Applications in Geopolymer: Sea Wall Stabilization

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: John, today we’re talking about seawall stabilization. Can you tell us about a project that really stands out to you?

I recall a project that I worked on several years ago in Southern California. The city municipality started noticing large sinkholes on their beach and had to close the beach. The seawall that was retaining the beach was failing, allowing water through the joints and under the concrete panels. This was creating erosion and causing the soils to collapse, leading to large (and dangerous) holes in the beach.

Q: This sounds like a costly and dangerous issue. What were they doing to fix the problem?

The public works department had tried a few different solutions, but the sinkholes kept coming back. Eventually, the city’s consulting engineers helped to design a solution using geopolymer to stabilize the seawall – a solution proven to work based on another municipality in the area. My team at the time was barged over with their equipment and we got to work implementing the solution.

Q: This was a complex job. What were some of the challenges you faced in stabilizing the seawall?

To begin with, the area is a tourist destination, so it was a concern to not have big trucks and construction crews in the view of the tourists. That actually made geopolymer injection the perfect solution because it’s a very surgical procedure and doesn’t require huge trucks, large crews, and bulky equipment.

We had to inject under and just behind the seawall, essentially extending the seawall vertically and plugging any gaps where the seawall was failing. This restored structural integrity to the seawall so it could properly sit with its load evenly distributed.

Q: With water leaking under the seawall, how were you able to complete the work?

Our team completed the work at low tide and a temporary containment boom was used as a precaution. We drove metal tubes into the sand under the wall foundation and then injected the geopolymer. As it comes out the end of that tube, it will follow the path of least resistance, naturally filling voids and loose soil. Once it is in place, it will begin to expand, in some cases up to 20 times its’ liquid state. The geopolymer cures almost instantly and can even be used to lift the wall in areas if desired. This set of injections essentially sealed the bottom of the wall and simultaneously restored the load bearing capacity of the soil.

A second set of injections was performed just behind the wall. Tubes were driven from above to avoid drilling through the wall. One of the beauties of working with the geopolymer is how versatile it is. The injections were able to back seal any gaps or cracks in the wall as well as void fill and densify the soil. All of this was achieved with a small crew and without any excavation or demo.

Q: Essentially, you were injecting the geopolymer into the water. How safe is geopolymer injection to use in public waters like this?

Geopolymer is safe to use in ocean environments because it’s inert and does not leach chemicals. It is environmentally neutral and accredited to be injected in and around potable water supplies. I have led projects for the U.S. Army Corps of Engineers doing just that. The geopolymer has a very high compressive strength and relatively low tensile strength. This means that if you ever have to come back and dig everything up, it can be excavated through with regular tools just like soil. It tears apart rather easily.

Q: How well did it work for the city? Was everyone happy?

The project was considered a success and city officials were happy with the results. Looking back on the project, I really don’t see how they could have chosen any other method. The old-fashioned way would be to just dig it all up and tear everything out.

Q: What would you tell engineering professionals? What’s the lesson in all this?

More and more engineers these days are beginning to see how geopolymer truly is the way of the future. The way I see it, geopolymer can be just another tool in your toolbox. There is a time and a place for a hammer and there is a time and a place for a screwdriver. Educating yourself on its’ many applications can set you apart from the rest and make your projects a complete success, too.