Claim Reduction is a monthly series by the ASCE Committee on Claims Reduction and Management designed to help engineers learn from problems that others have encountered.
Whenever a claim against an engineer goes to trial, valuable lessons can be learned. The following case study has two key takeaways:
- Treat underground plastic stormwater detention systems with caution.
- Your professional responsibility when specifying engineered products.
The first takeaway is covered in part 1 of this two-part article. This part covers the second takeaway: your responsibility when specifying engineered products.
Background
A civil engineer contracted directly with a church for civil engineering services, including designing an onsite stormwater management system. It was decided to place the detention system below a 94,500-square-foot surface parking lot. Review part 1 for a more complete description of the case.
The contract documents specified the use of the tank system by incorporating the manufacturer’s prescriptive specifications and installation methods. The tank system would be buried beneath up to 9½ feet of soil, which is deeper than the engineer’s previous applications of the system but, importantly, within the upper range of the burial depth reported in the manufacturer’s literature. It’s also worth noting that the civil engineer had used the same stormwater detention system on other projects previously, all without incident.
The church hired a general contractor after the design was completed and permitted. A third party, under contract with the owner, was responsible for construction inspection. The civil engineer, who was not contracted to monitor construction, did not observe the tank placement. However, the engineer did respond to the general contractor’s requests for information, including one about the tank system’s suitability for the high groundwater conditions at the site. The engineer confirmed the system’s suitability, and the installation was completed. However, based on construction documentation from the third-party inspector, the general contractor did not adhere to several of the tank installation specifications.
The first sign of a problem could be seen when the parking lot above the tanks began to settle, indicating a failure of the plastic tanks to support the overburden. This failure occurred four months after the overburden was placed, raising the question: why didn’t the tanks fail when initially loaded?
Cause of the failure
The tank system’s non-conforming installation went undisputed, including these deviations from the engineer’s specifications: the tank system was not installed on a level surface; it was not installed on a stable subgrade; the foundation on which the tank rested contained oversized rock; modules were not installed in the specified orientation; the number of units installed was less than specified; backfill material used did not meet the specifications; the contractor failed to compact the backfill material as specified; and excessively heavy compaction equipment weighing more than 17 tons was used, well beyond the 6-ton limit included in the project specification.
According to the church’s causation expert, all these construction deviations likely contributed to the failure. Two expert witnesses retained by the church opined that if the system had been installed correctly and in accordance with the civil engineer’s design and the manufacturer’s specifications, the system should not have failed.
The trial
Dispute resolution efforts failed; the general contractor sued the church, the church counter-sued the general contractor and the third-party inspector, and the general contractor sued the tank manufacturer and the subcontractors. The church also sued the civil engineers directly.
The tank manufacturer, in Australia, never responded to the complaint. Eventually, the tank’s U.S. distributor was dismissed based on a limited warranty, and the church settled independently with the third-party inspector, likely with a contribution. The civil engineer defended the claim, arguing that its services were provided within the applicable standard of care, that it relied on information in the general contractor’s product submittals, and that the failure was due to the improper installation of the rain tanks by the general contractor and subcontractor, as well as contract provisions that transferred responsibility for system performance to the general contractor.
The decision
The court concluded, based on other expert testimony, that the deviations from specifications were immaterial and did not contribute to the failure.
It accepted the general contractor’s argument that the civil engineer had specified an unsuitable product for the project. The tank module strengths also were alleged to be insufficient to support the depth of the soil overburden. The manufacturer’s literature included module strengths based on short-term compression tests under ideal laboratory conditions, with limited applicability to field conditions. The general contractor’s expert argued that the civil engineer should have known of the limitations of the manufacturer’s data and conducted independent testing of the system. The expert further opined that the plastic creep of the polypropylene was one of the causes of the tank failure (see part 1).
The civil engineer’s insurance carrier paid.
In summary
The hope is that through this story, the civil engineer’s awareness is raised about the potential pitfalls of designing projects using new, innovative products for which thorough technical information has not yet been developed or disseminated (see also the recent Claims Reduction article about thermal break connectors in concrete slabs). The story of this trial highlights the need for manufacturers to provide adequate information to allow engineers to use these products appropriately and safely. It highlights the need for engineers to be skeptical of data being provided.
The Committee on Claims Reduction and Management supports innovation in civil engineering but urges civil engineers to be cautious of unintended consequences when using new products with limited research, experimental, and field performance data. As gatekeepers, civil engineers have the right to demand detailed information from manufacturers if we intend to specify their products. Manufacturers must understand our obligations to our clients and public safety and provide the information vital to ensuring their products are suitable for use. While we may not be able to test and evaluate every new product independently, we must carefully assess whether the information provided is sufficient to instill confidence in our designs. Finally, contractors must do their part by ensuring that projects are built following the specifications.
John Godwin Tawresey, S.E., F.SEI, FTMS, Dist.M.ASCE, has 52 years of experience as a structural engineer. As chief financial officer of KPFF Consulting Engineers for 35 years, he was responsible for the firm’s risk management education program.
