Soil Mechanics(CENG-2202) Chapter 1 : Introduction - 1 - Department of Civil Engineering, Faculty of Technology Addis Ababa University 1. INTRODUCTION 1.1 DEFINITIONS The definition given to the word soildiffers from one discipline to another. To a geologist, soilis the material found in the relatively thin surface region of the earth's crust where roots of plants occur. For the agriculturalist on the other hand, soilis the top thin layer of the earth where organic forces are prevalent and which supports plant life. Moreover, soilrepresents the products of past surface processes to a geologist while it denotes currently occurring physical and chemical processes to the agriculturalist. The engineering definitions of soilis however quite different from those given in geology and soil science. Eventhough there is still no official and conventional definition of the word soilin Civil Engineering the following have been suggested. •Soil is the uncemented aggregate of mineral grains and decayed organic matter (solid particles) with liquid and gas in the empty spaces between the solid particles. •Soil is the portion of the earth's crust which can be separated by gentle mechanical means and excavated without blasting. •Soil is a natural aggregate of mineral grains, loose or moderately cohesive, inorganic or organic in nature that could be separated by means of simple mechanical processes and is thus distinguishable from a rock, which is a natural aggregate of minerals connected by strong and permanent cohesive forces. •Soil is any uncemented or weakly-cemented accumulation of mineral particles formed by weathering of rocks, the void space between the particles containing water and/or air. Soil Mechanicsis a branch of Civil Engineering that deals with the application of mechanics and hydraulics to engineering problems dealing with sediments and other unconsolidated accumulation of solid particles produce by the mechanical and chemical disintegration of rocks regardless of whether or not they contain and admixture of organic constituents. It is one of the youngest and fast developing fields of engineering that deals with the application of soil science, the laws of statics and dynamics and the principles of mechanics and hydraulics to understand the behavior of and use of soil as and engineering material. Structures such as buildings and bridges are eventually supported on soil. Soil is also used as a construction material as in the case of dam and highway embankments. Tunnels are burrowed
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