I would think the least expensive method is to punch through the old pipe with a new pipe. the method is called pipe bursting. Less expensive than insitu form and potentially less expensive than retrenching and placing a new pipe.
Pipe Bursting-Trenchless Pipe Replacement
Pipe bursting is a trenchless method of construction used to rectify underground pipelines. A bursting tool replaces pipes by breaking them open from within by applying radial forces. A new pipe is simultaneously pulled in behind the bursting tool.
An expander device on the bursting tool pushes the fragments of pipe into the surrounding ground. A thin walled sleeve is generally pulled into the newly formed bore directly behind the 'expander'. This sleeve prevents the product pipe from being damaged by fragments of the old pipe in the surrounding ground.
Advantages
In comparison to conventional open trench method of pipe replacement, pipe bursting has several advantages that make it an economical option as costs is reduced by as much as 40 per cent.
1. Upsizing
One of the principal advantages of pipe bursting is its ability to increase pipe capacity by upsizing the original pipe diameter. This can be accomplished without excavation along the same alignment and grade of the original pipe.
2. Structural replacement
Pipe bursting provides total pipe replacement as a new pipe is structurally independent of the original pipe.
3. Rehabilitation time significantly reduced
Considerable time is saved compared to open trench methods with minimal excavation required to facilitate installation. As a result, the need for site reinstatement is reduced. The time to complete the entire installation decreases as much as 30 per cent.
4. Reduced impact on traffic
Pipe bursting reduces social costs associated with construction projects. Generally, when replacing pipes under a carriageway, only the localized area within a single lane is required to place the necessary equipment for the replacement job. Minimal traffic disruption will take place.
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