Masonry Magazine July 2002 Page. 22
Cover
STORY
Always have a soil test done. It is a **small price** to pay to ensure that the soil **layers** below and **around** the **wall** are **taken** into consideration during the **design phase**.
Tips and tricks
NCMA'S CARTER considers the backfill process to be extremely important for a good, solid SRW. He tells mason contractors, "One trick, when placing the soil in lifts of 6- or 8-inches, the height of the unit, right behind the wall, they can fill in behind the wall at a thickness of say half the height and then walk that half height lift in with their foot. Generally the soil behind the wall is placed with a front-end loader, but as they spread it out the mason can walk down and push that soil against that block with his foot. A simple method but it saves time and effort in the compacting of the backfill. Then it will take less effort to compact the material directly behind the wall face with light-weight compaction equipment."
According to Steve Hooker, national sales manager for Rockwood Retaining Walls, Rochester, Minn., all SRW systems require some alteration at the job site. "A hand splitter that can split concrete units easily, versus a hammer and a chisel, can save a lot of time and time is money," he says. "Ensure that the base pad or leveling pad is 100 percent level. This will prevent adjustments or shims between successive courses. Be sure to obtain proper compaction and compact every course to ensure that the system will work. It also will save time in the long run."
Hooker makes a commonsense statement saying, "Building one wall twice will erode profits from other jobs. That means do the wall right the first time. Follow the design manual or instructions for the block being installed and the engineer's design. This will release the installer from liability in case of problems if the wall proves to have been installed correctly."
He adds, "Always have a soil test done. It is a small price to pay to ensure that the soil layers below and around the wall are taken into consideration during the design phase."
ANGLE
OF FILL
POINT LOAD SURCHARGE
IF ANY KN/m
GEO-FABRIC FILLED
WITH COURSE SAND
SURFACE RUN
OFF CHANNEL
ALTERNATE COMPACTED TO
REINFORCED 98% MOD AASHTO.
EARTH VAYING FORMAT
RETAINING
CHIS
SYSTEM
ANGLE OF SOIL/STRUCTURE INTERFACE
ANCHORAGE LENGTH
BEYOND FAILURE
WEDGE
FAILURE WEDGE
ANGLE (CUT)
75 (OR AS SPECIFIED) GEODRAIN
WITH 19mm STONE WRAPPED IN
GEO-FABRIC (TO STORMWATER OUTLET)
200
MIN
'ECO MAX BLOCKS
CAVITIES FILLED WITH
COURSE SAND OR
GARDEN SOIL
GEO-FABRIC IS TO
EMERGE AT THE FRONT
OF THE BLOCK BELOW
AND BE TRIMMED TO
THE FRONT OF THE
BLOCK ABOVE
HORIZONTAL OFFSET
FLEXIBLE
REINFORCED
EARTH GRAVITY
SYSTEM
ANGLE OF FACING
GROUND
LEVEL
WEDGE
ANGLE FIL
SUB-BASE CRUSHER RUN 50mm COURSE
OR NATURAL GRAVEL
COMPACTED TO 98%
MOD AASHTO.
SECTION
SAND BED WHEN
SPECIFIED
Carter knows that some contractors are not familiar with the geosynthetic material, and when doing soil-reinforced SRW that can be a problem. "Geosynthetic material, especially those used for retaining walls, generally has a high-strength direction and a weak-strength direction. There's one direction that has a higher tensile capacity and that's the strength that needs to be placed perpendicular to the wall, because that provides the reinforcement to help stabilize the structure. In relatively small roll widths, it's fairly obvious when you roll them out that the strength direction is in the direction of the roll width. With wide rolls, some of the manufacturers do put markings on the outer edges of the roll with arrows saying strength direction. Yet, it is quite common for no clear marking to be present on the geosynthetic roll and the contractor should take care to label the materials in the field prior to cutting. Colored paint is commonly used to identify both strength direction and material types."
So there you have it, a possible new area for you to explore in expanding your business. It's not hard to make the transition as Carter says, "Once they've mastered placing the block and getting the fill in 6- to 8-inch lifts, it's just a repetitive sequence as they continue up the wall."
20 Masonry
July 2002
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