28 state occur in most tropical countries. onable assurance of safety. Figures 13 and 14 illustrate these in Puerto On the good side of the record, it is Rico. Each landform has its strength and certain that most limestones furnish one weaknesses, and hy identifying the land- of the best and most extensively used form and knowing its traits, a better job aggregates. With the exception of the of engineering can be done. In this way, very cherty limestones, it forms a de• the risk can be calculated with some reas• pendable and high quality material. ENGINEERING SIGNIFICANCE OF SAND AREAS' INTERPRETED FROM AIRPHOTOS A. Morgan Johnson, HiD, 4ssociate Professor of Civil Engineering Ylayne University The investigation summarized here was ment, drainage characteristics, texture, established as a doctoral thesis in the in• plasticity, and topography. In the in• terpretation of soils by the use of aerial terests of economy it is necessary to de• photographs, the interpretation to include velop rapid means of identification of both engineering mapping and analysis of soil types and of characteristics. Until highway problems associated with the types the recent advent of the techniques of air• of soils classified. It was attempted to photo soils interpretation, no rapid method interpret the complex patterns of the air- of soils mapping had been developed. To photos of northwest Indiana--patterns which the skilled interpreter, the aerial photo• have been made ccoiplex by the large variety graph, combined with a knowledge of the of glacial and post-glacial deposits which general development of the area being have provided the parent material for the studied and of some of the basic concepts developments of the soils of the region. of pedology, as well as a familiarity with All or portions of twelve counties were methods of soils engineering, is a rapid mapped, using airphotos, in the belief that method of obtaining knowledge of the engi• a good knowledge of the soil types of an neering characteristics of the soils of area is the basis of good highway design an area. in that area. Consequently, the area was The basic techniques of airphoto inter• studied both from the standpoint of de• pretation of soils have been described in veloping techniques of mapping engineering the past (1,2). They include acquaintance soils from aerial photographs and from the with geological developments and processes standpoint of determining applications of in the area being studied and with pedo- the knowledge of the mapped soils to prob• logical information as to profile develop• lems of highway design and construction. ment, erosion, and vegetative cover. Study Studies of pavement performance were made of broad areas is combined with stereos• during the spring breakup and during the copic examination of matching prints to sumner season to correlate soil types with determine the details of the surface feat• the performance of both rigid and flexible ures, llie elements of the airphoto pattern pavements. (color tones, drainage, erosion, vegeta• Before the variable of soil texture can tion, topography, and land use) are uaei be applied to the performance of a hi^way, to bound soil areas on the basis of origin, it is necessary to know what the soils in• developoient, texture, topographic position, volved are—their origin, profile develop• climate, drainage and plasticity. An im- 29 portant factor used in airphoto mapping is many areas. Many of these have been re• the concept that any given pattern will be ported in part and some have established changed if other deposits are accumulated strong correlation between soil types and on top of the soil of that pattern. The pavement performance (3,4,5). "Iliere are amount of modification depends upon the many factors which may affect the perfor• amount and nature of the overburden. The mance of a particular section of concrete complex patterns of northwest Indiana pavement; coarse aggregate, fine aggregate, proved to be modifications of the more mix design, construction procedures, joint standard patterns and could be worked out design, subgrade, base, drainage, and by a process of reasoning following careful others. A similar list of factors can be observation of the elements of the patterns. developed in regard to flexible pavements. Consequently, isolating one of these fac• Many states have realized that in their tors and successfully correlating it with highway system they have an extensive field pavement performance is not a simple task, research laboratory, and large-scale per• but it has been handled with apparent suc• formance surveys have been undertaken in cess in at least some areas. LAKE STATE OF MICHIGAN MICHIGAN OSEPH CALUMET LAPORTE LACUSTRINE s STEUBEN LAKE PORTER MORAlNAi:I ^ AKEISECTION ftJlK STARKE ARSHALC® PULASKI JASPER NEWTON WHITE BENTON TIPTON CARROL TILL PLAIN Figure 1. Physiographic Divisions and Federal Highways in Northwest Indiana 30 as*! rULTOM CO Figure 2. Typical County Engineering Soils Map. This soils map is of Starke County in Indiana in the Kankakee basin. It is typical of the several counties which have the Kankakee River for their northern boundary. The soils are largely of lakebed development except for a small area of outwash gravels in the northeast corner and an area of semi-plastic drift in the southeast por• tion of the county. Eight soils were mapped m this county and the detail is representative of that which can be obtained from airphotos. AREA AND ME1HGD6 been covered once or more by the glaciers and their heterogeneous deposits of drift. Seventeen counties in northwest Indiana The northern part of the state lies within were surveyed in order to map the sand the bounds of the last great advance of the areas described in this report. TTiey fall glaciers—Late Wisconsin--so that the soils within the region known physiographically and topography of that part of the state as the Northern Moraine and Lake Section, are almost wholly controlled by the glacial a region bounded on the south by the Tipton deposits and some subsequent development. Till Plain. Three of the divisions of the In the Valparaiso Moraine section and the section are involved in the area studied, Steuben Morainal Lake section the surface illustrated in Figure 1. These are the deposits are those of the glaciers--the Calumet Lacustrine section, the Valparaiso Valparaiso Moraine being the most promi• Moraine section, and the Kankakee Lacus• nent terminal moraine of the Michigan lobe trine section. "Die Steuben Morainal Lake of the glacier and the deposits in the section borders the area studied on the Steuben area being those of the Erie and east. The major portion of Indiana has Saginaw lobes. Hie rolling hills of the 31 terminal moraine are the predominant feat• ures of the topography in these areas. Actual till plains are rather rare in this section of Indiana. In the Lacustrine sections, the deposits are those which were laid down by running or impounded waters during and following the time of the gla• ciers. The entire region is so comparatively young that with the possible exception of sand dune formation there have been no great natural changes in topography since the respective deposits were laid down. Drainage developments and erosion have been relatively scant. Other surface changes have been wrought by the efforts of man in the past hundred years. Hiese are vegeta• tion, construction of highways and rail• roads, and artificial drainage of many of the swampy areas. The Calumet Lacustrine section is the former lakebed of glacial Lake Chicago—an extension of Lake Michigan --and is marked by several prominent beach ridges, plastic and sandy lacustrine de• posits, swamps, and the more recently de• veloped prominent dunes bordering Lake Figure 3. Airphoto of Large Flat Areas of Michigan. The Kankakee Lacustrine section Sands. This pattern of flat-lying sands in embraces a large area lying south of the Jasper County, Indiana, has been modified Valparaiso Moraine. It centers about the by wind-swept sands, both active and sta• Kankakee River which at one time carried bilized. The white spots are currently vast quantities of glacial waters and when shifting sands whereas the patches of trees dammed up to the west in Illinois, impounded mark dunes which have become stable. The water over a large area, giving rise to the main area shows the very flat topography deep sand deposits which cover much of the and uniform light-gray color tones of the basin. Extensive areas of outwash materials flat sand areas. There is almost complete occur about the borders of the basin and to lack of natural surface drainage but the the north and east. Artificial drainage has area has been ditched to lower the water lowered the water table in most of the table. sandy basin reclaiming a vast swamp for productive pursuits and drying the surface a particularly fruitful one for performance sands to the extent that many active dunes studies. have been and are being formed. Mapping was conveniently done in units Many prominent federal highways from the of counties. A mosaic of the prints of Chicago area fall within the area studied the county was assembled on a board and and other important east-west and north- studied. After a preliminary understanding south highways were available for perfor• of the area and its soils had been developed mance studies as well as many state high• and after preliminary approximate bound• ways and surfaced roads of lesser impor• aries had been lightly marked on the prints tance. The US highways crossing the area where it seemed possible to make an early are also shown in Figure 1 and include US prediction, the prints were examined ster- 6, 12, 20, 24, 30, 31, 33, 35, and 41.