How is soil reinforcement done using geogrids?
The emergence of geosynthetic materials has brought about a noticeable change in civil engineering as they address the industry’s technical and economic challenges. These materials not only act as a protective barrier but also reinforce weak soils, improving stability and load-bearing capacity. In this blog post, we will discuss geogrid soil reinforcement, how geogrids strengthen soil, how geogrid-reinforced soils work, and the key points to consider during their design and installation.
What is geogrid soil reinforcement?
Geogrid soil reinforcement is an innovative engineering practice to improve soil strength and stability using different types of geogrids. A geogrid is a polymeric grid structure, available in uniaxial and biaxial forms, typically made from high-density polyethylene (HDPE) or polypropylene, which ensures durability and resistance to environmental factors. When installed in layers in the bulk of soil, the geogrid becomes intertwined with soil particles, creating a composite material with significantly enhanced properties. One of the main applications of geogrid-reinforced soil is in the construction of retaining walls.
Traditional retaining walls normally require deep excavation combined with concrete or masonry, which could be expensive and time-consuming. Geogrids allow the use of locally available soils for reinforcement, reducing both material costs and environmental impact. The geogrid acts as a vital reinforcement that stops the soil from caving in, thereby enabling steeper and higher walls.
What is the interaction between soil and geogrid?
Many parameters affect this complex interaction and are important for the performance of the constructed system. When a geogrid is placed in the soil, the friction between the soil particles and the geogrid’s surface stops the reinforcement from being pulled out. The following factors influence this frictional force:
- Granular soil is made of particles like sand and gravel, which makes it a bit rough. When the interaction between the soil particles and the geogrid is enhanced, greater friction is produced. This is why granular soils are more effective in supporting geogrids overall.
- Clays and silts, classified as cohesive soils, are known for their binding nature. This reduces the contact friction between the soil and the geogrid, lowering resistance to movement.
- A rougher geogrid surface means that this material has a larger area to touch the soil, which in turn enhances shear resistance through extra friction.
- The rigidity of a geogrid is the capability to withstand deformation under loads, maintaining the soil contact and enhancing the frictional resistance.
- The size of the openings, or apertures, in a geogrid is crucial for how it interacts with soil. If the openings are too big, soil particles can slip right through, which decreases friction. On the other hand, if they’re too small, the soil particles won’t be able to interlock properly, which limits their interaction. This is the force applied by the soil against the geogrid. An increase in pressure leads to an increase in the shaft due to the frictional force between the soils and the geogrid.
- A geogrid embedded deeper in the soil has a larger contact area with the soil mass, which increases frictional resistance.
How does geogrid soil reinforcement work?
Geogrids use a rigid or flexible polymer grid structure to reinforce soil and improve its load-bearing capacity. To simplify, the soil provides compressive strength, and the geogrid gives the structure tensile strength to produce a composite material. First, the geogrid is embedded into the soil, allowing soil particles to interlock with the geogrid’s apertures. This interaction creates a bonded structure where the soil and geogrid work together as a single unit.
When the geogrid is under a load, it distributes stress evenly on a larger area, making this way of preventing local failure and ensuring not only local but also general stability. This magnified stability makes it a game-changer in many fields, such as road construction. A geogrid reinforcement is one of the most notable methods used in soil treatment, and one of the advantages is that less soil is needed. The technique of mixing sand, cement, gravel, and water with polyethylene geogrids is a brilliant one to lessen the number of soil layers, materials added, and project duration.
The aperture size of geogrids used in this process is a very important consideration here. Due to the design and material of the geogrids, they provide high tensile strength which is their typical behaviour. The right solution and proper installation are the two factors in each geogrid design; these are the main requirements to gain the desired reinforcement properties.
What are the guidelines for installing geogrid for soil reinforcement?
Pre- installation considerations
Design review:
The understanding of the project design is fundamental. These involve the geogrid type, dimensions, placement locations, and overlaps.
Soil properties:
Geogrids are affected by the soil’s attributes, such as its type, strength, and moisture content. These properties are the main considerations that can affect the selection and installation of the geogrid.
Site preparation:
The base of any land should be clean, even. If there is any existing vegetation or unsuitable formations, it should be removed.
Equipment and personnel:
The equipment required must be checked first for rollers, excavators, and spreading machines. Employees who are involved in the installation process need to be well informed.
Installation process
Geogrid placement
It is important to make sure that the geogrid is installed smoothly and uniformly, without any wrinkles or creases. Geogrid sheets normally have overlaps. The overlap length should stick to the design of the sheet.
Soil compaction:
The installation should be carried out in the units of layers, which are the design structures of the individual sections. Each layer of the project is required to undergo the process of being fully compacted to achieve sufficient density.
Geogrid protection:
There are times wherein a geogrid may not acquire protection through geometries and overlays from locations prone to construction damages. In circumstances such as this, geogrid protection necessitates a systemic approach that shields the aggregate surface from environmental action.
Draining:
Proper drainage is vital for uncontrolled runoff that may lead to water collection and then to a decrease in the geogrid performance.
Quality control
Inspection of geogrid:
Perform regular checks on the geogrid to identify rips, folds, or the outright wrong alignment.
Test for soil compaction:
Carry out the resultant performance of the in-situ densitometer and density strength of the soil during a verification test.
Documentation:
Keep accurate records of the process of installation, such as the amount of materials used, the machinery used, and the names of the personnel who were a part of it.
Case study of soil reinforcement using StrataGrid™
Client: Department of Transportation, South Carolina
Location: South Carolina, USA
Product used: StrataGridTM and StrataSlopeTM
Application: Construction of a steep soil slope
The South Carolina Department of Transportation (SCDOT) needed a new road next to a CSX railroad track. Strata’s engineering experts proposed the StrataSlope system. The StrataSlope system suggested by Strata’s engineering specialists is the product that utilizes StrataGrid 200 geogrid for geosynthetic reinforcement and a special slope covering.
Determined to shield the slope while the concrete covering was barely maintained, a temporary erosion barrier was used. Immediately after the concrete was installed, grass was sown on the farthest part of the slope, kept with another layer of reinforcement and a protective material. By doing so, we made sure the slope remained stable and resisted floods even after construction. Strata’s solution astutely met the demand for a steep, stable slope. The design provided for both the concrete protection and the grass to grow together.
By tightly binding the soil’s compressive strength to the geogrids’ tensile strength. The performance of geogrid-reinforced systems depends largely on proper soil-geogrid interaction, but success also relies on correct design, material choice, and installation.
Contact Strata Geosystems for reliable geogrid reinforcement solutions that improve soil stability and load-bearing capacity. Our expert team is ready to assist you with your construction projects, ensuring effective results and quality materials. Reach out today to discuss your project needs!