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Engineering Geology UNit I power point presentation
- 1. IFET COLLEGE OFENGINEERING DEPARTMENT OF CIVIL ENGINEERING 19UCEES302 - ENGINEERING GEOLOGY UNIT-1 INTRODUCTION 1
- 2. Syllabus 1. Geology InCivil Engineering 2. Branches Of Geology 3. Structure Of Earth And Its Composition 4. Weathering Of Rocks 5. Scale Of Weathering 6. Soils - Landforms And Processes Associated With River, Wind, Groundwater And Sea relevance To Civil Engineering. 7. Seismotectonics plates 8. Seismic Zones In India. 2
- 3. Geology in CivilEngineering Geology = Earth + Science What is the meaning of geology? Geology is the study of Earth, includes,Chemical and Physical Properties, Earth Creation, Inner and Outer Processes Affected it, Since Its Creation To Present Day. 3
- 4. 4 Branches Of Geology A-Basicgeology:- B-Connected Branches:- C-Applied Geology:- 1- Crystallography . 1- Geochemistry. 1-Economic Geology. 2- Mineralogy. 2- Geophysics. 2-Engineering Geology. 3- Petrology . 3-Geomorpholpgy. 3-Petroleum Geology. 4- Paleontology . 4-Structural Geology. 4-Hydrogeology. 5- Stratigraphy . 5-Photogeology. 5-Mining geology. 6- Dynamic geology . 6-Oceanography. 6-Agricultural geology. 7- Historical geology . 7- Field geology. 7-Miltary geology. 8-Glacial geology. 9-Volcanology. 10-Cosmic geology. 11-Geodesy.
- 5. Structure Of EarthAnd Its Composition •Core – dense – Iron and Nickel – Inner Core - solid – Outer Core - liquid – Less dense than core – Iron and Magnesium silicates – Mostly solid – Upper mantle is partially molten •Mantle Outermost layer Very thin and rigid Continental – granite Density = 2.8 g/cm3 •Crust 5
- 6. Weathering of Rocks Weathering:the disintegration, or breakdown of rock material Types of Weathering: I. Mechanical (physical) weathering is the physical disintegration and reduction in the size of the rocks without changing their chemical composition. Examples: exfoliation, frost wedging, salt wedging, temperature changes, and abrasion II. Chemical weathering decomposes, dissolves, alters, or weakens the rock through chemical processes to form residual materials. Examples: carbonation, hydration, hydrolosis, oxidation, and solution III. Biological weathering is the disintegration or decay of rocks and minerals caused by chemical or physical agents of organisms. Examples: organic activity from lichen and algae, rock disintegration by plant or root growth, burrowing and tunneling organisms, and acid secretion 6
- 7. Ice Wedging When wateris frozen it expands, so when water seeps into cracks in rocks then freezes, the expanded ice can cause the rock to split and crack. This process is known as ice wedging and it can reduce a rock to rubble over time. 7
- 8. 8 Soil/Plant Wedging • Soilcan also collect inside of the cracks of rocks. Plants can grow in this soil and eventually the roots grow large enough to cause pressure on the rocks, causing the crack to expand. The rock can split apart from this expansion.
- 9. Chemical Weathering • Mineralsfound in the rocks can change to other minerals due to the reaction with water or air. Reactions such as rusting or acid formation can also cause the rock to break down into smaller fragments. 9
- 10. 10 Changes Over TimeErosion • Erosion carries away the rock debris caused by weathering. The eroded rocks and sediments are deposited by forces such as volcanoes, wind, water, ice and waves to various depositional environments on Earth’s surface.
- 11. 11 Scale of weathering 1)Reduces rock material to smaller fragments that are easier to transport 2) Increases the exposed surface area of rock, making it more vulnerable to further physical and chemical weathering 3) Joints in a rock are a pathway for water – they can enhance mechanical weathering
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- 13. 13 Soils - LandformsAnd Processes Associated With River, Wind, Groundwater And Sea Landforms: • Landforms are the natural features of the earth. • Mountains, plateaus, plains and hills are all examples of landforms. • Landforms are the individual topographic features exposed on the Earth’s surface. • Landforms vary in size and shape and include features such as small creeks or sand dunes, or large features such as the Mississippi River or Blue Ridge Mountains. • Landforms develop over a range of different time-scales. Some landforms develop rather quickly (over a few seconds, minutes, or hours), such as a landslide, while others may involve many millions of years to form, such as a mountain range.
- 14. Cont… • Landform developmentcan be relatively simple and involve only a few processes, or very complex and involve a combination of multiple processes and agents. • Landforms are dynamic features that are continually affected by a variety of earth-surface processes including weathering, erosion, and deposition. • Earth scientists who study landforms provide decision makers with information to make natural resource, cultural management, and infrastructure decisions, that affect humans and the environment. 14
- 15. Crustal Orders ofRelief 15 I. First Order or Relief: Continental Landmasses and Ocean Basins II. Second Order of Relief: Major Continental and Ocean Landforms Rivers and Flood Plains III. Third Order of Relief: Genetic Landform Features
- 16. 16 Geomorphology • Geomorphology isthe process-based study of landforms. • Geo-morph-ology originates from Greek: Geo meaning the “Earth”, morph meaning its “shape”, and ology refers to “the study of”. • Scientists who study landforms are Geomorphologists. • Geomorphology defines the processes and conditions that influence landform development, and the physical, morphological, and structural characteristics of landforms.
- 17. 17 Geological work ofRivers i. Origins and classifications ii. Lakes as open systems iii. Light and temperature iv. Lake chemistry v. Primary productivity vi. Secondary productivity vii.Lake evolution viii.Perturbations
- 18. 18 Lake classification: geological origin •Lakes result from impoundment of water by: • Tectonic down warping (e.g. Lake Victoria) • Tectonic faulting (e.g. Dead Sea) • Volcanic eruption (e.g. Crater Lake) • Landslide dams • Ice dams • Biotic dams (e.g. Beaver lake) • Glacial erosion (e.g. Lake Peyto) • Glacial deposition (e.g. Moraine Lake) • River channel abandonment (e.g. Hatzic Lake) • Deflation
- 19. 19 Lake classification: morphology •Lake morphology (size, surface area and depth) largely determined by origin. • Substrate (rocky, sandy, muddy, organic) initially determined by geological origin; thereafter by inputs.
- 20. 20 Lakes as opensystems
- 21. 21 Geological work ofground water Hydrogeology: The study of ground-water/earth-material interactions: – Geology controls ground-water recharge, flow, discharge and availability – Ground water acts as a geologic agent: Weathering, dissolution, volcanism, metamorphism, slope stability, earthquakes….
- 22. 22 The vadose zoneincludes all the material between the Earth’s surface and the zone of saturation. The upper boundary of the zone of saturation is called the water table. The capillary fringe is a layer of variable thickness that directly overlies the water table. Water is drawn up into this layer by capillary action. Essential components of groundwater The rate of infiltration is a function of soil type, rock type, antecedent water, and time.
- 23. 23 Groundwater - Rechargeand Discharge • Water is continually recycled through aquifer systems. • Groundwater recharge is any water added to the aquifer zone. • Processes that contribute to groundwater recharge include precipitation, streamflow, leakage (reservoirs, lakes, aqueducts), and artificial means (injection wells). • Groundwater discharge is any process that removes water from an aquifer system. • Natural springs and artificial wells are examples of discharge processes. • Groundwater supplies 30% of the water present in our streams. • Effluent streams act as discharge zones for groundwater during dry seasons. • This phenomenon is known as base flow. • Groundwater overdraft reduces the base flow, which results in the reduction of water supplied to our streams.
- 24. 24 Groundwater -- ArtesianConditions •Water pressure in buildings is maintained by a hydraulic head (h) and confinement of water beneath the pressure surface. •Natural artesian conditions occur when an aquifer is confined by a saturated, impermeable clay layer (aquitard or aquiclude) below the sloping pressure surface. •An artesian well flows continually. It is produced when a well penetrates the clay layer and the land surface is below the pressure surface.
- 25. 25 Springs • Discharge ofgroundwater, – from a spring in California. • Springs generally emerge at – the base of a hillslope. • Some springs produce water, – that has traveled for many – kilometers; while others emit – water that has traveled only – a few meters. • Springs represent places, – where the saturated zone – (below the water table) – comes in contact with the – land surface.
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- 27. 27 Geological work ofWind • Wind is one of several geological agents that can move mass over a distance by eroding, transporting, and depositing solid particles, although the particles are generally smaller than those moved by ice, gravity, or water. When wind blows constantly in one direction for long time spans, it can effect a net loss in surface material, particularly on islands. • Brava, Cape Verdes.
- 28. 28 Geological work ofSea • Convection currents in mantle rise under oceanic ridges and spread. • Driving force is here transferred from core to mantle. • Oceanic crust (basaltic) created at ridges. • Crust plus upper mantle (lithosphere) move laterally away – going along for the ride.
- 29. 29 Sea-Floor Spreading • Lithosphereplunges into oceanic trenches. Does this explain the anomalies of ocean floor heat distribution? • Continents don’t drift through the mantle but are passengers. • Oceanic crust has to be young because older rocks have been: – Plastered onto the edge of continents. – Thrust down into the mantle.
- 30. 30 Seismotectonics Plates • Collisionscan involve an oceanic plate and a continental plate, two continental plates, or two oceanic plates. • Continents do not drift, but are rafted about. • Some oceanic basins are steadily widening; others are closing. • Driving mechanism believed to be convection currents of some type.
- 31. 31 What are tectonicplates made of? • Plates are made of rigid lithosphere. The lithosphere is made up of the crust and the upper part of the mantle.
- 32. 32 Plate Movement • “Plates”of lithosphere are moved around by the underlying hot mantle convection cells
- 33. 33 • Divergent • Convergent •Transform Three types of plate boundary
- 34. 34 • Spreading ridges –As plates move apart new material is erupted to fill the gap Divergent Boundaries
- 35. 35 • Where platesslide past each other Transform Boundaries Above: View of the San Andreas transform fault
- 36. 36 - Subduction -Rifting - Hotspots Volcanoes are formed by:
- 37. 37 The tectonic platemoves over a fixed hotspot forming a chain of volcanoes. The volcanoes get younger from one end to the other.
- 38. 38 Where do earthquakesform? Figure showing the tectonic setting of earthquakes
- 39. 39 Earth quakes • Earthquakesare one of the most devastating forces in nature. • Earthquakes disasters have been known since ancient times. • Earthquakes have been instrumental in changing the course of history. • Some of the most significant disasters in the last hundred years have been caused by earthquakes. • A sudden release of energy accumulated in deformed rocks causing the ground to tremble or shake.
- 40. 40 What is theElastic Rebound Theory? • Explains how energy is stored in rocks – Rocks bend until the strength of the rock is exceeded – Rupture occurs and the rocks quickly rebound to an undeformed shape – Energy is released in waves that radiate outward from the fault
- 41. 41 What are Earthquakes? •The shaking or trembling caused by the sudden release of energy • Usually associated with faulting or breaking of rocks • Continuing adjustment of position results in aftershocks
- 42. 42 What are SeismicWaves? • Response of material to the arrival of energy fronts released by rupture • Two types: – Body waves • P and S – Surface waves • R and L
- 43. 43 Body Waves: Pand S waves • Body waves – P or primary waves • fastest waves • travel through solids, liquids, or gases • compressional wave, material movement is in the same direction as wave movement – S or secondary waves • slower than P waves • travel through solids only • shear waves - move material perpendicular to wave movement
- 44. 44 Surface Waves: Rand L waves • Surface Waves – Travel just below or along the ground’s surface – Slower than body waves; rolling and side-to-side movement – Especially damaging to buildings
- 45. 45 How is anEarthquake’s Epicenter Located? Seismic wave behavior – P waves arrive first, then S waves, then L and R – Average speeds for all these waves is known – After an earthquake, the difference in arrival times at a seismograph station can be used to calculate the distance from the seismograph to the epicenter.
- 46. 46 How is anEarthquake’s Epicenter Located? Time-distance graph showing the average travel times for P- and S- waves. The farther away a seismograph is from the focus of an earthquake, the longer the interval between the arrivals of the P- and S- waves
- 47. 47 How is anEarthquake’s Epicenter Located? • Three seismograph stations are needed to locate the epicenter of an earthquake • A circle where the radius equals the distance to the epicenter is drawn • The intersection of the circles locates the epicenter
- 48. 48 How are theSize and Strength of an Earthquake Measured? • Modified Mercalli Intensity Map – 1994 Northridge, CA earthquake, magnitude 6.7 • Intensity – subjective measure of the kind of damage done and people’s reactions to it – isoseismal lines identify areas of equal intensity
- 49. 49 What are theDestructive Effects of Earthquakes? • Ground Shaking – amplitude, duration, and damage increases in poorly consolidated rocks
- 50. 50 Seismic zones inIndia. The varying geology at different locations in the country implies that the likelihood of damaging earthquakes taking place at different locations is different. Thus, a seismic zone map is required to identify these regions. Based on the levels of intensities sustained during damaging past earthquakes, the 1970 version of the zone map subdivided India into five zones – I, II, III, IV and V. The maximum Modified Mercalli (MM) intensity of seismic shaking expected in these zones were V or less, VI, VII, VIII, and IX and higher, respectively. Parts of Himalayan boundary in the north and northeast, and the Kachchh area in the west were classified as zone V.
Editor's Notes
- #31 Plates are made of rigid lithosphere – formed of the crust and the extreme upper mantle (point out these layers on the figure).
- #32 How and Why do tectonic Plates move around? The question of how tectonic plates are moved around the globe is answered by understanding mantle convection cells. In the mantle hot material rises towards the lithosphere (like hot air rising out of an open oven - ever opened an oven door and felt the blast of hot air coming past your face?). The hot material reaches the base of the lithosphere where it cools and sinks back down through the mantle. The cool material is replaced by more hot material, and so on forming a large “convection cell” (as pictured in the diagram). This slow but incessant movement in the mantle causes the rigid tectonic plates to move (float) around the earth surface (at an equally slow rate).
- #33 Firstly, there are three types of plate boundary, each related to the movement seen along the boundary. Divergent boundaries are where plates move away from each other Convergent boundaries are where the plates move towards each other Transform boundaries are where the plates slide past each other. Presenter: See diagrams for each - it is important to remember the names of the boundary types and the motion involved.
- #34 In plate tectonics, a divergent boundary is a linear feature that exists between two tectonic plates that are moving away from each other. These areas can form in the middle of continents or on the ocean floor. As the plates pull apart, hot molten material can rise up this newly formed pathway to the surface - causing volcanic activity. Presenter: Reiterate the process by going through the diagram, including the presence of mantle convection cells causing the plates to break apart and also as a source for new molten material. Where a divergent boundary forms on a continent it is called a RIFT or CONTINENTAL RIFT, e.g. African Rift Valley. Where a divergent boundary forms under the ocean it is called an OCEAN RIDGE.
- #35 The third type of boundary are transform boundaries, along which plates slide past each other. The San Andreas fault, adjacent to which the US city of San Francisco is built is an example of a transform boundary between the Pacific plate and the North American plate.
- #36 Volcanoes can be formed in three ways: Via subduction. The subducting slab dehydrates to form new melt that will rise through the crust to be erupted at the surface. Via rifting. When two plates pull apart magma rises, producing volcanic eruptions at the surface. At “Hotspots”….hotspot do not necessarily occur along a plate boundary. So hotspot volcanoes can form in the middle of tectonic plates….Click for example.
- #37 Hotspot’s commonly form volcanic island chains (like the Hawaiian islands). These result from the slow movement of a tectonic plate over a FIXED hotspot. Persistent volcanic activity at a hotspot will create new islands as the plate moves the position of the “old” volcanic island from over the hotspot. Therefore at one end of the island chain you see the youngest, most active volcanic islands (directly over the hotspot) and along the island chain the extinct volcanoes become older and more eroded (see diagram). This way geologists can use hotspot volcano chains to track the movement of the tectonic plate through time.
- #38 We know there are three types of plate boundaries: Divergent, Convergent and Transform. Movement and slipping along each of these types of boundaries can form an earthquake. Depending on the type of movement, the earthquakes occur in either a shallow or deep level in the crust. The majority of tectonic earthquakes originate at depths not exceeding tens of kilometers. In subduction zones, where old and cold oceanic crust descends beneath another tectonic plate, “Deep Focus Earthquakes” may occur at much greater depths (up to seven hundred kilometers!). These earthquakes occur at a depth at which the subducted crust should no longer be brittle, due to the high temperature and pressure. A possible mechanism for the generation of deep focus earthquakes is faulting. Earthquakes may also occur in volcanic regions and are caused there both by tectonic faults and by the movement of magma (hot molten rock) within the volcano. Such earthquakes can be an early warning of volcanic eruptions.