There are a lot of systems choices and ways to build dry stack big block retaining walls. Our recommendations come from many years of experience. The first key is if you are building 4 ft (1.2m) or higher it’s important to have the proper Engineering and soils review of the site. Soils play and have an important role in designing walls. Before you start, contact a local engineer or review the product installation and technical manuals.
The base preparation in building a dry stack big block retaining wall is crucial for having a perfectly finished wall. Typically, the base preparation will consist of 6″ (150mm) of a well graded compacted gravel. Usually to 98% standard proctor density. It will be solid and compacted. A standard plate vibrating compactor is used to compact the base. Ensure that it is level front to back and side to side.
Weeping tile is placed either into the base or on top of the base. Weeping tile should be perforated and can also be wrapped in a filter cloth. The weeping tile is typically 4″ (102mm). It is used to carry any water that comes behind the wall away from the wall. Water should never be allowed to settle inside a dry stack big block retaining wall.
The Big Blocks will then be placed onto the compacted base. The width of the base should be 6″ (150mm) past the front and the back of the block. So if you have a 24″ (610mm) block to be installed. The width of the base should be 36″ (914mm). The block will be levelled front to back and side to side. Machine’s and hooks may be needed to lift and install the block into place. Consult the manufacturer if a machine is needed. Depending on the weight a skid steer or small backhoe can be used.
A wash rock gravel will be placed into the blocks hollow core. This will act as the drainage chimney to keep water out of the face and behind the retaining wall. On site soils may be compacted in lifts of no more than 6″ (150mm) high. The material should be approved by and Engineer. Organic soils should not be used as backfill materials. Sand, clay, rocks, gravel, well graded gravel, wash rock are all typically approved materials.
Filter fabrics can be used behind the blocks to separate the drainage chimney from the backfill materials.
Install the next courses and backfill material in the same manner as above. Dry stack big blocks will always be installed and levelled front to back and side to side. The Drainage materials will be placed and then the compacted backfill materials. Each course will follow in the same manner until the wall is completed.
Note: Geogrids can also be used in taller walls and will be designed by the Engineer. Most Big block companies have software’s to accomplish preliminary engineering.
The top of walls will be finished with organic soils to approximately 6″ thick where grass or small shrubs can grow. A swale can be placed at the top of the wall to divert water away from the front of the retaining wall. The swale can be made using clay or site materials but a concrete pre-cast swale can also be used. If a block has a large hollow core a fence post may be placed inside the hollow core and filled with concrete. If a wood fence it being installed the wind loading should be taken into account for design purposes. Chain link fences are common and have very little loading.
Congratulations!! you have successfully completed a Dry Stack big block retaining wall.
The author of this article is the owner of CornerStone® Wall Solutions that produces Magnumstone.