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The densification of soil by mechanical manipulation is called compaction. Although compaction has been a fundamental part of earthwork construction for decades, the development of compactors has evolved independently of the advances in soil mechanics for the most part and has concerned the properties of soil only in a qualitative way. This appears to be a result of the traditional separation of the two disciplines. The purpose of this paper is to discuss the important factors affecting soil compaction and to show their relationship to the resulting product. Common methods of evaluating properties of compacted soils are also described. The emphasis is placed on practical considerations rather than on theory.

The mechanics of soils is of fundamental importance in earthmoving and other soil manipulation operations. Future design of machinery for these purposes will make increasing use of this technical discipline. The first step which is to subdivide the soil-machine system into components based upon the phenomena involved is illustrated. The role of soil mechanics is shown and the important areas of study needed to develop design procedures are discussed. Finally, several topics expected to receive increasing attention in the future are considered. The overall objective of the paper is to show the importance of using soil mechanics in machine design and to encourage the further development of the interdisciplinary approach to problems dealing with soil-machine systems.

This paper reviews the state-of-the-art as regards the properties of compacted soils. In particular, the engineering properties of compacted soil are discussed in relation to soil structure, moisture content, interparticle (effective) stress, particle spacing, and particle orientation. The importance of compaction moisture content is emphasized because it is a critical factor in determining soil structure. In particular the effect of the aforementioned factors on the strength, volume change, compressibility, permeability, flexibility, and frost susceptibility characteristics of compacted soil are noted.

Full scale field tests on soil compaction were undertaken to evaluate the effectiveness of various methods of achieving compaction and to examine techniques for compaction control. The test variables included type of soil, moisture content, lift thickness, type of compactor, compactive effort, and number of roller coverages. Vibratory, pneumatic, segmented pad, and sheepsfoot rollers were investigated. Measurements of soil strength and density were made after a prescribed number of roller coverages. A comparison of results between the vibratory method and the other methods was made to provide insight into the role of vibration in compaction. The basic concepts of vibratory compaction are also discussed.

The prediction of the bulldozing forces on the basis of the geometric properties of the blade and the soil properties is of importance both in the agricultural industry and the construction industry. To achieve this objective, tests with small scale plane blades of various depths of cut, angles of inclination, widths, heights of backface, and blade surfaces were conducted in cohesionless soil. The measured forces were compared with forces obtained using the passive earth pressure theories. A very good correlation between the two was obtained when the blade length was replaced by the perimeter of the cut. Procedures are presented for the application of the theories to predict the bulldozing forces on actual blades in cohesionless soils.