The first step in the installation process is creating the leveling course foundation. A shallow trench should be excavated the length of the planned wall that is also wide enough for granular backfill behind the wall. The depth of the trench should be enough for any new foundation material (leveling pad or flowable fill) as well as the partially buried first course. As a rule of thumb, the first course should be below grade 1" for every 8" of height.

After excavating the trench, the foundation is prepared. Foundation soils must be level, firm, and have sufficient capacity to support wall system weight. For a larger wall, the bearing capacity of the foundation soils should be addressed by a soils engineer. Soil foundation should be compacted to at least 95% of standard Proctor density (the maximum density of the soil achieved in a laboratory using a standard amount of compaction effort). Granular leveling pad material is commonly used, as it compacts easily to a smooth and level surface. Flowable fill is great for jobs of several hundred feet because it does not need to be compacted.

Laying the Courses

Place the first course, making sure it is level with a transit, laser or just a carpenter's level in all directions and use a string line to verify straightness. If necessary, level and stabilize the first course with small handfuls of sand. Do not use soil, as this will settle over time. Lay the remaining courses as directed by the manufacturer. The final course, or cap needs to be adhered with paver grade adhesive for security.

Backfill & Drainage

Proper compaction of foundation and backfill soil is critical to long term performance. Loose backfill will add pressure on walls, collect water, cause settlement, and will not anchor soil reinforcement materials properly. Drainage, though, is the key to a retaining wall's survival because hydrostatic pressure is the biggest enemy of a retaining wall.

Each course is backfilled immediately behind the wall for about 8 inches with a granular drainage aggregate (3/4", free draining, angular gravel) that is free of fine dirt and soil and then further backfilled with compacted soil. Drainage aggregate is critical to the stability of the wall because it keeps water pressures from building up behind the wall face. For walls over 3 feet, a perforated drain pipe should be used to quickly remove large amounts of water along the base of the drainage aggregate. However, it is recommended to allow for the most drainage possible no matter what size wall.

The soil backfill is placed directly behind drainage fill in layers (lifts) no thicker than six inches. The amount and type of effort needed for adequate backfill compaction varies with soil type and moisture content. Generally, hand-operated vibratory plate compactors can be used to achieve adequate compaction of granular soils even on big projects. Fine soils such as clays should be compacted with kneading-type equipment like a sheepsfoot roller.

Reinforcement

Geosynthetic soil reinforcement is used to reinforce the backfill for walls above four feet. Reinforcement is used along with retaining wall blocks intended for larger walls, which will have fiberglass pins capable of anchoring the reinforcement that decorative blocks do not. Geosynthetics and soil combine to create reinforced soil structures that are strong and massive enough to resist forces exerted on them. Soil reinforcement type, length, and vertical spacing will vary for each project and should be specified by a qualified engineer. However, most manufacturers now offer software that is capable of computing installation layers based on soil analysis and the stone type. Geosynthetics are usually stronger in one direction. The strongest direction of the geosynthetic must be perpendicular to the wall face. For correct orientation, follow the goesynthetic manufacturer's directions.

Versatility

Tree rings, fences, ponds, and anything imaginable can be created easily with these products. Most manufactures of these systems count on this creativity. Pyzique blocks have 2 faces so they can be flipped around to create zig-zag effects and stairs. Keystone, in addition to making several shapes and sizes, has planter blocks designed with 1 gallon pockets ready for soil and flowers. To your client's delight, these systems will allow you to literally sculpt the landscape with minimal effort. LCM