Archive for the Category ◊ What is Soil? How soil mechanics work? ◊

• Monday, May 10th, 2010

Just like other construction materials soils has its own scientific analysis with regards to its abilities on dealing with forces. Being the oldest construction and probably engineering material soil is one of the most complex fields in civil engineering to the point that when it comes to the factor of safety in design whatever has direct contact with soils, e.g. foundations, or soil based constructions, e.g. embankments, requires a significantly higher safety factor compare with other construction materials, i.e. the uncertainty in soil analysis and design is higher. These is most likely resulted from the way soil originates.

Usage of soil as the main element of construction goes back to the first civilization when Sumerian built Ur, first city in the history, on south of Mesopotamia near the mouth of Euphrates River. They used bricks to build their first houses and earlier they built embankments and dams to direct the water for irrigation. The Western history of recognition the soil as a main element goes back to Romans, in the first century B.C., when their engineers used the trial and error experiences to construct foundations.

After all today soil and rock are still one of the most important materials used in construction. It is used or on its natural state or with improvements, such as compaction, reinforcement and etc., as the main component such as in dams, embankments and highways or as supporter element in every construction, i.e. foundation support.

What is soil?

All soils originate directly or indirectly from rocks and these are classified according to their mode of formation.  By a combination of physical and chemical processes rock masses are reduced to particles ranging in size down to 0.001 mm.  Soils result when collections of these particles are re-deposited, often in bodies of water, and are compressed and consolidated by further depositions above.

The nature of the subsequent soil depends not only on its parent rocks, but also on the processes and conditions of disintegration, transport and deposition – and on time.   The properties of clay minerals are important, in particular their very flaky nature.

Understanding the formation and nature of soils is an important precursor to understanding their engineering properties and their behavior under load.

Soils are, in the main, naturally occurring materials.  Engineers and builders who use soils have to take them as they find them; soils cannot be manufactured to order in the way of other materials, such as steel and concrete.  Soils are also highly variable and complex materials, possessing engineering properties that may have a wide range of possible values. Thus, at the start of any design process soils must be accurately and systematically described; classification is part of description.  The main components of soil description are:

• The nature of the soil:                shape, size and distribution of particles

• The state of the soil:                 density, relative density, water content

• The fabric of the soil:                  homogeneity or layer sequences, cementing

Physical Properties of Soils:

The basic physical properties of soils are those required to define its physical state.  The three constituent phases (solid, liquid and gas) must be quantified and relationships between them expressed in numerical terms to enable changes in physical state be measured.  A soil model is used in which the solid phases (rock or mineral particles) has one unit of volume;  the volumes and masses of the water and content are then related to this unit solid volume.  Density or unit weight and water content are important measures of physical state.

Soil Mechanics:

Soil Mechanics is the numerical science using principles of engineering mechanics such as fluid mechanics or mechanics of materials that was first used by Coulomb, 1773, a member of French Royal Engineers, to solve soil problems. It studies and defines mainly terms such as, shear strength, permeability, angle of friction, Critical state, effective stress, consolidation, slope stability, earth pressure and etc. that the website will focus on their definitions as well as their applications on today’s civil engineering.