NEW SEAWALL IN FRONT OF EXISTING SEAWALL
The new seawall which is installed directly in front of an existing seawall. The design requires that aluminum sheet piles or precast concrete sheet piles be installed directly in front of the existing seawall. After the sheet piles have been installed, then a new reinforced concrete cap is installed that is large enough to cover both the old and the new sheet piles. This cap is connected to a new anchor system.
This system can be installed prior to failure or where moderate movement has occurred. The new seawall can be used to correct some misalignment and raise the elevation of the existing seawall.
There are no problems with this type of new seawall system, unless it is installed incorrectly, or the design is inferior. It should be noted that designs and specifications for new seawalls differ from contractor to contractor. It is important that before choosing a contractor that the owner compares more than the price. In a majority of cases, the lower price will give the owner less in the specifications and would not always be the better deal.
The new seawall sheet piles should penetrate the existing ground a minimum of 40% of their length.
The new sheet piles used should be structurally designed to meet the required loads.
When choosing aluminum seawall sheet piles, the thickness of the metal is very important and can affect the cost drastically. Sheet piles less than .125" should not be used.
Concrete sheet piles up to 12' long should be a minimum of 6" thick. Size of the horizontal and vertical reinforcing steel in sheet piles up to 12' long should have #5 vertical bars spaced 6" on center and #3 horizontal bars spaced 24" on center.
Choosing alternative sheet piles such as vinyl, plastic, fiberglass and PVC are not recommended for seawalls 5' in height.
NOTE: These products have only been in use in this area for only a short period of time. Use of these products should be done cautiously.
Filling the void between the old and new seawall sheet piles with concrete is very important and should be insisted upon by the owner, no matter which sheet piles are to be installed.
The new seawall cap should be large enough to cover the old and new sheet piles.
If aluminum sheet piles are used, contact of dissimilar metals should not be allowed.
Contractor should provide a 10 year structural warranty for the new seawall.