What is the importance of slope protection?
Slope protection is a critical aspect of engineering and environmental management aimed at safeguarding slopes from erosion, instability, and failure. It involves the implementation of various measures to maintain the stability of slopes and prevent accidents or damage. Slopes with higher inclinations or erosive soils require more attention and protection measures, such as erosion control blankets, turf reinforcement mats, slope drains, gabion structures, and cellular mats.
Let’s look deeper into the importance of slope protection:
Prevent detachment or sliding
The main goal of slope protection is to reduce detachment or uncontrolled soil and rock movement on the slope face. This approach minimizes landslides that often occur in areas with unstable slope.
Maintain physical integrity of artificial slopes:
Construction activities for infrastructure development, agriculture, and mining often entail the creation of slopes. Improper slope protection leads to these slopes being vulnerable to erosion, weathering, and collapse.
Protect human safety:
Natural slopes that are in close proximity to populated areas present a potential hazard if left unprotected. Slope failures in such areas pose a significant threat to human life. Landslides triggered by heavy rainfall or seismic activity near residential areas may result in property damage and loss of life.
Minimize environmental impact:
Slope protection is beneficial in environmental conservation efforts as it curbs erosion of soil and rocks. Slope failures can lead to soil erosion and sedimentation in water bodies. This in turn can impact the aquatic ecosystems.
Protect infrastructure:
Roads, buildings, and other man-made structures are most at risk when constructed near unstable slopes. Implementing measures to ensure slope stability maintains the long-term integrity of infrastructure and lowers maintenance costs.
Mechanical causes of slope failure
The stability of a slope relies on a balance between the shear strength of the soil and the shear stress acting upon it. A disruption in this balance results in slope failure.
Decrease in shear strength of soil:
Shear strength represents the soil’s capacity to withstand deformation and sliding along internal planes. A comprehensive set of factors contribute to a decrease in shear strength.
Increased pore water pressure:
Heavy rainfall or rising groundwater can increase pore water pressure within the soil. This causes a reduction in the effective stress holding soil particles together, which weakens the soil’s shear strength. Highly impermeable clays face slower pore pressure changes when compared to permeable soils, affecting long-term stability in slopes.
Cracking:
Stresses exceeding the soil’s tensile strength can result in cracking near the slope crest. These cracks decrease the overall shear strength of the soil. Cracks also provide direct routes for water infiltration, which can further weaken the soil structure
Swelling:
Over-consolidated clay soils will generally absorb water and swell when the soil is subjected to water. This swelling breaks the structural soil, decreases inter-particle friction and cohesion, thereby decreasing the shear strength remarkably and increasing the likelihood of slope movement or failure.
Decomposition of clayey rock fills:
Claystone or shale used as compacted fill material can decay over time when exposed to water. Such a breakdown creates loose clay particles that swell and fill gaps within the fill, lowering its overall shear strength.
Creep:
Highly malleable clays undergo sustained deformation under perennial environmental loads. Gradually, even low shear stresses can lead to creep effects in the soil. Freezing-thawing cycles or wetting-drying cycles can result in creep.
Increase in shear stress on the soil:
Even if shear strength of the soil is unchanged, conditions such as imposed loads, fracture water pressure in fractures, sudden drawdown, and earthquakes can enhance shear stress and destabilize a slope by decreasing its general stability.
The critical importance of slope protection
Given the instability of slopes caused by various geological factors, slope protection measures are imperative to ensure the continued stability of man-made and natural slopes. Implementing these measures is crucial for several reasons:
Preventing landslides and slope failures:
Unprotected slopes are prone to landslides that endanger human life and property. Landslides disrupt infrastructure functionality, and cause drastic economic and environmental damage.
Protecting infrastructure and property:
Infrastructure made for human functioning like roads, buildings, and transportation networks are often constructed near slopes. Unstable slopes pose a direct threat to these structures. Slope protection measures safeguard against such threats and provide essential stability for these critical assets.
Maintaining ecosystem health and biodiversity:
Slope failures have adverse ecological effects on their surroundings. Erosion due to landslides leads to sedimentation in waterways, disrupting aquatic ecosystems and polluting water quality. Landslides can also destroy vegetation cover and disrupt natural habitats, negatively impacting biodiversity.
Community safety:
Populations living near slopes are vulnerable to potential dangers from landslides and slope failures. Effective slope protection strategies are essential in dealing with these risks. We can minimize the likelihood of catastrophes and create safer living environments.
Methods of slope protection
Slope stability needs a careful analysis of the area that needs to be stabilized and a strategic combination of techniques that address various destabilizing factors. Here’s an overview of the methods employed in slope protection:
Bioengineering Techniques:
Vegetation: Planting an array of grasses, shrubs, and trees on slopes provides a natural and aesthetically pleasing solution. The roots of these plants bind soil particles together and improve overall slope stability. Vegetation also works in intercepting rainfall and reduces its erosion potential.
Non-perforated geocell:
The non-perforated geocell is made from a polymer sheet and has a three-dimensional structure with no holes in its walls. These geocells are filled with sand, gravel, and clay to help expand and support the weak subgrade. The prominent feature of this geocell is its ability to be freely folded and stretched. This flexibility depends on the area in which it is being installed. The non-perforated geocell is easy to install and lightweight. These do not react to chemicals over time. They are skid-resistant and do not deform when exposed to excessive load and pressure. They are best used to stabilize the railway bed, construct roads, reinforce river soil, construct bridges, and retaining walls.
Strata Geosystems mitigates threats to slope stability through a combination of StrataGrid uniaxial (SGU) geogrids and vegetated facings. The geogrids reinforce the slope, while the vegetated facing utilizes the stabilizing effect of plant roots on the soil. Vegetated slopes provide an aesthetically pleasing approach that integrates with the landscape while also preventing erosion.
Erosion control blankets:
Erosion control blankets are biodegradable mats, often made from natural fibers or synthetic materials. They are applied to exposed slopes where they act as a temporary protective layer, shielding the soil from erosion. Moreover, erosion control blankets can promote seed germination and facilitate plant growth.
Strata Geosystems offers a comprehensive solution to control erosion on slopes with its state-of-the-art StrataWeb geocells. The solution is more sustainable and long-lasting compared to traditional erosion control blankets. The cellular confinement system uses a geogrid that is expanded on-site and filled with soil, concrete, or crushed rock. This infill material is encased within the StrataWeb honeycomb structure, constructing a stable and erosion-resistant barrier.
Structural measures:
Geogrids: Geogrids are a fundamental component of structural measures for slope protection, offering reinforcement and stabilization to slopes facing erosion or instability. StrataGrid uniaxial (SGU) geogrids and StrataGrid biaxial (SGB) geogrids manufactured by Strata Geosystems are utilized in various slope protection applications. These geogrids enhance the stability of reinforced earth slopes with face angles up to 70 degrees. These geogrids are laid horizontally back from the slope face to stabilize the slope and prevent erosion, providing a cost-effective and efficient solution for reinforcing steep slopes.
Drainage systems using geotextiles: Water is a significant challenge in civil engineering due to its ability to affect infrastructure. Any kind of water infiltration weakens soil and increases pore water pressure, which contributes to slope failure. To prevent this engineers must ensure that solutions are applied which actively drain water. Here, geotextiles are a good option. They offer 4 benefits: drainage, separation, and filtration and reinforcement. Slopes in particular are susceptible to run off. Geotextiles act as a separation layer between soil zones, preventing clogging of drainage systems. Their filtration ability allows water to pass while retaining soil particles.These permeable blankets allow water flow, and provide tensile strength, too.
Conventional drainage systems rely on extensive gravel layers, which are resource-intensive. StrataTex HSR geotextiles and StrataDrain geocomposites act as a high-flow filtration layer and effectively separate soil particles from water. This forms an efficient drainage system which also prevents clogging. StrataDrain reduces pore water pressure and safeguards against slope instability, by promoting water flow away from the slope face. Depending on the kind of reinforcement needed, we also offer uniaxial and biaxial geotextile products for projects which may need strength and drainage, both.
Successful slope protection cases by Strata Geosystems
Donzi, Atlanta Georgia in USA
The Donzi Landfill in Atlanta, Georgia, was adversely affected by population growth and rampant development activities. This demanded an increase in landfill capacity, but the landfill was hemmed in by existing properties. Outward or vertical expansion was not a viable option for the area. Building traditional containment embankments with gentle slopes (typically 3:1 or flatter) required more space than was available. The situation was further complicated by the presence of high-tension power lines crossing the landfill, which created a safety hazard for dump trucks operating near the slopes.
Strata Geosystem’s StrataSlope provided a solution to address these limitations. This reinforced soil containment system utilized geogrids to create stable slopes at steeper angles than most conventional methods. In the Donzi project, StrataSlope helped construct slopes with a 1V:0.3H inclination for the initial landfill area. Such a steeper inclination maximized the usable space within the existing footprint.
The vertical expansion section of the project presented another opportunity to employ StrataSlope. An earth embankment with a 1V:1H inner slope provided stability to the structure. The outer side of this embankment faced the same spatial constraints and safety concerns related to the power lines. A 1V:0.5H reinforced soil slope with a stone-filled steel wire basket fascia was constructed on the outer face. This steeper slope with added protection reduced the area where dump trucks needed to operate near the power lines, improving safety for workers.
The Donzi Landfill expansion project is a testament to the effectiveness of StrataSlope in overcoming complex engineering challenges. This case study shows how innovative reinforced soil technologies can play a role in achieving sustainable and safe landfill expansion projects.
Aamby valley: Rapid slope stabilization with StrataWeb® geocell
The courtyard area in front of a bungalow at Sundesha Properties faced severe erosion due to heavy monsoon rains. The erosion had reached a point where soil collapse threatened the structural integrity of the building. A permanent solution was necessary before the next monsoon season, leaving little time for construction.
Conventional retaining wall solutions, like masonry gravity walls or reinforced concrete walls, were deemed impractical due to the short timeframe. Strata Geosystems proposed a rapid and cost-effective solution – a geocell gravity wall system. The StrataWeb geocell was an integral part of this operation. Engineered perforations and deep texturing optimize drainage and frictional characteristics, which are vital for swift stabilization. The cellular confinement system effectively contains infill material, minimizing spreading and erosion on slopes. Moreover, the geocell’s rapid installation capability ensured effortless deployment. This innovative approach utilized high-density polyethylene (HDPE) geocells with a depth of 300mm and weld spacing of 356mm. The modular nature of the geocell system allowed for quick construction of a retaining wall stretching over 70 meters with a height of 3 meters.
The geocell gravity wall was composed of stacked and infilled geocell panels. The design considered the surcharge loads and ensured stability against overturning for each panel. Perforations within the individual geocells helped drain any subsurface water, preventing the buildup of pore water pressure behind the wall. A seismic analysis was also conducted to ensure the wall’s performance during potential earthquakes.
The StrataWeb geocell gravity wall system was constructed within a week, meeting the critical deadline well before the monsoon season. This rapid and cost-effective solution stabilized the slope, eliminated the risk of further erosion, and protected the structural integrity of the bungalow.
What types of slope failures do geosynthetics prevent?
Shallow surface failures:
Geotextiles are used to combat surface erosion, which is a major contributor to shallow slope failures. The geotextile functions as a separation layer, arresting the migration of fine soil particles that can weaken the slope surface. Geotextiles can also act as a filter, allowing water to drain while retaining soil particles, thereby reducing surface erosion caused by water flow.
Rotational failures:
Geogrids can be used in soil reinforcement within the slope mass, improving resistance to rotational failures. The geogrid’s cellular structure traps soil particles, creating a composite material with improved mechanical properties. This helps the slope resist the driving forces that can cause it to rotate about a critical point.
Internal shear failures:
Water trapped within a slope can drastically reduce its stability. Geosynthetics take care of internal shear failures by improving drainage and reducing pore water pressure.
Facing instability:
Steeper slopes may require some form of facing to prevent surface erosion. Geosynthetics can be used in facing systems, such as mechanically stabilized earth (MSE) walls, to better their functioning. Geogrids reinforce the soil behind the facing elements, while geotextiles behave like a separation layer and filter within the MSE wall.
At Strata, we help designers identify the most critical failure surface with the lowest factor of safety, offering tools for easy selection of reinforcements. Backed by expert consultation, our eco-friendly, cost-effective geotechnical solutions include high-quality products, precision engineering, and reliable installations. Beyond products and design, we also offer integrated construction services in select global markets. Contact us to see how we can support your next resilient and sustainable infrastructure project.