Black box repairs: when maintenance replaces verification

In long-life infrastructure, repairs are often presented as evidence of robustness.
Cracks can be injected, leaks can be sealed, and defects can be “managed” over time.

However, from a verification perspective, many repair strategies introduce a new form of black box into the structure.

Crack injection, in particular, is a reactive measure. While it may reduce visible leakage, it is rarely possible to verify full penetration, continuity or long-term performance of the repair across the entire crack path. Documentation typically confirms that an intervention was carried out — not that a durable, continuous barrier has been re-established.

More importantly, repair does not address the original design assumptions that allowed the defect to occur. Movement, restraint, interfaces, tolerances and execution variability remain unchanged. The structure is therefore dependent on the stability of the repaired zone and on the assumption that future behaviour will remain within expected limits.

Over time, this approach shifts the basis of durability:

• from verified performance before closure
• to repeated intervention during operation
  
  As accessibility decreases, each subsequent repair becomes more complex, more expensive and harder to assess. Uncertainty is not removed; it is deferred and accumulated.

When maintenance becomes the primary means of achieving watertightness, durability is no longer an engineered outcome. It becomes an operational obligation.

In long-life infrastructure, repairs should be the exception — not the mechanism by which unverifiable design assumptions are compensated.
True durability is achieved when performance can be inspected, tested and documented before access is lost, not when defects are managed after they appear.