The Science of Soil Stabilization HANS F. WINTERKORN, Director, Soil Physics Laboratory, Princeton University This paper defines the science of soil stabilization and views soil systems from many different angles in order to lay the proper foundation for an understanding of the dillerent soils encountered by the engineer, of the desirable and undesir­ able properties of these soils, and of the possible supplementation of these pro­ perties in order to change the soils into construction materials. This intro­ ductory paper is limited to the pointing out of important fundamentals and also to the presentation of certain approaches and data that are not normally found in soil-stabilization literature. e THE science of soil stabilization is that physico-chemical, or chemical terms; (2) body of principles that explains and guides tl'anslation of the supplementary require­ the practice of soil stabilization. Soil sta­ ments into available materials and pro­ bilization, in its widest meaning, com­ cesses and decision on use of specific prises every physical, physico-chemical, method (or choice of method) on the basis and chemical method employed to make a of economy, practical feasibility, or spe­ soil serve better its intended engineering cial (military or other emergency) con­ purpose. In its specific meaning, as com­ siderations; (3) construction, cons,isting monly understood in highway and airport normally of comminution, mixing with engineering, soil stabilization is the name stabilizing material, and densification; and given to those methods of construction in (4) economic considerations relating to which soils are treated to provide base the total cost composed of cost of mate - courses, and occasionally surface courses, rials, construction, and maintenance for which can carry the applied traffic loads the service life of the structure. under all normal conditions of moisture There exists a tendency on the part of and traffic for an economic service life of laboratory workers to overlook the im­ the paved area. The paved areas may be portance of Items (3) and (4). This may roads, airport aprons and runways, park­ lead to a dangerous self-deception andmay ing and loading places, feeding courts or even impede the proper development of the other surface structures of comparable science of soil stabilization. This science stability and durability requirements. is not a pure but an applied one, and the The major established uses of soil sta­ actual processes of application must not bilization are: (1) lifting a countryor re­ only be considered but must be analyzed gion out of the mud or out of the sand for scientifically in order that the most ra­ better economic development, now espe­ tional and most effective, i.e., the most cially important for under-developed economical, method of construction be areas; (2) providing bases and surfaces used in each particular case. In many for secondary and farm-to-market roads, cases, the use of a chemical construction where good primary roads are already in aid may increase only slightly the cost of existence; (3) providing bases for high­ stabilizing materials but decrease greatly type pavements where high-type rock and the cost of construction by facilitating the crushed gravel normally employed for mixing and compaction process. such bases are not economicallyavailable; (4) for city and suburban streets where the noise-absorbing and elastic properties of SOILS AND THEIR PROPERTIES certain stabilized soil systems possess The term "soil" covers a large variety definite advantages over other construction of materials existing under widely differ­ material:;;; and (5) for military and other ing conditions. For a thorough under­ emergencies where an area must be made standing of soils and their properties it is trafficable within a short period of time. well to look at them from different angles. Soil stabilization involves: (1) diagno­ A first step is to list definitions of the sis of the resistance properties of a given term soil as employed by different dis­ soil and required supplementation of these ciplines that deal intensively with the properties for the intended use in physical, material covered by this term. 1 2 . , DEFINITIONS OF THE TERM "SOIL" With respect to scientific content and general usefulness, the pedologic soil con­ Highway Engineering cept is the most important. It has resulted Soil consists of disintegrated rock and in a natural system of soil classification organic matter found on the surface of the and soil mapping which, though originally earth, the particles of which may range in qualitative, can be easily supplemented diameter from less than O. 0001 inch to a with semi-quantitative and quantitative few inches and in which the fines are a engineering information. General pedol­ product of natural, weathering forces. ogical soil maps exist for practically every Soil may or may not contain organic part of the world. For many localities, matter. Engineering soils include bank soil maps are available on a scale as low gravel, bank sand, blow and dune sand, TABLE l agricultural soils ranging from those of Size Fractions of Mineral Porllon~ of Solle predominatly sandy texture to colloidal ...... lnlnches InMll11ru~tn clays, and mixtures and combinations of these (1). Gravel .. o. oe 76.2 to 2.0 3-ln ~ lo No. 10 o.oa'·' 0. 002 l.O io o.05 No. 10 kl NO. 270 The different size fractions of the min­ Slit·~· 0. 002 .. 0. 0002 O. fl to o. 005 eral portions of soils are named and de - Cb.y <0.0002 .(0.005 Col~d• <0. 00004 .(o , 001 fined in Table 1. Textural classification of soil is based as one inch to the mile. on gradation. The scheme of classifica­ Pedological soil types can be rec­ tion and naming is shown by Figure 1. ognized easily from air photographs (7) and certain conclusions with respect fo Geology soil stabilization can be drawn solelyfrom recognition of the pedological soil type of Soil is the superficial unconsolidated a certain area. The principal soil areas mantle of disintegrated and decomposed of the world are shown in Figure 2. The rock material, which when acted upon by climatic and vegetational soil types of the organic agencies, and mixed with varying United States are shown in Figure 3. The amomtts of organic matter, may furnish general and specific application of pedol­ conditions necessary for the growth of ogy to engineering is treated in detail by plants. In its broadest sense the term Wooltorton in the third paper of this "soil" has been used to include all the symposium. mantle of rock decay (~). SOIL AS A POLYDISPERSE SYSTEM Pedology Soil is a polydisperse system composed Soil is the climatically conditioned of (1) solid inorganic and organic par­ petrologic and biogenic transformation ticles, (2) an aqueous phase carrying product of the outermost.layer of the solid matter in solution (and sometimes in dis­ earth crust (3); it is a natural body, <lif­ persion), and (3) a gaseous phase of ferentiated into horizons varying in type varying composition. The gaseous phase and a.mounts of mineral and organic con­ is functionally related to biologic activity. $tituents, usually unconsolidated and of The aqueous and the gaseous phases are varying depths (4); soil is a unique crea­ usually considered together as pore space tion that differs from the parent material or porosity. The porosity varies in below in morphology, physical properties amount and in dimensional and form char­ and biologic characteristics; and the soil acteristics from soil to soil, from layer mantle of the earth may be termed "the to layer, and in the surface layers from pedosphere'' alongside tbe atmosphere, season to season. the lithosphere, and the hydrosphere (5). The pedologic soil is a dynamic system Characteristics of the Solid Phase subject to temperature, moisture, and biologic cycles and developing in a cer­ Soils as polydisperse systems may con­ tain genetic direction under the influence tain particles ranging from atomic size of climate. The rate of this development (10-8 cm) to gravel and stone size. Since is influenced by parent material, vegeta­ the soil information of greatest interest is tion, and human activity (6). found mostly in the international pedologic 3 literature it is indicated to use the accep­ cordance with the identification chart in ted international terms and definitions in Table 2; this was taken from Reference 8, presenting granulometric compositions. and a.lea represents international pedol­ oglc usage: Designation Diameter in mm Combining 'tile sut and cla.yfru:tions as silt-clay materta.l.s, we mar utablish Stones >20 three grO\IP• Gravel 20 - 2 major physical of 1neral Coarse sand 2 - 0. 2 sotls. Fine sand o. 2 - o. 002 Percentage Silt o. 02 - 0. 002 Designation aiJt~clay Clay <0.002 Granular soils 0 - 20 Materials larger than 0. 02 mm. are us­ Cohesive-~ranular 110ils 20 - 35 ually called granular; those smaller than Cohesive-non~ranular soil8 $5 - 100 O. 02 are called silt-clay materials. Soila During the early days of ._lcultural containing more than 65 percent of coarse chemistry it was qtttte common to make material are called granular soils; those gross chemical analyses of soils and soil containing more than 35 percent of silt materials. However, the analytical data and clay are called silt-clay materials. did not indicate the availability as plant food of the determined elements, nor were EXAMPLE• SOIL A they of diagnostic significance with respect SAHD-25'IO to other soil p.roperties of practical agri­ 811..T:-GD'IO CLAY-15 'IO cultural value. This type of analysis was succeeded by determination of plant-food values, on one hand, and of the granulo­ metryandmineralogyof the solid soil con­ stituents on the other hand. The recent introduction of nuclear mete!'S for dete!'­ minations in situ of soil moisture and soil density, and the possibility of further development for other puFposes of this type of methodology has given real sci­ entific and practical value to the "obsolete" data on elementary soil composition.