What are the disadvantages of not using a geocell in road construction?
A geocell, with its three-dimensional honeycomb design, confines the infill soil or aggregate, providing a robust and stabilized configuration for pavements and other applications. This design also allows the geocell to distribute the applied load more effectively over a wider area, thereby increasing the bearing capacity of the system and improving load distribution. A geocell is manufactured using HDPE (High-Density Polyethylene); the resulting geocell structure is excellent for stabilizing weak or soft subgrades.
Geocells act like a semi-rigid mattress, improving the in-fill material’s apparent cohesion and overall stiffness, thereby increasing its load-bearing capacity by reducing the flexibility of the soil layer and increasing its flexural rigidity. The confined space provides a stable and rigid structure that resists bending and deformation. The geocells affect the modulus of subgrade reaction (ks) by creating a stiffer and more stable composite base, which means this reinforced layer is more resistant to deformation, leading to more even load distribution. Another essential effect of using geocells as a reinforcement layer is to prevent rutting on the surface material. This issue [rutting], which is caused by the lateral and vertical displacement of unbound materials under repeated traffic loads, is effectively addressed by using geocells, showcasing their versatility in road construction
The most common applications of geocells in roadways includes:
– Embankment stabilization
– Slope stabilization
– Earth retention
– Channel and riverbank stabilization
– Pavement edge support
What types of road construction require geocells?
While each project, and each site has a whole host of conditions to consider, each site, and requirement needs to be evaluated separately, which is where the Strata team’s design inputs in for the entire project are an added insight. The structural design of a highway, which includes elements like bridges, culverts, subways, footbridges, pipes, retaining walls, and the road itself, helps determine the type of reinforcement or soil improvement required. We often see the following applications or scenarios where geocells are chosen in conjunction with other geotechnical solutions.
Highways and freeway embankments:
The most common instance we have deployed geocells is the trapezoidal highway embankment, since they increase the stability of slopes, allowing them to be constructed steeper or to better resist lateral earth pressures. By virtue of the structure, which has a base, and 2 inclines on either side, the geocell is used for stabilizing the inclined slope face, to control erosion and surficial stability. When used within the pavement base, geocells also confer more even load distribution and reduced settlement. Depending on soil conditions, and other factors, we can see bearing pressures of up to 100 kPa (~14.5 psi) for moderate loading conditions, by using geocells.
Mountainous roads:
Geocells are used to stabilize slopes and prevent surficial erosion and shallow soil failures since the use of a mix of aggregate, soil and other localized in-fill materials not only reduce the need for reinforcement materials but also allow inclines of up to 70 degrees to be created.
Coastal roads:
Geocells are used to prevent erosion due to wind and wave action. In this context, the ability of a team to use geocells on the fascia of a slope, or retaining wall means not only providing durable protection for the facing, but also retaining soil itself by adding localised vegetation that retains the in-fill material itself. When used in conjunction with geotextiles for drainage and separation, we’re looking at savings of up to 35-50% for the project. Without them, we’d need a high volume of reinforcement soils, compaction materials, and other ways to improve subgrade, and fix surface erosions issues.
Riverine roads:
Geocells are used to stabilize riverbanks, access roads in riverine areas, or even bridge abutments. In such locations, the soil is typically more moisture laden, and has a number of challenges such as soil prone to slippage and deformation. With riverbanks, geocells are deployed when some of these conditions are encountered:
High water velocities
Soft or unstable soil conditions
Limited space for traditional erosion control measures
Hydraulic infrastructure and canals:
In unlined channels, water flow can cause scour and erosion, leading to bank instability. Geocells provide a stable lining that confines the infill material, protecting the channel banks and bed from erosive forces. This protects the integrity of the channel and associated infrastructure like culverts and abutments.
Since the geocells manufactured by Strata are perforated, strategically, they confine the in-fill material, while also letting liquids pass through. Thus, the material migration is minimized, relatively, while reducing hydrostatic pressure.
Rural roads and unpaved roads:
Geocells are used to stabilise embankments and slopes in rural areas. Examples of challenging terrain include soil meant for agriculture which is clayey in nature, due to which the soil is plastic and has a low load bearing capacity. With unpaved roads, the core issue is settlement from repeated loading on the soil/road. Since unpaved roads lack asphalt, concrete, or brick/stone, they also suffer from drainage issues. One might consider where the unpaved roads lead to and from –before defining the ideal solutions for the terrain.
Access roads:
Access roads, often the unsung heroes of connectivity, are roads leading to industrial sites, waste sites, mines, emergency services, remote locations. They typically accommodate heavy duty traffic in the form of trucks, dumpers, emergency vehicles, or pedestrian type of traffic. Each of these have very different implications of load bearing on the subgrade, and subbase. Especially, with mines, and other industrial zones, having access roads, which are well-maintained, and safe is a crucial requirement. Often, we employ embankments, or reinforced subgrades which can handle the weight of trucks going over them several times a day.
Why was the geocell invented?
In the late 1970s, the US Army contacted a private-label consumer company, Presto Products Company. They requested that the company manufacture a more stable and robust honeycomb-shaped geocell to enhance the soil’s load-bearing capacity. The need for this invention was two-fold: speed of construction of roads compared to traditional methods, and improved load bearing capacity, under repeated loading conditions, across a wide variety of terrain conditions. Essentially, the army wanted roads which could carry heavy duty military vehicles, without collapsing or deforming.Typically, army vehicles are navigating unpaved roads, and constructing expedient roadways in new areas where they don’t have the luxury of full-scale paved road development. And yet, the geotechnical need was a solution that would allow movement of army supplies.
What are the different types of geocells?
Perforated geocell:
As the name suggests, perforated geocells have small, uniform holes on their walls to improve drainage, reduce hydrostatic pressure, and enhance frictional interlock with the infill. The perforations in the geocell walls enhance drainage, improve frictional interlock with granular infill, and can help reduce hydrostatic pressure, contributing to overall system stability. These geocells are ideal for erosion control and slope protection. The material used for manufacturing these geocells is HDPE (High-density Polyethylene), which provides extensive stabilization and soil reinforcement. These geocells are also appropriate for seepage control, tailing dams, retaining walls, road construction and highways. The seam strength (often determined by the weld strength between strips) of a geocell is a critical design parameter. For high-quality geocells, this weld strength should be a high percentage of the strip’s tensile strength, as the seam is often the limiting factor in performance. Geocells are characterized by parameters such as cell depth (hg), cell opening dimensions, and material properties like tensile strength.
Non-perforated geocell:
The non-perforated geocell is made from a polymer sheet and has a three-dimensional structure with no holes in its walls. These geocells are filled with sand, gravel, and clay to expand and support the weak subgrade. The prominent feature of this geocell is that it can be freely folded and stretched depending on the area in which it is being installed. The non-perforated geocell is easy to install and light in weight. Being made of HDPE, these geocells are highly resistant to chemical degradation, contributing to their long-term performance. They are effective at creating a stable base that resists deformation when exposed to excessive load and pressure. They are best used to stabilize the railway bed, construct roads, reinforce river soil, construct bridges, and retaining walls.
What are the applications of Strata’s geocell?
Erosion control:
StrataWeb reduces soil erosion caused by wind, rain, and other weather factors. This protection system is engineered to suit slope conditions, varying from steep 60-degree slopes to gradual 27-degree slopes. It is a cost-effective and durable solution. Once the slope is prepared, StrataWeb is installed depending on the surface area using Strata’s anchor systems and connectors.
Slope liner protection:
In some cases, geomembrane liners are used to surface the slope. These liners cannot be punctured or damaged. In such cases, the StrataWeb liner protection system is used. It can be installed easily on the slope without puncturing the liner and anchored effortlessly at the slope’s crest. Strata’s StrataWeb protection system can be tailored and made as per the slope inclination.
Retaining walls:
Retaining walls are used to accommodate abrupt changes in ground elevation. Compared to conventional cast-in-place concrete walls, which can be expensive and time-consuming, StrataWeb retaining walls are an economical alternative that serves as an optimized solution. This wall is designed using a geogrid reinforced wall or a gravity wall. Since the geocell components are manufactured and shipped to the site, this can lead to reduced construction time and overall project costs compared to some conventional retaining wall types. It also significantly reduces the labour cost as it is easy to install. Another advantage of the StrataWeb wall is that it enables vegetation to grow, promoting vertical gardens.
Load support:
StrataWeb has proven to be a helpful geomaterial for ground improvement and access roads and pavements. These geocells improve the soil’s load-bearing capacity by reinforcing and compacting it. It is an ideal option for low CBR grounds with heavy loading requirements and will help save on natural resources by reducing the aggregate layers. In the absence of geocells, foundation bases over soft or clayey soils can be unstable, leading to bearing capacity failure, shear failure, or excessive/uneven settlement that compromises structural integrity. StrataWeb’s confinement action plays a key role in preventing such failures.
Drainage/canal lining:
Strata’s geocell lining for channels is flexible, conforming to the channel’s shape while preventing erosion and deformation from flow. When used with a permeable infill, it provides excellent protection against scour while allowing for drainage. The ease of installation offers 30-40% less construction time and installation cost. Without proper lining like StrataWeb, excess water can accumulate around channels, potentially causing localized flooding and long-term degradation of surrounding infrastructure.
Strata’s geocell solutions
Case study 1:
Client: PWD (Buildings and NH), Government of Assam
Location: National Highway- NH 44, Churaibari, near Assam-Tripura border
Product used: StrataWeb®
Application: Constructing pavement section incorporating StrataWeb®
About the project:
NH44 is a significant highway connection of North East India. The road stretching the highway to the Assam-Tripura border is the only land connection between Tripura and the rest of the country. The major challenge with this highway was that the subgrade around it was highly plastic and weak. Heavy rains in March 2016 completely damaged the roads. Conventional repairs were attempted but unsuccessful in allowing smooth traffic across this 500m stretch. With several other efforts, the stretch could not regain momentum, and the connectivity between Tripura and Assam was severely disrupted.
The issue was escalated to the government of India, who then consulted Strata for the solution. Strata recommended StrataWeb within the pavement section to solve these issues with a CBR (California Bearing Ratio) low as 0.5% and a traffic of 20MSA (Million Standard Axles).
Case study 2:
Client: PWD- Karnataka
Location: Uttar Kannada
Product used: StrataWeb®
Application: Load-bearing application facility for movement of heavy vehicles
About the project:
Goa and Uttar Kannada are connected by one major highway, State Highway 30. Lush green forests and eye-smacking natural beauty surround the highway. However, the road has to bear a heavy traffic load as the surroundings have many sugar factories. This road enables the raw materials from the farms to the factories. The major setback of this highway was the weak subgrade with the poor drainage system. In addition, the area experiences heavy rainfall and severe water accumulation.
PWD, Karnataka, then approached Strata to resolve these issues for a section of the highway between Anmod and Belgaum. Considering the time factor, economy, and technical issues, a StrataWeb engineered solution was finalized. To add to the challenge, the awarded road stretch was located at the base of a slope where water accumulated the most.
In a nutshell, geocells have remarkably changed and enhanced the construction industry in numerous ways. With several daily challenges, some of the major challenges that StrataWeb has taken over have turned out to be highly successful. To know more about Strata’s StrataWeb geocells, contact us today!