How Soil Instability Causes Seawall Damage

‍This post is part of the Seawall Repair Network series, featuring views, news and case studies written by the Seawall Repair Network. 

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Erosion and Soil Loss (Void Formation – Landward Side)

Causation: As seawalls age, soil eventually starts to migrate through the vertical seawall panel joints and weep holes. At the time of original seawall construction, a geotextile filter fabric is installed on the landward side along the panel vertical joints and weep holes. Filter fabric serves the critical function of preventing soil loss into the waterway from the landward side.

An essential point to remember is that seawalls are designed to keep the land in more than to keep the water out. Seawall structures are engineered to allow water to pass through seawall vertical panel joints and weep holes. The engineering concept Equilibrium of Hydrostatic Pressure refers to neutralizing opposing forces caused by water pressure on both the landward side and the opposing waterward side of the seawall structure.

Over time, all filter fabric begins to deteriorate and become ineffective. Once this occurs, soil migration begins to occur during every water event (rain, irrigation, daily tide activity, storm surge, etc.). A slow process initially, soil migration leads to void formations on the landward side of the seawall. Void formations immediately begin to jeopardize the overall stability of the seawall structure. The loss of structural stability leads to unwanted movement of the structure. As the movement of the structure occurs, damage to the seawall cap and panels also occurs, and stress on the seawall tie-rods and deadman anchors will lead to damage or sometimes complete failure of the overall seawall structure.

The Domino Effect

When considering the relationship between the various causes of seawall damage, simply think of the domino effect in order to clarify the complexities associated with seawall engineering:

Natural forces create a domino effect which causes seawall damage and eventually seawall failure if not mitigated and remedied in time:

1. Erosion due to filter fabric deterioration leads to…
2. Void formations behind the seawall, which lead to…
3. Deterioration of the seawall berm (or supporting soil) leads to…
4. A build-up of hydrostatic pressure behind the seawall, which leads to…
5. Damage to seawall the cap, seawall panels, and anchor system, which leads to…
6. De-stabilization of the entire seawall structure, which leads to…
7. Seawall failure, which leads to…
8. Financial loss, wasted time, destruction of property, and STRESS.

Has your seawall been damaged by natural forces? Click the button below to download an info-packed guide to permanent and lasting repair.

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