New Seawall Construction

Building a seawall is not the same problem as building a bulkhead, even though the finished structures can look identical from your back door. A bulkhead is designed around the soil behind it. A seawall is designed around the water in front of it — and water with fetch behind it delivers forces that soil never does.

Exposure drives the design

The first thing we establish is what the water actually does at your property.

Fetch — the distance of open water the wind can blow across before it reaches you. Fetch builds wave height. A property on a sheltered creek and a property on open river a mile away are different design problems.

Boat wake — on the Intracoastal and the main channels, wake is a near-continuous load and in some locations it is the dominant one.

Surge and storm water levels — a wall designed only for normal tide range is a wall designed for ordinary Tuesdays.

Orientation — which way the wall faces relative to prevailing wind and the worst-case direction.

This is why we do not price seawalls per foot from a phone call. The same length of wall is a different structure depending on what hits it.

The elements that matter

Cap elevation and freeboard. How high the wall stands relative to design water levels. Too low and overtopping becomes routine, which erodes the ground behind the wall — the side the wall cannot defend. Too high and you have paid for freeboard you do not need and lost the view you bought the property for. This gets balanced during design and has to sit within permitted elevations.

Toe protection. The defining difference between a seawall and a bulkhead. A vertical wall reflects wave energy downward and back into the water at its base. That reflected energy scours the seabed at the toe, removing the embedment the wall depends on — the wall actively undermines itself. Toe protection, usually armour stone or an equivalent detail, absorbs that energy before it can do the digging. On exposed shoreline it is part of the design, not an optional add-on.

Embedment. Depth below the mudline, set by engineering for your soils, retained height and loading — and with an allowance for the scour the toe protection is there to prevent.

Tiebacks and anchors. Rods running back to deadman anchors set in undisturbed soil outside the active soil wedge. These resist the horizontal load. Corrosion protection on tieback hardware is specified, because tieback failure is what rotates walls.

Drainage. Water that gets behind the wall has to be able to leave. If it cannot, hydrostatic pressure loads the wall outward — a direction it was not designed for, and a leading cause of rotation. Weeps, filter fabric and a graded drainage layer.

The cap. Reinforced, with adequate cover for a marine environment, tying the pile tops together and anchoring the tieback connections.

Sequence

1. Survey, soils and exposure assessment
2. Design and engineering for the site
3. Permitting — normally the longest item on the schedule
4. Mobilisation and access protection
5. Driving the sheet piles to design embedment with interlocks engaged
6. Tiebacks installed to anchors outside the active wedge
7. Toe protection placed
8. Cap formed, reinforced and poured
9. Backfill in compacted lifts with the drainage detail
10. Grade, restore and walk through

Materials

Vinyl sheet pile handles most residential First Coast shoreline, provided the section is selected for the wave loading rather than just the soil. Concrete is the choice where exposure is high, where the wall is also the finished architectural edge, or where loads behind the wall are significant.

Permitting

Review may involve FDEP, the U.S. Army Corps of Engineers, the St. Johns River Water Management District and your county or city building department. Requirements depend on the site and scope and are revised periodically — confirm current requirements with the reviewing agency. We handle it on the projects we build.

Call (904) 327-3931 or request a free estimate.