Geopier Densipact® system provides cost-effective solution for support of 5,000 psf tank pressures
- Tank Designer/Contractor: CB&I
- General Contractor: T.D. Farrell Construction, Inc.
- Geotechnical Engineer: Terracon
The project involved support of a new, 174-foot diameter storage tank for chemical storage. The tank design incorporated a flexible-bottom steel tank with perimeter ring wall support. The tank pressure for design was 5,000 psf. A total settlement tolerance of 4-inches was required. The site grades generally required 4-feet of cut to reach the finished grades.
Borings revealed the presence of loose to medium dense, fine-grained sand with less than 10% fines in the tank location. The sand is medium-dense with depth and extends to 34 to 42 feet where very hard clay was encountered. Groundwater was observed at a depth of 36 feet below grade.
The geotechnical engineer raised concerns about settlement and bearing capacity of the loose sand under the large tank design pressures. Ground improvement options including a Rammed Aggregate Pier® solution and vibro stone columns were considered to treat the loose sand conditions to meet the performance requirements of the tank.
Geopier® developed and offered two solutions: a Rammed Aggregate Pier® solution using the Geopier Impact® system and a Rammed Compaction® solution using the Geopier Densipact® system. The Densipact® solution was selected as the most cost-effective option for the project compared with the other ground improvement options. The Densipact solution involved densification of the loose sand and was accomplished by installing a grid of closely-spaced Rammed Compaction Points uniformly beneath the entire footprint of the tank and the ringwall foundation. The densification system was designed to reinforce the upper 10 to 13-feet of the profile.