The Neoloy Geocell is a Cellular Confinement System developed and manufactured by PRS Geo-Technologies Ltd. Composed of ultrasonically welded strips, Geocells are opened up on-site to form a 3D honeycomb-like matrix, which is then filled with granular soil material to create a soil stabilization / road reinforcement system. In addition to reinforcement of the subgrade, subbase or base layer of roads and railways, cellular confinement is also used for soil stabilization and erosion control in slopes, channels, retention walls, reservoirs and landfills. Neoloy Geocells are manufactured from Neoloy, a novel polymeric alloy. This material provides high dynamic stiffness, resistance to permanent deformation and tensile strength. Research has shown a stiff geocell material better retains the cell geometry confinement and reinforcement. These geocell performance parameters are critical for the requirements of base-layer reinforcement of heavy-duty pavements and infrastructure. Neoloy Geocells are a sustainable solution for road construction as they reduce the use of virgin aggregate. This is achieved by the use of locally available but marginal-quality soils for structural infill and a reduction in the thickness of the pavement layers. Reinforcement with high modulus geocells also optimizes pavement design by enabling a longer design life and lower maintenance cycles/costs.
History
The geocell concept was originally developed by the US Army Corps of Engineers in cooperation with Presto Products in the 1970s as "sand-grids" to improve the soft subgrades of unpaved roads for short-term use by heavy military vehicles. PRS Geo-Technologies began manufacture of their brand of geocells. In order to improve the stiffness and long-term durability suitable to long-term use PRS developed Neoloy, a polymer alloy based on a polyolefin matrix reinforced by polyamide nano-fibers. NPA, as it is termed in the research literature is used to create a multi-layered geocell featuring durable outer layers between a high strength inner core layer for optimal performance. Geocells made from Neoloy are suitable for long-term structural reinforcement in critical applications such as the structural pavements, embankments and high retention walls.
Research
Extensive research on exploring geocell reinforcement for roadway applications has been ongoing at the University of Kansas, as well as at other geotechnical/civil engineering research institutes, such as the Indian Institute of Technology, University of Delaware, Clausthal University and Columbia University in the past few years. The objectives of this comprehensive research was to understand the mechanisms and influencing factors of geocell reinforcement, evaluate its effectiveness in improving roadway performance and develop design methods for roadway applications. This research - over 75 published papers on Neoloy Geocells - included laboratory box tests, accelerated moving wheel tests, field demonstration and development of design methods. Comparative test results that Neoloy Geocells made from NPA had the highest improvement in stiffness, bearing capacity, stress distribution and reduced deformation.
Applications
Neoloy Geocells are suitable for use in the base layer reinforcement of asphalt paved roads, where high tensile strength, resistance to permanent deformation and dynamic stiffness are required to retain the geocell geometry even under repeated dynamic & cyclical load stresses. Applicable for new road construction, as well as for rehabilitation, Neoloy Geocells are typically used to reinforce the base and subbase layers of pavement types, such as highways, railways, intermodal ports, storage yards and unpaved haul, access and service roads. One notable unpaved road project was undertaken by the UK Royal Engineering Corps Route Trident under difficult conditions in Afghanistan to create a secure patrol road for the benefit of troops and civilians alike.
Design methodologies
Research includes the development of road design methodologies for Neoloy Geocells. In particular, a Modulus Improvement Factor, verified in research and field demos was developed as a reliable method for quantifying the Neoloy Geocell contribution to a pavement structure. The MIF value obtained from field tests, laboratory tests and finite element studies varies between 1.5-5 dependent upon the material of infill, subgrade and location of reinforced layer.
Sustainable transportation
Neoloy Geocells are considered a sustainable road construction method as by improving the structural properties of low strength materials, they enable the replacement of quarry aggregate with lower cost lower quality granular infill materials. These lower quality materials include locally available but weak soils, sand; recycled and reclaimed construction materials, such as RAP and recycled concrete. Not only does the use of such materials in road construction conserve quarry resources and recycle waste. It also reduces quarry, haul and infill activities, which in turn decreases the amounts of fuel, pollution and the carbon footprint. Neoloy Geocell reinforcement can also increase the lifespan of pavement structures, which means less repairs and maintenance, further enhancing sustainability.
How it works
When Neoloy Geocells are deployed and compacted with soil/aggregate, a composite structure is created from the geotechnical interaction of the material, soil and geometry. Soil confinement retains infill materials in three dimensions providing high tensile strength on each axis. Under loading Neoloy Geocells generate lateral confinement while soil-to-cell wall friction reduces vertical movement. The high hoop strength of the cell walls, together with the passive earth and passive resistance of adjacent cells, also increases soil strength and stiffness. Aggregate abrasion is minimized by the cell confinement, thereby reducing attrition of the base material. Vertical loading on Neoloy Geocells with compacted infill creates a semi-rigid slab or "beam effect" in the structure. This distributes the load evenly and effectively over a wider area, thereby increasing bearing capacity and decreasing differential settlement. Research of the reinforcement mechanisms in geocells shows that the stiffness of the geocell material as well as geometry are the most important confinement parameters.
Environmental durability
Neoloy Geocells are a non-corrosive, inert engineering thermoplastic resistant to extreme environmental conditions, heat, cold, water, wind and dust. Effective service temperature is -60 °C to +60 °C, and they have been used in environments from deserts to saturated peat bogs to arctic tundra. Special additives and manufacturing processes provide Neoloy Geocells with long-term environmental durability from UV radiation / oxidation, during outdoor storage, installation and long-term project design-life.
