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Soil stabilisation techniques: common methods and products

What is soil stabilisation?

Soil stabilisation involves alteration of the soil’s physical, chemical, or biological characteristics to improve its stability, shear strength, load-bearing capacity and other geotechnical features to render the terrain usable in construction.This process of transforming a soil’s physical properties falls under a branch of geotechnical engineering. This is done by reducing permeability and increasing its overall strength before construction commences.

What are the common methods of soil stabilisation

Soil stabilisation is broadly classified into three types. While there may be other bifurcations that further delve into the subcategories, we focus on the overview of techniques.

  • Chemical stabilisation: Chemical stabilisation is a stabilisation method that involves the addition of secondary materials or components to an existing substrate. This is done to change the density and ability to support weight. Materials such as Portland cement, sodium chloride, lime, polymers and others are used to alter the structure of the soil. The purpose of doing so is to make the soil more dense and less permeable.
  • Mechanical/ Physical stabilisation:  Mechanical or physical stabilisation methods involve physical modifications to the soil. These mechanical methods include compacting, preloading, soil replacement and reinforcement. The purpose of this kind of soil stabilisation is to increase the density of soil particles and improve its load-bearing capacity. While traditional methods of mechanical soil stabilisation can be resource intensive, the ready-to-use and ease of installation of various geotechnical products such as geocells, geogrids, geomembranes or geocomposites make them an easy-to-use soil stabilisation tool.
  •  Biological stabilisation: The biological method of stabilising the soil utilises natural processes to stabilise the soil. These processes include planting vegetation, to stabilise soil through root systems. The logic behind this is that roots help to hold the soil together. This helps in reducing erosion and improving the stability of soil particles. Soil properties can also be improved by microbially induced precipations.

What is the purpose of soil stabilisation?

Soil stabilisation aims at enhancing the engineering properties of soil, and render it usable for civil engineering needs such as creation of roadways, mining, building bridges, canal draining, or even landfill management. The need for soil stabilisation is broken down into five key geotechnical aspects.

  • Enhanced mechanical strength: Soil stabilisation plays a crucial role in enhancing the mechanical strength of soil. By improving the interlocking between soil particles, it improves the soil’s shear strength and load-bearing capacity, resulting in a more stable foundation. If you’re operating with weaker subgrades, or other challenging terrains, use of a geocell which confines soil and distributes loads is a particularly useful addition to the list of soil enhancement materials.
  •  Reduced permeability: Stabilising soil helps reduce its permeability, limiting the flow of water through the soil mass. This is beneficial in areas where excessive water flow could lead to erosion, instability, or other geotechnical issues. Think of areas prone to excessive and unpredictable rainfall where water logging leads to the road caving in. Here, geocells uphold the structure by allowing water to pass. Further, by adding layers of a geogrid to hold the aggregate, we add more structural strength to the road structure.
  •  Improved compressibility: Stabilisation of road soil improves its compressibility, which is crucial for load distribution during construction and over the lifespan of the structure. This helps minimise settlement issues, ensuring the long-term stability and performance of the engineered structure. Soil compression occurs due to the expulsion of water and air from the soil voids, leading to a decrease in overall soil volume –another reason for paved roads to cave in, and crack. The addition of a geogrid, for example, not only affects the shear strength of the soil during the subgrade improvement stage, but also positively influences the soil compression curve for soil types.
  •  Durability: By improving the soil’s resistance to environmental factors and loading conditions, geosynthetics reduce the need for maintenance and repairs, ultimately saving costs over the structure’s lifespan.
  •  Plasticity: Plasticity refers to the ability of soil to deform without breaking apart. It improves plasticity, facilitating easier handling and shaping of the soil during construction. Geocells physically confine the soil within their cells, limiting its ability to deform and reduce plasticity, and therefore are an ideal supplement to soil subgrade improvement measures.

Common types of soil requiring stabilisation

If you want to construct strong foundations and infrastructure it is important to understand what types of soil require soil stabilisation. Below we have listed the kind of soils and the methods that are employed to stabilise them.

  • Clayey soil: Clayey soils have high water retention capacity which affects its plasticity in addition to low shear strength and high compressibility, leading to settlement and instability issues. As a result, clay is prone to expansion during monsoon and contraction during dry periods. This is where geogrids come in with improving localised stress concentrations, confinement of soil, and minimising deformation. With an improved ability to resist deformation, and lateral movement, geogrids improve the California Bearing Ratio Value, bringing structural integrity to the layers as a whole.
  • Sandy soil: Sandy soils have a low force of cohesion. This makes them more susceptible and prone to erosion and compression. While sandy soils have better drainage and higher shear strength compared to clayey soils, they do need reinforcement. The most common challenge with sandy soil is erosion which is ideally prevented by the use of geogrids. Since the chief role of geogrids is to manage and evenly distribute loads, due to the juncture strength, it works to protect sand against erosion, settlement. For example, especially ports tend to suffer with a mix of clay and sandy soil while needing strong load bearing capacities for containers. Here, complete geotechnical solutions are useful –right from subgrade improvement, load support, to lining surfaces for improved life of the port area.
  • Silty soils: One of the most challenging soil types, but also found in areas which need roads and bridges, silty soils are found near river beds, with historic sedimentation. Since they contain deposits, they have low permeability, very high plasticity, low cohesion leading to compaction issues, and high chances of erosion. This soil is the biggest contender for soil stabilisation and use of geogrids as they typically address all of these issues. From geocells, geomembranes, to geogrids – a wide suite of products can meet the industry specific applications for soil improvement.
  • Peat soils: Peat soils are organic soils that are prone to rapid decomposition. Their porosity means poor load bearing capacity, high compression, prone to settlement, and water logging. It’s one of the terrains needing the most amount of soil stabilisation which is non-chemical. Normally, stabilisation methods like incorporating inorganic materials can highly improve their performance. While the stabilisation needs will vary depending on the topography, and the geo-technical application, the typical application for soil stabilisation comes with wetlands. While India has low incidence of such soil types, projects needing work in Kerala backwaters, Brahmaputra basin would need geosynthetic interventions for soil stabilisation.
  • Loamy soils: Loamy soil is a combination of clay, sand and silt and can be deemed as a geotechnical engineer’s preferred soil. Thanks to the composition, it’s moderately stable when compared to other soils. However, if they are subjected to Extreme moisture fluctuations, they can have adverse responses. Depending on soil mix ratio, the shear strength may vary and as a result the soil stabilisation technique needed will also change. Since it’s sensitive to moisture content, load bearing capacity is the most important challenging aspect of soil stabilisation that needs to be addressed in the long run.

Benefits of soil stabilisation

Soil stabilisation is important and it offers various benefits. This is usually done on construction sites before the actual construction begins. Some of the benefits of soil stabilisation have been listed below.

  • Improved soil strength: Soil Stabilisation helps to improve soil strength. It offers greater tensile and compressive strengths when compared to untreated soil. This makes it more resistant to deformation and failure.
  • Reduced settlement: Stabilising soil reduces the chances of settlement. This is mainly due to its enhanced strength and lower permeability.
  • Enhanced load- bearing capacity: Stabilised soil has higher load-bearing capabilities when compared to unstabilised soil. This allows heavier structures to be built safely on soils which are stabilised.
  • Increased resistance to erosion: Soil stabilisation makes the soil less prone to erosion. This is developed by making it more resistant to erosion caused by wind, rain and flowing water.
  • Improved durability: Stabilised soil is better held. Stabilised soil lasts longer and requires less frequent maintenance. This helps to save a considerable amount of time and money that might otherwise have been spent.

Geosynthetics- based soil stabilisation

Geosynthetic products are made of durable polyethylene [PET] and polypropylene polymers. Geosynthetics are preferred in soil stabilisation owing to the high tensile strength of the products.

  • Geogrids: Geogrids are geosynthetic materials whose function is to provide reinforcement to the soil. These are made of high-density polyethylene or polyester. They provide high tensile strength to the soil and are used in areas that have poor soil conditions.
  • Geotextiles: Geotextiles are another commonly used type of geosynthetic material that is used in soil stabilisation. Geotextiles are designed to reinforce the soil in areas having high water content. They are put to use because they improve soil drainage and reduce soil erosion.
  • Geomembranes: Geomembranes are used in soil stabilisation because they provide a barrier against water and other liquids. These are usually made of high-density polyethylene (HDPE) or synthetic materials. Their main function is to prevent the water from seeping through the soil.
  • Geosynthetic clay liners: Geosynthetic clay liner is another type of geosynthetic material that is used in a number of construction sites. These are made of bentonite clay sandwiched between two layers of geotextile or geomembrane. Areas having high water content use geosynthetic clay liners.

How to choose the right material for soil stabilisation?

Picking the right materials for stabilising soil can be a difficult task. It forms an important part of construction projects. The first step is testing the soil to check its composition, and other properties before arriving at various steps of addressing the topographical challenges.For soil stabilisation StrataGrid™ uniaxial geogrids are a popular choice of material. This is due to its high tensile strength and durability. Made of high-density polyethylene (HDPE) or polyester, geogrids are useful in areas that have poor soil conditions. They are easy to install and significantly reduce construction cost. Strata Global is a popular choice of engineers who are looking for geogrids and if you would like to consult with us, we’re just a call away.

Benefits of using geogrids for soil stabilisation
Benefits of using geogrids for soil stabilisation

Geotextiles are another popular and multifaceted choice for stabilisation among engineers who are looking for geosynthetic-based soil stabilisation materials. Geotextiles are useful in areas that have high water content and help in improving soil drainage and reducing erosion. Since it achieves 3 functions in 1 product – separation, filtration and reinforcement, it’s a unique geotechnical product.

StrataTex HSR™ knitted geotextile by Strata Global
StrataTex HSR™ knitted geotextile by Strata Global

StrataDrain™ is often the choice for projects due to its ability to work in different environments, be it aggressive Ph, or aqueous environments. A high performance drainage composite product, it’s a non-woven geotextile that functions both as a separator and filter. It’s composed of high flow, geonet-geotextile drainage composites manufactured with high-density polyethylene (HDPE) geonet and polypropylene nonwoven fabric bonded to one or both sides.

As a result, it allows for liquid and gas –both to pass into the geonet core. This geonet in turn collects and allows the flow of liquid and/or gas into a collection system. With a width of upto 3.8 m, laminated in PP geotextile varying from 90 to 1 gsm, on one or both sides – StrataDrain™’s properties make it a versatile product for soil stabilisation in a wide range of soil types and are an excellent choice for your next project. Choose from different types, and consult with us for more insights on how we can design and implement your next engineering challenge.

StrataDrainTM product range by Strata Global
StrataDrain™ product range by Strata Global

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