How are Geocells Made?

Geocells, also called cellular confinement systems (CCS), are used in road construction, embankments and landforms, agriculture, green roofs, trails, golf courses and general construction.

What is Geocells?

Geocells are three-dimensional, expandable panels made from high-density polyethylene (HDPE), polyester or other polymers. On site, the collapsed panels are stretched open into a flexible honeycomb of cell walls, and the cells are filled with sand, soil, rock or other infill and compacted. The cells hold the infill in place and stop it moving, while water can still drain through. The result is a stronger, stiffer layer than the soil or aggregate would make on its own.

When a load presses on soil inside a geocell, the soil pushes outward against the cell walls. The walls resist that lateral movement, and friction develops between the infill and the walls, so the confined soil can carry more load and deforms less.
Geocells are used in erosion control, soil stabilisation, channel protection, and structural reinforcement for load support and earth retention. Development began in the late 1970s and early 1980s. Most geocells are made from HDPE strips that are ultrasonically welded together and then expanded on site into a honeycomb that is filled. (Geosynthetics is the umbrella term for synthetic materials used with soil in this way.)

The Cellular Confinement System

The extra strength comes from confinement. When infill inside the cells is loaded from above, for example by vehicle wheels, part of the load is taken by the cell walls and the rest is spread over a wider area of the soil below. The pavement layer or retaining structure lasts longer as a result.

The three-dimensional confinement keeps infill where it is needed and improves how the aggregate layer behaves. It also holds compaction over time. The filled cells act as a stiff “mattress” for the layers above. Because confinement does much of the work, a range of infill materials can be used: sand, local soils, rock, recycled asphalt, gravel or concrete, depending on the project. Using whatever suitable fill is on hand often cuts the cost of a project and allows recycled materials to be used.

Geocells are also used to build green walls, where plants grow from the soil in the outer (fascia) cells. Each cell holds its own pocket of soil, which keeps moisture and nutrients near the roots while still letting excess water drain. The result is a planted alternative to a concrete wall.

What are Geocells made from?

Geocells are usually made from one of two materials: HDPE (high-density polyethylene) or a nano-polymeric alloy (NPA), such as Neoloy.
HDPE cells are the standard material for geocell systems. They are flexible and suit most slope, channel and load-support work. Ocean supplies HDPE geocells; one example is the 330 × 100 mm HDPE geocell used at an Air Force project in Gwalior.

NPA cells are a newer, stiffer type that their maker promotes for heavy-duty, long-term uses such as highways, railways and airports.

HDPE geocells are made by extruding HDPE into long strips, which are usually textured and perforated. The strips are stacked and ultrasonically welded together at regular spacings across their width. When the stack is pulled open, the welds become the corners of the cells. The weld spacing sets the cell size, and the strip width sets the cell height.

How are Geocells Placed?

On site, the geocell sections are laid out on the prepared subgrade or foundation layer, joined to each other, and stretched open. Once expanded over the required area and pinned at the edges, the cells are filled with the specified infill and compacted, usually with a small overfill layer on top.

History and Recent Variation

The US Army Corps of Engineers began researching cellular confinement in 1975, looking for a way to build roads quickly over soft ground for military use. Its Waterways Experiment Station in Vicksburg, Mississippi tested several options, including steel sheets and sand grids, before arriving at a system similar to the one used today.

Today, CCS panels are usually made from polymer strips (HDPE or NPA, as above) welded ultrasonically into a standard configuration. PRS Geo-Technologies developed NPA, which disperses polyester and polyamide nano-fibres in a polyethylene matrix, to make stiffer cells.

Benefits of Using Geocells Technology over Traditional Stabilization Methods:

• Lower construction and repair costs in load-support work such as roads, railways, ports and airports, mainly because a thinner or lower-grade aggregate layer can do the job.
• Faster construction, and flexible earth-retaining walls that tolerate settlement and ground movement.
• Better control of drainage, surface erosion and slope protection.
• A smaller carbon footprint, since less quarried stone has to be transported.
• Local and recycled materials can be used as infill.

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