Trenchless Technology Tech Forum: Tips for Pipe Bursting Technique

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Mark MaxwellNearly 40 years of evolution in pipe bursting equipment, tooling and technique enables today’s contractors to avoid many of the obstacles it posed to the technique’s pioneers. Yet I still occasionally run across a contractor in trouble that could have been prevented. I have been an operator, technician and consultant in the pipe bursting method and its equipment almost as long as it has been available in the United States. Following this advice increases chances of successful pipe bursting job completion.

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PRIOR PREPARATION

My first contractor tip is “Do your homework.” Know everything you can about a job before you begin. Get access to soil sampling results. Know any work that’s been done on the line. Even check what the temperature’s going to be.

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Preparation should include knowing product specifications and manufacturer recommendations. If the equipment manufacturer offers project consultation, make use of it. HammerHead engineers, for instance, walk a contractor through the project, accounting for factors the contractor might not have thought of.

One obvious consideration is to have equipment properly sized to the job. You don’t want to use your 50-ton static machine for 2- to 8-in. pipe on a 12-in. pipe installation. If contractors don’t own equipment matched to the job, they should rent it or consider buying it, expanding their capabilities for future jobs.

Be prepared to alter pit size. The industry rule of thumb is 3 to 1. A pipe 10 ft down would need at least a 30-ft long entry pit. However, pit length often needs to be longer. The pipe’s wall thickness, the manufacturer’s own recommendations, and even ambient temperature must be factored in since cold pipe cannot bend as easily. One pipe manufacturer. recommends a 12-to-1 ratio for the pit for one of its products. Sure, contractors could try to use their bucket to push the pipe down, but why struggle with it? Plus, you’re marring up brand new pipe before you even put it in the ground.

SOIL CONDITIONS DETERMINE LENGTH OF RUN

Runs of 1,000 ft or more have been completed in a single pull. Contractors and even their customers may have overambitious expectations due to these successes. Soil conditions determine length of pull. Always. You can’t see the soil the pipe is lying in. Start small.

Even with soil samples in advance, contractors should start with 350 ft. At the end of that run, if you’re still pulling at 8 tons, you don’t want to increase the length. We did a 900-ft pull recently on an extensive pipe replacement job, but only after we started with a 350-ft, then increased to 500 and 750. We knew then we could attempt a 900-footer.

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Soil conditions also determine lubrication requirements. Clay soils typically require polymers. For sandy soils, the contractor can use bentonite. Upsizing pipe almost always requires lubrication to get the pipe in place before returning, displaced soil seizes it.

PNEUMATIC VS. STATIC TECHNIQUE

When soil conditions are wet, I caution you not to use the pneumatic pipe bursting method. Think of it in terms of working with cement. Cement contractors vibrate concrete to increase its density and strength. Pneumatic bursting tools can make wet soil conditions so difficult, it can stop progress midway through.
Static pulling method in difficult soil raises its own concerns. When a pull gets too tough for your pneumatic tool, it simply stops progressing. But static pullers will just continue pulling. It’ll tear the pipe apart. Watch your gauges.

GIVING LONGER RUNS A REST

Pushing to beat a deadline might tempt contractors to reconnect laterals prematurely. Longer runs stretch pipe as it’s pulled in. You may have quit pulling, but the pipe continues moving.
Reconnecting laterals before the pipe contracts completely results in lateral connection failures. Some longer projects might require waiting overnight before connecting laterals.

TRAINING

Although workers should be trained for any task they are assigned to do, working with fusible pipe is especially critical. An inexperienced fusion welder’s joint might look good enough at the surface but come apart later in the ground. Two supervised fusion welds is not sufficient training. Get your fusion welders trained.

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SAFETY, MAINTENANCE

My final advice deals with routine worksite safety measures and machine care. Contractors should ensure they properly shore the pits, set cribbing and brace the wall. Hydraulic hoses should be inspected and kept from damage during transport and as the machine is raised and lowered in the pit. Learn and follow safety requirements and observe your equipment manufacturer’s recommended maintenance routine.
No one can completely avoid unexpected surprises on a given job, but these common-sense tips ensure pipe bursting contractors of their greatest chances for successful runs.

Mark Maxwell is a trenchless application specialist at HammerHead Trenchless.

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