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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 5 (65 results total)

  • Difficult lining task

    April 1, 2010

    This is going to be an extremely difficult job to accomplish with 2mm-thick HDPE liner.

  • Geocell application

    April 1, 2010

    The suitability of geocell as slope surface protection on acidic soil conditions.

  • Optimum height for geotextile storage

    April 1, 2010

    In the waste containment QA/QC technical guidance book by Daniel and Koerner (ASCE Press, 2007, ISBN 0-7844-0859-9), there is a section regarding geotextile storage at a field site.

  • Questions about GM/GCL composite liners

    April 1, 2010

    Three questions and answers about GM/GCL composite liners.

  • Testing HDPE geomembrane liners

    April 1, 2010

    Testing a 30-mil HDPE liner to a pressure between 22-27psi with a maximum pressure drop of 4psi over 3 minutes.

  • Textured HDPE?

    April 1, 2010

    While sand on smooth HDPE is at or slightly higher than 14 degrees, when you have drawdown of the water the hydrostatic forces are sure to bring the sand covering with it.

  • Veneer stability

    April 1, 2010

    Veneer stability in moving earth upslope vs. downslope.

  • Welding LLDPE/HDPE

    April 1, 2010

    How to achieve a satisfactory extrusion weld between a 1mm LLDPE geomembrane and a 2mm HDPE geomembrane.

  • CQA test frequency for geomembranes and geocomposites

    October 7, 2009

    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.

  • Floating interface testing for direct shear

    October 7, 2009

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

  • Geogrid reinforcing behind rigid concrete retaining walls

    October 7, 2009

    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.

  • Geomembrane installations

    October 7, 2009

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

  • GSI/GRI-GG5 and ASTM D6706

    October 7, 2009

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

  • HDPE welding

    October 7, 2009

    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.

  • Installing prefabricated vertical drains

    October 7, 2009

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

  • 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)