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From the GMA Techline
Subject: Geocomposite question We are looking into installing prefabricated vertical drains to relieve excess pore water pressure for a surcharge fill.
Following the information listed in Designing with Geosynthetics, 5th Edition, the statement 1-2 meters is the typical spacing for PVDs. Are there any in-depth investigations, studies, or publications that have been done to determine if the spacing can exceed the industry standard of 1-2 meters? (Gary, Tennessee)
Reply: Thanks for your question, but the guy (moi) who wrote 1-2 meters was only stating what is often seen. The actual spacing should come directly from the time required for consolidation. If the soil has a high permeability and is not too deep, and also has double drainage, the spacings will be considerably greater. Five or more meters is not out of the question.
Do let your calcs determine the spacing and don’t listen to that Koerner guy!