In the past, engineers have faced challenges related to unstable soil formations. In construction projects, poor soil conditions can lead to structural failures, increased expenses, and project delays. Before the invention of geogrids, conventional techniques usually called for the use of large quantities of expensive aggregate materials.
Alternatively, complex soil reinforcement techniques were implemented.
The precursor to modern geogrids was developed by Dr. Brian Mercer in the 1950s. Mercer’s initial “Netlon process” was later refined, resulting in the invention of high-strength geogrids for soil reinforcement.
Although this was commercially successful, Mercer set his sights on a wide range of uses for geogrids. He thought that the advancement of stronger geogrids could enhance their reinforcement capabilities by a factor of ten. With this vision, he diligently pursued technological innovations, culminating in the introduction of the “Tensar process” in 1978. This novel process created geogrids with remarkable strength and durability. Since that time, geogrids have become an essential solution in many land reinforcement endeavors.
Geogrids are polymeric grids manufactured from high-strength materials like polyester, polyethylene, or polypropylene. These grids reinforce soil, transfer loads across a wider area, and prevent soil from pulling apart under tension.
How are geogrids installed?
Nowadays, geogrids are an essential component of any building project that calls for soil reinforcement. An outline of the ideal geogrid installation procedure is given by the following points:
1. Subgrade preparation:
Engineer verification
An engineer evaluates the subgrade’s readiness for geogrid installation. It involves gauging elevations and analyzing unsuitable materials. Proof rolling can be employed to locate weak areas, and ruts can be smoothed out by backdragging. However, it’s worth noting that saturated, or very soft soils may not withstand this technique and would typically need modified techniques for testing.
Soft ground considerations
In soft terrain like peat or wetlands, achieving a smooth slope can be difficult. In these cases, priority should be given to establishing adequate drainage away from the construction zone. The subgrade must be free of destructive debris.
2. Geogrid placement:
Roll positioning
Unroll the geogrid to match the contours of the prepared surface. Project specifications indicate the direction for laying and the spacing between layers. The orientation of the geogrid is important and relies on the product type, whether uniaxial or biaxial, and its application. Uniaxial geogrids should be placed with their main strength direction perpendicular to the expected tensile forces. This means they should be laid perpendicular to a retaining wall face or along the direction of an embankment slope.
Overlapping
Geogrid rolls adjacent to each other should overlap at sides and ends as per the specified guidelines. Overlaps should be ‘shingled’ in the direction of the fill to prevent peeling. Consider starting with rolls at the far end of the coverage area and working toward the fill placement point.
Cutting
Utilize sharp shears or a utility knife to trim geogrids around curves, manhole covers, or other obstacles. Ensure that cuts are clean and precise to prevent fraying. Wearing gloves and eye protection is always advised when cutting.
3. Placing the cover fill
Initial lift thickness
The first lift of aggregate fill over the geogrid should be 150mm (6 inches) thick at a minimum. A thicker layer can help avoid rutting on soft ground surfaces. This initial lift thickness is important because it helps keep the geogrid from getting damaged and gives later layers a firm foundation.
Competent subgrades
On competent subgrades, fill material should be placed adjacent to the geogrid and then pushed over it in a controlled manner, typically with a low-ground-pressure dozer. Direct dumping from a height can damage the geogrid. To place the fill, rubber-tired trucks can drive at low speeds (less than 5 mph) over the previously placed fill material as they move forward to dump the next load. The fill material should be evenly spread to maintain uniform contact with the geogrid, ensuring optimal performance and structural integrity.
Softer subgrades
The next step involves the trucks backing up and dumping fill onto the previously placed layers. In very soft subgrades, use lightweight fill and restrict equipment loading. Initial lifts should be spread using low ground pressure dozers, working from firm to weak zones to avoid overstressing. A qualified geotechnical engineer such as our consultants can be consulted in such situations.
Equipment restrictions
No heavy construction equipment, tracked or rubber-tired, should ever traffic the geogrid directly. Always maintain a minimum 150mm (6 inches) lift of aggregate as a working platform between the geogrid and the equipment.
Spreading fill over soft subgrades
Use a low-ground-pressure dozer to spread the fill evenly on soft ground surfaces. The dozer blade is to be raised gradually as each lift is pushed out to create a cascading effect on the geogrid. Prioritize working from stronger to weaker areas while maintaining the shingle pattern for fill overlaps.
4. Compaction
Standard compaction is suitable for most projects. In the case of soft soils, static compaction with a light roller is recommended to negate subgrade disturbance. Maintaining optimal moisture content in the fill helps with compaction. For soft soil foundations, the initial layer of compacted material may be looser than usual. This prioritizes a stable work surface for construction activities before focusing on achieving maximum density.
Common challenges faced during geogrid installation
Contractors can mitigate risks by understanding the potential barriers to geogrid installation. Here are some of the challenges listed below:
Subgrade preparation
The preparation of a smooth and uniform subgrade is of utmost importance. Irregular surfaces create voids beneath the geogrid, which impedes proper interlock with the aggregate fill and results in inadequate performance or differential settlement. Proof rolling identifies these areas. Back dragging may be necessary to ensure a level surface for appropriate placement. Moreover, ensuring that the subgrade is compacted and stable prevents settlement or displacement of the geogrid during the installation phase.
Anchoring and positioning
Geogrids tend to shift during installation if secured inadequately. This results from substandard anchoring or uneven backfill placement. To prevent this, contractors should ensure that anchors are spaced correctly. They should verify that the backfill material is placed and compacted evenly, preventing any voids or unevenness.
Overlap integrity
It is important to overlap adjacent geogrid rolls according to project requirements. If overlaps aren’t done properly or are too short, the reinforcement will have gaps that weaken its ability to spread loads and handle stress effectively.
Weather conditions
Geogrids made from HDPE can become brittle and prone to damage in cold conditions. To ensure durability and performance, avoid using or installing geogrids in extremely low temperatures unless they are specifically designed to handle such environments. Or, choose geogrids manufactured from PET which are resistant to weather conditions, apart from carrying a proprietary coating, offering mechanical and chemical durability in harsh conditions. Strata Geosystems manufactures polyester (PET) geogrids that offer excellent durability and long-term strength. While HDPE geogrids exist in the industry, Strata’s polyester-based grids are well-suited for various temperature conditions.Additionally, contractors need to account for possible effects of severe weather conditions, including heavy rain or strong sunlight, on the installation of geogrids.
Aggregate fill compatibility
The effectiveness of geogrid reinforcement depends on the mechanical interlock between the grid and the aggregate. Use well-graded crushed aggregate with the right particle size and minimal fines to ensure the particles properly penetrate and lock into the geogrid apertures. Also, check that the aggregate and geogrid are compatible to avoid any compromise in performance or durability. This helps prevent any adverse chemical reactions or degradation over time.
Environmental regulations
These regulations focus on reducing the impact on the ecosystem throughout the project lifecycle. With geogrid, can at times be in hazardous situations such as landfills, or industrial waste. In such scenarios, being cautious is necessary since geogrid rolls need to be rolled out and necessitate laying out the materials. Geogrids over the life of the project over positive carbon impact.
What are the benefits of using Strata Geosystems' geogrid?
StrataGrid is designed for straightforward and efficient installation. Its lightweight construction makes handling easy, while its sturdy design minimizes the risk of accidental damage. These features contribute to a faster, more reliable installation process that can be completed by general construction crews, empowering contractors to succeed on a broader range of projects.
Strata Geosystems is the first choice for most engineers due to its commitment to innovation. Their extensive portfolio showcases many cases where expert guidance and top products solved client challenges.
Curved reinforced soil wall at NH-227, Trichy, using StrataGrid™
The construction of a reinforced soil wall on NH 227 in Trichy, India, presented Strata with several challenges. The flood-prone paddy land required an elevation above ground level. The design needed a curved wall that reached up to 11 meters in height while incorporating a 6-meter-wide slip road for access to the village. To add to the challenge, the project involved a critical junction where the highway transitioned from four to two lanes.
Strata’s solution used ‘selected fill’ to increase the ground level and reduce the risk of floods. To achieve a curved wall design with an integrated slip road, the strategy StrataBlock was deployed. This block system provided a smooth, curved beauty by adjusting the access road within the wall. In curved sections, the layout of StrataGrid was carefully planned to manage and minimize complex overlaps, ensuring continuous reinforcement throughout the structure. Finally, a strategically deployed cross wall facilitated the construction in the lane domination. With the guidance of its expert engineers, Strata gave a functional and visually attractive curved reinforced soil wall.
Efficient landfill capping with StrataGrid™ and StrataDrain™ in Villena, Spain
The Villena MSW Landfill in Spain required an enclosure that preserved the ecological makeup of the area. Strata’s challenge was to design and install anchor trenches within some space constraints. The design also had to ensure efficient rainwater drainage, gas collection, and slope stabilization. Strata developed an effective installation method for the anchor trenches within the limited workspace. StrataDrain drainage composite was implemented to improve the flow rate, design efficiency, and reduce overloads. The revamped drainage system improved upon the existing rainwater management and gas collection systems. StrataGrid geogrids were also used to reinforce and stabilize the landfill slopes. Strata ensured successful landfill capping that met all environmental requirements by adapting their solutions to the complex terrain. The project is a testament to Strata’s expertise in delivering innovative solutions for environmental projects.
Partner with Strata for success!
Strata Geosystems is world-renowned for its commitment to innovation and extraordinary engineering. Through the combination of its high-performance products and a focus on client needs, Strata continuously delivers successful projects.
The innovative solution and dedication of Strata to extraordinary client service make it a reliable partner for any civil engineering enterprise. Are you considering Strata for your next project? To find the perfect fit for your specific requirements, take a look at our roster of geosynthetic products. Reach out to our team of experts today to discuss how Strata can help you achieve success.