Masonry Magazine June 2001 Page. 19
EASY STEPS TO BUILDING SRWS
Excavation: Segmental retaining walls eliminate the need for deep excavation. Because they do not need concrete foundations, a minimal trench is needed for the required six- inch thick granular leveling pad and the embedded SRW units. Usually, walls should have at least 1/10 of the planned, exposed wall height embedded below grade. Also, excavate areas where geosynthetic soil reinforcement will be placed.
Leveling Pad Construction: The leveling pad is simply used to create a level working surface, it is not a structural footing. The leveling pad does not need to be below frost depths, but it should be at least six inches thick and 24 inches wide. Material should consist of granular road base material.
Base Course Installation: Placing the first course of SRW concrete units is one of the most critical steps in proper SRW construction. Make sure each base unit is level front-to-back, side-to- side, and with adjacent units. Minor unevenness in the base course will be amplified and difficult to correct after several courses have been installed.
After installing the base course, place and compact soil backfill behind and in front of the embedded units.
Place Succeeding Units: Succeeding courses should be set back from lower courses to create a canted wall; battered walls are more stable than vertical walls because gravitational forces pull walls into retained soils. Stack no more than three courses before backfilling.
Drainage Aggregate: Directly behind the concrete units, place granular, free-draining fill to a minimum thickness of 12 inches. Drainage aggregate is important to wall performance because it keeps water pressure from building up behind the wall face.
Compaction: Proper compaction of backfill is critical to the stability of the wall, as poorly-compacted backfill puts extra pressure on a wall.
Geogrid Installation: Site, soil, wall- loading, and seismic conditions all influence the amount, length, spacing, and strength of geogrid reinforcement. Lay geogrid horizontally on top of SRW units one inch back from the front edge of SRW units onto compacted backfill at the same level. Geogrids are usually stronger in one direction. The strongest direction of the grid must be perpendicular to the wall face. Never overlap layers of ge- ogrid soil reinforcement. Slick surfaces of the grid will not hold in place properly when placed directly next to each other. Always provide at least three inches of soil fill between over- lapping grid layers. To ensure stabil- ity during construction, vertical spacing between geosynthetic layers should not exceed two feet.
Continue placing additional courses, drainage material, com- pacted soil backfill, and geosynthetic soil reinforcement as specified until desired wall height is achieved. Finish the wall by placing cap units along the top of the wall.
By following these steps in con- structing segmental retaining walls, an endless variety of creative ma- sonry landscapes may be accom- plished. "It's a craft," Steven Fechino of Wasco, Inc. said about working with SRW units. "It's not just a land- scaping item - it's a craft."
W. Rose-BRICKLAYER'S TOOLS
NOW AVAILABLE...NEW full line W. Rose™ Brochure!
Offering a choice of over 200 styles and sizes of brick trowels and many Masonry accessories.
W. Rose™, a company with a 203 year history of manufacturing brick trowels and Kraft Tool Co., team up to be your leader in Masonry tools.
W. Rose™ Trowels have only one quality... The Best!
Visit us online: www.krafttool.com
KRAFT TOOL CO.
8325 Hedge Lane Terrace, Shawnee, Kansas 66227
913-422-4848 FAX 913-422-1018
FREE
BROCHURE!
Available to Masonry Professionals
MASONRY JUNE, 2001 19