Applications in Geopolymer: Trenchless Storm Drain

Welcome to our series on applications in geopolymer injection, where we invite technical experts from around the globe to share applications and use cases where geopolymer injection worked to solve critical challenges when nothing else would.

This month’s expert is John Silva, National Director of Operations for Geobear USA. With more than 20 years in the ground engineering industry, he brings with him a wealth of expertise in geopolymer injection, ground stabilization, and various methods of increasing ground strength.

Q: We’ve talked about some interesting cases where geopolymer injection was applied in challenging cases.

Discussing all the ways to use geopolymer is an exciting topic for me. I’ve been able to work on some pretty interesting projects where geopolymer was involved – from military Air Force bases to extensive tunneling projects and everything in between. There are so many cases where using geopolymer can save extensive time, money, and resources – and several cases where no other solution is feasible.

Q: Today, let’s talk trenchless storm drain and pipe repair. I understand you have a pretty interesting case you can tell me about.

In a previous role, I served as a project lead for an interesting case at a Southern California airport. Their runway was experiencing issues due to the soil below getting soft. The storm drain system below the runway was leaking at the joints and water was washing out the fines that were used to backfill the pipe.

Q: For a busy airport, this sounds like quite an issue. What was causing the issue with the storm drain system?

Due to its close vicinity to the ocean, the storm drain system was located at or even below sea level. it would intermittently flood with ocean water at high tide. This daily fluctuation of water coming in and out caused the pipe to leak at its joints allowing sea water to push fines into the pipe and out to the ocean. As this soil that was used to backfill the pipes washed away, the pipe would also become unstable and make small movements. All of this would lead to destabilized sections of the runway above, putting planes and passengers at danger.

Q: What challenges were posed because of the problem location being at an airport?

The biggest issue was trying to minimize disruption to flights. The airport is a very busy single runway airport and, without a secondary runway to divert traffic to, it was challenging to find a solution that would not disrupt thousands of passengers. Conventional repair methods would have entailed cutting out sections of airport runway concrete. This would have been highly invasive and would require the airport to shut down. This was not an option, but neither was allowing a landing plane to be in danger of crashing. The project’s engineers had to come up with something – and they had to do it fast.

Q: Obviously, safety was an issue here. What was the plan the engineers ultimately approved?

The idea was to repair the storm drain system, stabilize the soil, and maintain safety for passengers and planes. The engineers approved a repair method that would utilize geopolymer injection. The first part of the process involved inflating a rubber bladder at the end of the outlet in the 6’ diameter pipe. This kept the ocean water from flowing into the pipe. We also ran water pumps to keep water levels down during the work.

We injected geopolymer through the pipe from the inside. A small team went into the pipe and drilled a set of holes through the pipe near the leaking joints. Almost all of the backfill had washed away and our goal was to inject the geopolymer to stabilize the soil and fill voids around the pipe.

Q: This sounds like a fairly dangerous situation. Were there extra safety precautions taken for a project of this nature?

This is a rare project where the government required that we have an emergency fire and rescue team on site while we were completing the work. The plan had to be carefully executed and have several redundancy strategies. First, everyone who entered the pipe had to confined space certified and carry an emergency oxygen tank. We only used battery-powered tools to prevent electrical safety issues working around water. Also, we used more water pumps that were actually required to ensure we were consistently pumping water, had backup water pumps, and maintained safe water levels in the pipes.

Q: With all the water in the pipes and the risk of ocean water in the pipes, what challenges did that pose to the project?

Fortunately, geopolymer itself is hydrophobic, so the presence of water is not an issue when it comes to injecting geopolymer and the material curing as required. Due to the washout of the fines, we did experience some issues while drilling and had water shoot through our drilled holes as soon as we pulled out the drill bit. Proper planning, patience, and experience helped us to mitigate most of the risks associated with working near water.

Q: This is a fairly complex project. What really stands out to you?

Experience really matters in work like this. Geopolymer will naturally follow the path of least resistance thus causing it to find its way into any voids or loose soil. It will continue to expand until the desired density is obtained. Whether we want our polymer to stay localized near the injection location or to travel down the trench and then expand, we are in direct control of this. On this particular project we did both. If we just went down there and injected without fully taking the big picture into consideration, we could have easily over lifted the runway above, or even shifted the pipe out of alignment.

Q: What was the end result of the project?

The project was a complete success and there were no safety incidents. The airport avoided a shut down and passengers did not even know what was going on below them as they were coming in for a landing.