Densification of Soils by Explosive Vibrations

Densification is compaction applied to unlimited depths from the surface. Densification allows building on granular soils with original bearing values below minimum, reduces or eliminates piles or raft foundations, decreases permeability, and increases slopes for excavation purposes. Densification of loose granular soils can be economically accomplished by numerous small charges of explosives individually detonated. This method can not be used in cohesive soils. Saturated or dry soils produce maximum densification of from 75% to 85% relative density. Type of explosive combined with soil amplitude and velocity are important factors. Small engineered charges produce a safe densification method despite common prejudice against explosives. Operations must be carefully engineered as to explosive type, size, spacing, depth, and firing pattern in relation to soil, water table, dimensions, and required densification. Limitations include excess pore pressures, liquefaction, and damage to existing structures. History, theory, construction procedures, testing, and current cost estimates are examined. Data on completed jobs with different soil conditions in the United States and abroad are given.