How geogrids are used to create vertical landfills?
Geogrids, often overlooked but essential in the construction of efficient landfills, play a critical role. In this blog, we discuss the use of geogrids in vertical landfills, their benefits, and why Strata Geosystems has emerged as a global leader in optimizing landfill and waste management projects.
What is vertical landfill expansion?
As the name suggests, vertical expansion of landfills involves creating a new landfill above the existing site. In simpler terms, it refers to increasing the landfill’s capacity by building upward within the existing site boundary. These landfills, also known as piggyback landfills, have gained popularity due to their ability to maximize waste storage within the permitted land area. However, it’s crucial to remember that the key to their success is ensuring the stability of the underlying waste and foundation, which will be subjected to increased stress from the additional vertical layers. This is crucial because the stress on the underlying waste and foundation increases with added vertical layers. Factors such as slope stability, foundation support, leachate management systems (including collection and removal), waste management, and proper drainage installation need to be carefully considered.
Various techniques, each tailored to the specific site conditions and the layout of the existing landfill structure, can achieve vertical expansion of landfills. These techniques, including perimeter implementation, wall retention, and MSE perimeter berms, aim to maximize the airspace and ensure efficient waste storage.
Traditional methods for achieving stable, steep slopes involved constructing massive concrete retaining walls or using flatter, land-intensive slope angles. However, with ongoing innovations, traditional approaches like extensive concrete retaining walls for steep grade changes has been successfully replaced in many applications by geosynthetic materials like geogrids for constructing reinforced soil slopes and walls. This geomaterial is used in MSE berms to reinforce the soil slope and enhance stability.
What is the role of geogrid in creating a vertical landfill?
At Strata Geosystems, we use geogrids to reinforce the structural fill, creating a stable, engineered mass. With geogrids, the soil is reinforced to ensure the overall stability of the MSE berm, allowing it to safely support the weight of additional waste. This feature in design is a newer method of improving the structural integrity of the site, allowing for more waste to be added vertically.
One of the most essential techniques for vertical landfill expansion involves the use of Mechanically Stabilized Earth (MSE) berms. These berms create additional capacity on top of the existing landfill by forming a near-vertical retaining wall. Geogrid layers are placed horizontally within the MSE berm to reinforce the soil, creating a stable, near-vertical structure. In vertical landfills, an MSE berm allows for the construction of steep, stable slopes, which increases the achievable height (elevation) of the landfill and thereby maximizes the available airspace for waste disposal. By using geogrids to stabilize the berm, we ensure the soil can withstand pressure from the new waste. The geogrid reinforcement minimizes and controls soil movement and deformation under the additional pressure, preventing stability failure. Besides the environmental risks of gas and leachate leaks, a primary geotechnical risk for older landfills is global instability, where the entire waste mass could fail in a “landfill landslide,” which is extremely dangerous. Therefore, depending on the site requirements, the berm would undergo reinforcement primarily laterally, by placing geogrid layers horizontally within the reinforced soil mass. Geogrids prevent slippage of internal layers, by confining materials. This property means that the soil stays in place, and doesn’t move relatively when the site experiences higher pressure and load.
Why use geogrids for landfills?
- Soil reinforcement: Using geogrids considerably increases the load-bearing capacity of soil. They reinforce weak subgrades and improve resistance to surface deformation and localized ground movement. It provides stability to the soil, especially weak subgrades, and prevents any significant damage to the structure.
- Landfill construction: For the construction of a landfill, geogrids are used to reinforce foundation soils, provide stability for liner systems on steep slopes (veneer stability), and build structurally sound access roads and MSE berms.
- Erosion control: Geogrids contribute to erosion control primarily by enhancing the veneer stability of the final cover system, preventing shallow slope failures. The geogrid itself is not an impermeable erosion barrier. The grid-like aperture structure of geogrids locks in the soil, helping to stabilize it against displacement. However, dedicated erosion control products (e.g., erosion control blankets, turf reinforcement mats, geocells) are often used in conjunction with or over geogrid-reinforced slopes for more direct surface erosion protection. Adding vegetative layers on top promotes a green fascia, and geocells can further enhance this for steeper slopes.
- Stable foundation: The grid structure of geogrids helps confine soil, distribute loads more evenly, and improve the foundation’s stability and performance under load. By minimizing lateral soil movement, geogrids help prevent settlement, tilting, or slumping of the structure.
- Rapid construction: Unlike traditional methods of constructing landfills, geogrids offer rapid construction, as they are relatively lightweight and easy to handle. While installation requires skilled heavy equipment operators for earthmoving and compaction, it typically involves fewer specialized trades and less complex machinery than constructing large-scale concrete retaining walls. It offers a faster construction method for walls and slopes compared to some traditional techniques.
- Economical choice: The installation of geogrids can lead to cost savings through reduced material quantities (e.g., less structural fill compared to unreinforced slopes), faster installation times, and potentially lower labor costs compared to conventional construction methods, making them an economical choice for many applications.
Projects by Strata Geosystems
Case study 1:
Client: Modern landfill of Model City
Location: New York, USA
Product used: StrataGrid™
About the project:
A huge challenge was encountered in the Modern landfill of Model City. A high-pressure gas line (or pipeline) was running through this landfill site. The original plan was to move the gas line to meet the landfill capacity; however, this plan was quite expensive and time-consuming. Hence, it was decided that another option should be considered.
Strata Geosystems suggested using StrataGrid geogrid, as soil reinforcement. For primary reinforcement and strengthening of the soil, StrataGrid 350 and 500 were used. For secondary reinforcement, a lighter-weight StrataGrid 150 was used. Secondary reinforcement typically addresses localized facing stability, improves compaction near the face, or acts as a construction aid; it does not contribute to the primary structural capacity for resisting global forces. With careful installation of multiple geogrids and soil layers, Mechanically Stabilized Earth (MSE) berms were constructed. Due to this, the capacity of the existing landfill site was also maintained without the requirement to shift the high-pressure gas line. This solution also resulted in being cost-effective and highly efficient.
Case study 2:
Client: Vapo Green Enviro Limited
Location: Vapi, Gujarat, India
Product used: StrataGrid™, StrataSlope™ and StrataBlock™
Application: Vertical expansion of existing cell for a landfill
About the project:
Vapo Green Enviro Limited, a landfill situated in Vapi, Gujarat, faced a shortage of storage space. Due to the unavailability of space and increasing cost concerns, horizontal expansion of the landfill was quite impossible.
Strata Geosystems came in with an innovative solution. We suggested using the airspace instead of landscape and constructing a vertical landfill. Theoretically the idea seemed highly successful, however there were 3 challenges:
- Vertical expansion over existing embankments in some parts of the landfills.
- Proper soil reinforcement in steep slope areas.
- Enhancing the strength of the existing embankment with soil nails to ensure it could serve as a stable foundation for the new reinforced soil structure.
These problems were successfully tackled by Strata Geosystems with their innovative geo-synthetic product StrataGrid. The new, steep slopes were constructed using the StrataSlope and StrataBlock systems, which incorporate StrataGrid geogrid for primary soil reinforcement. The primary containment of landfill leachate is achieved by a dedicated impermeable liner system (e.g., geomembrane and/or GCL) within the landfill cell. The StrataGrid geogrid reinforces the soil mass, including any soil bags used in wrapped-face construction, to ensure the stability of steep structures, but it does not itself prevent leachate leakage. Vapi Green Enviro Limited was highly satisfied with this landmark solution provided by Strata Geosystems.
In a nutshell, geogrids are a vital component in modern construction, especially for soil reinforcement and stability. They play a significant role in constructing vertical landfills. These landfills utilize vertical airspace rather than expanding horizontally, creating more capacity within the same footprint by enabling the construction of stable, steepened waste containment structures. The actual containment of leachate and contaminants is provided by dedicated liner systems (e.g., geomembranes, GCLs) that are often supported by these geogrid-reinforced structures.
Strata Geosystems’ StrataGrid geogrid has played a key role in the success of numerous vertical landfill projects worldwide. To know more about the services provided by Strata Geosystems or to get expert advice from their experts, get in touch with us!