CHAPTER 15 MATERIALS TESTING: SOIL AND CONCRETE

CHAPTER 15 MATERIALS TESTING: SOIL AND CONCRETE In previous chapters of this TRAMAN, you studied the importance of many and various con- struction materials. However, one material that was not discussed was SOIL which, as you will learn in this chapter, is perhaps the most impor- tant material of all. Just as a poorly constructed and weak concrete foundation will not support a building, neither will a poorly “constructed” and weak soil, since the ultimate foundation for any road, airfield, building, or other structure is the natural earth upon which it is built. During this chapter you will learn what soil is. You will learn the different types of soil you might encounter. You will also learn the basic properties and characteristics of soil and the importance those characteristics play in deter- mining the adequacy of a soil for use as a con- struction material. In addition, you will learn how to collect (sample) soil for testing purposes and how to perform certain tests that you, as an EA3, will be responsible for performing. Most impor- tantly, you will learn why those tests are per- formed and their importance in properly and correctly identifying and classifying the many types of soil that exist in nature. Finally, this chapter begins your studies of concrete testing. In this chapter you will learn what the various tests are and the purpose and importance of those tests. You will learn how to perform certain tests and how to prepare concrete samples for other tests that will be performed by more senior EAs. SOIL ORIGIN As defined by Webster’s New World Dic- tionary, soil is the surface layer of the Earth that supports plant life. While that is certainly a correct definition and one that is perfectly satis- factory to many groups of people, it lacks the precision required by the civil engineer and soil technician. A more precise definition is that soil is a mixture of uncemented or loosely cemented mineral grains enclosing various sizes of voids that contain air (or other gases), water, organic mat- ter, or different combinations of these materials in varying amounts. The importance of under- standing this definition will become obvious as you progress through this chapter; but, first, let us consider where soil comes from. SOIL FORMATION The formation of soil is a continuous process that is still in action today. Basically, the Earth’s crust consists of rock, which geologists classify into three groups: igneous, which is formed by cooling from a molten state; sedimentary, formed by the accumulation and cementing of existing particles and remains of plants and animals; and metamorphic, formed from existing rocks that have been subjected to heat and pressure. When exposed to the atmosphere, this rock under- goes a physical and chemical process called WEATHERING, which, over a sufficient length of time, disintegrates and decomposes the rock into a loose, incoherent mixture of gravel, sand, and finer material. It is this process that produces soils of various designations. RESIDUAL SOIL Any soil that results from weathering in place, and that is not moved during the weathering pro- cess, is called a RESIDUAL soil. A mantle of residual soil reflects the characteristics of the underlying parent rock from which it was derived. TRANSPORTED SOIL When the forces of nature cause the mantle of soil to be moved to a place other than that of its origin, the soil becomes a TRANSPORTED soil. One of these soils often bears properties in- duced by its mode of transportation. The chief agents of transportation are water, wind, ice, and the force of gravity. 15-1