, faster and cheaper than digging, industry professionals are using them more often to replace laterals and other underground piping. Their usage will most likely continue to increase rapidly in the coming years.

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