Help with Mini design project

A 60m x55m storage facility with max floor slab loading of 50kN/m^2 to be built. Ground conditions; upper layer 5m of sandy fill material placed in 1992 Underlain by estuarine silt, 4-6m thick Max settlement; 25mm (Bearing capacity to be ignored) What steps should be taken in approaching this problem? In particular what types of lab/in-situ tests would need to be carried out and what would be the best approach to consolidate the soil, vertical drains or vibro-ground improvement and why? (piling and surcharging deemed too time consuming or expensive) Any help would be greatly appreciated!

Geotechnical Investigations & In-Situ Testing Ground Improvement Shallow Foundations Analysis Soil Mechanics / Geotechnical Design