Geosynthetic drains

Geosynthetic drains that may compress under load and lose structural integrity and associated functional flow capacity... 

Figure 9.15 Example of compressive creep test results of a geosynthetic drain at various load levels.

Short-term reductions in flow are generally measured via short-term hydraulic testing of the geosynthetic drain (examples are ASTM D4716 and ISO 12958). However, the time-dependent compression and intrusion will lead to a reduction in flow capacity and are critical to the long-term determination of flow. Indeed, collapse of the core will lead to significant flow reduction. 

For geosynthetic drains, the main property of interest is hydraulic flow in the plane of the drain, which is affected by time-dependent compression and intrusion, and chemical, particulate, and biological clogging. The resulting allowable flow may then be determined as follows ... 

Geosynthetic drains often exhibit most of their thickness reduction and associated intrusion within the first 100 h of loading. As such, many determinations of allowable flow incorporate a 100-h flow (Gioo) test result replacing the (2 it. This 2ioo serves to capture the plastic deformation of the drain and associated intrusion whereas the creep and intrusion reduction factors are determined to have a duration of 100 h to design life duration. 

After Chai, J.-C., Miura, N., Nomura, T. 2004. Effect of hydraulic radius on iong-term drainage capacity of geosynthetics drains. Geotextiles and Geomembranes 22, 3—16. 

Backfills for geosynthetic reinforced walls should be free draining,because unexpected failure of these structures can be caused by lack of control of groundwater or seepage. An appropriate geocomposite can therefore be incorporated horizontally and/or vertically to provide adequate drainage. 

Pradhan,T. B. S., Shiwakoti, D. R. and Imai, G. (1996), Effect of normal pressure and width of geosynthetic horizontal drain in pullout behaviour using saturated clay. Proceedings of the International Symposium on Earth Reinforcement, Kyushu, Japan, Vol. 1, pp. 133-138. 

Table 3.5. Transition temperatures (in °C) of thermoplastic materials used for geosynthetics (geomembranes, nonwoven geotextiles, geocomposite drains, geogrids etc.). In addition to polyolefins PE and PP, polyester PET and polyamides PA 6.6 and PA 6 and polyvinyl chloride PVC are also used, the letter, however, only to a small extent...

Shallow or deep trench drains filled with free-draining geomaterials (coarse granular fills and geosynthetics)... 

Drainage composite (chimney drain) Geosynthetic reinforcement Geotextile separator/fllter... 

---