Talk:Geocells

The title should probably be Geocell but I have left it as Geocells because a single Geocell would not be much use. Biscuittin (talk) 19:32, 16 June 2014 (UTC)

<!-- Talk:Geocells Proposed changes to article YSchary (talk) 18:28, 29 May 2014 (UTC)

Geocells (also called Cellular Confinement Systems, or CCS's) are used in civil engineering for roadway load support, walls and steep slopes, channel protection and erosion control. They are typically made from ultrasonically welded high density polyethylene strips and expanded on-site to form a honeycomb structure which is subsequently filled with sand, gravel, locally available soil, or concrete.

Background
The US Army Corps of Engineers (1981) in Vicksburg, Mississippi, experimented with a number of confinement systems, from short pieces of sand-filled plastic pipes standing on end to cubic confinement cells made from slotted aluminum sheets to prefabricated polymeric systems called sand grids and then, geocells. Today geocells are typically made from HDPE OR NOVEL POLYMERIC ALLOY(NPA)50 to 200 mm wide and approximately 1.2 mm thick STRIPS. They are ultrasonically welded along their LENGTH at SET 300-700 mm intervals and are shipped to the job site in a FOLDED configuration (see the following figure).

At the job site (road, slope or wall application) they are placed directly on the SUBGRADE, SUBBASE OR BASE LAYER SOIL (or on a geotextile FOR SEPARATION) and propped open in an accordian-like fashion with STAKES, J-BARS OR an external stretcher assembly.  ALTHOUGH VARIOUS SIZES ARE AVAILABLE, A TYPICAL section may expand to a 2.8 m by 8-10 m area and consist of hundreds of cells, each approximately 250 mm in size. These are then filled with soil and compacted using a vibratory hand-operated plate compactor. MANY TYPES OF infill materials are possible depending on site-specific conditions AND THE APPLICATION TYPE SUCH AS SAND, GRAVEL AND TOPSOIL. THE roadway WEARING COURSE layers may be asphalt OR emulsified asphalt (approximately 60% asphalt in a 40% water suspension), PAVING BLOCKS OR GRAVEL.



Available Theory
In terms of design for the above referenced soil stabilization and roadway systems, they are quite complex to assess. If we adapt the conventional plastic limit equilibrium mechanism as used in statically loaded shallow foundation bearing capacity the failure mode is interrupted by the geocell system. For such a failure to occur, the soil in a particular cell must overcome the side friction, punching out of it, thereby loading the sand beneath the level of the mattress. this in turn fails in bearing capacity, but now with the positive effects of the small surcharge loading and typically higher-density conditions. The relevant equations are given in Koerner (2012) and a recent comparison of methods are given in Neto, et al. (2013).

Geocells are also used in constructing the facing of mechanically stabilized walls (MSE) along with geogrid, geotextile or geostrap reinforcement. In such cases the geocells are built up in a pyramid fashion with the reinforcement embedded between layers at designed intervals. Design in this regard follows standard procedures as given in FHWA (2009).

Testing
Unfortunately, the ASTM/ISO procedures commonly utilized by most other geosynthetics to evaluate performance have not been developed or adopted by the geocell industry. Current standards evolved from the 2D planar geosynthetics. These do not fully reflect the composite behavior of 3D geometry of geocells, nor do they test long-term parameters such as: dynamic loading, permanent plastic deformation, effect of temperatures, environmental durability, etc. That said, new standards for geocells are under discussion by ASTM technical committee D-35. The goal is to set new industry standards that more accurately reflect 3D geocell geometry and material performance in the field rather than lab tests of individual strips and virgin materials that are typically used for geomembrane products.

Major Applications
Roadway Load Support - Geocells are regularly used for unpaved HAUL, ACCESS as well as for stabilization of parking and staging areas.

Walls and Steep Soil Slopes - Geocells can form the facing of mechanically stabilized earth walls and steep soil slope. They can be built in such a fashion so as to be a gravity mass themselves or be used as facing for geosynthetic reinforcement.

Foundation Reinforcement - Geocells have been used to reinforce soft or uneven soil foundations for large area footings, for retaining wall strip footings, for load sharing of covers over pipelines and other geotechnical applications.

Additional Details

 * Geocell strip widths, hence the in-situ height, come in various sizes from 50 to 300 mm.
 * Geocell walls are usually made from textured or structured HDPE sheet so as to increase frictional resistance against the infill soil from displacement.
 * Geocells have also been made from hybrid HDPE materials, low density polyethylene and nonwoven heat-bonded geotextiles.
 * Geocell walls are typically perforated so as to allow for drainage from one cell to another.
 * On steep slopes geocells can have a steel cable extending through the central region up the slope and anchored to, or within, a concrete plinth so as to resist downgradient sliding of the system.
 * The backfilling of geocells on long and wide slopes is quite labor intensive. Construction equipment called phneumatic sand-slingers or stone-slingers have been used advantageously.