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Soil Compaction and Swelling R 94 REFERENCES Prediction of Swelling Potential for Compacted Clays. Journal of the Soil Mechanics and Founda­ 1. G. Kassiff, M. Livneh, and G. Wiseman. Pave­ tions Division, Proc., ASCE, Vol. 88, No. SM3, ments on Expansive Clays. Academic Press, 1962, pp. 53-87. Jerusalem, Israel, 1969. 13. J. K. Mitchell. Fundamentals of Soil Behavior. 2. R. E. Means. Buildings on Expansive Clay. Wiley, New York, 1976, p. 422. Colorado School of Mines Quarterly, Vol. 54, No. 14. D.R. Snethen, F. C. Townsend, L. D. Johnson, 4, 1959, pp. 1-31. and D. M. Patrick. Review of Engineering 3. J. V. Parcher and R. E. Means. Soil Mechanics Experiences with Expansive Soils in Highway Sub­ and Foundations. Charles E. Merrill Publishing grades. Federal Highway Administration, Interim Company, Columbus, Ohio, 1968, p. 573. Rept. FHWA RD-75-48, June 1975, p. 137 . NTIS: 4. T. A. Haliburton. Final Report of the Subgrade PB 248 658/7ST. Moisture Variations Research Project. School of 15. G. J. Gromoko. Review of Expansive Soils. Civil Engineering, Oklahoma State Univ., Stillwater, Journal of the Geotechnical Engineering Division, Aug . 1970. Proc., ASCE, Vol. 100, No. GT6, June 1974, 5. T. W. Lambe. Compacted Clay: Structure. pp. 667- 694. Trans., ASCE, 125, 1960, pp. 681-717. 16. Proc., 3rd International Conference on Expansive 6. T. W. Lambe. Compacted Clay: Engineering Clay Soils, Haifa, Israel. Academic Press, Jeru­ Behavior. Trans., ASCE, 125, 1960, pp. 718-756. salem, Aug. 1973. 7. H. B. Seed and C. K. Chan. Compacted Clays: 17. J. G. Laguros. Predictability of Physical Changes Structure and Strength Characteristics. Trans., of Clay Forming Materials in Oklahoma. Univ. ASCE, 126, 1961, pp. 1343-1425. of Oklahoma Research Institute, Norman, 1972. 8. W. G. Holtz and H.J. Gibbs. Engineering Proper­ 18. J. G. Laguros, S. Kumar, and M. Annamalai. ties of Expansive Clays. Trans., ASCE, 121, 1956, A Comparative Study of Simulated and Natural 'l1'3!'.ltho.,..;n,.,. nF Qnmo n1,.1 .... 'h,..."'.....," Clhnl ...... ,.. r"l ....... ,. .-..-..J DD. 641-663. •• -· ·· ~ · -- -•--o - · - - -•- - · --••v •••-- .., ..._. ., ....,....., , '-'.&.&.4.. J ~ UJ.L\A. 9. M. G. Spangler and R. L. Handy. Soil Engineering, Clay Minerals, Vol. 22, No. 1, Nov. 1974, pp. 111- 3rd ed. Intext Educatiuual Pulilishen;, New Yui·k, 115. 1973, p. 748. 19. R. M. Hardy. Identification and Performance of 10. R. E. Grim. Clay Mineralogy, 2nd ed. McGraw­ Swelling Soil Types. Canadian Geotechnical Hill, New York, 1968, p. 596. Journal, Vol. 2, No. 2, May 1965, pp. 141-153. 11. C. C. Ladd. Mechanisms of Swelling by Com­ pacted Clay. HRB, Bull. 245, 1959, pp. 10-26. Publication of this paper sponsored by Committee on Physicochemical 12. H.B. Seed, R. J. Woodard, and R. Lundgren. Phenomena in Soils. Soil Compaction and Swelling R. J. Hodek, Department of Civil Engineering, Michigan Technological University, Houghton C. W. Luvell, Department of Civil Engineering, Purdue University, West Lafayette, Indiana Prediction of the characteristics and properties of compacted fine-grained was to develop a model and a mechanism that can ade­ soils is much aided by a physical soil mechanism or model. This model quately explain the achievement of compacted unit should, as nearly as possible, fit the observed soil conditions during and weight for kaolinite statically compacted in the labora­ after compaction. This paper describes an extension to existing soil com­ tory. Such an explanation should be complete enough paction models and uses it to explain the behavior of kaolinite com­ pacted in the laboratory by static pressures under conditions of no lateral to explain the condition of the soil before compaction, strain. The experimental investigation included an examination of the the interactions within the soil mass during compaction, kaolinite aggregations at the compaction moisture content but before and the observed behavior of the compacted soil. compaction. This was followed by the determination of the relation­ The model hypothesized was one in which the soil is ship between the net energy input during compaction and the compacted made up of macroscopic aggregations of clay particles. unit weight. Finally, constant-volume swelling-pressure measurements During compaction, it is the interactions of these aggre­ were made on selected compacted samples. The swelling pressures were gates, their deformation characteristics, and their monitored continuously after giving the samples access to water; the results are presented as swelling pressure versus time relationships. The ability to fit together in a compact mass that determine experimental results confirm the appropriateness of a deformable­ the end result unit weight for a given type of compaction aggregate soil model to explain the compaction of kaolinite as prepared and amount of effort. It is this same compacted macro­ in the laboratory and then compacted statically. The model is also structure-an assemblage of aggregates-that, to some appropriate for understanding the constant-volume swelling-pressure pat­ extent, determines the engineering behavior of the com­ tern that develops on wetting the compacted soil. pacted soil. The experimental approach was to study certain of the properties of the soil aggregates before compaction, The objective of the research described in this paper monitor the compaction effort, and then subject the 95 compacted samples to a test significant to engineering in number and, as the addition of water continues, the practice. The achievement of compaction was examined water will inevitably be unevenly distributed among the by calculating the energy required to densify the soil many aggregates and domains. Hence, domain­ continuously from a low unit weight to the final unit aggregate growth continues because the water-poor weight achieved for each sample. The correctness of domains are held at the water-rich sites on the surfaces the model was determined by analysis of existing re­ of the aggregates. sults, especially stress-strain and volumetric swelling, At some point during the mixing operation, the quan­ and from the results of constant-volume swelling­ tity of water on the surface of an aggregate may be large pressure determinations on the compacted samples. enough so that this water will exhibit, at least tempo­ [The relevant literature is reviewed elsewhere (!).] rarily, bulk water properties. Collisions and contacts among aggregates in this state will cause the aggre­ COMPACTION-MECHANISM gates to fuse due to capillary pressures caused by the HYPOTHESIS menisci developed near their points of contact; these fused aggregates will be called apparent aggregates. This paper attempts to explain the compaction of fine­ By this process, the apparent aggregates continue grained soils in terms of soil structure and changes in to grow as the water content increases. However, be­ it. The explanation is based in part on the results of cause of the shear strains developed within these previous investigators, principally Lambe (2, 3) and relatively large apparent aggregates as they collide with Olson (4), and on tests on a single commercial clay each other and the components of the mixture, they will (Edgar Plastic Kaolin) in a single compaction mode in time lose their indi victual identity. Thus, the effect (static). The hypothesis states the necessity of recog­ of the shear strains and their accompanying moisture nizing (a) that there are a number of fabric levels and redistribution is to cause a more-dispersed structure (b) that the stress history before compaction can strongly to occur within and among the domains. influence the compaction result. The postulated expla­ This characterization of the soil fabric is similar to nation for laboratory static compaction of kaolinite, from that described by Yong and Warkentin (5), who recog­ dry soil to the as-compacted state, is described below. nize the arrangement of clay particles as domains, the grouping of domains as clusters, and the arrangement Initial Soil Structure of clusters in peds. Many more fabric features, pri­ marily in naturally occurring soils, have been reported Before the addition of water to kaolinite, the layers of and are reviewed by Mitchell (6). However, the soil adsorbed water present on the particles are no more model used for this study appears to be the appropriate than a few molecules thick. In this state, many of the one for this laboratory-compacted soil. particles, each being many unit layers thick, are floc­ Thus, at the end of the mixing operation, the soil culated in face-to-face fashion due to Van der Waals' batch consists of aggregates and apparent aggregates over forces and, probably, hydrogen bonds (which had a large size range, having a considerable range of water developed as the Van der Waals' forces brought the content and a water state that varies from almost bulk particles closer together). Each group of face-to-face to tightly held in a thickness of only a few ·molecules. particles can be thought of as a domain. Depending on The water distribution within each aggregate (we will no the amount of hydrogen bonding, the adsorbed water will longer differentiate between aggregates and apparent more likely be found on the domain surface rather than aggregates) is not at equilibrium and can be expected being uniformly distributed around each flocculated to change with time and the pore water pressure is nega­ particle in the packet. Figure 1 presents an idealized tive, yet the degree of saturation of the aggregate is representation of the effects
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