Large segmental retaining walls are constructed using precast concrete blocks that weigh in excess of 100 lbs each. These blocks come in a variety of shapes and sizes, and some weigh as much as 5,000 lbs. Large precast retaining wall blocks are more suited for building medium to heavy-duty retaining walls that are usually above 5′ in height. As these blocks must be placed using heavy equipment, adequate site access is a prerequisite.
Quick answers
Short, direct answers to the questions homeowners ask most about large precast block walls.
- What is a segmental retaining wall?
- A segmental retaining wall is built from precast concrete blocks that interlock course by course. Each course is offset by half a block in a running bond and set back slightly into the slope, called a batter, so the whole wall acts as one rigid unit. Top Mark builds large-block segmental walls across Toronto and the GTA with blocks over 100 lb, some up to 5,000 lb.
- When do I need large precast block instead of small block?
- Large precast block suits medium to heavy-duty walls, usually above 5′, and any wall with a driveway, garage, pool deck or walkway on the high side. Under about 6′ with nothing pressing down behind it, small block is usually the more economical choice. Top Mark weighs the height, load, soil and access at a free consultation anywhere in Toronto and the GTA.
- Can a large block wall be built without machine access?
- Yes. On tight Toronto and GTA lots, Top Mark uses hollow, pinned blocks such as Oaks Precast Hewnstone or Techo-Bloc Suprema: each unit is carried in, set, pinned and filled with clear gravel, so the wall gains its weight in place. The 60-foot Sandie Dix wall was built entirely by hand this way. The largest mass blocks, such as Redi-Rock, still need a machine.
- What is a surcharge load on a retaining wall?
- A surcharge is any extra weight on the soil behind a retaining wall, such as a driveway, garage, foundation, pool deck or walkway above it. It adds to the pressure the wall must resist, so the wall has to be designed for it, often by a professional engineer. In Toronto and the GTA, Top Mark uses large precast block for loaded walls like the Pinkus driveway wall.
- Why are hollow precast blocks filled with gravel?
- Filling the hollow cores with clear gravel adds weight that locks the courses together, and it lets water drain through the wall instead of building pressure behind it. Top Mark filled the cores on the Sandie Dix and Pinkus walls, with clear ¾″ stone backfill, filter fabric and drainage pipe behind, a build-up that matters on Toronto’s slow-draining clay soils.
- What affects the cost of a large precast block wall?
- Height matters most: soil force grows roughly with the square of height, and taller walls need more geo-grid, deeper excavation and usually an engineer’s design and permit. Machine access or hand building, removal of the old wall, drainage and caps also move the price. Top Mark’s retaining wall cost guide sets out typical Ontario and GTA ranges.
How a segmental retaining wall works
Precast retaining wall blocks work by interlocking with each other to provide great stability and strength. Each block interlocks with the one beneath it, and every course is offset by half a block so that a running bond is created to provide maximum strength and stability. Each course will often have a slight setback, called a batter, to improve stability by leaning back into the retained soil.
Rigid, but strong as one unit
Unlike armour stone retaining walls, segmental retaining walls are fairly rigid, and are incapable of minor movements without undermining the structural integrity of the retaining wall. However, because the entire wall is interlocked and is acting as one unit, even a comparatively slender wall can withstand more robust lateral earth pressures than an armour stone retaining wall of the same depth.
When you need a large block wall
Under about 6′, with nothing pressing down behind it, a small block wall is usually the more economical choice, and in a garden natural stone may suit better. Large block earns its place when:
Height
The soil force on a wall grows roughly with the square of its height, so a 6′ wall resists about four times the force of a 3′ wall.
Surcharge loads
A driveway, garage, foundation, pool deck or walkway on the high side adds load on top of the soil. The wall must be designed for it.
Slopes and tiers
Steep yards, ravine lots and grades that change along the wall, like the Sandie Dix wall’s 4′ to 10′ grade change.
Redi-Rock, Techo-Bloc and geo-grid reinforced walls
A precast block retaining wall reinforced with geo-grid can withstand substantial loads and can be built up to 50′ in height. For retaining walls in excess of 6′ in height, or walls that will have to bear additional loads, large precast concrete blocks such as Redi-Rock are better suited. These types of retaining walls should always be designed by a professional structural engineer.
Pinned block or mass block?
Hollow, pinned units such as Techo-Bloc Suprema and Oaks Precast Hewnstone are filled with clear gravel on site and tied back into the slope with layers of geo-grid. The largest units, such as Redi-Rock, are set by machine and rely more on their own mass. Height, load, soil, access and the engineer’s design decide which system fits.
Engineering and permits for tall walls
Large block walls are, by their nature, the ones most likely to need approvals. Ontario generally requires a building permit for a retaining wall taller than 1 m (about 3′3″) of exposed face where it borders public property, a way into a building or private property open to the public, and that wall needs a professional engineer’s design. The engineer sets the block type, the geo-grid lengths and spacing, the base and the drainage, and accounts for any driveway or structure above.
A lot in a Toronto and Region Conservation Authority (TRCA) regulated area, or one covered by Toronto’s ravine and natural feature protection by-law, can need further approvals. Requirements differ between municipalities, so ask yours early; we work through it with you while the wall is being designed.
If your retaining wall project requires a wall in excess of 3′ in height, it is best to contact a specialized retaining wall contractor well in advance, as the design and permit phase of the project could take considerable time and resources.
We are fully equipped to service residential, commercial and industrial clients across Toronto and the GTA, from Thornhill, Vaughan, Richmond Hill and Markham to Mississauga, Burlington, Hamilton and surrounding areas. Give us a call today at 416.728.2159 to set up a free consultation.
What goes behind a precast block wall
Most of a wall’s life is decided by what goes behind the block. Clay soils, common across Toronto, drain slowly, and wet soil pushes far harder than dry soil, then freezes and expands each winter. You’ll see the same build-up in the projects below:
- Compacted gravel base under the first course
- Heavy filter fabric between the soil and the drainage stone
- Clear ¾″ stone backfill behind the block
- Clear gravel in the hollow cores
- Perforated, socked weeping tile
- Geo-grid layers as designed, often every 24″
- Pins locking each course to the next
- A coping cap to finish the top
Leave any of these out and a wall can look fine for a few seasons, then start to lean. Poor drainage and a badly installed base are exactly what made the old Kaivan wall lean and crumble.
Built by hand where machines can’t go
Large block is normally set by machine, but shared single driveways, tight lots and pool decks often leave no way in. A hollow, pinned system can still be built by hand: each unit is carried in, set, pinned and filled with gravel, so the wall gains its weight in place. That’s how we built the Sandie Dix and Perry walls. Hand work protects the garden and the neighbours’ property.
Signs an old wall needs replacing
- Leaning or bulging. The face tipping forward or kicking out at the base.
- Crumbling or cracking. Loose stone, spalled concrete and open joints that let soil wash through.
- Shifting on top. A path, patio or driveway dropping or tilting along the wall.
- Water problems. Wet ground at the base, or water running through the joints after rain.
- Rotting timber. Railroad tie and timber walls rot over time, usually from the back, against wet soil.
- Patchwork repairs. A wall pieced together from stone, concrete, pipe and wood, like the old Sandie Dix wall.
Replace it, don’t patch it
If a driveway, building or walkway sits on the high side, have the wall looked at early. The fix is usually a new wall with a proper base and drainage, not a patch.
That’s where the old Sandie Dix wall had got to, with the neighbours on both sides worried about erosion and the integrity of the structure.
Precast block retaining wall projects
Four precast walls, from old structure to finished job. More on our projects page.
Sandie Dix Wall
The existing wall between the neighbouring properties was a hodgepodge of natural stone, pieces of concrete and cement, reinforced with old pieces of pipe and wood. The difference in elevation ranged from 4 feet to 10 feet along the length of the 60 feet of wall. The slope of the property dictated that the wall was to be higher at the bottom of the garden, and was to step up with the incline of the land.
The concern of the neighbours was the erosion and integrity of the existing structure. The homeowner on the high side of the wall was worried about damage to the existing forsythia hedge, while the lady on the low side of the wall was afraid her garden would get trampled during the rebuilding of the wall. Care had to be taken to ensure that the issues expressed by the adjacent property owners were addressed.
As the homes were built close together, sharing single driveways, there was no access for equipment, so the existing wall had to be demolished carefully and removed by hand. The old wall stones were taken away by wheelbarrow, and all new materials had to be delivered by wheelbarrow and placed by hand. The base gravel and all backfill were also brought in and installed manually.
Drainage pipe and filter fabric were required behind the wall, and geo-grid mesh was placed every 2 feet of wall height to ensure tieback strength throughout the length of the structure.
The block used is an Oaks Precast product, Hewnstone, a hollow block with a smooth decorative face. The fibreglass (yellow) pins ensure further locking of the blocks. The strength of the wall and drainage is increased by filling the hollow space with clear gravel.
- Before
- Stone, concrete, pipe & wood
- Size
- 60′ long, 4′ to 10′ grade change
- Block
- Oaks Hewnstone, fibreglass pins
- Access
- No machines, all by hand
Perry Wall
This wall was also built by hand using a rough-faced Oaks Precast block. The patterned concrete pool deck and the confined space prevented access by machinery. The previously existing railroad tie retaining wall was removed by hand from the property, and the new concrete block structure was installed by hand to minimize damage.
The hollow block filled with gravel and the pinned retaining system allow for both strength of the wall system and sufficient drainage behind the wall. Perforated weeping tile pipe, filter fabric and geo-mesh are all recommended to enhance the integrity of the finished product. The rough split face of the exposed wall offers a decorative appeal.
- Before
- Railroad tie retaining wall
- Block
- Rough-faced Oaks Precast
- Site
- Patterned concrete pool deck
- Access
- Confined space, built by hand
Pinkus Wall
The original wall, adjacent to the driveway, was a brick facing backed by a concrete block wall. The existing combination had long since outlived its structural life and was in need of replacement.
Techo-Bloc Suprema Wall System, a one-hundred-pound block with a rough-finished split face and a groove-and-pin locking system, provides the structural integrity for a large wall while giving a visual appeal.
The block is laid on a gravel base and back-filled with clear ¾ inch aggregate. A layer of heavy filter fabric separates the soil to be retained from the wall and the drainage system installed behind the block. The added weight of the gravel inside the block locks this wall together for years and prevents excessive movement for the life of the wall. Geo-grid reinforcing is installed along the length of the wall at a height interval of every 24 inches, or 3 courses of block.
Piedmonte Onyx wall cap by Techo-Bloc is installed atop the wall as a finished coping.
- Before
- Brick facing on concrete block
- Block
- Techo-Bloc Suprema, 100 lb
- Geo-grid
- Every 24″ or 3 courses
- Coping
- Piedmonte Onyx wall cap
Kaivan Wall
The previous installation had deteriorated to the point of crumbling. Poor drainage and an improperly installed base had caused the wall to lean and the pathway atop the wall to shift.
Upon demolition of the wall, we found that a pre-existing layer of railroad tie had been left in the wall, and poorly installed drainage behind the wall had contributed to the shortened lifespan of the existing structure.
After installing Techo-Bloc Suprema Wall System to replace the leaning, crumbling existing wall, a Unilock Artline interlocking stone pathway with an inlaid Black Series 3000 border was installed.
Proper installation of base, backfill, filter fabric and socked drainage pipe is essential to the long life of a retaining wall. The strength and integrity of this wall will last for decades, as long as proper installation techniques are followed. The installed Piedmonte coping has the ability to support a decorative fence or railing for safety, as seen in the accompanying pictures.
- Before
- Leaning, crumbling wall
- Found inside
- Old railroad tie layer
- Block
- Techo-Bloc Suprema
- On top
- Unilock Artline path, railing
Leaning wall or a steep slope?
Tell us about the grade, the load and the access. The consultation is free.
Common questions
How tall can a precast block retaining wall be?
Reinforced with geo-grid, up to 50′. Over 6′, or carrying a driveway or structure, large blocks such as Redi-Rock suit better, and the wall should be designed by a professional engineer.
What finishes do precast wall blocks come in?
Manufacturers offer split, smooth and textured faces in a range of colours. The Sandie Dix wall uses Oaks Hewnstone, a hollow block with a smooth decorative face; the Pinkus and Kaivan walls use Techo-Bloc Suprema, with a rough split face. Matching or contrasting caps, like the Piedmonte Onyx cap on the Pinkus wall, finish the top.
How long does a precast block retaining wall last?
Decades, as long as proper installation techniques are followed. What shortens a wall’s life is usually below and behind the block: a poor base, missing drainage, or old material left buried, like the railroad tie inside the old Kaivan wall.
What is geo-grid, and does my wall need it?
Geo-grid is a strong polymer mesh laid between block courses and run back into the compacted backfill, tying the wall to the soil behind it. Taller and loaded walls usually need it, at the spacing the design calls for. On the Pinkus wall it went in every 24″, or 3 courses.
Can I put a railing or fence on top of the wall?
Yes, if it’s planned for. The Kaivan wall’s coping carries a black safety railing. Include the posts and their load in the design, and ask your municipality whether a guard is required where the wall drops beside a walkway.
