Trenchless technology has revolutionized sewer rehabilitation and repair.

One such trenchless method, pipe bursting, is increasingly preferred for small diameter yet large-scale and complex sewer systems, giving old pipes new life without compromising paving or roadway access. But the greatest system rehabilitation results can be achieved when pipe bursting is combined with manhole rehabilitation. 

Best practices

Sewer systems are subjected to extreme conditions every day. The waste that sewers carry away produces corrosive hydrogen sulfide gas as it deteriorates, eating away at infrastructure and risking the health of anyone exposed to it. This degradation leads to infiltration of groundwater and inflow from stormwater runoff, which severely compromises existing pipes’ structural integrity. When the additional complicating factor of soil shifting is added into this process, it further destabilizes pipes.

Pipe bursting offers significant advantages compared to open-trench pipe replacement. In addition to avoiding paving restoration time and costs as well as roadway closures, it is one of the few trenchless rehabilitation methods that can upsize a pipe. With pipe bursting, a small entry point can be made in a low-impact area rather than paved surfaces and a downstream manhole is established to run a cable through the line. The existing pipe fractures as a new high-density polyethylene pipe is pulled in. This process eliminates the need to trench the entire run of the pipeline.

In addition to HDPE pipe’s notable advantages, including high H2S resistance and 50-year design life, this process creates a monolithic pipe as all segments are fused together, which minimizes access points for roots and infiltration. However, without manhole remediation, a risk of leaks at those structures may also remain. As concrete and brick manholes age and the mortar, joints and gaskets deteriorate, leaks can occur through these penetration points. When these eroded manhole areas are sealed after pipe bursting is performed, all potential points where water could enter the system are eliminated. This best practice method essentially provides a “belt and suspenders” approach to keeping sewer systems running smoothly for the long term.

San Antonio case study

Recently, the city of San Antonio applied this pipe bursting best-practice approach to repair its sewer infrastructure.

San Antonio, the third-largest city in Texas, has nearly 3 million residents and more than 30 million yearly tourists, making it vital that its sewer lines reliably function. The city was dealing with about 5,500 linear feet of pipe in need of repair. The pipe was constructed of multiple materials — not only reinforced concrete and clay, but also truss pipe from the 1970s, which used plastic with a corrugated inner layer and an outside layer of plastic. The truss pipe in the system, chosen for its resistance to H2S, was very brittle — a result from the clay in the surrounding soil regularly shrinking and swelling, which can cause the material to move and crack. The reinforced concrete and clay pipes, though stronger than the truss pipes, had also developed several intrusions and cracks over the years.

Several mitigating factors were taken into consideration for the repair process. The Edwards Aquifer on the northeast side of town provides the majority of the city’s drinking water and is vulnerable to environmental disruption. Opencut sewer repair raised the risk of contamination from exposed sewers. The city’s tourist business was also at risk from environmental contamination and surface disruptions from sewer repair work.

For these reasons, pipe bursting fit with San Antonio’s needs and priorities. HDPE pipe was used with the pipe bursting process to replace existing infrastructure, providing a structure capable of providing high resistance to the instability of the surrounding soil, I&I and H2S gas. The new pipe allowed improved levels of water flow and eliminated the risk of exposing sewer waste to the environment. 

The system’s manholes posed a leak risk, however. More than 10 precast manholes had been eroded by H2S gas, making them prime targets for I&I. The city used Quadex GeoKrete, a corrosion-resistant geopolymer mortar that blocks groundwater infiltration, to restore the manholes to useful life and rebuild culverts. Applied by low-pressure spraying — in one pass —  the geopolymer eliminated any potential leak paths that could result now that the pipe was impenetrable. 

From start to finish, the project took four months — less than half the time an opencut replacement would have lasted and without the traffic disruption and environmental impact for residents and tourists. The new pipe system has an expected life of 50 years and is significantly more resistant to I&I, corrosion and ground shifting.

Performing manhole rehabilitation simultaneously with pipe bursting ensures a watertight structure as all infiltration access points are eliminated. As engineers and asset owners seek ways to restore critical sewer infrastructure faster without creating significant pavement repair or disruption, pipe bursting combined with manhole rehabilitation offers the most durable and practical solution. This field-proven best practice offers the reliable and long-lasting performance municipalities demand.