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. Engineers implement 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 geosynthetic solutions including cellular confinement systems (e.g., StrataWeb), geogrid reinforcements, and engineered retaining wall facings.
Prevent detachment or sliding
The primary objective of slope protection is to minimize the detachment and uncontrolled movement of soil and rock on the slope face. This approach minimizes landslides that often occur in areas with unstable slopes.
Maintain physical integrity of artificial slopes:
Construction activities for infrastructure development, agriculture, and mining often entail the creation of slopes. Inadequate slope protection makes slopes vulnerable to erosion, weathering, and potential 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 plays a role in the downstream effects of aquatic ecosystems. When erosion control measures are in place, apart from improving structural life of slopes, the upside is conservation; of flora, fauna, and localized ecosystems. Without erosion control measures, which also risk the local stability of slopes, we also see surface run-offs that affect the water table, and contaminate wider areas.
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 is governed by the balance between the soil’s shear strength and the shear stress acting on it. When this balance is disturbed, slope failure can occur. Heavy rains, earthquakes, and human interventions such as excavation may weaken the strength of the soil or add stress. When the driving forces overpass the resisting forces, then the slope collapses, resulting in landslides or ground movement.
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 contributes to a decrease in shear strength.
Increased pore water pressure:
Heavy rainfall or rising groundwater can raise pore water pressure in the soil. This lowers the stress that keeps soil particles bound, making the soil weaker. Slopes made of dense, impermeable clay see slower changes in pore pressure compared to more permeable soils, which can affect their long-term stability.
Cracking:
Stresses above the soil’s tensile strength may lead to fissures near the slope apex. These fissures diminish the total shear strength of the soil. Cracks allow direct pathways for water infiltration, which can further compromise the soil structure.
Swelling:
When over-consolidated clay soils take in water, they swell. This swelling disrupts the soil’s structure, reduces friction and cohesion between particles, and lowers shear strength, raising the risk 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 experience continuous deformation under constant environmental loads. Over time, even small amounts of shear stress can cause the soil to creep. Creep can happen when something freezes and thaws or gets wet and dries.
Increase in shear stress on the soil:
Even if the shear strength of the soil is unchanged, conditions such as imposed loads from structures or earthquakes can increase the shear stress on the soil. Other factors, like rising water pressure in fractures or sudden drops in nearby water levels, can make a slope unstable. This happens because the pressure change reduces the stability, even if the soil itself doesn’t get weaker.
Methods of slope protection
Ensuring slope stability requires a thorough assessment of the site and a strategic combination of techniques to address the various causes of instability. This includes controlling drainage, building retaining walls, installing erosion control mats, and planting vegetation. Together, these measures reduce water infiltration, prevent soil erosion, and manage external pressures on the slope. The aim is to make the slope more stable and stop failures by addressing both surface and internal forces.
Bioengineering Techniques:
Vegetation: Planting 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:
StrataWeb geocells are perforated, three-dimensional polymer cells specifically engineered for slope protection. Expanded on-site and filled with soil, gravel, or other appropriate infill material, they create a stable, erosion-resistant layer to enhance slopes and minimize surface failure.
The openings in StrataWeb® permit free drainage of water, lowering pore pressure and enhancing the stability of the slope. StrataWeb geocells are light-weight, simple to install, and versatile to suit any slope angle. StrataWeb® has been effectively employed in various slope stabilization applications across the globe, providing long-term structural stability and erosion protection.
At Strata Geosystems, we tackle slope stability with StrataGrid uniaxial (SGU) geogrids paired with vegetated facings. The geogrids strengthen the slope, while the vegetation adds root support that naturally binds the soil. Vegetated slopes provide an aesthetically pleasing approach that integrates with the landscape while also preventing erosion.
Slope Protection using StrataWeb Perforated Geocells:
StrataWeb® perforated geocells provide a strong and long-lasting solution for erosion control and slope protection. The cellular confinement system, which is perforated, is inflated on-site with soil, gravel, or crushed rock. Water drainage is free through the perforations while cellular confinement restricts the infill, creating an erosion-resistant, stable barrier. The system stabilizes the slope, stops soil detachment, and provides long-term structural stability even in heavy rain or high-flow conditions.
StrataWeb® perforated geocells are used for long-term slope stabilisation and erosion control. Upon on-site expansion with soil, gravel, or crushed rock, the perforated cells enable free drainage of water and immobilise the infill material. It creates a stable, erosion-resistant barrier that reinforces slopes, inhibits soil detachment, and ensures long-lasting structural strength against rainfall, runoff, or other environmental stresses.
Structural measures:
Geogrids: Strata Geosystems manufactures StrataGrid uniaxial (SGU) and StrataGrid biaxial (SGB) geogrids for slope protection. When combined with engineered facings, StrataGrid® geogrids can reinforce earth slopes at face angles up to 70 degrees. They are laid horizontally back from the slope face to stabilize the slope and prevent erosion.
Drainage systems using geotextiles: Water getting into the ground can make the soil weaker and raise the water pressure in the soil, which can cause landslides. To prevent this, engineers use slope stabilization techniques that help water flow away. Geotextiles are a good choice here, as they offer four benefits: drainage, separation, filtration, and reinforcement. Slopes are especially prone to runoff. Geotextiles act as a separation layer between soil zones, preventing clogging of drainage systems. They filter water by letting it pass through while holding back soil particles. These permeable blankets also let water flow freely and add tensile strength to the ground.
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 that 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 steep 1V:0.3H inclination (an angle of approximately 73 degrees from the horizontal) 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 the embankment had similar space limits and safety risks from nearby power lines. To address this, a 1V:0.5H reinforced soil slope with a stone-filled steel wire basket fascia was built. The slope, which is steeper and protected, minimized the area in which dump trucks needed to operate near the lines, thereby enhancing safety for the workers.
The Donzi Landfill expansion project stands as proof of how effectively StrataSlope can address 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. Erosion had advanced to a level that endangered the structural stability of the building due to soil collapse. A permanent solution had to be in place before the next monsoon, leaving very little time for construction.
The short timeframe made it impossible to use traditional retaining wall options like reinforced concrete walls or masonry gravity walls. Strata Geosystems suggested a geocell gravity wall system as a quick and economical solution. This process was largely dependent on the StrataWeb geocell.
The engineered perforations and deep texturing boost drainage and friction, which are key to fast slope stabilization. The cellular confinement system keeps the infill material securely in place, limiting spreading and protecting the slope from erosion.
The geocell’s fast installation made deployment straightforward and efficient. This approach used high-density polyethylene (HDPE) geocells, 300 mm deep with 356 mm weld spacing. Thanks to the modular design, a retaining wall over 70 meters long and 3 meters high could be constructed quickly.
The geocell gravity wall was made by stacking and infilling geocell panels. The design considered surcharge loads and ensured each panel remained stable against overturning. Perforations in the geocells let subsurface water drain, preventing pore pressure from building up behind the wall. A seismic analysis was also done to check how the wall would perform during earthquakes.
The StrataWeb geocell gravity wall was completed in a week, well before the monsoon. It stabilized the slope, stopped further erosion, and protected the bungalow’s structure.
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 reinforce the soil inside the slope mass by providing tensile strength through horizontal layers. Being positioned in these layers, increases the soil’s resistance to rotational forces and thereby reduces the risk of rotational failure. This arrangement produces a composite soil–geogrid mass with improved mechanical properties, which helps the slope resist the driving forces that could cause it to rotate about a critical point.
Internal shear failures:
Water trapped within a slope can reduce its stability. Geosynthetics mitigate internal shear failures by reinforcing soil structure and facilitating drainage, thereby reducing pore water pressure.
Facing instability:
Steeper slopes often require a facing system to control surface erosion. Geosynthetics are commonly incorporated into such systems—like mechanically stabilized earth (MSE) walls—to improve performance. In these applications, geogrids reinforce the soil behind the facing elements, while geotextiles act as a separation and filtration layer within the MSE wall.
At Strata, we aid designers in recognizing the most significant failure surface with the least safety margin, supplying tools for simple reinforcement choices. With expert guidance, our sustainable and cost-efficient geotechnical solutions encompass high-quality materials, accurate engineering, and trustworthy 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.
FAQs
What are the three methods of slope protection?
Strata employs geosynthetic solutions that ensure solid and lasting slope stability:
StrataWeb® perforated geocells: Soil, gravel, or crushed rock-filled expandable 3D cells. They restrain infill, prevent erosion of the soil, and stabilize slopes against detachment and surface failure.
StrataGrid® geogrids: Strengthen soil internally by imparting tensile strength, enhancing slope resistance to rotational and internal shear failures.
StrataDrain® geocomposites: Drain, decrease pore water pressure, and increase slope stability by transferring water away from exposed areas.
What is the factor of safety for slope protection?
Factor of Safety (FoS) compares resisting forces, e.g., soil strength, with driving forces, e.g., gravity. A FoS value larger than 1 means that the slope will be theoretically stable, whereas a FoS value smaller than 1 may indicate instability. In real engineering practice, however, greater minimum FoS values are used to allow for uncertainties and risk:
Temporary slopes: Usually, FoS ≥ 1.3
Permanent slopes: Usually, FoS ≥ 1.5 or greater
These threshold values provide sufficient safety for construction, long-term stability, and safety against unforeseen loads or environmental factors.
What are the factors responsible for slope failure?
Slope failure results from two primary mechanisms: reduction in shear strength (due to pore pressure, weathering, creep, swelling, decomposition) and shear stress increase (due to loads, excavation, earthquakes, water drawdown). Knowledge of these is crucial for effective slope protection.