Structural Soil Stabilization

Soil Stabilization Under Structural Columns Inside Commercial Building in Virginia Beach, VA.

Structural Engineer:
Fadi Debbas, PE, ABC Consulting, Inc., Norfolk, VA, www.abcnorfolk.com

Problem:

Three structural columns inside of a commercial building supporting roof for four units settled.  Two columns had settled around 1 inch, the third had settled 6 inches.  Geotechnical investigation showed loose, unstable soils in the area of the columns.  However, due to unusual construction method related to abandoned basement on site, testing of soils immediately under spread footings was not possible.

The original assumption of the construction method was that the spread footings were installed 2 feet above the abandoned basement floor.  The planned repair was to chemically stabilize the band of soil between the base of the spread footing and the abandoned basement floor below the spread footing.

Constraints: 

Budget and limited work area were the primary concerns.  Two of the columns were adjacent to shared walls with still-operating restaurants, so no disturbance was allowed.  All injection equipment had to be silent, dustless and compact.  Access for third column was from inside of bathroom of a restaurant closed for renovations and floor stabilization and lifting (project profile for floor lifting), so no large drilling or placement equipment could access the work area.

Soil stabilization had to address loose nature of soils and create an adequate bearing capacity under the spread footings.

Solution:

Soil stabilization with single component resin soil stabilizer injection was chosen to meet the requirements of compactness, quietness and effectiveness at binding loose soils into solid, plasticized masses.

Installation sequence was to drill 1 5/8″ holes through the floor above the footing, then drill 5/8″ holes through the soil between the floor and top of the spread footing and then through the spread footing.  Small diameter injection pipes were then passed through these access routes and driven into the soil below the bottom of the spread footing.

Lifting of columns was not desired due to potential for disturbing finishes that had been installed after settlement occurred inside of the units.

Result:

CJGeo installed single component polyurethane chemical grout to refusal under each of the three columns to fill any voids and stabilize the soil in place.