What causes settlement and depressions around manholes?

Depressions forming around manholes are a universal and persistent challenge across all forms of infrastructure — from highways and ports to major airports.

The root cause is a material mismatch: manholes are rigid concrete structures, while surrounding pavements are flexible asphalt or granular bases. Achieving perfect soil compaction directly against the stiff manhole base during construction is almost impossible.

 

What causes settlement and depressions around manholes?

Depressions forming around manholes are a universal and persistent challenge across all forms of infrastructure — from highways and ports to major airports.

The root cause is a material mismatch: manholes are rigid concrete structures, while surrounding pavements are flexible asphalt or granular bases. Achieving perfect soil compaction directly against the stiff manhole base during construction is almost impossible.

Manhole depression

Over time, this mismatch leads to two primary issues:

Erosion

If the manhole structure acts as a soakaway, water flow can gradually wash away supporting soils such as fines and sands.

Void formation

Loss of soil support creates voids and localised settlement, forming visible depressions.

Structural support is not just about the frame of a building; it's also about the ground beneath it. When ground becomes weak due to poor compaction, water erosion, or soil movement, it can lead to subsidence. This means the foundation of the asset is no longer properly supported, and the structure can begin to crack, shift, or sink. This can be a serious problem for our heaviest and most critical public assets.

This issue impacts all types of infrastructure:

  • Bridges: The foundations of a bridge, including its abutments and pillars, can lose support, leading to dangerous structural weakness.
  • Large buildings: Heavy, multi-story buildings, critical facilities, and warehouses can be compromised, leading to floor collapse or dangerous sinking.
  • Retaining Walls: The ground supporting a retaining wall can fail, causing dangerous movement and instability.
  • Other Infrastructure: Heavy machinery foundations, large industrial slabs, and airport runways are all susceptible to ground failure, leading to expensive and unbudgeted repairs.

Shildon-coal-drops-improvement

 

How can we relevel settled infrastructure—fast?

The fastest and least disruptive solution is precision Geobear's ground improvement method.

Traditional repair methods—like milling and asphalt overlay—require extended closures, heavy plant, and multiple days of downtime. In contrast, our geopolymer injection process relevels settled pavement from below the surface, restoring the original profile within hours.

 

How it works

Our engineers identify the voided zones, then inject a rapidly expanding geopolymer resin beneath the surface. As it expands, it re-compacts and stabilises the soil, lifting the pavement to its exact target elevation with millimetre precision.

Case snapshot: Al Maktoum International Airport

At Al Maktoum International Airport, a pavement area surrounding a manhole had settled by 60 mm.

A conventional repair would have required several days of closure. Using Geobear’s geopolymer releveling solution, our team restored the area by the full 60 mm in just three hours, keeping operations fully active throughout the works.

Depressions lifted

Depression lifted

 

Engineering benefits of precision releveling

 

For infrastructure asset managers, Geobear’s precision injection technology delivers:

1
Millimetre-accurate control

Achieve exact elevations and surface smoothness.

2
Zero operational downtime

Work completed rapidly without full closure.

3
Rapid return to service

Assets are fully operational within hours.

4
Reduced whole-life cost

Minimal disruption reduces indirect costs that often exceed the repair itself.

Why speed matters for high-demand infrastructure


In sectors like aviation and major transport corridors, downtime translates directly into financial loss. Even brief closures can cascade into delays, diversions, and cancellations worth millions.
Adopting Geobear’s non-intrusive, high-speed repair method ensures infrastructure remains operational and financially efficient—preserving both asset integrity and economic continuity.

Key takeaway for asset managers


Manhole settlement is a symptom of sub-surface soil instability, not an isolated defect. Geobear provides a proven, engineered, and rapid re-leveling solution that restores safety and function without disruption.
With over 40 years of global experience and more than 20,000 projects completed, Geobear is the trusted partner for maintaining the ground integrity of critical infrastructure assets.

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