Subsurface Soil-Improvement
Using Shallow Soil Mixing
Honolulu, Hawaii

Geo-Con's work consisted of designing and constructing a Subsurface Soil Improvement System utilizing Shallow Soil Mixing (SSM). Geo-Con's design was required to reduce settlement, improve structural bearing capacity and reduce liquefaction potential of the in-situ soils to facilitate the construction of above-ground fuel storage tanks over soft, saturated soils. shallow soil mixing work consisted of installing a total of 185 soil-cement columns, 6-foot in diameter, 12-foot deep underneath three proposed tank foundation rings. Soil-cement columns were constructed on 11-foot centers with columns staggered in adjacent rows. The soil-cement spoils generated during the shallow soil mixing work were mixed with additional cement grout to construct a 2-foot thick soil-cement relieving platform above the columns to support each tank foundation ring. The utilization of the soil-cement spoils in constructing relieving platforms also eliminated the off-site disposal potential of the spoils which were contaminated with jet fuel. Post treated soil-cement columns and relieving platforms achieved a minimum unconfined compressive strength of 200 psi.

Equipment used in constructing the Subsurface Soil Improvement System included a grout batch plant, crane-mounted turn table (Stratadrill 100), and an 80-ton crawler crane. Other support equipment consisted of a small hydraulic excavator and bulldozer for spoils grading and site restoration.

• Start: 7/6/98
• Completion: 8/14/98