Many old quays look fine from above while the ground underneath them is quietly washing away. By the time anyone notices, there can be a hollow space meters long under the deck, and the area gets fenced off.
The usual assumption is that the only fix is to rebuild the quay. Often it isn't. In many cases the empty space can be filled and the surrounding soil firmed up from above, through small drill holes, while the structure stays where it is. This post explains how that problem starts, how we approach it, and what we tell owners honestly before they decide.
A lot of quays built in the 1970s and 80s follow the same pattern. A row of interlocking steel sheet piles forms the wall against the sea. Behind it, sand or gravel fill carries a concrete deck, often supported on piles of its own.
The weak point is the steel. Decades of salt water, waves and changing water levels thin it, and eventually small holes rust through. That is when the trouble starts:
Water moves in and out through the holes as the sea level rises and falls.
Each time it flows out, it carries a little fine sand with it.
The fill directly behind the wall goes first, so the hole is usually deepest right against the piles and shallower further inland.
The concrete deck bridges over the gap, so the surface can look normal for years.
The first visible signs are often small: a dip in the asphalt, a crack along a joint, or a hatch that no longer sits flat. Underneath, the void can already be a meter or two deep.
Why the obvious fixes are painful
Rebuild the quay. This solves everything, but it is a major capital project. It takes years to plan and fund, and the berth is out of use while it happens.
Dig it out and refill. This means breaking out the deck, excavating next to a weakened wall and working around whatever services run through the structure. It is slow and disruptive, and digging next to a corroded wall carries its own risk.
Pump in cement grout. This can work, but grout is heavy, slow to set and easily washed away by moving water before it hardens.
There is often a gap between doing nothing and spending heavily on a full rebuild. That gap is where injection works best: buying the structure safe, usable years while the long-term plan is made.
Our approach uses geopolymer injection. We drill small holes through the deck, push slim tubes down to set depths and inject a material that flows into the empty space and the loose soil around it. It expands as it reacts, fills the gaps it reaches and sets hard within minutes. That speed matters next to the sea: it sets before moving water can carry it away.
On a quay, the work usually follows these steps:
Find out what is really down there. Before pricing anything seriously, we measure the void with ground-penetrating radar and probing. An owner's best estimate is a starting point, not a design basis.
Lay out a grid. Injection points run in rows parallel to the wall, typically about a meter apart. Each row goes deeper the closer it is to the wall, because that is where the void is deepest.
Work from the land side towards the sea. We treat the inland rows first and finish against the wall. That way each row has firm ground behind it, and we are not pushing loose material towards the piles.
Inject from the bottom up. At each point we treat the deepest level first and then step upwards, so every layer is built on one that has already set.
Watch the wall the whole time. Survey points on the piles and the deck are read during the work. If anything moves beyond agreed limits, we stop and adjust.
Filling a void under a house and filling one behind a sea wall are not the same job.
These are the points we plan around:
The wall is already weak. Expanding material creates pressure. Next to sound ground that is useful; next to thin, corroded steel it has to be controlled. We use low pressures and small amounts per level near the wall, and we monitor throughout.
The holes work both ways. Water came in through them, and injected material can find its way out through them too. That wastes material and is not something anyone wants in a harbour. We sequence the work to seal the zone next to the wall early and keep watching the waterline.
Space is tight. Quays often have service tunnels, pipe channels or ducts running along the edge. Working inside them can mean low headroom, confined-space rules and permits around live services.
Weather and water levels matter. Material behaves differently in near-freezing ground. Rising and falling sea levels change how much water is moving through the fill on any given day.
Ports are live sites. Security rules, traffic and vessel movements all shape when and how the crew can work.
We would rather say this up front than have an owner find out later.
What injection does well: it fills the empty space, firms up the loose soil around it and gives the deck solid support again. Done well, it can turn a fenced-off area back into a usable one in weeks rather than years, at a fraction of the cost of a rebuild.
What it doesn't do: it doesn't repair corroded steel. The wall is still the same wall, and its condition still sets the long-term plan. Injection treats the effect of the damage, not the damage itself.
That is why we agree on measurable results before starting, not promises about how many years the structure will last. A good result looks like this:
the void is filled, confirmed by a repeat survey;
the ground is measurably firmer than before treatment;
the wall stayed within agreed movement limits during the work.
For most owners, that is exactly what they need: a safe, usable quay and time to plan the next step properly.
Small surface signs along a sea wall are worth checking early. A survey is quick and costs little compared with the repair, and it tells you how big the problem really is before anyone talks about rebuilding.
If you manage a port, harbor or waterfront structure and want a second opinion, get in touch. We will start by measuring what is under the deck.