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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 4 (47 results total)

  • CQA test frequency for geomembranes and geocomposites

    The CQA plan on tests and their frequencies is the right and duty of the CQA organization, since they are signing off on the completed project.

    October 7, 2009

  • Floating interface testing for direct shear

    The first test using multiple interfaces was actually conducted in the bed of a dump truck in about 1985.

    October 7, 2009

  • Geogrid reinforcing behind rigid concrete retaining walls

    One can construct a wraparound geotextile reinforced wall to the effect that 100% of the lateral load is carried by it and zero goes to the concrete, which now acts as a facing.

    October 7, 2009

  • Geomembrane installations

    Let me mention that moisture in the seam area to be bonded is the most important detriment to the making of quality seams.

    October 7, 2009

  • GSI/GRI-GG5 and ASTM D6706

    GRI–GG5 was the original test method on the subject but, subsequently, ASTM provided its own.

    October 7, 2009

  • HDPE welding

    I think that many field welding technicians would love to weld at 104°F during the summer. It is really very doable, especially on a white sheet.

    October 7, 2009

  • Installing prefabricated vertical drains

    Following the information listed in Designing with Geosynthetics, 5th Edition, the statement 1-2 meters is the typical spacing for PVDs.

    October 7, 2009

  • Liner thickness

    I doubt if thickness is calculated by most engineers and they simply “go with the flow.”

    October 7, 2009

  • Ageing standard

    The GRI–GM11 Test Method has now been superseded by ASTM D7238 and ours has been discontinued.

    April 1, 2009

  • Comparing specs

    The two groups, ASTM and ISO, act independently from one another although ASTM does have liaison people attending the ISO meetings as observers.

    April 1, 2009

  • Comparing warp and fill

    Defining the terms warp and fill mean with regard to tear strength of a polypropylene liner.

    April 1, 2009

  • Geocomposite drainage

    Back in 1985, the state of Pennsylvania felt uneasy about geonets so we did a full-scale experiment on a landfill cell measuring about 400m by 50m.

    April 1, 2009

  • Reinforcement geosynthetics

    Using such a geosynthetic material over the entire footprint of a building will simply not cure a uniformly weak subgrade soil.

    April 1, 2009

  • Study on pH and geogrids

    Getting a copy of the study.

    April 1, 2009

  • Technical articles on geosynthetics

    There are probably 30,000 technical articles on geosynthetics at the current time.

    April 1, 2009

  • 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)