Basic Characteristics of Soils
Soil consists of different phases of solid, liquid, and gas and its characteristics depend on the interacting behavior of these phases, and on the stress applied. The solid phase includes clay, non-clay minerals, and organic matter. These elements are categorized by their size as clay, sand, and gravel. The liquid phase is composed of water that contains organic compounds available from chemical spills, wastes, and ground water, while the gas phase is normally air. The size, form, chemical properties, compressibility, and load carrying capability of the soil particles are determined by soil mineralogy, which is a science related with the chemistry, structure, and physical properties of minerals. The structure of a soil depends upon the arrangement of particles, particle groups, pore spaces, and the composition. These basic characteristics determine the type of structure to be built and what external support measures, if any, has to be taken to make the structure last long and bear the effects of earthquake, water seepage, and other external factors.
Consolidation of soils is also an important factor that needs to be studied to make strong and durable structures. Consolidation is a procedure according to which the volume of soils is reduced, by the application of a stress due to which the soil particles are packed together firmly, thereby decreasing the volume. With the removal of the stress, the soil will bounce back and recover some of the volume lost during the process of consolidation. While studying consolidation, the crucial factors to be analyzed are the rate of consolidation and the amount of consolidation. Another important factor is permeability of the soil. All the factors are closely associated with each other and they affect the overall design and construction process.
For instance, ff a structure is to be built on a soil with fine grains that have a low permeability, the flow of water through the soil voids will be less. Large water content in this soil may cause the structure to sink due to its weight. The process of consolidation in fine grained soils is slow. However, the extraction of pore water is simple in coarse grained soils since it moves freely within the region. The consolidation rate will be influenced by the soil history, nature of soil, and the load on the soil. Thus all the factors like water content permeability, consolidation, liquid limit are analyzed collectively.