Erosion is a significant problem in many settings. From agricultural land to construction sites, water and weather get everywhere, and it’s essential to prepare for this. Some precipitation is acidic, which will cause even more damage to your school, airport, or shoreline. With a national shoreline erosion rate of 0.40 m/yr, you can’t afford not to raise your defences.
Articulated Concrete Block
A single articulated concrete block won’t do much to protect against erosion. An Articulated Concrete Block (ACB) system offers excellent protection from erosion. A network of blocks laid together to create an erosion-resistant overlay, an ACB, is a powerful tool to prevent erosion. Beneath an ACB system is an underlay that acts as a filter. The underlay allows for infiltration and exfiltration while retaining soil particles. Underlays are usually made of geotextiles, graded aggregate, or both. The blocks used in the ACB system must be dense and durable, but also flexible and porous.
To protect underlying soil materials from erosion, an ACB system is an excellent solution. The blocks interlock, but each block can still adapt to changes in the subgrade, otherwise known as ‘articulating.’
ACB systems usually rely on the way the blocks interlock geometrically, but additional components such as ropes, cables, geotextiles, and geogrids can enhance the ACB, making it stronger.
The structure of an ACB system allows for expansion and contraction. An ACB system can expand when it gets hot and contract when it gets cold, and as it will be outdoors in all weathers, expansion and contraction becomes a significant factor in durability. ACBs have excellent resistance to hydraulic shear and overtopping.
It can be all too easy to lay any ACB system down, but the best system for you is a site-specific design. The durability and sustainability of your ACB lie in appropriate engineering based on the hydrological and geological conditions of the site.
ACBs can be laid by hand or purchased as pre-made mats. The articulated concrete blocks are then laid over a filter layer on the pre-treated subgrade. ACB systems can then act as a soil revetment. Revetments take the energy out of the water and thus decrease erosion.
Where to Use An Articulated Concrete Block
ACB systems work well in many places, such as:
Wildlife habitat: ACBs can protect from loss of habitat, or loss of protected land
Boat ramps: Concrete blocks help protect against the destruction of your boat ramp, which could damage your boat or even result in stranding.
Drainage channels: The use of ACBs protects human-made and natural drainage channels. Drainage channels can be crucial to safeguarding roads, rails, and other infrastructure.
Dikes and levees: Dikes and levees are susceptible to overtopping—ACBs help to prevent this. There are 100,000 miles of levee in the US, and most of them are inadequately protected from erosion.
Dam overtopping: ACBs can help prevent overtopping, and thus, damage to dams.
Overflow channels: Susceptible to high-velocity water, overflow channels are crucial to maintaining infrastructure. Erosion can cause breaches, which means the overflow channel fails.
Articulated concrete blocks help protect structures from erosion in a wide variety of places, like shorelines and piping. Many people prefer ACBs to cast-in-place solutions like paving, concrete bulkheads, or rock riprap.
The use of ACBs is environmentally-friendly, and they’re easy to install. You can find them in a wide range of shapes and thicknesses, but it’s always best to use the aesthetic designed for the site you want to protect.
How to Install An Articulated Concrete Block
Only a small construction team is required to install articulated concrete blocks with minimal equipment. ACBs are fast and easy to assemble, and it is quick to check the layout, too, due to the visibility of each piece.
A step-by-step guide to installing articulated concrete blocks includes:
Soil samples to the lab: A necessary step to find out what kind of subgrade you have and ensure you choose the right ACB system to support it.
- Subgrade preparation: Prepare the soil to the lines and cross-sections depicted on the plans.
- Geotextile placement: Place flat, directly on top of the prepared subgrade.
- ABC system placement: Place directly on top of the geotextile, ensuring a smooth and flat position.
- Finishing: Backfill the holes in your concrete blocks with soil suitable for vegetation or crushed stone.
- Inspection: The entire process should be inspected and signed off by an engineer.
Rainwater run-off can damage infrastructure, threaten the environment, and disrupt areas such as construction sites or roads. Erosion is worse with acidic or weighty rain. Other forms of precipitation, such as hail, ice, or snow, can cause damage too.
In built-up areas, with many concrete and metal textures, surface run-off is worse, which can severely damage your site. Areas most likely to generate surface run-off include:
- Roads and sidewalks
- Driveways and parking lots
- Building roofs
- Some lawns
Heavy rain will cause the surface run-off to travel at high speeds, increasing the water’s energy. In turn, the water will cause more damaging erosion to infrastructure and other sites.
Extensive, fast-moving surface run-off will inevitably end up in the sewers, with all the pollutants it’s picked up along the way. This excess water and dissolved contaminants will then make its way to streams and rivers, contributing to shoreline erosion.
In urban areas with heavier surface run-off, there is also less porous surface to absorb water. Less infiltration leads to unanticipated erosion.Armor Against Shoreline Erosion
Once a series of articulated concrete blocks have been laid out, it creates a ‘hard armor’ between the shoreline and any potentially eroding rainwater. Each block in the armored network offers the durability, density, and impact resistance of a concrete block, thus protecting your landscaping or other infrastructure.
There are many different configurations of ACB systems, and each one has been carefully designed to suit specific settings. ACB configurations vary in locking mechanisms, layout, and cross-section. Nevertheless, these configurations are proprietary.
A vital element of the ACB systems that give them an edge is their flexibility. A flexible revetment will adapt to variations in the soil subgrade, making it much more effective in protecting against erosion. Nevertheless, the subsoil should be prepared for the addition of an ACB. Although, subsoil will still shift, and the ability of your ACB to change with it is crucial.
Another way articulated concrete blocks can be useful lies in their individuality. Single blocks can be arranged around trees or in tricky corners to protect valuable property from erosion. You can also safeguard drain pipes or other piping with an articulated concrete block or two.An Articulated Concrete Block and Vegetation
One characteristic of articulated concrete blocks is their capacity to grow vegetation. This is possible because of the vertical spaces at the core of each block. ACBs that allow for plant growth help protect against erosion. Some of the benefits of vegetated concrete blocks include:
- Blend in with site features
- Help with water absorption
- Purify water from pollutants
- Helps prevent erosion
However, choosing the right vegetation for your ACB system is essential. This will usually depend on the site you’re basing the system on.Environmental Benefits of Articulated Concrete Block Systems
A significant benefit of using ACB systems is their contribution to supporting the environment they are situated in. Some environmental benefits of articulated concrete block systems include:
- Preservation of natural drainage and treatment systems
- Reduce water run-off
- Improve water quality
- Reduce pollutants
- Recharge aquifers
- Prevent erosion
- Blends into an existing site
- May be able to use for green building rating credits
If you install your ACB over a drainage layer, it’s eligible for use in a Best Management Practices (BMP) plan to protect and preserve existing sites. You can also use a BMP in new developments. An ACB over a drainage layer helps maintain natural drainage and treatment systems that act on the soil. These biological processes, coupled with the ACB, reduce run-off, flooding risks, and pollutants and prevent erosion. It will also recharge aquifers and improve water quality.
Alternatives: Erosion Control Matting and Erosion Control Blanket
If you need an alternative to ACBs, there are options available to you, such as erosion control matting.
Erosion control matting comes in seeded or non-seeded types, meaning you can opt for vegetated matting or non-vegetated matting. For areas kept purposefully without vegetation, try a non-vegetated mat. However, vegetation does help protect against erosion.
Matting and erosion control blankets function in similar ways; they slow down the flow of water across the surface you wish to protect, thus decreasing the amount of energy the water has to erode. They come in various materials, from synthetic to biodegradable, and everything in between. Matting or a blanket also covers the soil, protecting it from rain and melting snow.
Another term for erosion control matting is ‘wattle.’ Wattle is a natural method of controlling sediment and water erosion. Silt wattles slow the flow in channels and are ideal for fast-flowing drainage or overflow channels. Straw wattles can help prevent soil erosion and chemical and water run-off. They also increase infiltration in the ground.
The best place to use erosion control blankets is on slopes, where they are efficient at absorbing water before it flows down the slope.
Articulated concrete block systems also come in cabled or non-cabled varieties. The cabled version has steel or other high-strength cables threaded through preformed horizontal holes in the blocks. The cables help to connect the blocks into a concrete mattress. Cabled mats can be assembled offsite. Non-cabled ACBs are designed to interlock with each other, with no ropes, cables, or other ties.
Shoreline Erosion Case Studies
If you’re undecided about articulated concrete blocks for your site, take a look at some case studies. For instance:
- Lake LaMoure, North Dakota: Overtopping undermined the lake, causing soil destruction and severe erosion to the lake banks. A massive ACB system resolved the issue and helped to control flooding.
- A levee on Lake Pontchartrain, New Orleans: Overtopping and scour were causing the lake to breach the levee. Articulating blocks paired with an erosion control mat armored up to six miles of the levee against erosion. This protected a road and rail system, allowing all-weather access.
- Holly Beach, Louisiana: River channels and jetties caused limited sediment availability, and erosion was frequently accelerated by storms, causing shoreline erosion. Two ACB mattresses now protect one side of the highway, and the unarmored side shows significant signs of deterioration.
- Arkansas National Wildlife Refuge: The aim at the Wildlife Refuge was to protect the whooping crane’s habitat. With more than 2 acres lost per year and the whooping crane still in recovery from near extinction in the 1940s, it could have been disastrous. More than a million ACBs now protect 73000 feet of shoreline, to significant effect.
- Barker Canal, Louisiana: With high water velocities and a highly erodible native soil, the Barker Canal suffered severe erosion and embankment failure. However, with an articulated concrete block mat, erosion stopped in its tracks.
- Pipe Creek, Texas: A small creek in Texas became a fast-running river during heavy rain, which affected piping. Articulated concrete matting solved the problem, protecting pipelines from erosion.
- Boat Ramp, Texas: The shoreline erosion at this site comes from severe prop wash from boats. An ACB system now protects the basin from erosion.
With over 30 years of trading behind them, Flexamat is an expert in preventing erosion. Flexamat pioneered the first tied concrete block mats almost 20 years ago and are specialists in vegetated concrete erosion mats. We also invented the technology to package Flexamat products into rolls and successfully vegetate articulated concrete block systems fully.
Flexamat is available worldwide, with material available locally across the USA and Canada. We’re from Ohio and sell a variety of vegetated concrete mats. Some of the types of Flexamat we sell include:
- Underlayment options
- Interlocking Geogrid options
- Flame resistant Geogrid
- Polypropylene Geogrid
- Optional cores inside the rolls; custom ordered to suit you
There are so many ways an articulated concrete block can help you. If you have an erosion problem, don’t let it keep washing your infrastructure away; call Flexamat today.