Geology in Civil Engineering

Geology

• Geology is the science that deals with the study of Earth's physical and chemical changes that occur on its surface and in its interior.
• It overlaps with other Earth sciences, including hydrology and atmospheric sciences.
• Geology plays a major role in different engineering disciplines, including Civil Engineering and Earthquake Engineering.

Importance of Geology in Construction

• Geology helps understand Earth's processes and is essential for understanding both natural and anthropogenic catastrophes.
• It provides knowledge about the site used in construction of buildings, dams, tunnels, and bridges.
• Geology helps identify areas susceptible to failures due to geological hazards such as earthquakes, landslides, and weathering effects.

Branches of Geology

• Physical Geology / Geomorphology: deals with the study of Earth's physical features, such as mountains, valleys, rivers, and lakes.
• Mineralogy: deals with the study of minerals.
• Petrology: deals with the study of rocks.
• Historical Geology: deals with the study of Earth's history and the changes that occurred in the past.
• Economic Geology: deals with the study of minerals and their economic importance.

Internal Structure of the Earth

• Crust: the uppermost solid shell of the Earth, making up less than 1% of its mass.
• Mantle: the zone within the Earth that lies between the core and the outermost layer, making up about 68% of the Earth's mass.
• Core: the very hot and dense center of the planet, making up about 31% of the Earth's mass.

Plate Tectonics

• The lithosphere is divided into several smaller parts called tectonic plates.
• These plates move and interact with each other, driven by convectional forces within the Earth.
• The movements and interactions of these plates produce earthquakes, volcanoes, mountain ranges, and other geological processes and features.

Plate Tectonic Boundary

• Three types of plate boundaries:
  • Divergent boundary: where two tectonic plates are moving away from each other.
  • Convergent boundary: where two tectonic plates are moving towards each other.
  • Transform boundary: where two tectonic plates are moving past each other.

Earthquake Engineering

• Defined as the branch of engineering devoted to mitigating earthquake hazards.
• Scope: seismicity, nature, measures, and recording of earthquakes, planning for seismic risk assessment and mitigation, analysis, design, and construction of earthquake-resistant structures.

Earthquakes

• Motion or vibration of the Earth's surface that follows a release of energy in the Earth's crust.
• Can be generated by a sudden dislocation of segments of the crust, volcanic eruptions, or man-made explosions.
• Can trigger other natural hazards, such as slope failure, tsunamis, and floods.

Sources of Ground Movements

• Tectonic earthquakes
• Volcanoes
• Explosions
• Collapse of mines and large reservoirs

Earthquake: Fault Lines

• Faults are cracks in the lithosphere caused by the stresses created as sections of a plate are moving in different directions.

• Three types of faults:

  • Normal fault: where one mass of rock slides downward and pulls away from another mass of rock.
  • Reverse fault: where plates are being pushed together, involving upward movement as the plates collide and buckle upwards.
  • Strike-slip fault: not mentioned in the text.### Earthquake Fault Lines

• A strike-slip fault occurs when two plates slide past each other horizontally.

• The San Andreas fault in California is a famous example of a strike-slip fault, causing many powerful earthquakes.

• Other examples of strike-slip faults include the Anatolian Fault in Turkey and the Alpine Fault in New Zealand.

Earthquake Seismic Waves

• Earthquakes release energy as shock waves, known as seismic waves, which ripple across the Earth's surface.
• Seismic waves can travel up to 2 miles per second.
• There are two types of seismic waves: Body Waves (P and S waves) and Surface Waves (Love and Rayleigh Waves).

Seismology

• Seismology is the study of earthquakes and seismic waves that move through and around the Earth.
• A seismologist is a scientist who studies earthquakes and seismic waves.

Earthquake Focus and Epicenter

• The focus of an earthquake is where pressure builds along a fault line, causing it to fail deep underneath the Earth's crust.
• The point directly above the focus is termed the epicenter.
• Earthquake foci are confined to within a limited zone of the upper Earth, with a lower boundary at around 700 km depth from the surface.

Earthquake Strength: Intensity and Magnitude

• Earthquake intensity is a measure of the severity of an earthquake at a particular location, based on human reactions, observed damage, and physical effects.
• Intensity scales are subjective and dependent on construction practices and socio-economic conditions of a country.
• Magnitude is a quantitative measure of earthquake size that does not depend on population density or construction type.

Effects of Earthquakes

• Comprehensive regional earthquake impact assessments require an interdisciplinary framework that incorporates physical damage, social and economic consequences.
• Physical damage includes damage to buildings, lifelines, and critical facilities.
• Social and economic consequences include short- and long-term effects on communities and urban and industrial regions.

Damage to Buildings and Lifelines

• Extensive structural damage can occur to buildings, bridges, highways, and other lifelines during earthquakes.
• Lifelines include essential services such as electric power, gas, water, and wastewater systems, as well as transportation systems and infrastructure.

Effects on the Ground

• Ground effects are a significant contributor to damage of the built environment.
• Local geology and topography influence the travel path and amplification characteristics of seismic waves.
• Surface rupture can occur due to intense and long shaking, as well as fault ruptures, generating deep cracks and large gaps.
• Fault ruptures can cause large vertical movements of the ground, leading to severe damage to building foundations and underground networks.
• Liquefaction can occur due to excessive build-up of pore water pressure during earthquakes, leading to loss of stiffness and strength of soils.
• Landslides, including rockfalls, deep failure of slopes, and shallow debris flows, can be generated by the loss of shear strength in the soil.

Human and Financial Losses

• Over 1200 destructive earthquakes occurred worldwide in the 20th century, causing estimated damage of over $1 trillion.
• Annual losses average around $10 billion.
• Monetary losses due to collapsed buildings and lifeline damage are substantial.
• The cost of recovery and reconstruction is a severe consequence of earthquakes.