CE442 Geotechnical Earthquake Engineering

Introduction to Geotechnical Earthquake Engineering

• Earthquake engineering aims to mitigate the impacts of earthquakes on people and their environment.
• It combines aspects of geology, seismology, geotechnical engineering, structural engineering, risk analysis, and other technical fields.
• Hundreds of millions of people worldwide live with significant earthquake risk, posing an economic threat to local, regional, and national economies.

Historical Perspective

• Earthquake records date back 3000 years in China, 1600 years in Japan and the Eastern Mediterranean, and 350 years in the United States.
• Human experience with earthquakes is brief compared to the millions of years over which earthquakes have occurred.
• Earthquakes cannot be prevented, but the goal is to mitigate their effects to reduce loss of life, injuries, and damage.

Principal Types of Earthquake Damage

• Structural damage: harm inflicted on buildings, bridges, roads, and other infrastructure due to the forces generated by an earthquake.
• Liquefaction: a process that causes soft, young, water-saturated, fine-grained sands and silts to behave like viscous fluids, leading to ground failure.

Seismic Hazard

• Building codes: seismic design requirements have continuously improved, incorporating lessons from past earthquakes.
• Strength and ductility: modern design practices emphasize not only structural strength but also ductility, allowing buildings to withstand and absorb seismic energy.
• Geotechnical role: accurate prediction of ground motions is crucial for earthquake-resistant design, with geotechnical earthquake engineers providing essential data for structural engineers.

Liquefaction

• Occurs when an earthquake causes water-saturated, fine-grained soils to lose their strength and behave like a liquid.
• Can lead to ground failure, causing damage to buildings and infrastructure.

Earthquake-Induced Landslides

• Occur when an earthquake triggers the collapse of potential landslide areas.

Significant Historical Earthquakes

• 1556 Shaanxi Earthquake (China): the deadliest earthquake in recorded history, with an estimated death toll of 530,000.
• Various earthquakes in the Philippines, including the Ragay Gulf Earthquake (1973), Casiguran Earthquake (1968), and others.

Geotechnical Earthquake Engineering

• Deals with the design and construction of projects to resist the effects of earthquakes.
• Requires an understanding of geology, seismology, and earthquake engineering.
• Activities performed by geotechnical engineers include:
  • Investigating the possibility of liquefaction at the site.
  • Calculating the settlement of the structure caused by the anticipated earthquake.
  • Checking foundation design parameters to ensure the foundation does not fail during the anticipated earthquake.

Fundamentals of Earthquake

• Earthquake is manifested as ground shaking caused by sudden release of energy in the Earth's crust.
• Can originate from different sources, such as dislocations of the crust, volcanic eruptions, or man-made explosions.
• Plates are large and stable rigid rock slabs with a thickness of about 100 km, forming the crust or lithosphere and part of the upper mantle of the Earth.

Three Types of Plate Boundaries

• Divergent Boundaries: regions where two tectonic plates are moving apart from each other, resulting in the creation of new crust.
• Transform Boundaries: regions where two tectonic plates slide past each other horizontally, causing earthquakes due to the build-up and release of stress along the fault lines.
• Convergent Plate Boundaries: regions where two tectonic plates are moving towards each other, resulting in the formation of mountains, earthquakes, and volcanic activity.

Interiors of the Earth

• The Earth is composed of a sequence of shells or layers called geospheres, including the lithosphere, asthenosphere, outer core, and inner core.
• Lithosphere: the thinnest outer solid shell, 200 km thick with a density of 1500 kg/m3.
• Asthenosphere: the mantle, 2685 km thick, surrounding the core, composed of hot, dense ultrabasic igneous rock in a plastic state.
• Outer Core: a molten layer of iron and nickel beneath the mantle, extending from 2,900 km to 5,150 km depth.
• Inner Core: a solid, dense region at the center of the Earth, extending from 5,150 km to the core at 6,371 km depth, composed of solid iron and nickel.