Marina Apron and Seawall Maintenance

Having repaired numerous Marinas, we have seen firsthand the many problems that Marina owners are faced with daily! Marinas that have on-site boat storage have many more problems as the weights of forklifts that traverse the aprons cause problems all their own!

This document will help Marina owners and management to identify problems early, allowing for a much more economical repair.

There are two components to a Marina apron structure, the first being the seawall/retaining wall and then the concrete apron area for forklift travel.
The seawall is the most critical structure as its job is to hold the supporting soils in place and not allow any erosion to occur. What most people do not know is how land-born water affects the hydraulic pressures that are exerted on the landward side of the seawall panels. Any kind of soil will percolate water! If you were to dig down directly behind your seawall panels, you will see that the water table within the soil directly collates with the water height on the water side. This is a natural occurrence and cannot be manipulated. This level rises and falls with the tides…both sides of the seawall in unison. Problems begin when you have a storm/rain event that introduces large amounts of water into the soils, causing a positive hydraulic pressure as the water level rises above the normal water-side level. Knowing how heavy water is, this newly introduced pressure will exert strain on any panel joint, pipe penetration or anchor attachment. This water WILL find a way out, either through a weak panel joint or in a worst-case situation, under the panel “toe” of the wall.

This pressure zone is known as the VADOSE zone. Pressures found in this vadose zone are directly controlled by the amount of newly introduced water and the time of accumulation. In other words, a slow, steady, ¼” per hour rainfall will not produce the pressures that a 3” per hour rainfall event will produce. You should also evaluate the runoff zone on the landward side! Is there a building or structure that is draining additional water into this area? Is the property elevation lower at the seawall than the adjoining area?

When considering this, you must also know how most concrete panel/pile are originally constructed. The panels are typically pre-cast and each panel end has a “keyway”. These panels are joined end-to-end at the king piles, either in front or back and attached to the piling. Depending on the depth of the panels (Florida can vary…short panels on the west coast and long panels on the east coast), one would assume that they are straight and mounted flush with the piling, all the way down to at least 2’ below the mud line. Not necessarily so…as you will see below!
The keyway between the panels is “sealed” by inserting a nylon sock-like fabric tube and injecting it with concrete. In theory, if the panels are mounted flush and plumb, this would work fine! But assuming perfect construction is a mistake made by many! If the panels are not flush and plumb, there is no way to attain a perfect seal using this method! If it’s real bad, we have found attempts to mask using filter cloth that over time, deteriorates.

Below is a photo taken by USPG crews that illustrates the panel mis-alignments!

This photo shows the panels on the left and the king pile on the right. This gap is approximately 3” at a total panel depth of 8.5’. If you look close, you can see the attachment anchor right above the red arrow point in the gap. Notice the sloping, exfiltrating soils.

This photo shows the dramatic elevation change between the normal bottom of the canal and the exfiltrating soils. And please note: This was at a very busy Marina that experiences heavy prop wash from boat traffic.

The soils seen in these inspection photos are slowly being drawn out from under the slab aprons.

The easiest way to spot this problem is to ALWAYS look at your apron slabs to inspect for any cracking! Once the supporting soils become disturbed, slab cracking will occur! Basically, the slab acts as a tread surface for forklift traffic, being wholly supported by the retained, compacted soils on the landward side of the seawall. Once it cracks, you know that the soil compaction values are dropping, pointing to leaking panels or panel “toe”.

Once cracking begins, it causes a 2-fold problem. Now there are new paths of entry for land-born water to enter and accelerate erosion of the soils. Couple that with both rainfall and dripping lift/boat water intrusion contacting the steel reinforcing within the apron slab. This causes rapid deterioration of the steel and will begin spalling the concrete!

To key to protecting your investment is to constantly inspect the area for ANY settlement or cracking of the apron slab. Should you begin to see these tell-tale signs, it’s very important to contact us for a free inspection. Our crews are thoroughly trained to identify and photograph our findings both under water and above. We have the equipment needed to spot the issues…we may dive your wall, drill a few test probe holes and/or penetrometer the soils underneath.

The best outcome for your structure is based on your quickness to act once you see the signs of possible failure. Our method of repair is very non-invasive to your operations and your business will not be affected by our presence. Quick, Clean, Quiet! Oh, and did I mention fast?

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US Precision Grout
520 E. Ft. King St.
Ocala, FL 34471

David Tuck
Sr. Project Manager, S. FL
352-342-2511 cell