Challenge
A brick manhole was found to have significant structural deterioration and infiltration, leading to soil migration and recurring sinkholes in the surrounding area. Despite early indicators of washouts and infiltration, the condition was not addressed in a timely manner, allowing progressive damage to occur over several years.
Technical Analysis
Back Municipal Consulting performed a detailed inspection and review of reports, photos, videos, and field data. Findings included:
- Severe Structural Deterioration – Missing mortar joints, thinned walls with exposed aggregate, and sections of missing block wall created direct pathways for infiltration.
- Voids & Soil Intrusion – Large voids were observed behind the manhole walls, with mud and soil visibly entering through openings around pipes and joints.
- Infiltration Evidence – Active water staining and sediment deposits confirmed infiltration at multiple locations.
- Progressive Defects Over Time – Historical reports and inspections documented washouts (2014), sinkhole formation (2016, 2018), and MACP™-coded defects, including missing mortar, surface spalling, aggregate protrusion, and fine root intrusion.
- Missed Diagnostic Opportunities – Dye testing, an established standard practice per USEPA technical guidance, CMOM protocols, and NASSCO recommendations, was requested but not performed at critical times. This would have confirmed the link between the sinkholes and infiltration.
Outcome & Lessons Learned
The case illustrates that:
- Long-term infiltration without rehabilitation leads directly to soil migration and sinkhole formation.
- Dye testing is a low-cost, industry-standard diagnostic that should be applied whenever washouts or sinkholes occur near sewer structures.
- MACP Level 2 inspections are necessary when significant defects are suspected, ensuring thorough documentation and rehab recommendations.
- Rehabilitation or replacement with watertight structures should include ASTM F1244 vacuum testing, ASTM D7234 adhesion testing, or holiday testing to verify watertightness and liner integrity.
BMC’s Role
BMC performed direct entry inspection and technical analysis of the manhole, documenting significant wall loss, voids, and infiltration pathways. Leveraging over 30 years of trenchless expertise and referencing ASTM, USEPA, CMOM, and NASSCO standards, BMC demonstrated how industry-standard inspections, testing, and rehabilitation methods would have prevented soil loss, void formation, and recurring sinkholes.
