Engineering Geology UNit I power point presentation

Engineering Geology

1. IFET COLLEGE OF ENGINEERING DEPARTMENT OF CIVIL ENGINEERING 19UCEES302 - ENGINEERING GEOLOGY UNIT-1 INTRODUCTION 1

2. Syllabus Geology In Civil Engineering Branches Of Geology Structure Of Earth And Its Composition Weathering Of Rocks Scale Of Weathering Soils - Landforms And Processes Associated With River, Wind, Groundwater And Sea relevance To Civil Engineering. Seismotectonics plates Seismic Zones In India. 2

3. Geology in Civil Engineering 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. Branches Of Geology A-Basic geology:- 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. 4

5. Structure Of Earth And 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/cm 3 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 water is 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. Soil /Plant Wedging Soil can 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. 8

9. Chemical Weathering Minerals found 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. Changes Over Time Erosion 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. 10

11. Scale of weathering Reduces rock material to smaller fragments that are easier to transport Increases the exposed surface area of rock, making it more vulnerable to further physical and chemical weathering Joints in a rock are a pathway for water – they can enhance mechanical weathering 11

12.  pH Scale 12

13. Soils - Landforms And 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. 13

14. Cont … Landform development can 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 of Relief 15 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. Geomorphology Geomorphology is the 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. 16

17. Geological work of Rivers Origins and classifications Lakes as open systems Light and temperature Lake chemistry Primary productivity Secondary productivity Lake evolution Perturbations 17

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 18

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. 19

20. Lakes as open systems 20

21. Geological work of ground 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…. 21

22. The vadose zone includes 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. 22

23. Groundwater - Recharge and 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. 23

24. Groundwater -- Artesian Conditions 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. 24

25. Springs Discharge of groundwater, 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. 25

26. Ground water systems 26

27. Geological work of Wind 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. 27

28. Geological work of Sea 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 . 28

29. Sea-Floor Spreading Lithosphere plunges 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. 29

30. Seismotectonics Plates Collisions can 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. 30

31. What are tectonic plates made of? Plates are made of rigid lithosphere . The lithosphere is made up of the crust and the upper part of the mantle. 31

32. Plate Movement “Plates” of lithosphere are moved around by the underlying hot mantle convection cells 32

33. Divergent Convergent Transform Three types of plate boundary 33

34. Spreading ridges As plates move apart new material is erupted to fill the gap Divergent Boundaries 34

35. Where plates slide past each other Transform Boundaries Above: View of the San Andreas transform fault 35

36. - Subduction - Rifting - Hotspots Volcanoes are formed by: 36

37. The tectonic plate moves over a fixed hotspot forming a chain of volcanoes. The volcanoes get younger from one end to the other. 37

38. Where do earthquakes form? Figure showing the tectonic setting of earthquakes 38

39. Earth quakes Earthquakes are 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. 39

40. What is the Elastic 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 40

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 41

42. What are Seismic Waves? Response of material to the arrival of energy fronts released by rupture Two types: Body waves P and S Surface waves R and L 42

43. Body Waves: P and 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 43

44. Surface Waves: R and 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 44

45. How is an Earthquake’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. 45

46. How is an Earthquake’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 46

47. How is an Earthquake’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 47

48. How are the Size 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 48

49. What are the Destructive Effects of Earthquakes? Ground Shaking amplitude, duration, and damage increases in poorly consolidated rocks 49

50. Seismic zones in India. 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. 50