installation instructions for keystone retaining walls
- Before any excavation is started, be sure to contact Dig Safe to locate any utilities that may be in the area to be excavated. If there are any utilities located in the area, contact the related utility company before starting.
- Remove all surface vegetation and debris. This material should not be used for backfill.
- Excavate the Base Trench a minimum 24” wide and 6” deep. Additional excavation width may be required if the use of geogrid is required. Also, depending on wall height, the base trench must be dug deep enough to allow for placement of the base leveling pad and any buried Keystone units. As a rule of thumb, generally 1” of wall is buried for every 8” of wall above grade. For example: if your wall was a total of 8’ high, then you would bury 12” of wall unit below grade. (8 x 1.5 = 12) Therefore, the total depth of the base trench would be 18” in this case. (6” minimum + 12” buried block = 18”) Poor soil conditions would change that 6” minimum depth.
- Use a Dense Grade or ¾” Crushed Stone for bedding material under your first course of Keystone units. Compact with a vibratory compactor. You can use sand or ¾” Crushed Stone to level the first course after compaction.
- When setting the first course of block it is very important to level the block side-to-side and front to back. A four-foot level may be used to level the block side to side. A two-foot level may be used to level front to back. A rubber mallet will also be helpful to settle the block into the base pad if a little high.
- Once you have installed the first course of block, you need to determine a batter option. Batter is the slope of the face of the wall upward and backward so the wall leans into the embankment being retained. With Keystone Block, the batter is mechanically controlled by the pin position. Placing the pins in the front hole locations will result in the wall being built “near vertical”. Placing the pins in the back hole location will result in the wall being built with an 8.8 degree slope.
- Next, fill in the Keystone Unit Voids with ¾” Crushed Stone, as well as behind the block a minimum 12”. A perforated pipe to aid in drainage may also be installed behind the wall, wrapped in filter fabric. Install pipe with a slight pitch, and run to daylight, to ensure water will be moved from behind the wall. Keystone Block is a “dry” wall system, meaning it is not built with mortar joints so that water may seep through the wall if needed. The perforated pipe will aid with any added water pressure.
- Sweep off any remaining stone from the top of the first course and install the second course. Keeping the four pinholes at the top, lower the block onto the first course, with the kidney shaped holes overlapping the previously installed pins. Pull the block forward until the pin prevents it from moving further.
- Continue Steps 6-8 until you have reached the desired wall height.
- Once all block have been installed and the desired height is reached, cap will be installed. If due to final alignment using the pins for the cap is not going to work, remove the pins and use a Heavy Duty, Polyurethane Adhesive to glue the caps into place. It is strongly recommended that glue be used anyway even if pins are installed with capstone.
- If wall requires Geogrid see Instructions for Geogrid Installation.
