What causes retaining walls to fail in New Brunswick?

The most common causes of retaining wall failure in New Brunswick are inadequate drainage, footings above the frost line, and walls that were simply undersized for the soil pressure they were asked to resist. NB's climate — with its 4-5 foot frost depth, 150+ annual freeze-thaw cycles, heavy spring snowmelt, and saturated clay soils in many regions — is particularly hard on retaining structures that cut corners in design or construction.

Poor drainage is the leading cause of retaining wall failure in NB. When water cannot drain freely behind a wall, hydrostatic pressure builds and can exceed the lateral earth pressure the wall was designed to resist. During spring thaw in Fredericton, Moncton, and Saint John — when several feet of frozen ground is releasing its water simultaneously — a wall with no weeping tile and no drainage stone behind it faces enormous pressure. The wall that looked perfect all summer will begin to lean, crack, or overturn in March or April. The fix requires demolishing the wall, installing proper drainage, and rebuilding — far more expensive than doing it right initially.

Footings above the frost line cause a different but equally destructive failure mode: frost heave. A footing at 2-3 feet depth in NB will freeze and be pushed upward every winter, sometimes by several inches. The wall above moves with the footing, creating horizontal cracks, tilting, and eventually structural separation. This failure happens gradually over 5-15 years and is often attributed to the wall "just getting old" when the real cause was a footing that was never deep enough.

Undersized or over-built walls — walls that were designed for less soil pressure than they actually retain — fail through forward rotation or sliding. This can happen when the soil above a wall is subsequently loaded with a deck, vehicle parking, or additional fill that the original design did not account for. It also happens when contractors build walls to a standard template without accounting for the actual soil conditions — clay-heavy, poorly draining soil in Saint John River valley communities exerts significantly more pressure than sandy soil.

Tree roots are an underappreciated cause of retaining wall failure across NB, particularly for older wooden or concrete block walls. Roots growing toward and under a wall displace the footing and create cracks that allow water infiltration, accelerating freeze-thaw damage.

Mortar joint failure in older CMU or stone walls occurs as mortar deteriorates over decades of freeze-thaw cycling. Once water infiltrates mortar joints and freezes, the expansion can dislodge blocks or stones. Repointing deteriorating mortar joints every 15-20 years extends the life of masonry retaining walls significantly.

Poor backfill material — using clay or organic soil immediately behind the wall instead of clean crushed stone — traps water against the back face of the wall and contributes to both drainage failure and frost pressure.

If your retaining wall is showing signs of forward lean, cracking, or separation, get a professional assessment before it progresses. New Brunswick Concrete can connect you with experienced contractors across the province.