This paper is a continuation of the work previously reported by Dahl, Handy and Davidson (1), and summarizes currently available information on properties of the Wisconsin loess. New areas of investigation are in northwest and eastern Iowa. Depth measurements and samples in the bluffs region were obtained mostly from the traverses of Hutton (2) and Davidson, et al. (3). Riggs (4) continued these traverses and the northwest-southeast traverses of Lyon, et al. (5), and established a grid-like sample pattern in southwest Iowa. Dahl (6) and Hansen (7) extended the grid eastward to the Mississippi River. Data on northwest Iowa was obtained from the east-west traverses initiated by Davidson (8)

Dahl, A. R.

Davidson, D. T.

Hansen, J. A., Jr.

English

University of Northern Iowa

Proceedings of the Iowa Academy of ScienceVolume 65 | Annual Issue Article 461958Further Studies of Loess in Iowa: Thickness, ClayContent, and Engineering ClassificationJ. A. Hansen Jr.Iowa State CollegeA. R. DahlIowa State CollegeD. T. DavidsonIowa State CollegeCopyright © Copyright 1958 by the Iowa Academy of Science, Inc.Follow this and additional works at: https://scholarworks.uni.edu/piasThis Research is brought to you for free and open access by UNI ScholarWorks. It has been accepted for inclusion in Proceedings of the Iowa Academyof Science by an authorized editor of UNI ScholarWorks. For more information, please contact scholarworks@uni.edu.Recommended CitationHansen, J. A. Jr.; Dahl, A. R.; and Davidson, D. T. (1958) "Further Studies of Loess in Iowa: Thickness, Clay Content, and EngineeringClassification," Proceedings of the Iowa Academy of Science: Vol. 65: No. 1 , Article 46.Available at: https://scholarworks.uni.edu/pias/vol65/iss1/46Further Studies of Loess in Iowa: Thickness, Clay Content, and Engineering Classification By J. A. HANSEN, JR., A. R. DAHL, and D. T. DAvrnsoN1 INTRODUCTION This paper is a continuation of the work previously reported by Dahl, Handy and Davidson ( 1), and summarizes currently available information on properties of the Wisconsin loess. New areas of in-vest:gation are in northwest and eastern Iowa. Depth measurements and samples in the bluffs region were ob-tained mostly from the traverses of Hutton (2) and Davidson, et al. ( 3). Riggs ( 4) continued these traverses and the northwest-south-east traverses of Lyon, et al. ( 5), and established a grid-like sample pattern in southwest Iowa. Dahl ( 6) and Hansen ( 7) extended the grid eastward to the Mississippi River. Data on northwest Iowa was obtained from the east-west traverses initiated by Davidson ( 8). LOESS THICKNESS A tentative map of Wisconsin loess thickness in western, southern, and eastern Iowa is shown in figure 1. From this map it is apparent that two areal distribution patterns in western Iowa are separated by the border between the Iowan-Tazewell and Kansan drift sheets. Loess thickness which is significantly greater south of this drift border, reaches a maximum depth of over 150 feet immediately adja-cent to the Missouri River floodplain. North of the drift border, adjacent to the Big Sioux River, the maximum depth of the loess is only about 25 feet. Because of the differences in the two areas, no attempt has been made to connect thickness contours. Figure 1 indicates a major thinning trend of the loess eastward from the Missouri River floodplain. In eastern Iowa there is a second thinning trend in which loess diminishes to the north and south of a contoured high located near the approximate terminus of the Iowan drift. 1 Research Assistant, Associate in Civil Engineering, and Professor of Civil Engineering, respectively, Engineering Experiment Station, Iowa State College, Ames, Iowa. 317 1Hansen et al.: Further Studies of Loess in Iowa: Thickness, Clay Content, and EnPublished by UNI ScholarWorks, 1958318 IOWA ACADEMY OF SCIENCE [Vol. 65 L,.qe•11J -- W15cons1n dr1f• tlod•• C M Cory-Mankato I Iowori T Tazewell -15- Th1ck11ess contour Isololed lh1ckness contour Flood plain Figure I. Map showing thickness of Wisconsin loess. CLAY CONTENT The percent of minus 5 m:cron clay in the C-horizon loess is shown in Figure 2. 2 Clay content increases eastward from the Mis-souri River and is at a maximum in south-central Iowa. Clay content decreases to the northeast from the maximum area shown by the 45 percent contour, reaching a minimum within the 20 percent con-tour. North and east of this area, clay content again increases toward the Mississ'.ppi River. From a comparison of figures 1 and 2, a generalization may be made that as loess thickness decreases, clay content increases. (Fig-ure 4). This seems to agree with previous investigations conducted by Davidson, et al., (9), Simonson, et al., ( 10), and Ruhe, ( 11). MAPS Both the loess thickness and clay content maps must be considered as tentative although nearly 200 sample sites were analyzed for each. Few samples have been obtained within the area of the Iowan drift east of the Cary-Mankato lobe. Since contour accuracy depends on the frequency of control, occasionally it becomes necessary to locate approximate boundaries by means of dashed lines. Ruhe ( 11) has shown that loess thickness varies significantly with respect to topographic position, commonly thinning below crests of divides in an east-west direct'.on. Primary consideration was given to data representing sample sites known definitely to be located at or near the crest of topographic highs. Equal importance was at-2Analyses by hydrometer method (ASTM Designation D 422-54T) 2Proceedings of the Iowa Academy of Science, Vol. 65 [1958], No. 1, Art. 46https://scholarworks.uni.edu/pias/vol65/iss1/461958] FURTHER STUDIES OF LOESS 319 tached to sample locations designated or observed to be located on the very flat terrain of the uplands. It is hoped that erosion effects may be reduced by the use of samples so chosen. ENGINEERING CLASSIFICATION Classification of the loess for engineering purposes is indicated in figure 3 following the standards of the American Association of High-way Officials ( 12). Samples representing C-horizon loess were ob-tained at depths which ranged from around 60 feet near the bluffs bordering the Missouri River flood plain to as little as two to four feet in south-central Iowa. Seven major soil groups have been proposed by the AASHO. As indicated by figure 3, loess falls into the A-4, A-6, and A-7 groups. The general description of the A-4, A-6, and A-7 groups is as follows: Legend - r--- Wisconsin drift border C-M Cciry ·Mankato I Iowan T Tazewell "'2!1-5 Micron cloy content ~ Flood plain Figure Z. Map of Wisconsin loess clay content. Group A-4. This group contains nonplastic or moderately plas-tic silty soil usually having 7 5 percent or more passing the No. 200 sieve (74 microns). Mixtures of fine silty soil and up to 64 percent of sand and gravel retained on the No. 200 sieve are also included. Group A-6. Group A-6 contains plastic clay soils usually having 7 5 percent or more passing the No. 200 sieve. Mixtures of fine clayey soil and up to 64 percent of sand retained on the No. 200 sieve are included. Group A-7. Plastic clay soils similar to those in Group A-6, but having higher liquid limits, make up Group A-7. The soils may occasionally be elastic as well as subject to high volume changes. 3Hansen et al.: Further Studies of Loess in Iowa: Thickness, Clay Content, and EnPublished by UNI ScholarWorks, 1958320 IOWA ACADEMY OF SCIENCE [Vol. 65 Soils of several major groups are subdivided on the basis of tex-ture, liquid limit, and plasticity index. All groups are further di-vided by means of a numerical group index, a feature intended to place a relative index of performance upon individual soils within a group. In this report, only the major group designations are used. Figure 3. Map showing engineering classification oi \Visconsin loess. Note traverses A-A and B-B. Clay content has a direct relation to plasticity (13, 14). In west-ern Iowa in the narrow band which parallels the flood plain, clay content is 2 S percent or less, and the plasticity index of most samples is less than 10. These samples are included in the A-4 group. As clay content increases, the plasticity index usually is greater than 10. This area is shown by the A-6 band. Proceeding further east and southeast the clay content reaches a maximum (see figures 2 and 4) and it is within the area designated A-7 that liquid limits and plas-ticity indices are greatest. Samples obtained in southeast Iowa indi-cate a second broad A-6 area extending towards the Mississippi River. ACKNOWLEDGMENTS The subject matter of this report was obtained as part of the re-search being done under Project 283-S of the Engineering Experiment Station of the Iowa State College. This project entitled, "The Loess and Glacial Till Materials of Iowa; an Investigation of Their Physi-cal and Chemical Properties and Techniques for Processing Them to Increase Their All-Weather Stability for Road Construction,'' is being carried on under contract with the Iowa Highway Research 4Proceedings of the Iowa Academy of Science, Vol. 65 [1958], No. 1, Art. 46https://scholarworks.uni.edu/pias/vol65/iss1/461958] z 0 1-cn 0 a.. :E 0 (.) .....J <( a: ::::::> I-x LaJ I-CD ID .. • o~ u ;; i c_ O-U') ;.C:'f:i: c C( ~ ~ .. -3: = "' .. .. . -~ 0 .. "'.,, .. = _ O ~,..._o .,,. u en . on " C( ..J ... ... c ~ " .. .... . "5 ~ 0.,, "'-,,, ~~';-;: 0 C( ...... ...... cc ·- " a: ~" FURTHER STUDIES OF LOESS .., c .. ... .. ...J c e u e on c .. = .. .. .! c c ~ ~ u u ·e-e on .. ;jt-.c c - .. ~ .c ,. _ :'.! ~ .... 0 -~ u-U) 321 c ~ 0 • ~ -u. e~ ;!: e CN .. .c c - .. ~ .c .. -.. ~ g~ u_ I .., c 0 U) Ill Figure 4. Textural composition of six loess samples with depth obtained along traverses A-A and B-B, showing relationship of loess thickness to clay content and engineering classification. 1 Board (Project No. HR-1) and is supported by funds supplied by the Iowa State Highway Commission and the United States Bureau of Public Roads. 5Hansen et al.: Further Studies of Loess in Iowa: Thickness, Clay Content, and EnPublished by UNI ScholarWorks, 1958322 IOWA ACADEMY OF SCIENCE [Vol. 65 Literature Cited 1. Dahl, A. R., Handy, R. L., and Davidson, D. T. 1957. Variation of loess thickness and clay content in southern Iowa. Iowa Acad. Sci. Proc. 64: 393-399. 2. Hutton, C. E. 1948. Studies of loess-derived soils in southwestern Iowa. Proc. Soil. Sci. Soc. Am. 12 :424-431. 3. Davidson, D. T., Handy, R. L., and Chu, T. Y. 1953. Depth studies of the Wisconsin loess in southwestern Iowa: I. Particle-size and in-place density. Iowa Acad. Sci. Proc. 60:333-353. 4. Riggs, K. A., Jr. 1956. Pleistocene geology and soils in southern Iowa. Ph.D. thesis, Iowa State College Library, Ames, Iowa. 5. Lyon, C. A. 1955. Petrography of four northeastern Iowa !oess samples. M.S. thesis, Iowa State College Library, Ames, Iowa. 6. Dahl, A. R. Petrography of till and loess, south-central Iowa. M.S. thesis, Iowa State College. (In preparation). 7. Hansen, John A., Jr. Geologic and engineering properties of loess and till, southeast Iowa. M.S. thesis, Iowa State College. (In preparation). 8. Davidson, D. T. Unpublished data. Engineering experiment Station, Iowa State College, Ames, Iowa. 9. Davidson, D. T., and Handy, R. L. 1952. Property variations in the Peorian Ioess of southwestern Iowa. Iowa Acad. Sci. Proc. 59:248-265. 10. Simonson, R. W., Rieken, F. F., and Smith, G. D. 1952. Understanding Iowa Soils. Dubuque, Iowa, Wm. C. Brown Company. 11. Ruhe, R. V. 1954. Relations of the properties of Wisconsin loess to topog-raphy in western Iowa. Amer. Jour. Sci. 252:663-672. 12. American Association of State Highway Officials. 1950. Standard Specifi-cations for highway materials and methods of sampling and testing, Part I. Specifications. The Association, Washington, D. C. 13. Davidson, D. T. and Handy, R. L. 1953. Studies of the clay fraction of southwestern Iowa loess. 14. Sheeler, J.B. and Davidson, D. T. 1957. Further correlation of consistency limits of Iowa Ioess with clay content. Iowa Acad. Sci. Proc. 64 :407-417. loWA ENGINEERING EXPERIMENT STATION IowA STATE COLLEGE AMES, IowA 6Proceedings of the Iowa Academy of Science, Vol. 65 [1958], No. 1, Art. 46https://scholarworks.uni.edu/pias/vol65/iss1/46

Further Studies of Loess in Iowa: Thickness, Clay Content, and Engineering Classification

Name not available

https://scholarworks.uni.edu/cgi/viewcontent.cgi?article=2734&amp;context=pias

Further Studies of Loess in Iowa: Thickness, Clay Content, and Engineering Classification

Abstract

Similar works

Full text

Available Versions

University of Northern Iowa

Name not available