A Tale of Two Buildings: Case Studies of Underpinning by Compaction Grouting


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Title: A Tale of Two Buildings: Case Studies of Underpinning by Compaction Grouting

Author(s): Frederick R. Rutz, Jennifer Harris, and James Robert Harris

Publication: Special Publication

Volume: 316


Appears on pages(s): 39-54

Keywords: Case Study, Hydro-Compressive Soil, Compaction Grouting, Debris Fan, Underpinning

Date: 4/1/2017

Two concrete masonry buildings, at adjacent sites in Glenwood Springs, Colorado, are located atop existing collapsible debris fan soils. Both buildings were constructed on concrete foundations with spread footings, and both suffered serious and damaging differential settlements. Compaction grouting was utilized for underpinning and lifting both buildings. Compaction grout columns are comprised of a low slump and low strength grout made from a combination of sand, soil, pea gravel, cement, and water. When installed under pressure, the grout densifies the surrounding soils supporting the building foundation, and when carried to the underside of footings, the grout can offer direct support. The grout was also used to lift and partially level the buildings. But here the similarity ends; each had unique circumstances and the repair designs were custom tailored. One was underpinned with deep (100’) compaction grout columns while the other received a much shallower underpinning treatment. Each had unique drainage problems. Both projects were challenging and required cooperation among the Owners, Structural, Geotechnical and Civil Engineers, and the Contractors. The geotechnical studies, the structural design for repair, the drainage provisions for each, and the construction are described, with a focus on structural damage, design of the underpinning to be compatible with the structural capacities, and control systems utilized during construction.