Static soil compaction was used for years, until mechanical tampers, vibrating plates and rollers became popular in the 1960's. With this type equipment, large scale excavation is necessary. Where unstable sub-soil is present, the foundation has to be prepared in lifts (layering) with known soils. Each lift has to be hauled, graded, watered and compacted. Some areas may require as many as 18 lifts, each being 1½ feet thick. Needless to say, this method is not only time-consuming, but costly.
With dynamic compaction-the use of a drop weight, some soil conditions can be improved up to a depth of 60 feet. Using a 35 ton drop weight and a lift height of 100 feet, the energy produced is 7,000,000 ft. lbs. Now when we condense that energy into a known area, say 49 square feet, the ground pressure under that weight is 142,857 lbs. per square foot at time of impact.
Use of conventional hoisting equipment, by numerous commercial construction firms for dynamic compaction has, in most instances, proven to be less than desirable. Drum designs, braking systems, controls, and drive trains do not meet the requirements for compaction operation.
Where conventional cranes and their draw works are designed for heavy loads handled at slow controlled speeds and slow drum rotation. Dynamic compaction requires fast lifting speeds and an uncontrolled drop, resulting in fast drum rotation.
This cyclic operation, combined with the high r.p.m. of the drum, and a twenty-hour per day operating schedule requires specific design parameters. This paper will outline design goals, component specification, test procedure, and in-field economics of dynamic compaction.
The overall configuration of the LDC-350 shown in Figure 1 features a 120′ boom and consists of the following assemblies: (A) Crawler Transporter; (B) Sub-frame; (C) Boom; (D) Erecting Tower; (E) Draw Works; and (F) Operator's Control Cab.