Masonry Magazine June 2001 Page. 18
As a superintendent, I trained my guys to build segmental retaining walls and the guys in the masonry department converted right to it," said Joe Marsh, superintendent at Wasco, Inc., one of the largest masonry construction firms in the nation. Marsh supervised a 13,000-square foot SRW project for Skyline Medical Center in Nashville. "SRWs are a great product - they don't crack and they don't have to be built on a concrete foundation. You've got a wall that moves with the earth and it's going to stay there - it'll sure outlast me. The hospital job is one heck of a wall and it looks just beautiful." Some masonry contractors think that SRW installation is more time consuming and more expensive than installation of a traditional retaining wall system. But the overall costs and time spent building SRWs beats that of building a traditional cantilevered wall. Another plus is that no scaffolding is needed to construct SRWs - even with walls that that soar upwards to 40 feet in height.
Because SRWs do not use mortar, there is less room for error. There is no luxury of a mortar joint to correct the levelness. When constructing SRWs, levelness is extremely important at the base course to eliminate potential problems as the wall gains height. However, SRWs do not require control joints, bond beams or rebar. When using solid SRWs there are no cores to fill and units can be placed on variable bond without compromising structural integrity. The shape of SRW units allows construction of free-formed curves and steps from one standard unit. This cannot be easily done with concrete masonry block.
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Generally, a masonry crew is not directly responsible for backfill placement behind a traditional masonry wall. However, crews installing SRWs are often responsible for backfill placement and the geogrid in the reinforced zone. On many projects, SRWs work purely as gravity systems unit weight alone provides resistance to earth pressures. Frictional forces between units hold the blocks together so walls behave as coherent structures. Setback of wall faces offers additional resistance against overturning. Maximum allowable wall height for gravity walls varies with soil and loading conditions. Generally, with level backfill, good soils and no excessive loading, gravity walls are stable to heights of four feet.
When weight of units alone is not enough to resist soil loads, horizontal layers of geogrids are used to reinforce soil behind walls. With proper soil reinforcement and design, SRWS can be constructed to heights exceeding 40 feet. Geogrids do not act as tie-backs for wall faces. Rather, geogrids and soil combine to create reinforced soil structures that are strong and massive enough to resist forces exerted on them. In soil-reinforced walls, SRW units simply retain soil between layers of geogrids and provide attractive, durable faces. "You can do anything with these units," said Steve Fechino, a mason contractor with Wasco, Inc. "We've been able to do some extremely creative things with retaining wall units and the creativity is virtually unlimited."
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