Deep Soil Mixing for Foundation Support of a Parking Garage

A design-build foundation system consisting of 6 and 8 ft. diameter soilcrete columns was constructed to support spread footings for a five level parking garage in Allentown, Pennsylvania. The soil mixing method was selected over stone columns/aggregate piers because it provided a more rigid foundation system, and would not create vertical drainage paths in the potentially karst terrain. The load on the supported footings varied between 200 and 2,200 kips. The design was subject to settlement criteria of 1.25 in. total movement and 0.75 in. differential movement. The soilcrete columns were installed through medium and stiff clay, bearing on dense sand or weathered limestone rock. A total of 120 columns were constructed below the parking structure foundations. Three soilcrete columns were core drilled using a 2 in. diameter barrel, with each achieving over 95% recovery. Twenty-eight day unconfined compressive strengths of the cores and wet-grab samples averaged 900 psi.