Reinforced Wall Construction using AB Fieldstone

For the proper first steps on site prep, drainage requirements and installing the base material, see Reinforced Wall Construction. Projects must be built to the approved plans and specifications provided by a local engineer.

Step 1: Install Base Course for AB Fieldstone

• Begin at the lowest wall elevation by placing the AB Fieldstone facing units on the base material towards the front of the trench, leaving room for the AB Fieldstone anchoring unit so when entire assembly is installed it is centered on the base materials. Install a string line at the back of the facing unit to ensure the proper positioning of all facing units.
• Adjust for level and alignment as each facing unit is installed.
• For proper placement of the AB Fieldstone anchoring units, use a brick hammer to create a small trench to allow for the lip.
• Install the anchoring units into the receiving slots of the facing units with the lip facing down in the trench just created. Make adjustments to ensure anchoring units are installed reasonably level with the facing unit. The anchoring units should never be installed higher than the facing unit. Except for special applications like corners, each anchoring unit should match up with one facing unit.
• A drain pipe is required for any reinforced wall, gravity walls over 4 ft. (1.2 m) tall or sites with poor drainage. Place the drain pipe at the lowest possible point toward the back of the trench and vent to daylight every 50 ft. (15 m). See approved plans for location and specifications.

Install AB Fieldstone facing units. Level and adjust.

Install AB Fieldstone anchoring units.

Step 2: Install Wall Rock and Backfill Materials

• Fill the hollow cores and a minimum of 12 in. (300 mm) behind the wall with wall rock. Install the wall rock to be level or below the receiving notch of the anchoring unit. A compactible aggregate ranging in size from 0.25 in. to 1.5 in. (6 mm to 38 mm) in diameter, and containing less than 10% fines is recommended.
• Use approved soils to backfill behind the wall rock and in front of the base course.

Step 3: Compact

Compaction of the material behind the block is critical for a quality wall

• Use a mechanical plate compactor to consolidate the wall rock, then compact the backfill material immediately behind the block. Compact in a path parallel to the wall, working from the back of the block to the back of the backfill material See page 33 for additional details on compaction.
• Check the base course for level and adjust as necessary
• All backfill soils must be compacted to a minimum 95% Standard Proctor. Use equipment appropriate for the soil being compacted.
• Remove all excess material from the top surface of all AB units. This prepares a smooth surface for placement of the next course. This can be assisted when installing the next course of block, by sliding the block into place.
• Every course after the first course requires compaction starting on the block.

Compact wall rock and backfill soils.

Sweep to remove excess materials for proper placement of the next course.

Step 4: Install Geogrid

• Cut sections of geogrid to specified lengths. Check manufacturer’s grid specifications for strength, and roll or machine direction. Refer to the approved plans for exact size and location.
• After the base course of blocks has been installed, roll out the geogrid reinforcement starting in the middle of the AB Fieldstone facing unit and extending back to the excavated area. The excavated area must be fully compacted and level.
• Stack the next course of block (facing and anchoring units) on top of the geogrid so the blocks are offset from the blocks below. Each new course should be positioned so the vertical seams are offset by at least 3 in. (75 mm) or 1/4 the length of the block. Perfect running bond is not required. The facing units can be randomly flipped upside down to give different facing appearances.
• Sight down the retaining wall line to check for a straight wall. Blocks may be adjusted slightly to form straight lines or smooth flowing curves.
• Pull on the back of the geogrid to remove any slack. Stake in place before installing wall rock and approved infill soils.

Install geogrid. Start in the middle of the facing unit and extend behind wall.

Stake geogrid in place. Install next course of block.

Step 5: Backfill & Compact

• Install wall rock in block cores and 12 in. (300 mm) behind wall. Use approved infill soils to backfill behind the wall rock in the reinforced zone.
• All wall rock and infill soils within 3 ft. (0.9 m) of the wall must be properly compacted using a mechanical plate compactor. Compact in maximum 8 inch lifts (200 mm), this time starting on the block and working in a path that runs parallel to the block towards the back of the reinforced zone. Compact all materials to a minimum 95% Standard Proctor.
• Never operate compaction equipment directly on geogrid.
• All heavy equipment must be kept at least 3 feet (0.9 m) from the back of the retaining wall. Wall designs typically do not account for surcharges from heavy compaction equipment. Even a properly installed and compacted wall will rotate forward when extreme surcharges from heavy equipment are applied to the top of the retaining wall during construction and final grading.
• Check and adjust for level, alignment and the wall batter as the wall stacks up. It is acceptable to shim under blocks to compensate for a build up of tolerances or an out of level base condition. Asphalt shingles or geogrid work well when shims are required. The maximum allowable shim thickness per course is 1/8 in. (3 mm).
• Remove all excess wall rock and ridges or slag material from the top surface of all AB units. This prepares a smooth surface for placement of the next course. Plate compactors operated on top of the block will remove most slag material and prep the block for the next course. When installing the next course of block, sliding the block into place will also remove any slag material.

Step 6: Install Additional Courses

• Repeat steps 3 & 4 to complete wall to height required, installing geogrid where needed per the approved plans.
• Use 8 in. (200 mm) of impermeable fill on the last lift to finish off wall.

From the second course and up, compact starting on the wall and working to the back of the reinforced zone.

Using AB Fieldstone, taller gravity walls can be achieved with the Long Anchoring Unit (LAU).