General Geology Acknowledging Dr.V.Nagarajan. UNIT I General Geology CONTENTS Geology in Civil...

General Geology Acknowledging Dr.V.Nagarajan

UNIT I General Geology CONTENTS Geology in Civil Engineering Branches of geology, Earth Structures and composition, Elementary knowledge on continental drift and plate technologies. Earth processes and Ground Water Weathering, Work of rivers, wind and sea and their engineering importance and Earthquake belts in India. Mode of occurrence of Ground water, Prospecting & importance in civil engineering. 2

UNIT I General Geology Geo logy Earth Science It is concerned with engineering properties of geological materials, including strength, compatibility, porosity and permeability Present is the key to the past Branches of Geology 1.Study of composition of earth mineralogy 2.Study of earth structure 3.Study of earth surface features 4.Study of earth history 5.Engineering Geology 3

UNIT I General Geology 1.Study of composition of earth mineralogy a. Mineralogy b. Petrology c. Economic Geology d. Hydrology and ground water e. Geochemistry f. Geochemical Problems 2.Study of earth structure a. Geodesy b. Geophysics c. Structural Geology d. Volcanology 3.Study of earth surface features a. Geomorphology / Physical Geology 4.Study of earth history a. Historical Geology b. Palaeontology c. Astrogeology 5.Engineering Geology 4

UNIT I General Geology 5

UNIT I General Geology 15 Earth Processes It refers to the geological events, such as weathering, deposition, erosion, earthquakes, volcanic eruptions and mountain building, that shape and reshape the surface of the earth. Deep Earth Processes i. Heat -Radioactive decay. -Gravitational energy released during accretion and formation of earth ii. Mantle convection iii. Gravitational forces associated with density differences, due to hot less-dense magma from mantle. This affect plate movement.

UNIT I General Geology Transformation of rocks into soil 16 Weathering of Rock Soft-weathered rock Soil-forming processes Hard Rock Soil

UNIT I General Geology Rock Cycle 17

UNIT I General Geology Weathering Total sum of decomposition and disintegration 18 Magma Magma Solidification Formation of Rocks & Minerals Deposition Weathering of Rocks Landforms of weathering eg. Soil, caves etc. Sediment Production Land formation by erosion processes eg. River, valley etc. Erosion Process Landform formation by deposition of sediments eg. Sand bars, glacial, deltas, etc. Sediment Transportation Deposition of Sediments Decomposition of rocks and minerals Erosion of sediments by wind, water and ice Decomposition of sediments by wind water, water and ice

UNIT I General Geology Types of weathering 1.Physical Weathering 2.Chemical Weathering 3.Biological Weathering 1.Physical Weathering / Mechanical weathering Caused by the effect of changing temperature on rocks i.Freeze thaw a. water seeps into cracks of rock, freezes and expands b. Most effective in jointed rocks c. Volume expands by 9% in volume d. Alternate freeze thaw results in spilt of rocks and it breaks off ii. Exfoliation a. Cracks develop parallel to land surface as a result of uplift and erosion b. Rocks get peeled off in sheets rather than eroded grain by grain Physical weathering does not lead to alternation of rocks 19

UNIT I General Geology 2. Chemical Weathering Process of mineral alternation due to chemical reactions Process : Carbonation, Hydration, Hydrolysis, Oxidation and ion exchange in solution i. Carbonation a. Carbon di oxide reacts with rocks, which contains calcium carbonate (limestone and chalk) b. It takes place when rain combines with carbon di oxide or organic acid to form weak carbonic acid with calcium carbonate c. Decrease in temperature ii. Hydrolysis a. Water combines with substances in rocks, which is softer than original rock b. Silicate and Carbonates are affects the minerals c. Pure water ionizes and reacts with silicate minerals iii. Oxidation a. Oxygen combines with other element to form new rocks b. New rock softer and easy to break Temperature is in equilibrium - minerals in rock formed beneath the surface 20

UNIT I General Geology 3. Biological Weathering/Organic Weathering Biological process of weathering that breaks down the rock i.Physical penetration and growth of roots and digging activity of animals ii.Release of chelating compounds and acidifying molecules 21

UNIT I General Geology Factors affecting weathering 1. Composition of rocks Acidic rocks weather more quickly than basic rock. Limestone and chalk are soluble in rain water and subjected to carbonation - solution 2. Climatic condition Moisture, temperature, wind and air pressure determines the weathering action by making it more rapidly 3. Topography and vegetation By exposing rocks to sun, wind and vegetation 4. Grain Size Rate of weathering is high in coarse grain soil than fine grain soil 5. Human activity Industrial activity and human development 22

UNIT I General Geology Erosion Wearing away of earths surface material by any natural process and its transportation by natural agencies ( Wind and running water) Agents of Erosion 1. Water Erosion Hydraulic action of the water itself moves the sediments, water acts to corrode sediments by removing ions and dissolving them and particles in the water strike bedrock and erode it 2. Wind Erosion Occur in the place where there is less rainfall. Movement of material by the wind and occurs when the lifting power of moving air is able to exceed the force of gravity 3. Glacial Erosion Wearing-down and removal of rocks and soil layers by a glacier. The erosion work of glaciers is accomplished through the processes of abrasion, plucking and polishing 4. Water Erosion Wind blows over the ocean and sea surface. Top layers move faster than the lower layers and tumbles over it. Erosion of sand is more easier for the waves as compared to rock. 5. Gravity Erosion Gravitational erosion causes mass movement of rock and sediments due to the force of gravity. Different form of gravitational erosion include avalanche, landslide, debris flow, mudflow and sinkhole formation 23

UNIT I General Geology PLATE TECTONICS 24

UNIT I General Geology PANGAEA Most species exist for a limited period of geological time and then become extinct. Within the fossil record there are also instances of mass extinctions. Evidence of six mass extinctions can be seen in the fossil record. There are two primary events that are believed to have contributed to these mass extinctions. The movement of the Earth's surface via continental drift is one such event. Plate tectonics provides the explanation for why continental drift occurs. The earth's crust is made up of many different plates that move around independently of each other. Where the plates collide with each other, mountains can be formed and there are earthquakes. Mount Everest is getting measurably taller each year because of this activity. The current direction of the drift of the plates has been determined using GPS data from satellites. By assuming that the plates have always been moving in the directions they are moving now, all the plates would have been connected together as a huge supercontinent called Pangaea. 25

UNIT I General Geology Plate Tectonics is a geologic theory explaining the movements and forces in the Earth crust. Earth's surface is made up of tectonic plates. A tectonic plate is a large section of land made of the Earth's crust and the upper layer of the Earth's mantle. Tectonic plates vary in size and shape. The theory of plate tectonics was first formulated by the scientist Alfred Wegener at the beginning of the 20th century. According to this theory, the Earth's crust is divided into about 28 large, slowly- moving plates, called tectonic plates. The movement of tectonic plates is called plate tectonics. All continents, oceans and islands sit on tectonic plates. Scientists are still arguing about the exact number of tectonic plates, so different sources might have different numbers. Tectonic plates are constantly moving and interacting with each other, generating enormous and very powerful forces. These forces are the main and the strongest 'shapers' of the Earth's landforms. Plate tectonics cause continents to move and shake and volcanoes to erupt. 26

UNIT I General Geology Continental drift Continental drift is the movement of the Earth's continents relative to each other by drifting across the ocean bed. The speculation that continents might have 'drifted' was first put forward by Abraham Ortelius in 1596. The concept was independently (and more fully) developed by Alfred Wegener in 1912. The theory of continental drift was superseded by the theory of plate tectonics. The hypothesis that the continents had once formed a single landmass before breaking apart and drifting to their present locations was first presented by Alfred Wegener to the German Geological Society on 6 January 1912. 27

UNIT I General Geology Types of Plate boundaries There are three types of boundaries between lithospheric plates: 1. Convergent boundary plates converge, or come together. If a plate of oceanic lithosphere collides with thicker and less dense continental lithosphere, the denser oceanic plate will dive beneath the continent in a subduction zone. 2. Divergent boundary two plates diverge or move apart New crust or lithosphere is formed. 3. Transform fault boundary plates slide past one another with no creation or destruction of lithosphere 28

UNIT I General Geology Implications of Plate Tectonics 30 Oceanic lithosphere is constantly being created at divergent plate boundaries, destroyed at convergent plate boundaries, and offset at transform plate boundaries Oceans are temporary features In the past 600 million years, Atlantic has opened, closed and reopened (we are now witnessing only the latest opening event)

UNIT I General Geology Types of Convergent Boundaries 31 Oceanic-oceanic convergence -subduction of oceanic lithosphere under another plate of oceanic lithosphere -molten material from subducting slab rises to form an island arc (e.g. Japan) Oceanic-continental convergence -subduction of oceanic lithosphere under a continental lithosphere -molten material from subducting slab rises to form an continental arc (e.g. Cascades with Mt. St. Helens) Continent-continent collision -where two pieces of continental lithosphere meet (intervening ocean becomes completely closed) -continental lithosphere cant be subducted, so basically shortens -Earths highest mountain belts produced in this way (e.g. Himalayas)

UNIT I General Geology 32 Model for sea-floor spreading showing expansion of ocean ridges (divergent) and arc- trench (convergent) systems. Three lithospheric plates are shown moving over the weak low-velocity zone of the upper mantle. Magmas are produced in arcs by heating along the subduction zone. Deep earthquakes are concentrated in the relatively cool, brittle downgoing slab. Shallower earthquakes occur under the spreading ridges.

UNIT I General Geology Importance of India's Seismic Zoning Map This kind of map is mainly used by the Department of Disaster Management of the different state governments in the country. This map helps them in planning for a natural disaster like earthquake. An Indian seismic zoning map assists one in identifying the lowest, moderate as well as highest hazardous or earthquake prone areas in India. Even such maps are looked into before constructing any high rise building so as to check the level of seismology in any particular area. This in turn results in saving life in the long run. Following are the varied seismic zones of the nation, which are prominently shown in the map: Zone - II: This is said to be the least active seismic zone. Zone - III: It is included in the moderate seismic zone. Zone - IV: This is considered to be the high seismic zone. Zone - V: It is the highest seismic zone. Indian Standard Code Available IS 1893 Criteria for earth resistance structure IS 4326 Code of Practice for earth quake resistance 33

UNIT I General Geology Geological work of Water >> Approximately 75 % of earths surface is covered with water. Out of which 97% is salt water, 2% is glacier ice at north and south poles and 1% is fresh water >> Water present in earth -> channels, streams, rivers, lakes, ground water, sea and oceans >> Hydrological cycle components like evaporation, transpiration, condensation, precipitation and runoff -> reaching sea 1.Geological work of running water 2.Geological work of ground water 3.Geological work of sea and ocean 4.Geological work of Glaciers 35

UNIT I General Geology 1. Geological work of running water a.River Profile b.River Meanders c.Oxbow lake d.Levees e.Gorges and Canyons f.Deltas a.River Profile Longitudinal profile and it is function of lithology of area through which stream flows, discharge, amount and texture of channel, regional gradient Flow and discharge depends upon climate, geologic and geomorphic properties of river drainage basin area Water in river is accumulated from precipitation of ground water 36

UNIT I General Geology b. River Meanders River flowing over gently in sloping ground, begin to curve back and forth across the land scape It forms when moving water in a stream erodes the outer banks, widens its valley and deposit it on inner curve in further down stream Its sinuosity is very high i.e > 1.5 Deepest part of the channel is outside the bed. The water flows faster in these deeper section and erodes the material. The water flow slowly in shallow depth and it cannot carry much sediments Helps in under standing the reason behind change in river flow over time, direction and flow of river Coriolis force generate erosion on one bank and deposit of sediment on the opposite bank and secondary currents cause flow erode portion until redistribution of velocity forming tortous water course 37

UNIT I General Geology c. Oxbow Lake Crescent shaped lying alongside, formed due to erosion and deposit of soil along the river course Area : Flat, low-lying plains, rivers often empties into another body of water Have high sinuosity and opportunity for longer lake formation River with lower sinuosity characterised by fewer cutoffs and shorter oxbows due to shorter distance of their meanders (Constantine and Thomas, 2008) 38

UNIT I General Geology d. Leeves Embankment raised to prevent a river from overflowing which runs along banks of river or canal Can be man made or naturally formed Natural : due to sediments settle on river bank, raising the level of the land around the river Artificial : to prevent flooding, to slow down the natural course of watercourse. usually built by piling the earth on cleared and levelled surface It is made from stones laid in horizontal rows with bed of spetchel Formation of Natural Leeves 39

UNIT I General Geology e. Gorges and Canyons Deep, narrow valley with steep rocky sides Canyon: formed by erosion caused by rivers. Cliff of canyons are made of harder rock. These are recent addition of rocks. Formed mainly due to physical weathering Gorges: small and narrow than Canyon Canyons Gorges 40

UNIT I General Geology f. Deltas Low-lying landform at mouth of a river, known for fertile soil and abundant vegetation River reaches a lake or sea. Flow is slow and have less power to carry sediments River drop so much sediment that waves and tides cant carry. It builds up in layer forming delta. Area: Flat and plain above water Tide dominant delta : Long and narrow offshore basin or islands at mouth of the river Wave dominant delta : triangle in shape River dominant delta : birds foot 41

UNIT I General Geology 2. Geological work of ground water Found beneath the earths surface and occupies cracks and pores within rock material. Can cause erosion because the GW begins to wear away the materials and soil in ground Formation of acid is possible and possibility to dissolve the minerals a.Formation of Karst Topography b.Formation of caves c.Karst Valley a.Formation of Karst Topography Landscape are characterised by numerous caves, sinkholes, fissures and underground streams. It is formed by dissolving action of water. Karst landscape develop where bedrock is comprised of extremely soluble calcium carbonate rock and mainly where bed rock is limestone Karst landscape constitute only about 10 to 20 % of earths surface (Palmer, 1991) 42

UNIT I General Geology 43 Active Process of Karst Topography

UNIT I General Geology b. Formation of caves Underground passages and chambers are commonly known as caves or caverns It is seen in areas where limestone is abundant and rainfall is sufficient ground water may be significant erosion agent producing large cavities and caves The cave thus formed mainly depend upon the lime in the limestone. Formation begins when rainwater absorbs carbon di oxide as it falls on the atmosphere. 44

UNIT I General Geology c. Karst Valleys Blind Valley: Abrupt end of karst formation Half blind Valley: Surface is occasionally present downstream of sinkpoint Allogenic Valley : Deep gorge like valley formed as a stream flows from non krastic region into karstic region Dry Valley: Well developed valley without any stream. de as it falls on the atmosphere. 45

UNIT I General Geology 3. Geological work of sea and ocean (Stagnant Water) Approximately 70 to 75 % of earth is ocean and sea. Processes of hydraulic action, corrosion and attrition play vital role in sea and oceanic water formation Geological features a.Coral reefs b.Deep water clastic reefs a.Coral Reefs Built on hard surface and found in oceans and lagoons. It is type of marine ridges or mounds formed as a result of accumulation, deposition and compaction Great barrier reef is the largest coral reef in world Types of coral reefs : Fringing,Barrier reefs and Atoll b. Deep water Clastic reefs Deposited on continental slope between neritic and abyssal zone Deepwater deposit provide excellent reservoirs of oil and gas world wide Thick and sandy turbid layers to form excellent oil and gas reservoirs burried deeply beneath the sea floor. 46

UNIT I General Geology 4. Geological work of Glaciers Glaciers themselves do relatively little significant erosion because ice is so soft. Under the weight of an ice sheet thousands of feet thick continental glaciers detach material from the surface by crushing the underlying bedrock. Once the material is loosened from the surface, ice can quarry (also known as plucking) the rock by freezing around and into fractures, then lifting it from the surface. The rock embedded in the ice gouges and smoothes bedrock surfaces by abrasion. Striations are fine scratches left in bedrock by abrasion. At a larger scale, linear grooves are ground into the bedrock in the direction of ice movement. Episodic movement leaves crescent-shaped marks called chatter marks gouged into the bedrock. The constant abrasion of exposed rock also creates polished bedrock. Glacial drift is the general term applied to materials eroded from the surface and deposited by glaciers. Glaciers transport the embedded material towards the front of the glacier as if they were on a conveyor belt, or is deposit directly beneath the ice. Most material is embedded in the lowest few meters of the glacier and along its sides. Little drift material is lodged in the interior as flow through most of the glacier is laminar, except at the nose where thrust faulting of the ice occurs. When the ice becomes so burdened by its load of soil and rock fragments, it deposits the mixture of fine and coarse textured material in place as glacial till. Till is distinguished by its lack of sorting. 47

UNIT I General Geology Mode of soil transportation through water Rain fallGroundwater 48

UNIT I General Geology Hydrogeological Investigations: This enable to predict the influence of GW upon engineering works i.e as a source of water supply. The location and thickness of aquifer horizons and zones, their confinement and their hydrogeological boundaries. The GW levels,their variation over area and fluctuation with time. The storage and transmissive characters of the ground. Quality of the GW. Sub surface Investigations are required to confirm: The GW level The depth, thickness and lateral extent of aquifers and aquicludes. The permeability of these zones and the storage of the aquifers Chemistry of the aquifers and their contained water, Temp, if required. 49

UNIT I General Geology Geophysical methods suitable for most bore holes and commonly used in Hydrogeology 50 S.No Logs for defining condition of Strata 1B.H.MeterCalipers: reveals fractures, cavities, strata boundaries 2Electrical- Potential Self potential : for boundaries and type of strata. 3RadiationNeutron for porosity Gamma for density 4Visual Television- for visual Logs for defining fluid conditions 5TemperatureReveals permeable horizons intersected by bore- hole 6FlowAs for temperature 7 Electrical- Potential Conductivity: for fluid composition salinity.

UNIT I General Geology Importance of Geology in Different Civil Engineering Projects 1.Systematic knowledge of construction materials, their structures and properties such as quality of stones, lime, cement, etc. 2.Knowledge of foundation engineering like assessment of soil, rate of erosion, transportation and erosion by surface and ground water which helps in soil conservation, river control, coastal and harbours. 3.Knowledge about nature of rocks, necessary for all tunnelling and dam projects, construction of roads and in determining the stability of cuts and slopes. 4.Foundation problems of dams bridges and buildings are directly related with geology. The location of bridge, tunnel and dam construction site are decided after detailed geological survey 5.All water resources engg projects -> subsurfcae lithology, quality and discharge capacity 6.Geological map and section help in planning engineering projects 7.Any geological structure like faults, joints, beds, folds, solution channels, dyke and fractures -> if found check for stability 8.Knowledge of natural diasters -> earthquake, flooding and drought 9.Pre-geological survey ->reduces the cost of engineering works 51

General Geology Acknowledging Dr.V.Nagarajan. UNIT I General Geology CONTENTS Geology in Civil...

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