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.

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

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.

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.

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.

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.