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What is Soil Mechanics?

written by: Tarun Goel • edited by: Lamar Stonecypher • updated: 9/30/2011

Soil is formed in layers due to the physical, chemical, and biological processes that include transformation of soil materials. Soil mechanics is basically the study of soil and its properties in regard to construction purposes.

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    What is Soil Mechanics?

    Soil mechanics is a discipline of civil engineering that predicts the soil performance characteristics utilizing the engineering techniques of dynamics, fluid mechanics, and other technologies. Soil mechanics includes the study of soil composition, strength, consolidation, and the use of hydraulic principles to deal with issues concerning sediments and other deposits. Soil mechanics is one of the major sciences for resolving problems related to geology and geophysical engineering. Soil mechanics studies are very important for civil engineers because based on the findings of soil mechanics studies, engineering structures are constructed. The type of construction, type of equipment to be used, type of foundation, support material, and many other aspects of construction works are largely affected by the soil mechanics studies. Basically we study about soil formation modes, physical and chemical properties of soil, dynamic loading of soils, permeability, consolidation, etc. In the subsequent sections of this article, we will discuss in detail about major aspects of soil mechanics studies.

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    Formation of Soils

    Soil is a combination of minerals and organic elements that are in solid, gaseous, and aqueous form. Soil consists of particle layers that are different from the original materials in their physical, mineralogical, and chemical properties because of the interactions between the atmosphere and hydrosphere and other reasons. The particles of the soil are created from broken rocks that have been changed due to the chemical and environmental effects, including weather and erosion. Particles of soil are filled loosely, creating a soil formation that consists of pore spaces. Studying soil formation modes is important because it helps in determining properties of soil. Cohesiveness, adhesiveness, acidity of soil, and other related factors can easily be determined by knowing about the type of soil w have to deal with. We cannot draw any concrete conclusions merely by conducting soil studies but we surely can narrow our research parameters by studying the basic characteristics of soil like color, texture, and nature of soil.

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    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.

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    Soil mechanics studies are used to determine lateral earth pressure, bearing capacity of soil, and conduct slope stability analysis. These studies always help a civil engineer to design and construct better structures and indirectly these studies help in risk mitigation too because if we know beforehand how the soil mass is going to behave, we can take precautionary measures at the time of construction itself.

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