Instructions for Geogrid Installation:
Step 1: Determining Need for Reinforcing
Geogrid reinforcements should be placed
continuously throughout their embedment lengths and placed side-by-side to provide 100% coverage at each level. They are anchored at the retaining wall and extend deeply into the soil behind the wall. The geogrid works with the compacted soil and/or stone behind the wall to stabilize the soil and keep it from moving forward and pushing against the back of the block wall. Walls don't have to be very high to warrant the use of geogrid reinforcing. For smaller
residential applications, the minimal additional cost is excellent insurance to ensure that the wall is structurally sound and will not deflect over the years. Geogrid reinforcing should be used (or may even be required) for reinforcing segmental retaining walls whenever the retaining walls are higher than 3 feet, where the retaining wall slopes, where there are surcharges (any downward pressures imposed above the wall level, such as parking areas, etc.), where the retaining walls are created by moving soil to create additional useable space, or for walls surrounding swimming pools when the wall is being used to hold back soil. A typical wall is reinforced every two courses. Geogrid is
available in different strengths. Nitterhouse stocks Geogrid in pre-packaged rolls 4 ft. wide x 50 ft. in length. Selecting the exact quantity, length, and number of layers will be dependent upon each particular application. As a rule of thumb, the heavier the surcharge, the greater the need for geogrid reinforcing and the amount required. If you're not sure whether or not your particular application requires the use of geogrid, consult with your Nitterhouse representative or contact a geo-technical
engineer to provide technical assistance to determine if this type of system is required. Computer programs are also available to develop wall designs that might not require an engineer's stamp of approval. If professional engineering approval is required, Nitterhouse can obtain professional engineering services and stamped drawings for you.
Step 2: Prepare the First Two Courses
Before installing geogrid reinforcing, first follow installation instructions for preparing the site, installing the base material and base course, installing drainage material, backfilling and compacting, and installing the second course of block.
Step 3: Installing the First Layer of Geogrid
Cut sections of the geogrid to specified lengths. Check the product specifications for strength or machine direction of the geogrid. Place the geogrid behind the lip of the block with the machine direction extending back into the slope. When placing grid along curving walls, the grid should always follow the back of the lip. To accommodate the curves, simply slit the grid with a utility knife, and either overlap it for outside curves, or feather it out to follow
inside curves. When placing grid at corners, simply lay grid into the corner and cut it to fit with a utility knife. Place the next course of block on top of the geogrid. Pull back on the grid to remove any slack. Stake in place before
installing drainage and backfill material.
Step 4: Backfill and Compact
Fill the hollow cores and drain field with drainage rock, and use on-site soil to fill behind the drain field as before. All drainage material in the drain field and infill soils within 3 feet of the wall must be properly compacted using a walk-behind plate compactor. Compact in maximum 8-in. lifts, with the first pass directly over the top of the blocks, starting on the wall and working in a path that runs parallel to the wall towards the back of the reinforced zone.
CAUTION! Do NOT compact directly over the reinforcement grid, and do NOT drive heavy machinery or within 3 ft. of the wall. Heavy machinery could cause the wall to rotate forward out of alignment.
Step 5: Install Additional Courses
Geogrid reinforcement is typically installed every two courses. Repeat the above steps when an additional row of geogrid is required. Each lift of drainage and backfill material should be installed in the same manner. Compact in lifts of 8 inches or less. Check the block for level after compacting each lift.