NPTEL Online - IIT Kanpur. Course Name Geotechnical Earthquake Engineering. Department IIT Kanpur

Transcription

1 NPTEL Online - IIT Kanpur Course Name Geotechnical Earthquake Engineering Department Instructor Civil Engineering Department IIT Kanpur Prof. N.R. Patra

2 Module 1 INTRODUCTION TO GEOTECHNICAL ENGINEERING (Lectures 1 to 6) TOPICS 1.1 HISTORY 1.2 SEISMIC HAZARDS Ground Shaking Structural Hazards 1.3 LIQUEFACTION 1.4 LANDSLIDES 1.5 RETAINING STRUCTURES FALIURES 1.6 LIFELINE HAZARDS 1.7 TSUNAMI AND SEICHE HAZARDS 1.8 SIGNIFICANT HISTORICAL EARTHQUAKES 1.9 INTRODUCTION 1.10 INTERNAL STRUCTURES OF THE EARTH Seismic Waves Internal Structure 1.11 CONTINENTAL DRIFT AND PLATE TECTONICS 1.12 PLATE TECTONICS 1.13 PLATE BOUNDARIES Spreading Rigde Boundaries Subduction Zone Boundaries Transform Fault Boundaries 1.14 FAULTS Fault Geometry Fault Movement Dip Slip Movement Strike-Slip Movement 1.15 ELASTIC REBOUND THEORY 1.16 RELATIONSHIP TO EARTHQUAKE RECURRENCE Dept. of Civil Engg. Indian Institute of Technology, Kanpur 1

3 1.17 RELATIONSHIP TO TECTONICS ENVIRONMENT 1.18 SEISMIC MOMENT 1.19 OTHER SOURCES OF SEISMIC ACTIVITY 1.20 GEOMETRIC NOTATION 1.21 LOCATION of EARTHQUAKES 1.22 SIZE OF EARTHQUAKES Earthquake Intensity Earthquake Magnitude Richter Local Magnitude Surface Wave Magnitude Body Wave Magnitude 1.23 OTHER INSTRUMENTAL MAGNITUDE SCALES Moment Magnitude Earthquake Energy REFERENCES Dept. of Civil Engg. Indian Institute of Technology, Kanpur 2

4 Lecture 1 Introduction to Geotechnical Earthquake Engineering Topics 1.1 HISTORY 1.2 SEISMIC HAZARDS Ground shaking Structural hazards 1.3 LIQUEFACTION 1.4 LANDSLIDES 1.1 HISTORY Earthquakes have occurred for millions of years and will continue in the future as they have in the past. Some will occur in remote, undeveloped areas where damage will be negligible. Others will occur near densely populated urban areas and subject their inhabitants and the infrastructure they depend on to strong shaking. It is impossible to prevent earthquakes from occurring, but it is possible to mitigate the effects of strong earthquake shaking: to reduce loss of life, injuries, and damage. 1.2 SEISMIC HAZARDS Hazards associated with earthquakes are commonly referred to as seismic hazards. The practice of earthquake engineering involves the identification and mitigation of seismic hazards Ground shaking When an earthquake occurs, seismic waves radiate away from the source and travel rapidly through the earth s crust. When these waves reach the ground surface, they produce shaking that may last from seconds to minutes. The strength and duration of shaking at a particular site depends on the size and location of the earthquake and on the characteristics of the site. At sites near the source of a large earthquake, ground shaking can cause tremendous damage Structural Hazards Without doubt the most dramatic and memorable images of earthquakes damage are those of structural collapse. From the predictable collapse of the unreinforced masonry and adobe structures in which many residents of underdeveloped areas of the world line (figure 1.1) to the surprising destruction of more modern construction (figures 1.2 to 1.4), structural damage is the leading cause of death and economic loss in many earthquakes. However, structures need not collapse to cause death and damage. Falling objects such as brick facings and parapets on the outside of a structure or heavy pictures and shelves within a structure have caused casualties in many earthquakes. Interior facilities such as piping, lighting, and storage systems can also be damaged during earthquakes. Dept. of Civil Engg. Indian Institute of Technology, Kanpur 3

5 Figure1.1: Damage to buildings in Huaras, Peru following the 1970 Peru earthquake. The adobe structures in the foreground were destroyed, but the reinforced concrete structure in the background suffered little damage (photo by G. Plafker, courtesy of USGS) Figure1.2: Collapsed portion of the reinforced concrete Hospital Juarez in Mexico City following the 1985 Mexico earthquake (Photo by E.V. Leyendecker, courtesy of EERI) Dept. of Civil Engg. Indian Institute of Technology, Kanpur 4

6 Figure 1.3: Effects of column failures of Olive View Hospital in the 1971 San Fernando earthquak Collapse of the canopy in the foreground pinned the ambulance beneath them, rendering them usele (courtesy of EERI) Figure 1.4: Reinforced concrete columns at Olive View Hospital following the 1971 San Fernando earthquake. Insufficient transverse reinforcement was unable to provide adequate confinement (courtesy of USGS) Dept. of Civil Engg. Indian Institute of Technology, Kanpur 5

7 1.3 Liquefaction Due to shaking when soil deposits lost their strength and appeared to flow like fluids, termed as liquefaction. During this condition the strength of the soil is reduced, often drastically, to the point where it is unable to support structures or remain stable. Because it only occurs in saturated soils, liquefaction is most commonly observed near rivers, bays, and other bodies of water. The term liquefaction actually encompasses several related phenomena. Flow failures, which can occur when the strength of the soil drops below the level needed to maintain stability under static conditions. Flow failures are therefore driven by static gravitational forces and can produce very large movements. Flow failures have caused the collapse of earth dams (figure 1.5) and other slopes, and the failure of foundations (figure 1.6). Figure 1.5: Liquefaction failure of Sheffield Dam following the 1925 Santa Barbara earthquake (K. Steinbrugge collection: courtesy of EERC, Univ. of California) Figure 1.6: Sand boil in rice field following the 1964 Niigata earthquake (K. Steinbrugge collection; courtesy of EERC, Univ. of California) Dept. of Civil Engg. Indian Institute of Technology, Kanpur 6

8 1.4 Landslides Strong earthquakes often cause landslides. Although the majority of such landslides are small, earthquakes have also caused very large slides. In a number of unfortunate cases, earthquake-induced landslides have buried entire towns and villages (figure 1.7). Figure1.7 (a and b): Village of Yungay, Peru, (a) before and (b) after being buried by a giant landslide in the 1970 Peruvian earthquake. The same palm trees are visible at the left side of both photographs. The landslide involved 50 million cubic meters of material that eventually covered an area of some 8000 square kilometers. About 25,000 people were killed by this landslide, over 18,000 in the villages of Yungay and Ranrahirca (K. Steinbruge collection; courtesy of EERC, Univ. of California) Dept. of Civil Engg. Indian Institute of Technology, Kanpur 7