What are the common challenges while installing geogrids?
Engineers have long faced challenges posed by unstable soil formations. Weak soil conditions lead to delays, increased costs, and even structural failures of construction projects. Before geogrids were invented, conventional solutions often involved using large quantities of expensive aggregate materials. Alternatively, complex soil reinforcement techniques were implemented.
Dr. Brian Mercer developed geogrids in the 1950s. Mercer’s initial “Netlon process” entailed extruding molten plastic into a grid-like structure that resembled a fishing net. Although this was commercially successful, Mercer set his sights on a wide range of uses for geogrids. He believed that through the development of stronger geogrids, their reinforcement capabilities could be improved tenfold. With this goal in mind, he relentlessly pursued advancements in technology, which resulted in the invention of the “Tensar process” in 1978. This process produced geogrids with superior strength and durability. Geogrids have since become the cornerstone of most land reinforcement projects.
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?
Geogrids have become a mainstay of any construction project where soil reinforcement is necessary. The following points provide an overview of the optimal geogrid installation process:
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.
Soft ground considerations
Achieving a smooth grade can be challenging in soft grounds such as swamps or peat. In such cases, prioritize creating positive drainage away from the construction zone. The subgrade must be free of any damaging debris.
2. Geogrid placement:
Roll positioning
Unroll the geogrid following the prepared surface’s contours. Project specifications dictate the direction of laying and spacing of multiple layers. Generally, geogrids are placed parallel or perpendicular to a road centerline.
Overlapping
Geogrid rolls adjacent to each other should overlap at sides and ends as per 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
Use sharp shears or a utility knife to cut geogrids around curves, manhole covers, or other obstructions. Ensure clean, precise cuts to avoid fraying. Always wear gloves and eye protection 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 the minimum. A thicker layer can help avoid rutting on soft ground surfaces. This initial lift thickness is crucial as it provides a stable base for subsequent layers and helps prevent damage to the geogrid.
Competent subgrades
The aggregate fill can be dumped directly onto the geogrid. Rubber-tired trucks can be driven over the geogrid at low speeds (less than 5 mph) to dump fill as they move forward. 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. Be prudent in the case of very soft subgrades to avoid stressing the soil. A qualified geotechnical engineer can be consulted in such situations.
Equipment restrictions
Avoid having tracked equipment directly on the geogrid. Ensure at least 150mm (6 inches) of aggregate fill between the geogrid and tracked equipment is maintained. If the subgrade is firm enough to resist rutting, you may use rubber-tired equipment on the geogrid.
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
Smooth and uniform subgrade preparation is essential. Uneven surfaces tear geogrids during the installation process. Proof rolling can pinpoint these areas. Back dragging may be required to create a level surface for proper placement. Additionally, ensuring the subgrade is compacted and stable can prevent settlement or shifting of the geogrid during installation.
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.
Seam integrity
It is important to overlap adjacent geogrid rolls according to project requirements and fully secure them. Improperly seamed geogrids can reduce their reinforcement capabilities, making them less effective at distributing stress.
Weather conditions
Colder weather conditions can make geogrids prone to fracturing under dynamic loads. Avoid deploying geogrids at low temperatures to prevent durability issues. Contractors should also consider the potential impacts of extreme weather conditions, such as heavy rainfall or intense sunlight, on the geogrid installation process.
Aggregate fill compatibility
Poorly chosen aggregate materials can cause separation between the fill and the subgrade. Well-graded crushed aggregate with the correct particle size and fine content should be used. It is also essential to ensure compatibility between the aggregate fill and the geogrid material. 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. The key considerations include appropriate waste disposal protocols, particularly for hazardous materials. Adhering to environmental guidelines promotes ecological welfare and public trust.
What are the benefits of using Strata Geosystems' geogrid?
Standard geogrid solutions require skilled labor for optimal subgrade reinforcement. StrataGrid, on the other hand, is designed to ensure successful installation even in the absence of a skilled workforce. The geogrid’s lightweight construction makes handling and deployment easier compared to other geogrids. Its sturdy design reduces the risk of accidental laceration during installation by less experienced crews. These advantages enable less skilled workers to install StrataGrid easily. Strata empowers contractors to succeed on a broader range of projects by enabling geogrid installation with unskilled labor.
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 ‘select fill’ to raise the ground level and reduce flood risk. To achieve the curved wall design with an integrated slip road, StrataBlock segmental blocks were deployed. This block system provided a smooth, curved aesthetic while accommodating the access road within the wall. StrataGrid was used to avoid overlapping in curved sections, especially at the junction. Finally, a strategically positioned cross wall facilitated construction at the lane bifurcation. With the guidance of their expert engineers, Strata delivered a functional and visually appealing 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 plied 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 exceptional engineering. Through a combination of their high-performance products and a focus on client needs, Strata consistently delivers successful projects.
Strata’s dedication to innovative solutions and exceptional client service makes it a trusted partner for any civil engineering venture. Are you considering Strata for your next project? Take a peek at our roster of geosynthetic products to find the perfect fit for your specific needs. Reach out to our team of experts today to discuss how Strata can help you achieve success.