Gravity Retaining Wall Construction
Gravity retaining wall typical cross section
Gravity retaining wall base course section
Install base material, level, and compact.
Level blocks, adjust where needed.
Step 1: Site Prep and Excavation
- Remove surface vegetation and organic soils
- Per the approved plan, excavate base trench a minimum of 610 mm wide and 300 mm deep.*
- Remove unsuitable soils and replace with compactible materials.
- Buried block should be a minimum of 150 mm. Check plans to see how much buried block is required.
- Compact and level trench.
Stepping up the Wall Base
Walls built on a sloping grade require a stepped base
- Begin excavation at the lowest point and dig a level trench into the slope until it is deep enough to accommodate the base material and one entire block.
- At this point step up the height of one block, and begin a new section of base trench.
- Continue to step up as needed to top of slope.
- Always bury at least one full unit at each step.
Start retaining wall at the lowest elevation
Step 2: Install Base Material
- Per the approved plans, place a minimum of 150 mm of wall rock in the base trench and rake smooth.*
- Compact and level base material.
- Site Soils Engineer should verify that a proper base is established.
Step 3: Install Base Course
- Begin at the lowest retaining wall elevation. Place retaining wall blocks on base material in the center of the trench. Check and adjust for level and alignment of each unit.
- Drain pipe is required for retaining walls over 1.2 m tall or are constructed in silty or clay soils. See approved plans for location and specifications. Refer to design details on an alternate drain location.
Step 4: Install Wall Rock and Backfill Materials
- Fill the hollow cores and a minimum of 300 mm behind the retaining wall with wall rock.
- Use approved soils to backfill behind the wall rock and in front of the base course.
- Use a plate compactor to consolidate the area behind the block. Compact in lifts of 200 mm or less.
Step 5: Install Additional Courses
- Remove all excess material from the top surface of retaining wall blocks. This can be done when installing the next course of block, by sliding the block into place.
- Stack the next course of blocks so that the vertical seams are offset from the blocks below by at least 75 mm or 1/4 the length of the block.
- Check and adjust for level, alignment and the wall batter as the retaining wall stacks up.
- Fill the block cores and behind the block with wall rock a minimum of 300 mm. Use approved soils to backfill behind the wall rock.
- From course 2 and above use a plate compactor to compact directly on the blocks as well as the area behind the blocks. Compact in lifts of 200 mm or less.
- Complete the retaining wall to required height. See finishing details for information on retaining wall ending options.
- Use 200-300 mm of low permeable fill on the last lift to finish off wall.
*For walls under 1.2 m, a 460 mm wide by 250 mm deep trench with 100 mm of wall rock base material is acceptable.