GEOTECHNICAL ENGINEERING MEU
Department of Civil Engineering Spring 2014-2015
INTRODUCTION
What do we mean by soil?
Solid Particles + Voids ↓ ↓ Particulate gas and/or water uncemented or weakly cemented accumulation of mineral grains formed by weathering of rocks.
INTRODUCTION
Why it is important in civil engineering to study soil? Soil is an essential construction material in many civil engineering projects.
Soil supports structural foundations. Solving Problems such as cleaning up polluted soils, building on expansive soils, building retaining walls to support soil masses and how water would flow through earth dams needs a good study of soil behavior and a well understanding of its mechanical behavior.
INTRODUCTION
Soil Mechanics:
is the branch of science that deals with the study of the physical properties of soil and the behavior of soil masses subjected to various types of forces.
Soil Engineering
is the application of the principles of soil mechanics to practical problems.
Geotechnical Engineering
is the subdiscipline of civil engineering that involves natural materials found close to the surface of the earth. It includes the application of the principles of soil mechanics and rock mechanics to the design of foundations, retaining structures, and earth structures.
Particle Size Definitions Soil = Solid Particles + Voids ďƒ˜ Solid particles vary in size, shape, and mineralogy ďƒ˜
Amount of voids are influenced by the size, shape and mineralogy of solid particles.
Particle Size Definitions
Clay Mineralogy When to consider a material a clay mineral? It should posses all the following properties as pointed by R.Grim: Member of the Phyllosilicates family Develop plasticity when mixed with limited amount of water Less than 0.002 mm in size
Clay Mineralogy What are the building blocks of clay minerals structures? Two basic units: 1- Silica Sheet : consists of silica tetrahedron, in which one silicon ion is tetrahedrally coordinated with four oxygen atoms. Silica tetrahedron
→
Clay Mineralogy 2- Al- or Mg- Octahedral Sheet : consists of aluminium or magnesium ion octahedrally coordinated with six hydroxyls. Al- and Mg-Octahedron →
Clay Mineralogy 1- Silica Sheet : ďƒ˜
ďƒ˜
in this sheet each six silicon tetrahedrons associate with each other to form hexagonal network. These hexagonal networks extend in all direction of the plane of the bases of the silicon tetrahedrons.
Clay Mineralogy 2- Al- or Mg- Octahedral Sheet :
→ Mg
→ Al
Clay Mineralogy
There are three of the most important clay minerals:
Kaolinite Illite Montmorillonite
Clay Mineralogy 
Kaolinite : 1Silca sheet:1Dioctahedral (t:o) Shape : Platy and Hexagonal
Clay Mineralogy 
Illite: 2Silca sheet:1Dioctahedral (t:o:t)
Clay Mineralogy
Montmorillonite : 2Silca sheet:1Dioctahedral (t:o:t)
Exchangeable cations: Ca,Na,Mg,K
Clay Mineralogy
Isomorphous Substitution: substituting one kind of inos by ions of another type.
conditions:
-equal or different valence - Keeping (retention) of the same crystal structure.
Clay Mineralogy The surface charge of clay mineral particles carry a net negative charge due to: - Isomorphous substitution. - Disassociation of hydroxyl ions. - Broken bonds. - Absorption of water.
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