Soil Mechanics concerns with the engineering mechanics and properties of soil .It applies the basic principles of mechanics of materials, fluid mechanics and hydraulics to soils. The founder of soil mechanics is Austrian born American professor Karl Terzaghi. The knowledge of soil mechanics has immense importance and vast application to the design and construction of various civil engineering structures. Some of prominent subjects are:
- Foundation of structure:
It deals with type, dimension and details of foundation on the strength and deformation characteristics and supporting soil.There two design criteria for foundation of a structure.They are bearing capacity & settlement of soil.
Fig: 1the leaning tower of Pisa, example of soil settlement.
- Earth retaining and subterranean structures:
The loading on the structures like underground pipelines,tunnels,earth retaining structures,sheet piles,bulkheads etc.is estimated by the properties and behavior of soil of their environment.
- Embankment, excavation and dam:
Construction of earth embankment and excavation requires knowledge of slope stability involving the soil behavior. Deep Excavations often need bracing for their stability; dams are designed against stability and seepage considerations. All these require the knowledge of soil mechanics.
The design of either a rigid or flexible pavement depends mostly on the behavior of subgrade soil in relation to settlement, swelling, repetitive loading, frost action etc.
- Soil subsidence, Soil heave, Frost action, Soil erosion, Shrinkage and Swelling:
These are the special problems affecting the design of foundations of any civil engineering structures which can only be looked to with the relevant knowledge of soil mechanics.
Formation Of soil:
Soil is a product due to disintegration and /or decomposition of rocks and organic matters, the process is known as weathering. The earth’s crust consists of both rock and weathered rock (as soil) up to an approximate depth of 20 km. A rock has variable properties and is formed of mixture of several minerals. Minerals have fixed properties and are formed of several chemical elements.
- Effective stress:
To know the mechanics of soils it is important to know the amount of normal stresses and shear stresses shared by the three phases of soil. Soil provides shear resistance by the frictional force and interlocking of the particles. This frictional force depends on the inter-granular contact stresses between soil particles. On the other hand, normal stresses are shared by the water, air and the soil particles.
Fig.: 2 Effective stresses
- Capillary action:
Water tens to rise up through a small capillary tube above a free surface of water because of surface tension. Water will rise up above the water level through the very small pore spaces within the soil particles in this way.
Keywords:effective stress, foundation, settlement of soil, seepage, capillary action.