Soil :

Introduction : - 

    •  the term 'soil' has different meaning in different scientific fields.  it has the originated from latin word Solum . 
    • To an agricultural scientist, it means "the loose material on the earth's crust consisting of disintegrated rock with an admixture of organic matter, which supports plant life".
    • Soil may remain at the place of its origin or it may be transported by various natural agencies. It is said to be 'residual' in the earlier situation and 'transported' in latter. 
Soil  mechanics:- 
    • Soil mechanics is the study of the engineering behavior  of soil when it is used either as a construction material or as a foundation material. this is a relatively young discipline of civil engineering, systematised its modern from by Karl Von Terzaghi , who is rightly regarded as the "Father of Modern oil Mechanics"
    • Father of Modern soil Mechanics   -  Karl Von Terzaghi 

    • According to him "soil Mechanics is the application of the laws of mechanics and hydraulics to engineering problems dealing with sediments and other  unconsolidated accumulations of soil particles produced by the mechanical and chemical disintegration of rock regardless of whether or not they contains an admixture of organic constiuents"

Fields of application of soil mechanics :

        The knowledge of soil mechanics has application in many field of civil engineering.

  • foundations : 
        the loads from any structure have to be ultimately transmitted to a soil through the foundation for the structure. This , the foundation is an important part of a structure , the type and detail of which can be decided upon only with the knowledge and application of the principles of soil mechanics.

  • Underground and earth retaining structure :
            underground structure such as drainage structure , pipe line ,and tunnels and earth retaining structures such as retaining wall and bulkheads can be designed and construction only by using the principles of soil mechanics and the concept of  'soil structures interaction'.
  • Pavement design :
        Pavement design may consists of the deign of  flexible or rigid pavement. Flexible pavements depend more on the subgrade soil for transmitting the traffic load. Problems peculiar to the design of pavements are the effect of repetitive loading ,swelling and shrinkage of sub soil and frot action.

  • Excavations, Embankments and dams:-
Excavations require the knowledge of slope stability analysis; deep excavations may need temporary support- 'timbering' or 'bracing,'  the design of which requires knowledge of soil mechanics. Knowledge of slope stability, of seepage, consolidation and consequent settlements as well as compaction characteristics for achieving maximum unit weight of the soil in situ is absolutely essential for efficient design and construction of embankments and earth dams.

Soil Formation : -

Soil is formed by the process of weathering of rocks, that is disintegration and decomposition of rocks and minerals at or near the earth surface through the action of natural or mechanical and chemical agents into smaller and smaller grains. 
The factors of weathering may be atmospheric, such as changes in temperature and pressure; erosion and transportation by wind, water and glaciers; chemical action such as crystal growth, oxidation, hydration, carbonation and leaching by water especially rainwater with time. 
Soil formed by mechanical weathering (that is, disintegration of rocks by the action of wind, water and glaciers) bear a similarity in certain properties to the mineral in the parent rocks, since chemical change which could destroy their identity do not take place. 
It is to be noted that 95% of the earth's crust consists of igneous rocks and only the remaining 5% consists of sedimentary and metamorphic rocks. However, sedimentary rocks are present on the 80% of the earth's surface area. Feldspars are the mineral abundantly present 60% in igneous rocks. 
'Leaching' is the process where by water soluble parts in the soil such as calcium carbonate, are dissolved and washed out from the soil by rainfall or percolating substances water 'Laterite' soil, in which certain areas of Kerala abound, is formed by leaching.