Engineering Geology MBCET__Module 1.pptx

Engineering Geology Module 1

1. Engineering Geology CE1U20D  

2. Syllabus Relevance of geology in Civil Engineering Hydrogeology Minerals Rocks as aggregates of minerals Attitude of geological structures Introduction to natural hazards

3. References Duggal, SK,Rawal,N and Pandey, HK (2014) Engineering Geology, McGraw Hill Education, New Delhi Garg, SK (2012) Introduction to Physical and Engineering Geology, Khanna Publishers, New Delhi Gokhale, KVGK (2010) Principles of Engineering Geology, BS Pubications , Hyderabad Kanithi V (2012) Engineering Geology, Universities Press (India) Ltd., Hyderabad Singh, P (2004) Engineering and General Geology, S. K. Kataria and Sons, New Delhi Bennison, GM, Olver , PA and Moseley, KA (2013) An introduction to geological structures and maps, Routledge, London Gokhale, NW (1987) Manual of geological maps, CBS Publishers, New Delhi

4. Geology Origin, age and structure of Earth. Evolution, modification and extinction of various surface and sub-surface physical features like mountains, plateaus, plains, valleys, basin, caves, etc. Materials making up the earth Nature and functioning of atmosphere The study of all water bodies existing on surface or underground Interaction of atmosphere, lithosphere and hydrosphere Physical, dynamic and physicochemical processes operating on and within the earth Agents and forces involved and evolved in such processes

5. RELEVANCE OF GEOLOGY IN CIVIL ENGINEERING Scope of Engineering Geology Engineering geology is the application of geology in design, construction and performance of civil engineering works. The objectives of engineering geology are: It enables a civil engineer to understand engineering implications of certain conditions related to the area of construction, which are geological in nature. It enables a geologist to understand the nature of geological information that is essential for a safe design and construction of a civil engineering project. The principle objective of an engineering geologist is the protection of life and property against damage caused by various geological conditions.

6. RELEVANCE OF GEOLOGY IN CIVIL ENGINEERING ( Contd …) The area covered by Engineering geology includes geological hazards, geotechnical data, material properties, landslide and slope stability, erosion, flooding, dewatering, seismic studies etc. The most important role of an engineering geologist is to interpret the landforms and earth processes, to identify potential geologic and related man-made hazards that may impact civil engineering structures and human development.

7. Importance of Engineering Geology The importance of Engineering geology in development can hardly be exaggerated. It helps to: Identify areas susceptible to failure due to geological hazards Establish design specifications Select the best site for engineering purposes Select best engineering materials for construction Recognize potential difficult ground conditions prior to detailed design and construction

8. The scope of engineering geology is best studied with reference to major activities of the profession of a civil engineer which are: Construction Water Resource Development Town and Regional Planning

9. Geology in Construction Jobs Full geological information about the site of construction or excavation and about the natural materials of construction is of great importance The aspect of geology has full relevance in all the three aspects of each construction i.e. Planning, designing and execution.

10. Construction Similarly for construction in geologically sensitive areas as those of coastal area, seismi c zones and permafrost regions, knowledge of geological history of the area is of great importance. Coastal area : behaviour of rocks towards waves, current and marine environment must fully be understood in planning and execution stage. Special type of construction may become essential in this area. Seismic region : Construction should be well balanced and light weight. Hence lightweight materials are used and architectural fancies are to be avoided. Permafrost region (soil remains permanently frost up to certain depth): Problems can be solved only by proper understanding of the ground below. Construction of underground projects like tunnels cannot be undertaken without a thorough knowledge of the geological characters and setting of the rocks and their relevance to the loads imposed on or relieved from them .

11. Planning Topographical maps Hydrological maps Geological maps

12. Design Some of the geological characters that have a direct or indirect influence on the design of a proposed project are: The existence of hard bed rocks and their depth from and inclination with the surface. The mechanical properties like compressive strength, shear and transverse strength, modulus of elasticity, porosity and permeability, resistance to decay and disintegration along and across the site of the proposed project. Presence , nature and distribution pattern of planes of structural weakness like joints, faults, folds etc. Presence nature and distribution pattern of zones of weak materials like shear zones, clay bands etc. The position of ground water table including points of recharge and discharge and variations during different periods of the year. Seismic character of the area as studied from the seismic history and prediction about future seismicity.

13. Geology in Water Resource Development Exploration and development of water resources have become very important areas of activities for scientists, technologists and engineers in all parts of the world. The water resource engineers have to understand the water cycle in all essential details . The study of water cycle is an essential prerequisite for effective planning and execution of major water resource development programmers on national and regional level. Geological information is of fundamental importance in exploration and exploitation of water resources of a region from surface and sub-surface reserves of water. The water bearing properties of rock bodies and factors that influence storage, movement and yield of water from aquifers are geological problem s A thorough geological knowledge about the rock strata is essential is essential for designing a water supply project.

14. Geology in Town and Regional Planning A town planner is concerned essentially with utilization of land in a best and aesthetic manner possible for developing cities and towns for meeting social needs in different areas. The primary aim of a town planner is to derive maximum benefit from natural environment with minimum disturbance. The roles played by the materials making the land like rocks, soils, vegetation, water bodies etc. in the evolution of natural landscape must be understood. The regional Town Planner is responsible for adopting an integrated approach in all such cases of allocation of land for developmental projects. Thus a change induced in the natural setup of an area due to a proposed new project is going to lead a series of changes in the adjoining and even in distant places. As such all sound planning must be in tune with the natural features and processes of a region.

15. Subdivisions of Geology

16. Minor branches of Geology Geo-chemistry Geo-physics Geo-hydrology Mining geology Rock mechanics Geo-mechanics Meteorology Oceanography Engineering Geology

17. Physical geology : deals with study of Erosion, Transportation and Deposition (ETD) Geomorphology : deals with the study of surface features of the earth Mineralology : deals with formation, occurrence, aggregation, properties and use of minerals Historical geology : deals with the past history of the earth Paleontology : deals with the study of fossils Economic geology : deals with the study of minerals and rocks and other materials occurring in or on the earth and that can be exploited for the benefit of man Engg geology- deals with the geological study of the site and location for major engg projects Mining geology- deals with the exploring and exploitation of minerals by mining and quarrying practice Petrology : study of rocks

18. Weathering Weathering is the disintegration or structural breakdown or chemical alteration of rock and soil minerals Weathering is the process of decay and disintegration of rocks under the influence of certain physical and chemical agencies of the atmosphere. The most important aspect of weathering is that the weathered product remains lying over and above or near to the parent rock unless it is removed from there by some other agency of the nature. Examples: Rocks exposed to frost action at higher altitude in cold climates disintegrate into small fragments. These fragments remain strewn over the slopes itself. Rocks exposed to high temperatures in deserts gradually disintegrate into smaller pieces that remain close to the parent rock.

19. Factors affecting weathering Susceptibility to weathering Structure Joints, faults and bedding.; their frequency Stratification Mineralogy (Bowen’s Reaction Series) Environmental factors Temperature Warm climate yields faster process Rainfall Heavy rainfall means faster weathering Freezing and thawing may occur Biological activity Presence of roots, breaking of rocks, mining Topography Amount of rocks exposed to agents of weathering Time

20. Bowen’s Reaction Series

21. Mechanical Weathering Breaking down to smaller size Through physical processes without change in their composition Driven by Uplift/exfoliation Erosion Temperature (expansion and contraction) Crystal growth Salt wedging - saltwater seeps into rocks and then evaporates on a hot sunny day, resulting in the formation of salt crystals. Colloid plucking – The wet soil particles or colloids that form on the rocks, dry up eventually and exert pressure on the minerals present in the rocks.  Biological activity (root wedging, burrowing)

22. Exfoliation This type of weathering is found in deserts and other areas of temperature extremes. In a thick rock body or where the rock is layered, upper layers are mostly affected due to temperature variations. As a result, the upper layers peel off from the underlying rock mass. In many cases, such a change is accompanied by chemical weathering, developing curved surfaces. The process of peeling off of curved shells from rocks under the influence of thermal effects in association with chemical weathering is called exfoliation.

23. Exfoliation: Castle rock track

24. Root/Frost action Pressure release causes Volume expansion Opening up of cracks, separation of foliation Water entry into cracks and root penetration Accelerated chemical weathering – crystal growth – disintegration Other agents accelerate the process

25. Erosion Action of water, wind and ice Water (streams and waves) Abrasion, lifting and deposition Wind Deflation and abrasion Ice (glacier) Plucking and abrasion

26. Chemical Weathering Alters the chemistry of parent material Main processes include Dissolution and precipitation Hydrolysis Carbonation Oxidation and reduction Ion exchange Chelation Leaching

27. Dissolution and precipitation Some rocks contain one or minerals that are soluble in water to some extent . Rock salt, gypsum and calcite are some of the minerals soluble in water. Some minerals are not soluble in water. The solvent action of water for many common minerals is enhanced when carbonated. For example limestone which is not soluble in water is soluble in carbonated water.

28. Hydration and hydrolysis These two processes indicate the direct attack of atmospheric moisture on individual minerals of a rock that affect its structural make up. When the surfaces of many crystals (having partially unsatisfied valences) come in contact with polarized water molecules, any one of the following reactions can occur: (1)The ions tend to hold the polarized side of water molecule and form a hydrate. This process of addition of the water molecule is called hydration. For example: CaSO 4 + 2H 2 O CaSO 4 .2H 2 O Anhydrite gets slowly converted to gypsum by hydration as shown above. (2) The process in which exchange of ions occur whereby water enters into the crystal lattice of mineral, is called hydrolysis. K + AlSi 3 O 8 + H + H Al Si 3 O 8 + K + Weathering of Orthoclase (K + AlSi 3 O 8 ) occurs as shown above.

29. Carbonation It is the process of weathering of rocks under the combined action of atmospheric CO 2 and moisture. The carbonic acid formed corrodes silicate bearing rocks. For example: 2KAlSi 3 O 8 + 2H 2 O+ CO 2 Al 2 Si 2 O 5 (OH) 4 + K 2 CO 3 + 4SiO 2 Felspar orthoclase decomposes to form a clay mineral, a soluble bicarbonate and silica.

30. Oxidation and reduction Iron bearing minerals and hence rocks are prone to oxidation and reduction. The effects are observed from colour changes produced in iron bearing rocks. For example: 4Fe + 3O 2 2Fe 2 O 3 (brown colour) Fe 2 O 3 +H 2 O Fe 2 O 3 .H 2 O Ferrous iron (Fe++) is oxidized to ferric iron (Fe +++) when exposed to air rich in moisture. Ferric iron is oxidized to stable ferric hydroxide. Iron oxide in rocks and minerals reduces to elemental iron in presence of decaying vegetation, which supplies carbonaceous content causing reduction.

31. Ion Exchange The processes of hydration, hydrolysis, oxidation and reduction on rocks and minerals often result in splitting of particles into smaller particles called colloids. These colloids are characterized by atoms with only partially satisfied electrical charges. Weathering of clay minerals, silica and iron oxides often results in colloid formation. These colloids are easily precipitated as their charges are satisfied and form stable products.

32. Chelation The chemical removal of metallic ions from a mineral or rock by  weathering  can provide their combination with organic compounds. The decomposition of dead plants in soil may form organic acids which, when dissolved in water, cause chemical  weathering .

33. Leaching Leaching is loss of soluble substances and colloids from the top layer of  soil by percolating  precipitation . The materials lost are carried downward (eluviated) and are generally redeposited (illuviated) in a lower layer. This transport results in a porous and open top layer and a dense, compact lower layer. The rate of leaching increases with the amount of rainfall, high temperatures, and the removal of protective vegetation. 

34. Environment for Chemical Weathering Low pressure (typically < 100 MPa) Low temperature (typically < 50 C) Abundance of free oxygen Abundance of free water (typically low pH) Formation of minerals that are stable under these conditions

35. Mineral Stability Near Surface Minerals formed at high pressure and temperature environment are least stable Mineral stability from highest to lowest Iron/aluminium oxides – quartz – clay minerals – muscovite – K/Na spar – biotite – amphiboles – pyroxenes – Ca plagioclase - olivine

36. SPHEROIDAL WEATHERING The breaking of original rock mass into spheroidal blocks is called spheroidal weathering. It is caused by the combined action of mechanical and chemical weathering . The original rock mass is split into small blocks by development of parallel joints due to thermal effects. Simultaneously, chemical weathering corrodes the border and surfaces of blocks causing their shapes roughly into spheroidal contours.

37. ROLE OF PLANTS AND ORGANISMS – Organic weathering Hydrogen ions (H + ) are released at the roots of plants during their growth and metabolism. These ions replace K+, Ca 2+ , Mg 2+ ions etc. from the rocks surrounding the root system. Thus these rocks and minerals undergo decomposition. Root systems of big plants and trees creep into the pre-existing cracks in the nearby rocks. Thus the cracks widen and the rocks break into fragments. Action of rodents on rocks will also cause the disintegration of rocks. Man has been breaking the rocks since very beginning for many purposes. The decay and disintegration of rocks by living things is called organic weathering.

38. PRODUCTS OF WEATHERING The product of weathering include (a) Regolith (b) Mineral and rock formation (a) Regolith : It includes all the weathered material, which covers the parent rock or is lying close to it. These materials deposit on the surface of the parent rock in huge thickness. In many cases, the weathering of rocks becomes slow after the formation of weathered layers at the top. It is because the overlying cover acts as a barrier for the atmospheric agencies to further act on the parent rock. The upper part of regolith is termed a soil.

39. Regolith has been broadly used to express: ( i )Eluvium: It is the end product of weathering that happens to lie over and above the parent rock. Eluvium forms a thin or thick layer on the parent rock, depending on the duration for which weathering has been operative on it. Regolith is another term for eluvium . (ii) Deluvium : It is the end product of weathering that has been moved to some distance after its formation due to weathering. The weathered products get deposited at the base of the slope and form heaps of various thickness. Gravity and rain-wash are the major agents which remove these weathered products to some distance.

40. Mineral and Rock Formation Weathering results in the formation of a few minerals and rocks . These include: Clay minerals: Weathering of silicate rocks under humid climatic conditions, results in the formation of Montmorillonite, Kaolinite and Illite . Montmorillonite is formed by the hydration of volcanic dust in semi dry climates. Hydration and carbonation of igneous rocks under humid climates form Kaolinite. Ores of Aluminium: The weathering of clay rocks produces ores of aluminium like bauxite (Al 2 O 3 .nH 2 O) and laterite.

41. ENGINEERING SIGNIFICANCE OF WEATHERING Soil is the ultimate product of weathering. A clear knowledge of the genetic background of soils is required for the better understanding of engineering properties of soil. It helps in proper planning and design of Engineering projects built on soil or rocks. When foundations are carried down to the bed rock, knowledge of degree of weathering, depth of weathered cover and the trend of weathering in that area is of utmost importance for the ultimate safety of the project. For a construction engineer it is necessary to find out: The extent to which the area for the proposed project has deteriorated due to weathering. It is necessary to remove loose weathered materials and carry foundation to solid rock. b. The effect of weathering on construction materials to be used in the project. This helps to select construction materials that are more durable to weathering.

42. ENGINEERING SIGNIFICANCE OF WEATHERING Chemical weathering breaks the bonds between the rocks that make the slope, causing the instability of slope. The slope rocks lose shearing strength and will finally fail. Therefore, slope stability must also ensure protection of slope rocks from weathering. The response of stones (like marbles, limestone and granite) to chemical environment must carefully be studied by the civil engineers prior to recommending them for major constructions. Disfiguring, pitting, honeycombing and loss of surface appearance are common effects of chemical weathering on stones.

43. Dearman Classification of weathering Descriptive terms for weathering of rock material were established on the basis that weathering involves a combination of mechanical disintegration, chemical decomposition and solution.

44. Soil Profile Soil is formed as a result of weathering of parent rock. Soil is a mixture of organic matter, various minerals and water which can support plant life on the surface of earth. A vertical section from the surface down to the bed rock reveals various layers of soil, which is termed as soil profile. Pedologists have identified these layers of soils and have designated them as different horizons. During the development of soil from a parent material, the actual transformation proceeds through certain well defined stages. In mature soils, these stages appear as a series of horizons. Such horizons, when arranged in descending order, are collectively said to form a Soil Profile for that particular area.

45. Soil Profile

46. A typical Soil Profile, beginning from surface and proceeding downwards, is generally made up of three main horizons (there may be many sub-horizons in each main horizon). ( i ) The A-Horizon : It is characterized by finely divided particles. It extends from a few centimetres to as much as a meter or more. It contains loose leaves, incompletely decomposed organic matter and good amount of humus in humid regions. In the basal zone of A-horizon, leaching effects may be seen. (ii) The B-Horizon : This zone lies immediately below the A-horizon. It is free from the staining of particles by humus. In arid regions, it may contain nodules of calcium carbonate or gypsum. Colloid accumulation is maximum in this zone. The lower region of B-horizon becomes more pebbly and coarse indicating transition to the C-horizon. The A and B horizon together form the true soil, called Solum .

47. ( iii) The C-Horizon : It is more a zone of weathered rock. In texture, it is often coarse grained and pebbly; in composition, it retains all the evidence of its parent rock. (iv) The D-Horizon : In a true soil profile, a sample from this horizon is the parent rock itself, unaltered as yet. In some cases, it may the solid rock mass on which the other zones are resting. O (humus or organic) Horizon: Mostly organic matter such as decomposing leaves. The O horizon is thin in some soils, thick in others, and not present at all in others. E (eluviated) Horizon: Leached of clay, minerals, and organic matter, leaving a concentration of sand and silt particles of quartz or other resistant materials – missing in some soils but often found in older soils and forest soils.

48. Colluvial soils : soil moved down largely under the influence of gravity for small distance Alluvial soil : soils that are spread out by streams along their banks Glacial soil : when ice melted, all the debris it carried was deposited in the form of soil Aeolian soil : wind is an active agent for transporting dust, silt and sand grade particles Lacustrine soil : accumulation of debris in lakes and other bodies of stagnant water

49. Colluvial soils Alluvial soil Glacial soil Eolian soil Lacustarine soil

50. Soil Erosion Loss or removal of superficial layer of soil by the action of wind, water or human action Causes Removing plant cover by burning pasture or felling trees Grazing too many animals on the land Bad cultivation practices Wind Frost Rain and water runoff Extreme climatic effects

51. Loss of top soil Whenever topsoil is exposed, water or wind can quickly erode it Plant cover can protect soil from erosion Plants breach the force of falling rain and plant roots hold the soil together Wind is another cause of soil loss Wind erosion is most likely to happen in areas where farming methods are not suitable to dry condition

52. Effects of soil erosion Loss of valuable top soil Burying valuable topsoil Damage to fields Plant productivity decline Desertification

53. Types of soil erosion Sheet erosion – Removal of thin layer of topsoil by raindrop splash or water run-off Rill erosion – If sheet erosion occurs with full force, the run off water moves rapidly over the soil surface. It cuts well-defined finger shaped groove like structures. It appears as thin channels or streams. Gully erosion – Here surface run-off is very high. Gullies resemble large ditches or small valleys and are metres to 10 metres in depth and width Stream bank erosion - The rivers during floods splash their water against the banks. In this way the water cuts through them. Particularly at curves, water strikes with great speed and the bank caves in alongside. This type of erosion is also known as Riparian erosion

54. Rill Erosion Gully Erosion Riparian Erosion

55. Other types Wind erosion – Soil erosion by wind is common in dry regions. Two characteristics of such region are: The soil is mainly sandy The vegetation is very poor or even absent Landslip or slip erosion – The hydraulic pressure which is caused by heavy rains increases the weight of the rocks at cliffs. As a result they come under the gravitational force and finally slip or fall off.

56. Soil Conservation Engineering Practices Windbreaks / Shelter Belts – Barriers formed by trees and plants with many leaves Check dams – Small check dams are constructed out of various materials like stones, timber, steel etc. to control erosion by reducing velocity of water flow. Contour Ploughing – The tractor operator follows the contours of hillside. The furrows thrown up by the plough stop the flow of water and encourage percolation in the soil Terraces – Large steps cut into a hillside which reduces slope length and steepness to limit the energy of running water and its ability to carry soil away. Agronomic Practices Strip farming – Different crops are planted and harvested at different times meaning that the amount of bare soil is minimised. Crop rotation – It is a method of growing a series of dissimilar crops in an area sequentially. Hence different crops are grown in the same area by rotation, that is , one after another. It helps in the improvement of soil structure and fertility.

57. Check Dams Windbreaks / Shelter Belts Contour Ploughing Strip Farming

58. Water erosion Water is the main agent of erosion; its power increases greatly with velocity. Rivers erode by downcutting and sides degrade to from V-profile valleys. On low gradients downcutting reduces so lateral erosion dominates notably on the outside of river bends Sediment is transported as rolled bedload and in suspension; particle size increases with velocity. Deposition is due to velocity loss, on gradient loss and inside bends so sediment is sorted by size

59. Geological Work of Rivers Being an exogeneous geological agent, a river carries out its work in a methodical way. Generally it is a slow process, but a steady one. Geological work of a river can be subdivided into three stages: River Erosion River Transport River Deposition

60. River Erosion Erosion means mechanical disintegration or chemical decomposition of rocks and their subsequent displacement. A river is a very powerful eroding agent and carries out its work in different ways such as hydraulic action, abrasion, attrition and solution (corrosion) Hydraulic action The inherent kinetic energy of running river water only takes part in causing the physical breakdown of rocs. Naturally, greater the momentum, greater will the erosion be. In the initial and youth stages, rivers which move faster along steep slopes acquire considerable kinetic energy. When such river water dashes against the rocks forcefully, it will break them down mechanically. This will be more effective if (a) the rocks have already weathered considerably (b) they are porous or not well cemented (c) they have easily soluble cementing material (d) they possess fractures, cracks or any other weak planes

61. The hydraulic action of rivers is due to inherent kinetic energy of river water The velocity of the river is the source of kinetic energy The river velocity or momentum is controlled by different factors like: ( i ) surface gradient (ii) form of the river (iii) rate of discharge The river gradient influences the velocity; if gradient is more, the velocity will also be more. When velocity is doubled, the erosive power of the river water increases four times The form of a river also influences the velocity; a river flows faster in a deep, narrow valley than in a shallow broad valley. This is so because the flow encounters greater friction from the ground. Therefore, erosion will be more pronounced in a deep and narrow river. The influence of volume of a river water on velocity is also considerable. The velocity increases with the volume. When a river has eight times larger volume, it will flow with a velocity doubly quicker. This is the reason why rivers become destructive during floods. Further, rivers which undergo considerable variations in velocity and volume cause more erosion than those which are uniform

62. Abrasion Physical breakdown of rock masses which are exposed along the sides and bottom of the river valley by the force of colliding sediments which are being transported by the river. The river along the course transports a a large quantity of sediments of various sizes and types By virtue of their movement, they possess energy and hence momentum During transport they hit the exposed rocks relentlessly leading to their breakdown

63. The preceding process is mainly influenced by The nature of transported sediments The nature of exposed rocks The nature of river water The attitude of rocks exposed Presence of joints in rocks Time factor

64. Potholes Abrasion action is observed in a spectacular way in potholes The potholes are cylindrical holes noticed in river beds. They are formed when the rock fragments of the river are caught in eddies. They revolve with great force round and round, moving downwards and scouring the river bed. The potholes continue to grow as long as eddies are powerful.

65. Attrition Erosion is with reference to transported sediments themselves When rock fragments hit the exposed rocks, not only the country rocks are affected but also an equal effect is borne by fragments Thus rock fragments during abrasion undergo wear and tear which is called attrition Attrition also occurs during the transportation of sediments When heterogeneous sediments are under transport, heavier and larger materials move slowly while finer and lighter materials move fast. The differential movement results in mutual collisions which occur again and again and causes attrition Large pebbles and small rocks generally roll down the valley floor, smoothening their edges. When attrition takes place first the angular edges disappear and the spherical, spheroidal and ellipsoidal stones are formed after a long journey.

66. Solution This process involves only chemical decay of rocks and no mechanical wear and tear . Among liquids, water is the most powerful solvent and dissolves many kind of materials When river water passes through different areas over different rocks its chemical potential increases with time. Depending upon their nature, some minerals are immediately affected while others are slowly affected Virtually there are no minerals which are completely unaffected Humid and temperate climates promote attack by corrosion process Eg. , Carbonate rocks (Limestone), marls, calcareous shales, dolomitic rocks Solution process will be more effective when River water has chemically more potential Time of contact between solutions and rocks is more The country rocks are calcareous

67. River Transport The load transported by a river can be grouped into three: 1. Bed load – heavier particles of sand, pebbles, gravels etc.. Transported mainly by rolling, skipping, bouncing or gliding along the bottom of the stream 2. Suspended load - fine silt, clay, fine sands etc carried by the river in its body of water in suspension 3. Dissolved load – Comprises all soluble matter and is transported in solution condition

68. Influencing factors of river transport Velocity of the river is its primary source of energy which enables it not only to carry out erosion but also to do transport work. The transporting ability of the river abnormally increases when the velocity increases. In the case of coarser sediments, when the velocity is doubled its transporting power increases 64 times The sediments with a higher density have a higher tendency to settle down, whereas the lighter sediments have a tendency to keep floating and are therefore transported over longer distances.

69. River Deposition Aggradation occurs The phenomenon of river deposition links up to the factors contributing to the loss of energy either temporary or otherwise Different kinds of river deposits: ( i ) alluvial cones and fans (ii) placer deposits (iii) delta deposits (iv) natural levees

70. Alluvial cones and fans In the youth stage, the river suddenly loses its energy partially because in the foothill regions it emerges out of the mountainous area and enters into a relatively plain ground. This transition involves loss of gradient which is responsible for loss if its velocities and consequently its energy. This leads to some deposition of river sediments at the foothills along its valley. If the deposit is spread over a small area but has a relatively steep slope, it is called an alluvial cone . If the deposit is spread over a large area and has a gentle slope, it is called an alluvial fan .

71. Placer deposits In the mature stage, the river is generally in balanced equilibrium condition i.e., its energy is just enough to transport its load Under such conditions when the river encounters any formidable obstacle or impediment, it shall not have capacity to uproot it and therefore it takes a diversion and continues its downward course. In this process the river loses a part of energy in dashing the obstacle and results in formation of deposits known as placer deposits. By virtue of its relatively weak condition, the river compulsorily undergoes a number of curves or bends which makes its path zig-zag and this process is called meandering

72. Meandering is a characteristic feature of the mature stage. In due course of time, these bends become more and more acute due to deposition of sediments along the inner curve and erosion along the outer curve Ultimately under favourable conditions such as floods these loops are cut off from the main course of the river. Such cut off bodies which are curved in plan are called cut off lakes or horse shoe lakes or ox bow lakes

73. Delta deposits Delta deposits are characteristic of old stage of the river The occurrence of these deposits is due to the exhaustion of the river energy which is spent by in transporting the load over a long distance. The favourable conditions for the formation of delta are: ( i ) the river should have large amount of load (ii) the river should have fully exhausted its energy at the time of its merger with the sea (iii) the ocean at the mouth of the river should not be turbulent otherwise as and when loose sediments are deposited, they are washed away by the waves and currents of the sea

74. Natural levees These are essentially riverbank deposits made by a river along its bank during floods. The natural levees are sometimes helpful in preventing further flooding in a river provided the volume of water a new prospective flood is not much higher than that of a previous floods.

75. Classification of Earth Movements Based on type of movement which the displaced mass has suffered Earth flows – movement is distributed throughout the displaced mass Landslides – movement is confined to a definite shearing plane or zone Subsidence – movement is vertically downwards

76. Earth flows Solifluction refers to the downward movement of wet soil along the slopes under the influence of gravity Creep refers to the extremely slow downward movement of dry surficial matter and is always limited to the surface or the area just below it. The rate of movement is so slow that it may not be detected until its effects on engineering structures can call attention to it. Rapid flows are similar to creep but differ with respect to the speed and depth of the materials involved. These are rapid earth flows and involve considerable depth. These are generally accompanied by heavy rains.

77. Landslides Downward sliding of huge quantities of landmasses Sliding occurs along steep slopes of hills or mountains May be sudden or slow in occurrence Loose and unconsolidated surficial material undergoes sliding Importance of landslides If they occur in places of importance such as highways, railway lines, valleys, reservoirs, inhabited areas and agricultural lands, they lead to blocking of traffic, collapse of buildings, harm to fertile lands and heavy loss of life and property

78. Landslides Debris slides – failures of unconsolidated material on surface of rupture. In a majority of the cases, debris slides represent readjustment of the slope of the ground. These are common along steep sides of rivers, lakes etc. they may occur on any slope where internal resistance to shear is reduced below a safe limit. Debris slides of small magnitude are called slumps. Slump is often accompanied by complementary bulges at the toe. Debris flows are generally graded into earth flows Rock slides – movements of essentially consolidated material which mainly consists of recently detached bedrock Rock falls – refers to the blocks of rocks of varying sizes suddenly crashing downwards along steep slopes. These are common along steep shore lines in the higher mountain regions during the rainy season

79. Subsidence Subsidence due to plastic outflow – Beneath heavy loads, plastic layers which become plastic due to disturbance may be squeezed outwards, allowing surface settlement or subsidence. E.g. Clay may be extruded from beneath a structure Subsidence due to compaction – sediments often become compact because of load. Excessive pumping out of water and the withdrawal of oil from ground also cause subsidence locally Subsidence due to collapse – in regions where extensive underground mining has removed a large volume of material, the weight of the overlying rock may cause collapse and subsidence. It may also happen when underground formations are leached by subsurface water

80. Causes of landslides Immediate causes Factors such as frictional resistance will cause the overlying mass to remain in a critical condition. When there is a sudden jolt or jerk or vibration occurs, the frictional resistance will be overcome and leads to destruction. Sudden jolting due to avalanche, violent volcanic eruption, fall of a meteorite, occurrence of an earthquake, tsunamis or blasting of explosives in quarrying, tunnelling, road cutting or mining.

81. Internal causes Effect of slope – steeper slopes are prone to landslips of loose overburdens due to greater gravity influence whereas gentle slopes are not prone to such land slips because in such cases loose overburden encounters greater frictional resistance and any possible slip is stalled Effect of water –Presence of water reduces the intergranular cohesion of particles of loose ground. This weakens the ground inherently and therefore makes it prone to landslide occurrence Effect of lithology – Rocks which are highly fractured, porous and permeable are prone to landslide occurrence. The clay content contributes to the slippery effect. Thinner strata are more susceptible to sliding. Effect of associated structures – Inclined bedding planes, joints, faults or shear zones increase the chances of landslide. When their dip coincides with that of the surface slope they create conditions of instability. Joints and faults provide scope for easy percolation of rain water and increases instability. Effect of human factors – Sometimes human beings interfere with nature by virtue of their activities and causes landslides. This may happen when undercutting are made along the hill slopes for laying roads or railway tracks. Such an activity eliminates lateral support which means gravity will become more effective leading to landslide occurrence

82. Effects of Landslides Disruption of transport or blocking of communications by damaging roads and railways and telegraph poles Obstruction to the river flow in valleys leading to their overflow and floods Damage to sewer and other pipelines Burial or destruction of buildings and other constructions Causes earthquakes

83. Preventive measures for landslides To counter the effect of slope: Retaining walls may be constructed against the slopes so that the material which rolls down is not only prevented from further fall but also reduces the slope. Terracing of the slope is another effective measure. To counter the effect of water: A proper drainage system is the suitable measure. This involves the quick removal of percolated moisture by means of surface drainage and subsurface drainage. Construction of suitable ditches and waterways along slopes and provision of trenches at the bottom, and drainage tunnels help in draining off the water from the loose overburden. To counter the structural effects: the different structural defects such as weak planes and zones may be either covered or grouted suitably so that they are effectively sealed off. These measures not only prevent the avenues of percolation of water but also increase the compaction or cohesion of the material concerned. Not to resort to reduce the stability of existing slopes: This is done by not undertaking any undercutting on the surface slope and by not undertaking any construction at the top of the hills To counter the loose nature of overburden: Growing vegetation, plants and shrubs on loose ground helps in keeping the loose soil together Avoiding heavy traffic and blasting operations near the vulnerable places naturally helps in preventing the occurrence of landslides

84. Sea Waves and Currents Waves Undulatory disturbances on the surface of the seawater due to strong rushing winds, earthquakes, attraction of sea water by sun and moon and similar reasons During the propagation of a wave, each water drop is distributed from its original place of rest and forced to follow a motion in a circular, ellipsoidal, elongated or irregular orbit before coming to rest again

85. Types of sea waves 1. Oscillatory Waves Each particle moves in a circular orbit The waves start from the deep portions of sea, when it reaches the shallow depth portions (i.e. near shore), these particles cannot follow a perfect circular motion. Consequently an oscillatory wave rushing towards the shore breaks at the crest region. A zone may be identified along the seashore where these waves regularly break is called a breaker zone.

86. 2. Translatory Waves Typically occurs at shallower depths (near shore) in the sea and thus move along the seashore They are commonly produced after the oscillatory waves break and rush forward In these waves, the water particles are actually moved or translated forward, rising and falling again and again in the process

87. Currents These are layers or strips of seawater that are actually pushed forward in any particular direction In most cases, sea currents are the results of dissipation of extra volume of water thrust on the shore by the advancing waves. Types 1. Littoral currents These are bodies of seawater of considerable volume moving along and parallel to the shore 2. Rip Currents These are bodies of seawater moving backwards to sea after having reached and struck the seashore They often move below the surface of the sea and reach varying distances up to the middle of the sea These are believed to represent that part of sea wave, which has been unable to form a part of littoral current but rip current’s development is independent of littoral currents

88. Rip Currents

89. Marine Erosion Marine water erodes the rocks at the shore by 3 ways: Hydraulic action : That is, by its very high wave velocity Abrasion : Sea water carries lot of sediment particle during its motion. These sediment particles have erosive power to erode the shore Corrosion : Sea water is Salish so due to its chemical properties it adversely affect the shore materials.

90. FEATURES OF MARINE EROSION Continued marine erosion results in considerable or even total modification of the original shoreline. Some very common features of marine erosion are headlands bays sea cliffs wave-cut terraces.

91. Headlands and Bays In an originally uniformly sloping shoreline composed of materials of unequal hardness, the softer rocks get eroded easily and quickly. Seawater enters the inland spaces so created along the shore. These form the bays. The stronger rocks, however, resist erosion to a great extent and stand outstanding for a considerable time. These may get smoothened and variously modified but still stand as projecting parts of original shoreline as headlands.

92. Headlands Bays

93. Sea Cliffs Sea cliff is a seaward facing steep front of a moderately high shoreline and indicates the first stage of the work of waves on the shore rocks. There may be a number of sea cliffs seen on a shoreline. They are outstanding rock projections having been smoothened here and plucked there, pitted at one place and polished at another spot by a combined action of waves and currents. These cliffs may ultimately be worn due to continued undercutting by the action of waves. Thus shoreline is reduced to a smooth, free from irregularities, seaward sloping surface ie cliff.

94. Wave-Cut Terraces Wave cut terrace is a shallow shelf type structure, caned out from the shore rocks by the advancing sea waves The waves first of all cut a notch where they strike against the cliff rock again and again. The notch is gradually extended backwards to such a depth below the overlying rock that the latter becomes unsupported from below. The cliff eventually falls down along the notch. A platform or bench is thus created over which the seawater may rush temporarily and periodically. The resulting structure is often called a wave-cut terrace, a platform or simply a bench.

95. LANDFORMS ON COAST MARINE DEPOSITION Seas are regarded as the most important and extensive sedimentation basins. This becomes evident from the fact that marine deposits of practically all the geological ages are known to occur in different parts of the world . These deposits are exposed at many places in almost all the continents. All the marine deposits or landforms are conveniently classified into two groups : Shallow water deposits Deep water deposits

96. (A)SHALLOW WATER DEPOSITS (Neritic deposits) These include marine deposits laid down in Neritic zone of the sea which extends from the lowest tide limit to the place of the continental shelf where the slope becomes abruptly steeper . The material that goes into the making of the shallow water deposits is derived from the land and shore rock, mostly through the action of waves . Besides these sediments, a group of marine organisms collectively known as Benthos also contributes greatly as a source material for making the shallow water marine deposits . Common examples of Neritic deposits are: beaches, spits, bars and tombolos .

97. Beach These are loose deposits made by the sea near the shore from the materials eroded from nearby regions. The lower margin of a beach is commonly beneath the waves whereas the upper margin is a few meters above the still water. Waves and currents play a great part in the formation of a beach. Streams entering the sea generally drop their load at some distance from the shore into the sea. A part of these sediments is brought back to the shore by the advancing waves that deposit them there due to a reduction in velocity. Beach formation is very much favoured when the continental shelf has a gentle slope.

98. SPITS AND BARS These are ridge shaped deposits of sand and shingle that often extend across the embayment . A spit is formed when a sediment laden shore current comes near an embayment on the coast, there is strong tendency for it to keep its normal course rather than to follow the shore line of the embayment; hence it moves through deeper and quieter waters where it lays down much of its sediments . This process may result in an incomplete ridge in continuity with the shore but terminating in open waters. This is the spit . When the ridge (spit) so formed in the above manner closes the mouth of the embayment completely, it is known as bar.

99. Tombola It is a form of bar (marine deposit) that connects a headland and an island or one island with another island. Tombola is developed in the same way as a spit or a bar i.e. by the deposition of materials carried away by the current.

100. (B) DEEP WATER DEPOSITS These deposits consist mostly of mud and oozes (a sea organism ) The oozes that form bulk of some of such deposits consist of small organisms known collectively as planktons . Death and decay of these organisms and plants followed by their accumulation in regular and irregular shapes eventually results in huge deposits . Sometimes these deposits take the shape of extensive ridge like formations that are partly or totally submerged under seawater thereby creating a great risk for ships and boats navigating on the sea . These deposits are commonly called reefs.

101. CORAL REEFS Definition These are peculiar type of ridge-like marine deposits that have been formed due to accumulation of dead parts of certain types of sea-organisms. Corals - a type of calcium secreting organisms - predominate among the source organisms for such reefs; hence they are commonly designated as coral reefs. These reefs may or may not be visible above the seawater depending upon the tide. Types 1. Fringing reefs 2. Barrier reefs 3. Atolls

102. The Fringing Reefs These are thin, tabular sheets of coral accumulations that are developed along the border (fringe) of a mainland coast or along the rim of an island. When they accumulate on border region of islands, they appear like a ring shaped deposit around the island during the low-tide. A simple fringing reef has a steeply sloping sea front and a flat pavement surface covered with veneer of growth.

103. The Barrier Reefs These are more common type of reefs and occur at a distance from the Shore or the island running in the form of parallel, flat-topped ridges. There is a body of water in between called lagoon that separate the reef from the shore or the island. The ridge may be continuous or broken here and there; it has a steep slope facing the sea and a gentle slope towards the lagoon.

104. Atoll An atoll is essentially an annular, circular or semi-circular coral reef surrounding a central body of water that is as usual called a lagoon. In a typical atoll, the ring made of coral deposits may be continuous or discontinuous, more often broken at places. The top of an atoll is generally flat and pavement like in appearance.

105. Origin of Reefs They are known to grow only in relatively warm waters (68-78°F), and at depths ranging between 20-60 m. The seawater should be clear and saltish. The direction of wind is also known to exert considerable influence on the growth of the corals. Darwin suggests that the coral reefs are formed on a subsiding or sinking platform which is formed due to the occurrence of earthquakes on the sea floor According to Darwin, the three types of reefs -the fringing reef, the barrier reef and the atoll, actually represent three stages in the development of a single reef deposit. Origin of reefs is based on Glacial Control Theory . According to him, the submergence of an old reef framework is due to rise in the level because of melting of ice.

106. COASTAL PROTECTION STRATEGIES HARD Engineering Strategies : Building or creating something which will interfere with coastal processes – usually to reduce the power of breaking waves against cliffs. SOFT Engineering Strategies : With the natural processes of sea and sand.

107. HARD Engineering Strategies (a) Groynes A barrier extending from the beach or offshore into the sea in the transverse direction to the sea shore. Groynes are used to reduce the loss of beach grade sediment through long shore drift. With proper groyne field design, beach erosion can be reduced due to trapped sediment on the up-drift side of the groyne. Groynes can be constructed out of wood, stone or concrete depending on the size of native beach material. Although acting to reduce the erosion on site, groynes typically cause sediment starvation down-drift, shifting the erosion further down the coastline.

108. HARD Engineering Strategies (b) Gabions Wire cages filled with stones/rocks stacked along the cliff base protect the shore. Advantages Easily installed Cheaper than sea wall Disadvantages Not very attractive Needs frequent checking & repair Not easy for people to get over to get to beach May contain rats nests

109. HARD Engineering Strategies (c) Rock Armour/ Rip-Rap Huge blocks of rocks is placed along the shore Advantages Popular option in recent years – seen to be effective Cheaper than sea wall Disadvantages Not very attractive Not easy for people to get over to get to the beach ( broken ankles) Rats may live in spaces

110. HARD Engineering Strategies (d) Sea Walls These structures are  designed to protect resources behind them from the impacts of wave energy and associated erosion . Although they hold soils in place behind the structure, seawalls usually accelerate erosion on adjacent beaches. It also protect areas of human habitation, conservation and leisure activities from the action of tides, waves, or tsunamis Seawalls are constructed from various materials, most commonly reinforced concrete, boulders, steel, or gabions. Other possible construction materials include vinyl, wood, aluminum, fiberglass composite, and biodegradable sandbags made of jute and coir. Vertical or near-vertical structures designed to limit erosion due to wave attack. Concrete curved superstructures can be incorporated to reduce wave overtopping of sea water.

111. HARD Engineering Strategies Advantages Deflects Waves Strong Effective Lasts a long time Disadvantages Expensive Likely to need repair fairly regularly Deflected waves can scour sea bed and undermine the sea wall foundations

112. HARD Engineering Strategies (e) Sea dike Large land-based sloped structures used to prevent overtopping during high tide and storm events . Sloped towards sea Instead of providing protection against wave action, sea dikes fix the land-sea boundary in place to prevent inland flooding . Sea dikes are usually built as a mound of fine materials like sand and clay with a gentle seaward slope in order to reduce the wave run up and the erodible effect of the waves.

113. HARD Engineering Strategies (f) Revetments Onshore sloped structures used to reduce the landward migration of the beach due to coastal erosion. The Structure reduces the water energy and thus reduces the erosive power of the wave . They can be constructed out of concrete, stone or asphalt. The structure should be designed to have a crest sufficiently high to stop wave overtopping during a storm event

114. HARD Engineering Strategies Advantages Provides hard face to cliff Easily installed Cheaper than sea wall Deflects wave power Disadvantages Can be eroded from below easily Needs frequent repair Not very attractive

115. HARD Engineering Strategies (g) Breakwater These are offshore sloped or vertical structures reducing incoming wave energy arriving at the coastline . As well as reducing erosion, this also creates calmer waters for harbours and shipping . They can be constructed out of concrete or stone and rock.

116. SOFT engineering strategies (a) Beach Beach - a beach in itself acts as a coastal defence as it reduces wave impact and prevents inland flooding. However the beach needs to be properly managed to ensure, it is wide and high enough to prevent from being overtopped during high sea levels. This can be done through beach replenishment where beach-grade sediments are used to top-up the beach, increasing its level of protections.

117. SOFT engineering strategies (b) Offshore Reef Man-made artificial reefs are built just out to sea to for the waves to break on them and create calmer water at the coast. Advantages Provides inshore area of calm water Effective at preventing the cause of cliff erosion Disadvantages Very expensive Need openings for fishing boats to get to sea Damages fish nets. Can be breached in stormy conditions and need repair.

118. SOFT engineering strategies (c) Reprofiling The sediment is redistributed from the lower part of the beach to the upper part of the beach Advantages Cheap and simple Reduces energy of waves Disadvantages Only works when wave energy is low Needs to be repeated continuously