Norfolk, VA

Geotechnical Engineer - Law Engineering

A proposed six story Hilton Hotel site was underlain by approximately 20 feet of loose clean to silty sand. The sand was underlain by soft clay to considerable depth. The groundwater table was about 6 to 8 feet deep.

The first option considered for foundation support was the use of a deep foundation system. However, the cost for this option was very high. The second option considered was improving the upper sands by dynamic compaction and using normal shallow foundations. This option was selected based on both cost and the engineering opinion that it was technically feasible.

Dynamic compaction was performed using an 8 ton weight dropped from heights of 50 to 60 feet. Crater depths of up to six feet were recorded. Clean sand was used as the crater backfill.

Following treatment by dynamic compaction, cone penetration testing indicated an allowable bearing pressure of 6 ksf. The building has been in operation since 1985, with no settlement problems.