INTERIOR
STRUCTURE OF THE EARTH
The interior structure of the Earth is layered in spherical
shells, like an onion. These layers can be defined by either their chemical or
their rheological properties. Earth has an outer silicate solid crust, a highly
viscous mantle, a liquid outer core that is much less viscous than the mantle,
and a solid inner core.
Mantle
Earth's mantle extends to a depth of 2,890 km, making it the thickest layer of Earth. The upper mantle is divided into the lithospheric mantle and the asthenosphere. The upper and lower mantle is separated by the transition zone. The lowest part of the mantle next to the core-mantle boundary is known as the D″ layer.
Crust
The crust ranges from 5–70 km (~3–44 miles) in depth and is the outermost layer. The thin parts are the oceanic crust, which underlie the ocean basins (5–10 km) and are composed of dense (mafic) iron magnesium silicate igneous rocks, like basalt. The thicker crust is continental crust, which is less dense and composed of (felsic) sodium potassium aluminum silicate rocks, like granite.
Outer core
The Earth's outer core is a liquid layer about 2,300 km (1,400 mi) thick and composed of iron and nickel that lies above Earth's solid inner core and below its mantle. Its outer boundary lies 2,890 km (1,800 mi) beneath Earth's surface. The transition between the inner core and outer core is located approximately 5,150 km (3,200 mi) beneath the Earth's surface.
The Earth's outer core is a liquid layer about 2,300 km (1,400 mi) thick and composed of iron and nickel that lies above Earth's solid inner core and below its mantle. Its outer boundary lies 2,890 km (1,800 mi) beneath Earth's surface. The transition between the inner core and outer core is located approximately 5,150 km (3,200 mi) beneath the Earth's surface.
Inner core
The Earth's inner core is the Earth's innermost part and according to seismological studies, it is a primarily solid ball with a radius of about 1220 kilometers, or 760 miles (about 70% of the Moon's radius). It is believed to consist primarily of an iron–nickel alloy and to be approximately the same temperature as the surface of the Sun: approximately 5700 K (5400 °C).
Influence of Geological Factors on the Civil Engineering
Construction
Geology plays a
very important role in the field of civil engineering. Lot of geological
factors have been to conceded in the civil engineering construction such as
Building, Road , Bridges, Water retaining Structures and tunnel etc.
For a
civil engineering project to be successful, the engineers must understand the
land upon which the project rests. Geologists study the land to determine
whether it is stable enough to support the proposed project. They also study
water patterns to determine if a particular site is prone to flooding and other
natural hazards.
The
importance of geology in civil engineering may briefly be outlines as follows,
§ Geology
provides a systematic knowledge of construction material, its occurrence,
composition, durability and other properties. Example of such construction
materials is building stones, road metal, clay, limestones and laterite.
§ The
knowledge of the geological work of natural agencies such as water, wind, ice
and earthquakes helps in planning and carrying out major civil engineering
works. For example the knowledge of erosion, transportation and deposition
helps greatly in solving the expensive problems of river control, coastal and
harbour work and soil conservation.
§ Ground
water is the water which occurs in the subsurface rocks. The knowledge about
its quantity and depth of occurrence is required in connection with water
supply, irrigation, excavation and many other civil engineering works.
§ The
foundation problems of dams, bridges and buildings are directly concerned with
the geology of the area where they are to be built. In these works drilling is
commonly undertaken to explore the ground conditions. Geology helps greatly in
interpreting the drilling data.
§ In
tunneling, constructing roads, canals, docks and in determining the stability
of cuts and slopes, the knowledge about the nature and structure of rocks is
very necessary.
§ Before
staring a major engineering project at a place, a detailed geological report
which is accompanied by geological maps and sections, is prepared. Such a
report helps in planning and constructing the projects.
§ The
stability of civil engineering structure is considerably increased if the
geological feature like faults, joints, bedding planes, folding solution
channels etc in the rock beds are properly located and suitably treated.
§ In
the study of soil mechanics, it is necessary to know how the soil materials are
formed in nature.
§ The
cost of engineering works will considerably reduce of the geological survey of
the area concerned is done before hand.
