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Soil erosion is a broad topic, but this article will focus on the impact of erosion along riverbanks and coastal areas due to water.
Erosion is a mechanism in which soil particles are detached and transported due to forces from flowing water and are subsequently deposited elsewhere causing impacts to the local ecology and environment through degradation of ecosystems.
It can also impact on our infrastructure by undermining foundations and embankments which support our roads, structures and utilities, possibly increasing risk to dams and levees which serve to protect the public from storm surges and floods.
Geosynthetics can and have been used in various applications to act as protective barriers, reinforcement and/or as a filtration layer.
There are several types of geosynthetics that can be used individually or in combination to address the required application(s).
Properly evaluating the site conditions and determining the specific requirements for geosynthetics is key in designing an efficient and constructable solution that will perform as intended and meet project requirements. For example, if the objective is to retain and separate a finer grain soil from being moved a geotextile that can function as a separator would work but if you also need to allow the free flow of water to avoid buildup of pore pressure then a geotextile that can function as a filter would be needed. In that case, the design would evaluate the geotextile aperture size, permittivity, as well as the survivability, to allow the flow of water while retaining the soil particles without clogging. This type of assessment is critical in the proper selection of these products.
One of the most common applications is the use of a geotextile under rip rap or other protection systems such as gabions or other similar systems. These systems provide hard countermeasures to reduce the impact of water on a riverbank, embankment or coastline.
Traditionally, an aggregate filter layer was used to retain the smaller particles being protected which could include multiple gradations. The construction of these systems was complicated and required complex construction procedures.
A properly designed geotextile can now replace the filtration layers. The geotextile would need to be selected with the ability to retain the natural soils below the geotextile while not clogging. Both conditions are important to eliminate particle transport without building pore pressure. The geotextile would also need to be sized to survive installation and placement of the rip rap or other systems over the geotextile.
Geotextiles have also been used to fabricate tubes which are filled with locally available sand. Depending on their size and site conditions these tubes can be filled in place or filled on a barge and then placed with a crane. These tubes have been used for many different applications such as coastal erosion, riverbank stabilization, and scour countermeasure for bridge piers and abutments. Geotubes can be used to replace traditional rip rap, concrete articulated block mats and other hard armor solutions. Since they can be filled with local materials, they can eliminate the transport of these large and heavy components.
These are two examples of how geosynthetics can and have been used to address erosion along riverbanks and coastal shorelines. There are other erosion control applications where geosynthetics can be considered when designing resilient and sustainable solutions.
In these two examples geotextiles reduce excavation and the need to import large volumes of materials while providing a durable and resilient solution. Geosynthetics help improve constructability, schedule, and cost as well as reducing the impact of construction to the environment.
Daniel E. Alzamora, P.E., is a contributing editor for Geosynthetics and has spent more than three decades in the geosynthetics industry in both the public and private sectors.