More recently, as a result of a ground failure associated with a stockpile load that resulted in the extended closure of Dearborn Street as well as damage to various utilities within the public rights-of-way, Detroit is drafting an additional ordinance that will require the engineering evaluation of any site where material stockpiles result in an equivalent surface surcharge loading exceeding 360 pounds per square foot (psf). The draft ordinance, to be added as Section 8-15-144 to Division 4 of the Detroit City code, will require that owners who stockpile any material on their site that exceeds the 360 psf threshold perform the following investigation and engineering evaluation:
- Conduct a geotechnical investigation of the site to characterize ground conditions and engineering parameters of the existing soils. As drafted, the ordinance stipulates the minimum number of test borings at one test boring per acre of the premises being used.
- Review the site for the presence of and the determination of conditions related to existing retaining walls.
- Perform an engineering evaluation of the site based on the results of the geotechnical investigation to document permissible site loading such that a minimum factor of safety of 1.5 is achieved for all potential modes of failure.
At the present time, the proposed ordinance has been finalized by the Detroit Building Safety Engineering and Environmental Department, is out of Committee, and will be brought to the City Council for consideration in the near future.
With more than 54 years of geotechnical expertise in the Detroit area, NTH staff are very familiar with the ground conditions throughout the City. If the proposed ordinance becomes codified, NTH staff have the expertise to perform the necessary geotechnical investigation and analysis so that site owners will be in compliance with the new regulation requirements.