How is soil stabilization for road construction done?

If you’re in the midst of a construction project in a coastal area, prone to high water saturation and weak subgrades, what would you typically do for soil reinforcement? You may choose compaction, i.e. adding more soil to improve density. The other traditional option might be to add drainage by creating culverts, and or other types of drainage to minimise saturation. You could also consider chemical reinforcement by adding lime, cement, or other materials with the soil.

However, most of these solutions are now suboptimal to some extent in the context of geosynthetics. Apart from being time intensive, and labour intensive, those methods are also typically more expensive. Here, in this blog, we review the usage of geocells – for road construction–for a number of reasons.

Geocell is a cellular-like net structure known as a cellular confinement system. These geocells are manufactured using long-lasting materials that provide uniform stability and are environmentally friendly. The geocell’s three-dimensional honeycomb design compacts the soil, providing a robust configuration in the infill and the pavement. This design also allows the geocell to divide the load and increase the bearing capacity uniformly.

A geocell is manufactured using HDPE (High-Density Polyethylene), an excellent agent for stabilizing weak or hazardous subgrades. This material minimises soil movement and makes it vertically dense.

Geocells act as a mattress, improving the in-fill material’s flexibility and strength to increase its load-bearing capacity. By reducing soil flexibility – by increasing the 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 providing a stiffer and more stable base, which means the in-fill is more resistant to deformation and more even load distribution.

Another essential effect of using geocells as a reinforcement layer is to prevent rutting on the surface material. This issue, which is caused by uneven weight allocation, is effectively addressed by using geocells, showcasing their versatility in road construction.

That said, it’s important to remember that typically, geocell usage is recommended for reinforcement of retaining walls, and vertical reinforcement, on slopes, abutments, and other similar use cases. For lateral load balancing, geogrids are an often preferred material, in the context of subgrade improvement.

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 need use of geocells?

While each project, and each site has a whole host of conditions to consider, we often see the following applications or scenarios where geocells are chosen in conjunction with other geotechnical solutions. It’s worth mentioning that 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. It’s also worth noting that often the use of geocells and geogrids can be confusing from one site to another. Our list here is meant to be illustrative rather than definitive, based on our experiences. The structural design of the highway, which may include elements such as bridges, culverts, subways, footbridges, pipes, and retaining walls, apart from the road itself, determine what kind of reinforcement, or soil improvement measures need to be deployed.

Highways and freeway embankments:

The most common instance we have deployed geocells is the trapezoidal highway embankment, since they allow for much higher lateral earth pressure for slopes. By virtue of the structure, which has a base, and 2 inclines on either side, the geocell is used for the vertical slope, which in turn confers more even load distribution, and reduced settlement and deformation. Depending on soil conditions, and other factors, we can see values of up to 100 kPa (7.25 psi to 14.5 psi) for moderate loading conditions, by using geocells.

Mountainous roads:

Geocells are used to stabilize slopes and prevent rockfalls and landslides 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 stabilize slopes and 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 improving the lateral load capacity, 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 projection –wherein, 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 stabilise 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

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 minimised, relatively, while reducing hydrostatic pressure. It’s worth mentioning that the design for Strata’s geocells take into account the optimal distance of the cavities to ensure the structure meets the core confinement without deformation requirement. This is one of the most fundamental aspects of geocell design that makes our StrataWeb a chosen product –for a nuanced understanding of the implications of geocell perforations.

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 charting new roads and 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.

Geocell technology has significantly evolved over the last four decades. During its early development, the materials used were basic: wax-coated paper, plastic pipe, a connected net using staplers, hexagon-shaped paper, thin aluminum foil, polyethylene without UV sterilisation, and square cells obtained from egg cartons. As the demand for geocells increased, these materials did not perform well, leading to use of different types of polymers.

What are the different types of geocells?

Perforated geocell:

As the name suggests, perforated geocells have small, uniform holes on their walls to enhance load distribution and reduce deformation. The perforation in the geocell enables it to hold weak soil and provide extensive support. 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. Engineers use the tensile testing machine to measure the tensile and seam weld strength. The tensile strength of an ideal geocell strip should be greater than or equal to the wield strength. StrataWeb® geocells of Strata Global have distinct cell depth hg and curvilinear rhomboid has average diagonal length d.

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. These do not react to chemicals as they are aging.. They are skid-resistant and do not deform when exposed to excessive load and pressure. They are best used to stabilise the railway bed, construct roads, reinforce river soil, construct bridges, and retaining walls.

What are the disadvantages of not using geocell in road construction?

We cannot advocate the usage of geocells, arbitrarily for all kinds of road construction. Typically, slope protection, retaining walls, abutments, or embankments benefit from the use of geocells since they offer a number of soil erosion measures, along with reinforcement. Principally, the role of geocells is to provide reinforcement –which can be applied in a number of road construction scenarios.

Geocells protect slopes from erosion and provide reinforcement to stabilise the surface. Over traditional methods, it provides more stability, and improvement in core modulus of elasticity values resulting in a higher flexural rigidity (EI). This is particularly important for clayey soils, silty soils, sandy soils, or soils with a higher than usual moisture content.
The function of the geocell is to confine infill material, using local materials becomes an option. We’re not dependent on using a specific type of material for compaction, and providing reinforcement. As a result, it reduces the overall volume of construction material leading to cost savings for the project, as a whole. Geocells also act as a protective lining to the hydraulic channels. They provide protection against the rainwater entering into the channels. The absence of the geocell can cause rainwater to enter the channel and significantly damage the heavy hydraulic machinery.
The channel lining made with geocells does not allow excess water to accumulate around the hem of the channel. If geocells are not used in the channel lining, the water collects, causing floods and significant damage.
Geocells greatly help prevent soil failure by providing static and dynamic load support. However, in the absence of geocells, the chances of the soil getting over-moisturised increase, causing soil failure and an unstable soil base.
Geocells offer durability to the infrastructure as they provide proper support from beneath, don’t allow water accumulation, and prevent soil erosion and potential damage caused by water accumulation to the infrastructure. The absence of geocells in the base of the infrastructure can rupture the foundation.

What are the applications of Strata’s geocell?

Strata’s game-changing product, StrataWeb, has significantly taken over the construction industry in numerous ways. The experts at Strata guide the engineers, contractors, and owners to use StrataWeb for the following applications:

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. Strata offers StrataWeb along with connector systems, such as StrataLock, StrataFast, and StrataCord.

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 inclement.

Retaining walls:

Retaining walls are used when subgrade replacement is required. They are made of concrete, which makes them expensive and time-consuming. StrataWeb retaining walls are an economical alternative that serves as an optimised solution. This wall is designed using a geogrid reinforced wall or a gravity wall. Since the wall panels are manufactured and shipped off to the site, there is minimal construction cost. 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. It is an excellent alternative to expensive soils and other materials. 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.

Drainage/canal lining:

Strata’s drain lining offers flexibility and can remove shape deformity. It also provides excellent protection against water seepage. The ease of installation offers 30-40% less construction time and installation cost.

Strata’s contribution in providing geocell solutions

Case 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 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. Strata has played a major role in this significant change. StrataWeb has transformed the construction outlook and made road structures more stable and durable. 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, please contact us today!

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How is soil stabilization for road construction done?