Masonry Magazine July 2002 Page. 18
Cover
STORY
Glossary
Geosynthetic Materials
# Geogrids
Geogrids are plastics formed into a very open, grid-like configuration, i.e., they have large apertures. Geogrids are either stretched in one or two directions for improved physical properties or made on weaving machinery by unique methods. By themselves, there are at least 25 application areas, however, they function almost exclusively as reinforcement materials.
# Geotextiles
Geotextiles consist of synthetic fibers rather than natural ones so biodegradation is not a problem. These synthetic fibers are made into a flexible, porous fabric by standard weaving machinery or are matted together in a random, or non-woven, manner. They are porous to water flow across their manufactured plane and also within their plane, but to a widely varying degree.
SEGMENTED RETAINING WALLS ARE OF mortarless construction, and that might explain why few mason contractors seem interested in constructing them. That's a shame because this is a growing market and one that fits nicely with the mason and stonemason's trade. Segmented or segmental retain walls (SRWs) are gravity structures-they depend on the weight of the block, not on mortar, to maintain their integrity and stability. These dry stacked blocks are used for large and often angled or sloping retaining walls and also for landscape elements where there is little soil pressure behind them around trees and plantings, rising no more than one or two courses tall.
The National Concrete Masonry Association (NCMA) represents manufacturers of the blocks and offers masons a variety of informational booklets, technical notes, and instructions on SRW, both online (at www.ncma.org) and on paper.
Lance Carter, manager of Engineered Landscape Products at NCMA explains, "The companies that produce the SRW units or SRW system licensors might have people come out to the site and get a contractor started when they're doing their first installation, to help them understand the process. Another avenue is our association. We have a number of resources from design manuals to inspection guides to installation guides on how the industry and association recommends installing the retaining wall systems-everything from preparing the foundation to guidelines on preparing the leveling pad for the wall itself."
NCMA defines two types of SRW: Conventional (gravity) and soil-reinforced. Both are durable, can be constructed in locations with difficult access, allow tight curves or complex architectural layouts, and provide design flexibility.
Conventional SRW
CONVENTIONAL- or gravity-segmented retaining walls block the movement of the soil behind them strictly by the weight of their blocks. They can be constructed of single or multiple depths of block and the maximum wall height of a single depth wall is directly proportional to its weight, width, batter, soil condition, and site geometry. By using multiple depths of units or by using tiered construction methods, the height can be increased significantly.
Carter notes that, while masons capable to place the units in these walls, they have to rethink some of the meth-
16 Masonry
July 2002
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