Pipe jacking has revolutionized pipeline construction, enabling the precise installation of piping systems with minimal disruption to existing infrastructure and the public. As a trenchless installation method, pipe jacking is cost-effective, causes less noise pollution, and releases fewer emissions than traditional pipe installation methods.
The most ubiquitous material for pipe jacking is concrete, thanks to its rigidity, strength, and overall durability. Although pipe jacking has come a long way, there are risk factors that project planners and engineers often consider before choosing this method. This article will explore the risk factors associated with pipe jacking, discuss alternative pipe jacking techniques that can help mitigate those risks, and introduce auxiliary products such as concrete protection liners (CPL). CPL is one way to improve the long-term success of a new piping system installed through the pipe jacking method.
Pipe jacking risk factors and mitigations
Trenchless methods include pipe ramming, horizontal directional drilling, and microtunneling—a pipe jacking technique. Before starting a pipe jacking project, project planners typically launch a geotechnical investigation to determine the viability of the installation technique for the selected location. If a trenchless installation method is practical, engineers choose a preferred method based on site conditions.
Pipe jacking involves consecutively thrusting pipe segments into the ground to form a pipe chain. As this pipe chain increases in length, stress grows and leads to the first risk factor: failures at pipe segments or joints. The best way to mitigate this risk is to utilize reinforced concrete jacking pipe with high rigidity to maintain its shape throughout the construction. Other essential factors include minimizing required jacking forces by “lubricating” the line with bentonite to reduce friction, managing axial loads, and ensuring the minimum pipe wall thickness is met (1).
The installation method is also susceptible to common issues related to leakage, such as infiltration, especially at the start and reception shafts that can extend below the water table. Shafts built with pressurized locking chambers can prevent infiltration (2).
Using concrete protective liners to enhance the long-term viability of concrete jacking pipe system
Concrete jacking pipes are typically kept in place after the installation, serving as the final conduit pipe. In these situations, the inner walls of the concrete pipe may require additional protection against long-term exposure to pipe contents such as wastewater. The longer the pipe can last in service, the more cost-effective the overall project becomes.
Concrete protective liners (CPL) are a way to maximize the service life of concrete structures such as concrete jacking pipes. CPL can often extend or augment pipe performance. While projects do utilize protective coatings to improve structural resistance to corrosion and other issues such as pitting, CPL is a way to mitigate a range of problems from the start without ongoing maintenance or reapplication. Depending on the diameter of the pipe and access limitations, coating reapplication or later CPL rehabilitation may not be practical. Therefore, installing creating precast concrete jacking pipes that integrate CPL from the start can help save time and money over the long-term.
Another benefit of CPL is that the smooth surface it provides does not degrade over time. Most materials have a smoothness coefficient (Manning’s Coefficient) that decreases throughout the pipe’s service life due to fouling or reactions to pipe contents, translating into lower flow capacity and/or increased pumping costs. By using CPL, engineers can protect the inner walls of the concrete jacking pipe and ensure the best flow capacity throughout the system’s service.
- 1. Ward, R. “What Makes a Good Concrete Jacking Pipe?” Trenchless Technologies. (2019). Accessed online 3 January 2022 https://trenchlesstechnology.com/what-makes-a-good-concrete-jacking-pipe/.
- 2. Sterling, R. L., “Developments and research directions in pipe jacking and microtunneling,” Underground Space. (2020). Accessed online 3 January 2022 https://www.sciencedirect.com/science/article/pii/S2467967418301065.