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The Geosynthetic Materials Association (GMA) offers the GMA Techline, a resource for technical questions about geosynthetics. E-mail: gmatechline@ifai.com for fast, free, direct answers to your technical questions.

GMA serves as the central resource for information regarding geosynthetics and provides a forum for consistent and accurate information to increase the acceptance, and to promote the correct use, of geosynthetics.

Browse the entries below list to find past answers highlighted in Geosynthetics magazine.

Page 1 of 6 (89 results total)

  • Comparing GCLs

    October 1, 2011

    A reader needs some assistance in comparing two geosynthetic clay liners for a project.

  • Draping and spraying

    October 1, 2011

    Reader seeks geosynthetic fabric webbing or netting to be draped and sprayed with concrete.

  • Extrusion welds

    October 1, 2011

    Destructive tests are indeed taken on both wedge and extrusion seams.

  • Leak location

    October 1, 2011

    A reader is designing a reservoir that will be around 50ft deep and has many 2:1 sideslopes.

  • Liner questions

    October 1, 2011

    A reader is designing a surface impoundment with interior side slopes of 1.5H:1V.

  • Pond liner

    October 1, 2011

    A reader has some air pockets under the geomembrane as the pond fills with water.

  • Grid zone backfill

    June 1, 2011

    Rounded river gravel would work with two obvious trade-offs.

  • GT ageing

    June 1, 2011

    There are many exhumed site papers (such as Valcros) in the literature on geotextiles.

  • GT seam strength

    June 1, 2011

    At 90% of fabric strength you are flirting with disaster.

  • GT weight

    June 1, 2011

    Historically, generic specifiers have stayed away from stipulating weight of fabrics.

  • HDPE & LLDPE rates

    June 1, 2011

    The elongation rate for HDPE should be 2.0ipm and for LLDPE it should be 20.0ipm.

  • Liner system

    June 1, 2011

    I am quite sure that there is nothing available on geomembrane to chipped tires but I suspect that the shear strength would be quite high.

  • Puncture resistance

    June 1, 2011

    The way a manufacturer would make such a thick fabric is to needlepunch each thinner layer and then do a secondary needling to put the multiple layers together.

  • GMA Techline’s 3rd 500 Q’s-and-A’s

    February 1, 2011

    The GMA Techline was initiated in September 2004 as a free worldwide service.

  • The 15 most difficult GMA Techline questions from the 3rd 500 Q’s-and A’s

    February 1, 2011

    Bob Koerner ranks the 15 most difficult GMA Techline questions from the 3rd 500 Q’s-and A’s.

  • Drainage and filter components for green roofs

    Sponsored by IFAI Expo

    The Purpose of Drainage for Green Roofs

    • Manage rainfall without sustaining damage from erosion/ponding of water
    • Provides void space and slope to transport subsurface water
    • Connects to roof drains, gutters, and scuppers and conducts water away from roof
    • Removes surface water from impervious surfaces
    • Maintains optimum growing conditions in the planting media

    The Purpose of Filter for Green Roofs

    • To prevent fine planting media particles from washing into the drainage layer
    • Prevents the reduction or clogging of drainage capacity
    • Usually a nonwoven geotextile, occasionally a woven fabric, is used

    Filter Components
    For retention:

    • The geotextile must have small enough openings to adequately retain the planting media
    • If not, soil particles will eventually clog the drain core

    For permeability:

    • The geotextile must have large enough openings to allow unimpeded flow of water
    • If not, hydrostatic pressure will build up and the planting media will not drain

    What are Geocomposite Drains?

    • A manufactured material that combines geotextiles and a polymeric core
    • The core composition varies in design and material
    • Geotextiles may be applied to one or both sides using heat bonding or adhesives
    • Geotextiles can filter, protect or hold water
    • Geotextiles are available in sheets or rolls that are overlapped or joined during construction

    Source: “How to Design Green Roofs & Landscapes” presented at the 2009 IFAI Expo, Sept. 22, 2009, in San Diego, hosted by the Geosynthetic Materials Association (GMA)