Geosynthetics’ contribution to mitigation of natural disasters
Although water is the origin of life, it can also threaten life when it goes beyond its normal limits: all human lifestyles require a balance between water and soil (Heibaum 2014). In regions of the world that are particularly exposed to the threat of climate change, the issue of water protection is becoming more important as population density increases. Geosynthetics can make a significant contribution to adaptation, including improving the resilience of communities and infrastructure to extreme weather disasters such as floods, landslides and droughts (Dixon et al. 2017).
Geosynthetics prevent coastal erosion
Coastal erosion can be defined as the continuous retreat of the shoreline over time. The advance and retreat of coasts is a natural phenomenon that has always existed and that, over time, has shaped the coast into its current form (Palma et al. 2016). However, to the perennial natural causes are now added the anthropogenic causes. The continued growth of construction near coastal areas increases human exposure to natural hazards. Since the causes of erosion cannot be eliminated and the increased vulnerability to hazards does not prevent people from settling on the coast, we must adopt measures that guarantee the security of goods and people without neglecting the natural advantages of coastal areas. Dikes (also called dikes) are one such measure and are used to protect developments from flooding. Artificial reefs and submerged breakwaters are other measures and consist of underwater structures that disperse wave energy into the sea, thus reducing the energy of waves reaching the shoreline and thus reducing their erosion action (Lawson 2016). The environmental awareness that developed in the last decades of the 20th century and the beginning of the 21st century and the scarcity of rock sources in particular for the construction of breakwaters led to the search for alternative materials such as geotextiles (Palma et al. 2016), which have a long history of use in marine engineering to prevent erosion.
When used to line containment units, geotextiles retain the sand infill, resulting in a stable, erosion-resistant, and structurally sound mass-gravity unit (Lawson 2016). They respond to growing concern for the environment and associated restrictions in mining and quarrying. Furthermore, by allowing the use of locally available natural materials, high transport costs and associated pollution are avoided (Venkatappa Rao 2016). An interesting element mentioned by Lawson (2016) is that artificial reefs and submerged breakwaters made of geotextile units provide a safe and injury-free environment for humans near populated beaches. Geotextile containers also attract an abundance of marine plants and life soon after construction, making these artificial reefs a prime habitat for fish.
Geosynthetics help flood protection
A flood is an overabundance of water that generally submerges dry land (Heibaum 2014).
River valleys, like the coastline, attract settlements. Various works such as dams, dikes and canal systems can be carried out to minimize the damage caused by flooding. Most dikes and flood protection dams are less than 10-15m in height and usually take the form of longitudinal barriers. Geosynthetics have also proved useful in these structures. Please note that different measures are required for permanent protection against temporary flooding.
In river structures, whether in the rehabilitation of existing dams or in the construction of new ones, geosynthetics perform the following functions (Brandl 2010, 2011):
(1) as filtering elements and horizontal, vertical and inclined separators.
(2) sealing the dike slopes by placing geomembranes on the water side.
(3) reinforcement of the slope, crest zone and access road to defend the dike.
(4) protection against surface erosion.
(5) vertical dividing walls.
(6) protection from burrowing animals.
For temporary protection against flooding, Brandl (2010, 2011) recommends using sandbags for local stabilization if there is a risk of hydraulic failure of a dam or dike due to uplift from seepage or internal or pipeline erosion. Geotextile filter sheets covered with granular material can also be used for large critical areas.
Although less used, geotextile tubes to attenuate the wave breaking process in meandering rivers or to fill broken sections of dams have proved to be very suitable as low-crest submerged structures to reduce the energy of waves incident on the banks.
Landslide prevention and soil reinforcement by using geosynthetics
Landslides are defined as a form of mass loss that includes a wide range of ground movements such as rockfall, deep slope failure and shallow debris flows. Landslides are caused by natural or man-made factors or a combination of these, such as poor soil conditions, heavy rains and seepage, erosion by streams and rivers, vibration caused by earthquakes, increased vegetation load, wind, excavation, increased load, vibration caused by traffic or deforestation (Shukla 1997). Landslides can be controlled by improving drainage conditions, cultivating more vegetation on slopes, providing adequate containment structures, and using some newly developed soil improvement techniques such as soil reinforcement (Shukla 1997; Mohri et al.. 2009; Cuomo et al. al. 2020).
Geosynthetics can be very interesting for jobs involving embankments built on soft foundation soils. They have proven to be a cost-effective alternative to other methods of stabilizing foundations, such as dewatering, excavating and replacing with selected granular materials, or using thicker or thicker layers of stabilizing aggregate. Basically, geosynthetic layers can serve as reinforcing materials or can accelerate the process of consolidation of soft subsoil. Reinforcement also reduces infill material consumption because it minimizes or avoids local failure mechanisms caused by construction equipment during transport, spreading and compaction of infill material (Palmeira 2012).
In addition to reinforcing geogrids, fibers randomly distributed throughout the soil mass or stacked infill can be used to increase soil strength (Heibaum 2014). More detailed information on these design approaches can be found, for example, in Palmeira (2012).
Stabilization of slopes and walls in reinforced soil by using geosynthetics
Slopes can be natural or man-made, and various natural and artificial factors contribute to soil instability (Shukla 1997). The advent of geosynthetic reinforcement materials has brought a new dimension of efficiency to the design and construction of reinforced slopes and retaining walls. Geosynthetic reinforced walls are now a mature and proven technology in almost all countries (Allen et al. 2002; Bathurst 2014). Geosynthetically reinforced slopes are typically compacted embankments that incorporate geosynthetic horizontal layers as tensile reinforcement to improve stability. The use of geosynthetics for slope stabilization allows reducing the size of earthworks by modifying their geometry and also allows the use of soils with average mechanical properties (Shukla et al. 2012).
Geotextiles, woven and non-woven, and geogrids are now increasingly used to reinforce steep slopes (Shukla et al. 2012). More complex structures are geosynthetic reinforced soil retaining walls (GRS) with full height rigid cladding (FHR), which are characterized by the following characteristics:
(1) the use of an FHR cladding that is cast in place using construction in stages,
(2) use of a reinforcing polymer geogrid for cohesive soils to ensure good interlocking with the soil,
(3) use of a non-woven and woven geotextile composite for near-saturated cohesive soils to facilitate drainage and embankment tensile reinforcement,
(4)) the use of relatively short reinforcement,
(5) the use of poor-quality soils at the site as embankment if necessary (Tatsuoka et al. 1997).