1.1. Definition of soil
1.2. Soil Mechanics
1.3. Importance of soil mechanics
1.4. Origin of soil, formation of soils, Transportation of soils
Definition of soil
Soil is an unconsolidated and particulate material composed of solid particles formed by decomposition or disintegration of rocks.
Soil compose of solid matter and voids, the voids between the particles is occupied by water and air.
In short , Soil = Solid + Void
or, Soil = Solid + water + air
Soil Mechanics
Soil mechanics is the scientific field of civil engineering which deals with the properties, behaviours and performance of soil as structural material. It focuses on understanding the physical, mechanical and hydraulic properties of soil and their influence on the stability and performance of structures.
Terzaghi in 1925 states that, “Soil mechanics is the application of laws of mechanics and hydraulics to engineering problems dealing with sediment and other unconsolidated accumulations of solid particles produced by the mechanical and chemical disintegration of rocks, regardless whether or not they contain admixture of organic constituents’’.
Objectives of Soil Mechanics
- To perform soil engineering survey.
- To develop soil sampling devices and methods.
- To investigate the effects of various factor on soil including static and dynamic loads.
- To analyze and interpret soil test and classify the soil.
- To formulate the empirical method of designs used in foundation engineering.
- To create different soil testing equipment and soil testing methods.
Origin and formation of soil
Soil is a most outer soft layer of earth, formed by different process which is generally called soil forming process. The topmost layer of the earth’s crust contains soil, a porous biologically active medium. Soil is an accumulation of unconsolidated sediments and deposits of solid particles as a result of rock breakdown. Rocks are a naturally occurring collection of minerals that are bound together by strong attraction forces and are regarded as consolidated materials.
Soil is a naturally occurring unconsolidated particle. The process of formation of soil is called pedogenesis. Following are the process of formation of soil :
1.Degradation
2.Transportation
3.Deposition
Degradation
Degradation is divided into three process. The process are; weathering, mass wasting and Erosion.
Weathering : The breakdown or dissolution of rocks and minerals on earth’s surface into soil is called weathering. There are three types of weathering; physical, chemical and biological.
Mass wasting: The movement of rock and soil downslope under the effect of gravity is known as mass wasting. Water may be present to perform the functions of a lubricant and a minor carrier, but its presence is not required for the process. There are many different types of mass wasting, including rock falls, slumps, and debris flows.
Erosion: The geological process of erosion is the wearing away and transfer of earthen materials by natural forces such as wind and water. Erosion can be caused by a variety of natural processes. Rock fragments usually suffer a slow but steady deterioration that causes them to break up into ever smaller pieces. A significant part of the deterioration process is played by the grinding, banging, and bouncing that occurs while the item is in transit.
Transportation
Rock fragments and materials that dissolve in water are the products of the process of degradation. In most cases, the resulting fragment is carried away by physical agents and transformed into clastic sediments. As a result of rock breaking up and fragmenting over time due to natural processes, smaller particles become easier for nature to move around. Working and reworking under the influence of wind, water, ice, and gravity is what makes the transportation effort possible.
Colluvial soil – transported by gravity
Alluvial soil – transported by moving water
Aeolian soil – action of wind
Lacustrine soil – deposits made in lakes
Glacial soil – transported by glaciers
Deposition
Deposition is the geological process in which sediments, soil and rocks are added to a landform or landmass Wind, ice, water, and gravity transport previously weathered surface material, which, at the loss of enough kinetic energy in the fluid, is deposited, building up layers of sediment.
This occurs when the forces responsible for sediment transportation are no longer sufficient to overcome the forces of gravity and friction, creating a resistance to motion.