Why is my Ottawa interlock driveway shifting in spring?

Spring shifting in Ottawa interlock driveways is primarily caused by frost heaving and thaw settlement due to our extreme freeze-thaw cycles, combined with inadequate base depth that doesn't extend below Ottawa's deep frost line of 1.2 to 1.5 metres.

The most common culprit is insufficient base preparation during original installation. Many Ottawa interlock driveways were built with only 200-300mm of total base depth, which is inadequate for our climate. Ottawa's frost penetrates much deeper than southern Ontario cities, and when water-saturated soil beneath your driveway freezes, it expands and pushes upward (frost heaving). During spring thaw, this frozen soil melts and contracts, causing the base to settle unevenly. Pavers that were pushed up during winter don't settle back to their original position — they shift laterally as the base moves beneath them.

Ottawa's clay soils make this problem worse. Large areas of Ottawa — including Barrhaven, Orleans, Gloucester, and parts of Kanata — sit on expansive clay that swells dramatically when wet and shrinks when dry. Spring snowmelt saturates clay subgrade beneath inadequate bases, causing significant movement. Clay also holds water longer than sandy soils, extending the freeze-thaw damage period. If your driveway was built without geotextile fabric between the clay subgrade and granular base, clay migration into the base layer reduces its stability and drainage capacity.

Snowplow damage during winter often becomes apparent in spring. Metal plow blades catch raised or shifted pavers and push them further out of alignment. Even careful plowing can displace pavers that have been loosened by frost action. The weight of accumulated snow (Ottawa receives over 200cm annually) also compacts base materials, particularly if the base wasn't properly compacted during installation.

Poor edge restraint allows pavers to shift outward under freeze-thaw pressure. Interlock driveways need solid edge restraint — either concrete curbing, steel edging, or soldier course pavers set in concrete. Plastic edging or loose-set edge pavers provide insufficient resistance to Ottawa's frost forces. Without proper restraint, the entire driveway can gradually spread outward, creating gaps and uneven surfaces.

Drainage issues accelerate shifting problems. Water pooling on or beneath your driveway saturates the base and subgrade, making them more susceptible to frost damage. Spring runoff from roof downspouts, poor surface grading, or clogged drainage can keep base materials saturated well into the thaw period.

Immediate steps: Walk your driveway and mark severely shifted or raised pavers with spray paint. Check for standing water or soft spots that indicate base failure. Look for gaps along edges where pavers have spread outward.

Professional assessment needed: If shifting affects more than 10-15% of your driveway area, or if you can rock pavers with foot pressure, the base has likely failed and needs rebuilding. A qualified interlock contractor should excavate test areas to assess base depth and condition. Proper repair involves removing affected pavers, adding granular base material to proper depth (minimum 450mm total in Ottawa), recompacting in lifts, and relaying pavers with fresh bedding sand and polymeric sand joints.

When to Hire a Pro: Interlock shifting indicates base problems that require excavation, proper granular materials, and mechanical compaction equipment. This isn't a DIY repair — improper base work will result in continued shifting and potentially worse damage next spring.

Need help finding a qualified interlock contractor? Ottawa Driveways can match you with local paving professionals experienced in Ottawa's challenging soil and climate conditions.