Neoweb

PRS-Neoweb Cellular Confinement System
High modulus geocell - cellular confinement system
Industry Geotechnical and civil engineering, landscape architecture, infrastructure
Website www.prs-med.com

PRS-Neoweb is a cellular confinement system (geocell) developed and manufactured by PRS Mediterranean Ltd. Composed of ultrasonically welded strips, the Neoweb geocell is opened up on-site to a form a 3D honeycomb-like matrix, and then infilled with soil material to stabilize and reinforce soil. In addition to the 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.

Neoweb is manufactured from Neoloy, a novel polymeric alloy (NPA), which provides a higher modulus, creep resistance and tensile strength to geocells than commonly available HDPE (High-density polyethylene)(Pokharel, et al., 2009).[1] Research has shown a stiffer geocell wall retains the cell geometry (dimensional stability) better and therefore confinement and reinforcement.[2] Neoweb is a sustainable solution for road construction as it enables the use of locally available but marginal soils for infill, thereby saving virgin aggregate; reduces the pavement layer thicknesses; and extends the service life of pavements, and thereby lowers operating and maintenance costs.[3]

History

The geocell concept was originally developed by the US Army Corps of Engineers in the 1970s as "sand-grids" to improve the soft subgrades of unpaved roads for short-term use by heavy military vehicles (Webster and Alford, 1977).[4] Subsequent production of geocells for civilian use began several years later, using HDPE, for slope stabilization and erosion control and in temporary and low volume roads. PRS Mediterranean (est. 1996) began manufacture of the Neoweb brand of geocells. However, in order to improve the stiffness and long-term durability suitable to long-term use[5] PRS developed Neoloy, a novel polymeric alloy (NPA), based on a polyolefin matrix reinforced by polyamide nano-fibers. This NPA, as is it is termed in the research literature[6][7][8] is used to create a multi-layered geocell featuring durable outer layers in 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,[6] as well as at other geotechnical/civil engineering research institutes, such as the Indian Institute of Technology (Madras),[9] University of Delaware,[5] Clausthal University (Germany)[10] and Colombia University (NY)[11] 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 included laboratory box tests, accelerated moving wheel tests, field demonstration and development of design methods.[6] The research summarized in over 40 published papers demonstrated that not all geocells are equal. Comparative test results that Neoweb made from NPA had a greater improvement in stiffness, bearing capacity, stress distribution and reduced deformation, when compared with conventional HDPE–based geocells (Pokharel, et al. 2011 and 2009).[1][12]

Applications

Neoweb with NPA (Neoloy) is suitable for use in the base layer reinforcement of asphalt paved roads, where high tensile strength, dimensional stability (low creep) and resistance to high temperatures are required to retain the geocell geometry even under repeated dynamic & cyclical load stresses.[6] Applicable for new road construction, as well as for rehabilitation, Neoweb is 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 roads that aided troops and civilians alike.[13][14]

Design methodologies

Research includes the development of road design methodologies for Neoweb geocells.[15] In particular, a Modulus Improvement Factor (MIF), verified in research and field demos was developed as a reliable method for quantifying the Neoweb 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.[9]

Sustainable transportation

Neoweb can be considered a sustainable road construction method as by improving the structural properties of low strength materials, it enables 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 recycled concrete and industrial byproducts, such as fly ash and furnace slag. 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. Neoweb reinforcement can also increase the lifespan of pavement structures,[6] which means less repairs and maintenance, further enhancing sustainability.

How it works

When Neoweb is deployed and compacted with soil/aggregate a cellular confinement 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 Neoweb generates 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.[10] Vertical loading on Neoweb 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. Extensive research of the reinforcement mechanisms in geocells shows that the stiffness of the geocell material and geometry are the most important confinement parameters.[7][16]

Environmental durability

Neoweb is a non-corrosive, inert engineering thermoplastic resistant to extreme environmental conditions, heat, cold, water, wind and dust. It operates in temperature extremes of -60°C to +60°C, and has been successfully used in environments from deserts to saturated peat bogs to the arctic tundra. Special additives and manufacturing processes make Neoweb highly resistant to environmental influences, such as UV radiation and oxidation, during long-term outdoor storage, installation as well for long-term project design-life.

See also

References

  1. 1 2 Pokharel, S.K. , Han J., Leshchinsky, D., Parsons, R.L., Halahmi, I. (2009). "Experimental Evaluation of Influence Factors for Single Geocell-Reinforced Sand," Transportation Research Board (TRB) Annual Meeting, Washington, D.C., January 11–15
  2. ↑ Pokharel, S.K., Han, J., Manandhar, C., Yang, X.M., Leshchinsky, D., Halahmi, I., and Parsons, R.L. (2011). "Accelerated Pavement Testing of Geocell-Reinforced Unpaved Roads over Weak Subgrade," Journal of Transportation Research Board, the 10th International Conference on Low-Volume Roads, July 24–27, Lake Buena Vista, Florida, USA"
  3. ↑ Thakur, J.K., Han, J., Leshchinsky D., Halahmi, I., and Parsons, R.L. (2010), "Creep Deformation of Unreinforced and Geocell-reinforced Recycled Asphalt Pavements." Advances in Geotechnical Engineering, Geotechnical Special Publication No. 211, Proceedings of GeoFrontiers 2011, Han J. and Alzomora, D.E. (editors), Dallas, Texas, March 13–16, 4723-4732
  4. ↑ Webster, S.L. & Watkins J.E. 1977, Investigation of Construction Techniques for Tactical Bridge Approach Roads Across Soft Ground. Soils and Pavements Laboratory, U.S. Army Corps of Engineers Waterways Experiment Station, Vicksburg, MS, Technical Report S771, September 1977.
  5. 1 2 Leshchinsky, D. (2009) "Research and Innovation: Seismic Performance of Various Geocell Earth-retention Systems," Geosysnthetics, No. 27, No. 4, 46-52
  6. 1 2 3 4 5 Han, J., Pokharel, S.K., Yang, X. and Thakur, J. (2011). "Unpaved Roads: Tough Cell – Geosynthetic Reinforcement Shows Strong Promise." Roads and Bridges. July, 49 (7), 40-43
  7. 1 2 Yang, X., Han, J., Pokharel, S.K., Manandhar, C., Parsons, R.L., Leshchinsky, D., and Halahmi, I. (2011)." Accelerated Pavement Testing of Unpaved Roads with Geocell-Reinforced Sand Bases", Transportation Research Board (TRB) Annual Meeting, Washington, D.C., January 23–27
  8. ↑ Pokharel, S.K., J. Han, R.L. Parsons, Qian, Y., D. Leshchinsky, and I. Halahmi (2009). "Experimental Study on Bearing Capacity of Geocell-Reinforced Bases," 8th International Conference on Bearing Capacity of Roads, Railways and Airfields, Champaign, Illinois, June 29 - July 2,
  9. 1 2 23. Kief, O., and Rajagopal, K. (2011) "Modulus Improvement Factor for Geocell-Reinforced Bases." Geosynthetics India 2011, Chennai, India
  10. 1 2 Emersleben A., Meyer M. (2010). The influence of Hoop Stresses and Earth Resistance on the Reinforcement Mechnism of Single and Multiple Geocells, 9th Internationational Conference on Geosynthetics, Brazil, May 23 – 27
  11. ↑ Leshchinksy, B., (2011) "Enhancing Ballast Performance using Geocell Confinement," Advances in Geotechnical Engineering, publication of Geo-Frontiers 2011, Dallas, Texas, USA, March 13–16, 4693-4702
  12. ↑ Pokharel, S.K., Han, J., Manandhar, C., Yang, X.M., Leshchinsky, D., Halahmi, I., and Parsons, R.L. (2011). "Accelerated Pavement Testing of Geocell-Reinforced Unpaved Roads over Weak Subgrade." Journal of Transportation Research Board, the 10th International Conference on Low-Volume Roads, July 24–27, Lake Buena Vista, Florida, USA
  13. ↑ Pannell, Ian (28 January 2010). "Progress slow and messy in Afghanistan". BBC News.
  14. ↑ Harding, Thomas (2009). "Afghanistan: Glimmers of hope in Helmand". Daily Telegraph.
  15. ↑ Han, J., Pokharel, S.K., Yang, X. and Thakur, J. (2011). "Unpaved Roads: Tough Cell – Geosynthetic Reinforcement Shows Strong Promise." Roads and Bridges. July, 49(7), 40-43
  16. ↑ Emersleben A., Meyer M. (2009). Interaction Between Hoop Stresses and Passive Earth Resistance in Single and Multiple Geocell Structures, GIGSA GeoAfrica 2009 Conference, Cape Town, South Africa, September 2–5

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