Soil is an important construction material that is 1. Oldest. 2. Cheap or available free of cost many a times. 3. Most complex, yet having interesting properties. 4. Modified to suit the requirements, many a times. Soil is used 1. to manufacture bricks, Tiles or earthenware. 2. as foundation material. 3. to construct dams and embankments. 4. to fill hollow zones behind retaining walls, low lying areas etc. 1.2 Why soil is complex? The following properties of soil make it perhaps the most complex construction material. 1. Porous 2. Polyphasic 3. Permeable 4. Particulate 5. Heterogeneous 6. Anisotropic 7. Non-Linear 8. Pressure Level Dependent 9. Strain Level Dependent 10.Strain Rate Dependent 11.Temperature Dependent 12.Undergoes volume change in shear
Yet, soil possesses some Interesting properties that relate with human beings, namely, 1. 2. 3. 4. Colorful Sensitive Possesses Memory Changes its properties with time 1.3 What is Geotechnical Engineering? It is an integration of Physics, Earth Science, Solid Mechanics, Geology and Hydrogeology. Soil Mechanics provides the theoretical basis for describing the mechanical behaviour of earth materials. Geotechnical Engineering involves application of theory of soil mechanics to a variety of field problems. For most other engineering disciplines, the material properties are well-defined or can be controlled. But, in Geotechnical Engineering, material properties are highly variable and difficult to measure with a reasonable degree of accuracy. Geotechnical Engineering is among the younger branches of Civil Engineering. Yet, it has evolved over centuries. 1. Geotechnical Engineering is probably one of the most challenging engineering disciplines. 2. For a geotechnical engineer, no two days at work are going to be similar. 3. Geotechnical engineering expertise is required in a vast variety of disciplines that includes the oil and offshore industry. 4. Being a relatively new discipline, there is ample scope for innovation. 5. For a geotechnical engineer, achieving job satisfaction is never a problem. 6. Material properties must be measured for each new construction site. 7. Remember that geotechnical engineers deal with natural materials and there can be no quality control.
8. Ground consists of innumerable variety of particle sizes and minerals. 9. To make matter worse, engineering properties of earth materials are strongly influenced by their past geological history that is normally unknown. Climatic conditions also influence these properties. 1.4 Sub-branches in Geotechnical Engineering The following are the sub-branches of Geotechnical Engineering. 1. Foundation Engineering 2. Deep Excavation 3. Tunneling 4. Earth Pressure and Retaining Structures 5. Earth embankments 6. Stability of Slopes 7. Environmental Geotechniques 8. Earthquake Geotechnical Engineering 9. Ground Improvement technique 10.Rock Mechanics 11.Engineering geology
Fig. 2 represents the family of Geotechnical engineering. Foundation Engg Earthquake Geotechnical Engg. Environment al Geotechnics Deep Excavations Geotechnical Engg. Tunneling Retaining Structures Embankment s Slopes Fig. 2 : Family of Geotechnical Engineering 1.5 Distinctions between Fine and Coarse Grained Soils Soil can be broadly classified in to two types, namely Fine grained soil and coarse grained soil based on the size, shape and behaviour. Table 1 provides the important distinctions. Table 1 : Distinctions between Fine grained soil and coarse grained soil Fine Grained Soil Coarse Grained Soil Size of particle is less than 75 microns Size of particle is mores than 75 microns Silt & Clay belong to this group Sand, Gravel, Cobble, Boulder etc. belong to this group Properties are influenced by gravity Dense packing, particle to particle contact enable strength Mostly round, sub-round, angular Void ratio & water content can not be very high Consistency (liquid, plastic & shrinkage) limits are absent Properties are influenced by surface area Attraction and bonding between particles enable strength Mostly plate-like Void ratio & water content can be very high Possess consistency (liquid, plastic & shrinkage) limits