Engineering geology lecture for engineering notes

Engineering geology notes

1. Engineering Geology By S.Deepika Assistant Professor Department of Civil Engineering SSIET

2. Definition, Branches of geology useful to civil engineering, Importance of geology from Civil Engineering point of view, Case studies of case histories of failure of some civil engineering structures due to geological draw backs. Interior of the Earth Weathering - Types and civil engineering significance. River and its action. Unit 1: Introduction & Physical Geology:

3. 1. Geology provides a systematic knowledge of construction materials, their structure and properties. 2. The knowledge of Erosion, Transportation and Deposition (ETD) by surface water helps in soil conservation, river control, coastal and harbour works. 3. The knowledge about the nature of the rocks is very necessary in tunneling, constructing roads and in determining the stability of cuts and slopes. Thus, geology helps in civil engineering. 4. The foundation problems of dams, bridges and buildings are directly related with geology of the area where they are to be built. 5. The knowledge of ground water is necessary in connection with excavation works, water supply, irrigation and many other purposes. 6. Geological maps and sections help considerably in planning many engineering projects. Introduction and Scope 7. If the geological features like faults, joints, beds, folds, solution channels are found, they have to be suitably treated. Hence, the stability of the structure is greatly increased. 8. Pre-geological survey of the area concerned reduces the cost of engineering work. SCOPE OF GEOLOGY FOR CIVIL ENGINEERING

4. Case Studies Of Histories Of Failure Of Some Civil Engineering Structures Due To Geological Draw Backs:

5. LAND FORMS ASSOCIATED WITH RIVER, WIND, GROUND WATER AND SEA

6. River Running water is the most important agent of erosion on the continents and the stream valleys are the most common landforms. Rivers flowing to the oceans drain about 68 % of the Earth's land surface. The remainder of the land either is covered by ice or drains to closed basins. River gradually mould the land by eroding away the material in some place and depositing it in other

7. Landforms created by River - Formation and Types of Landforms Landforms created by the river and depend on the channel gradient, velocity, and volume of water. The landforms formed due to the action of rivers are called Fluvial landforms. They are divided into two major groups, i.e., depositional and erosional . Depositional landforms are leeves , deltas, and plains, while erosional ones are waterfalls, potholes, and V-shaped Valleys. A river goes through three stages: youthful, mature, and old. The course of a river includes the upper stage, the middle stage, and the lower stage, and a kind of work dominates each stage of the River. Landforms such as rapids, waterfalls, and gorges are generally formed in the upper course of a river due to high energy flows and steep gradients. In the middle course, gentler gradients can lead to the formation of pools, riffles, natural levees, oxbow lakes, and floodplains in geographical locations as well as various other natural sources. Two landforms in the lower course of a river are the Delta and the estuary.

8. Processes of Landform Formation by Rivers Processes involved in landform formation by rivers are: Corrosion / Abrasion : It is the mechanical grinding of the traction load of a river against the River’s banks and bed. This process results in the hurling of the rock fragments against the sides of the River and their rolling against the bottom of the River. Corrosion takes place in two manners: Lateral corrasion : This results in sideways erosion and the widening of the V-shaped valley. Vertical corrasion : it is associated with the downward action of the River leading to the deepening of the river channel. Corrosion / Solution : this process involves the chemical action of the water on the soluble components of the rocks. It is most significant in carbonate rocks due to its easy solubility. Hydraulic action : It is associated with the mechanical loosening of the rocks due to the action of the River, which leads to the sweeping away of the rock materials. The continuous action of the river water on the rocks leads to the disintegration of the rock. Attrition : It is the wear and tear of transported materials while they roll and collide among themselves. The coarser boulders are broken down into smaller stones and then smoothened to form pebbles.

9. Types of Landforms created by River Potholes Potholes are kettle-shaped depressions in the rocky beds of river valleys. They are usually formed in coarse-grained rocks such as granites and sandstones. Formation: Whenever a soft rock comes in the way of the River, it is eroded and scattered all around. This results in the formation of eddies, and water whirls around and produces depression by plucking the sediment. This makes the depression deep and cylindrical. Stone pieces also enter the potholes along with water and act as grinders enlarging the diameter and depth of the holes. The potholes have a diameter varying from a few centimeters to several meters.  The depth of a pothole is greater than its diameter. Potholes of much larger size are called Plunge pools. In India, they can be discovered at Bhadbhada near Jabalpur, Madhya Pradesh.

10. Waterfalls When the river water falls down almost vertically from a sufficient height along the course of the River, it forms a waterfall. In the course of the River, there is the presence of hard and soft rocks at several places. The soft rocks are eroded easily and quickly, and the river bed is lower at the place of soft rock. Thus, the water falls from a height, and a waterfall is created. Waterfalls may be formed in several manners. When a bar of resistant rock lies transverse across a river valley. E.g., Niagara Falls, USA. When a fault line scrap caused by faulting lies across the River. E.g., Victoria Falls. When water plunges down the edge of a plateau. E.g.: Livingstone Falls When tributary streams reach the main U-shaped valley as waterfalls. E.g., Yosemite Falls.

11. Meanders  The word “meanders” is derived from the name of a small winding river’s meanders in Turkey. Meanders the longitudinal bends of river courses. Every bend of the river course has two slopes: A concave slope where the River strikes valley sides directly. This side is steeper and is referred to as the cliff slope side. A convex side receives the deposition of sand and gravel. This site is characterized by a gentle slope and is referred to as a slip-off side. Thus, Meanders are a result of both erosion and deposition. The shape of the meander is semi-circular though it may be circular. A river meanders almost in every terrain. However, the magnitude varies according to the slope of the terrain. It is most pronounced in an even and gentle slope. In India, the Gomti River is a typical example of a highly meandering stream.

12. Oxbow Lakes They are also referred to as cut-offs or buyouts in the Mississippi basin. Oxbow lakes are formed in the lower course of the River when a meander becomes more pronounced. The concave side of the meander is rapidly eroded and results in a complete circle. The curvature becomes so sharp due to the lateral erosion that the rivers break through the meander and form a loop. This is known as the Oxbow Lakes. Like meanders, oxbow lakes owe their origin to both erosion and deposition. In addition to the Meander River of Turkey, the Mississippi of the USA, the Ganga of India, and the Po of Italy are famous for oxbow lakes.

13. V Shaped Valley and Interlocking Spurs Most of the world’s rivers have formed V-shaped valleys. Such valleys are normally formed in areas of sufficient rainfall where the rocks are not very hard. Downcutting and side or lateral cutting are done simultaneously by the River, and a V-shaped valley is formed. The valleys are gradually widened due to lateral erosion with the advancement of the cycle of erosion, and they become broad with flat valley floors and rectilinear valley slopes in the mature stage.

14. Interlocking Spurs Interlocking spurs are ridges of hard rock that are resistant to the flow of the River. They are formed when a river is forced to swing side to side around the spurs of hard rock with an interlock. Fan-shaped plains are formed due to the accumulation of materials at the base of the foothills. At the foothills, the carrying capacity of the River is reduced enormously due to an increase in channel gradient and a decrease in the velocity of the River. Consequently, the river load is deposited with coarser material settling first and finer towards the mouth of the plains. The shapes of the alluvial fans are usually semi-circular, with the apex located at the mouth of the opening through which the stream flows out of the hills and the plains. They have a gentle slope. The diameter of the fans ranges from a few kilometers to several hundred kilometers. Fan-Shaped Plains

15. Flood Plains Rivers, in their lower course, carry large amounts of sediments. These sediments spread over the low-lying adjacent areas. These results in the formation of flood plains. Leeves Leeves are narrow belts of ridges of low height formed by the deposition of sediments by the River on either bank. They are most often formed during flood periods when water overtops the river banks and spreads over adjoining plain areas. They limit the lateral spread of water except during events of floods. They are also used for agricultural purposes due to the fact that the water table here is generally high. They also help in checking floods; however, during events of the breach, it may result in catastrophic floods since water gushes out in the plain areas with high velocity.

16. Braided Channels The lower River is characterized by an excess deposit of the load on the floor of the channel because of the reduction in carrying capacity due to the slow movement of water in the stream. The stream, which thus gets divided into a network of channels, forming bars of sand and islands, is known as a braided channel. Deltas The Greek letter ‘∆’ was first used by the Greek historian Herodotus to resemble the triangular Delta of the River Nile. Small or large, every River forms a delta. When the rivers enter the sea or lake, it deposits all the load at their mouth, giving rise to the formation of the Delta. It is a triangular feature with its apex pointing and is marked as a fan-shaped area of fine alluvium. The size of the Delta varies from a few square kilometers to thousands of square kilometers. The suitable conditions for the formation of deltas are: Shallow sea Long river courses Medium size sediments Calm or sheltered areas at the mouth of the River. Large sediment supply Stable sea coast. Eg : Ganga Brahmaputra Delta, Mississippi Delta

17. The wind is the main geomorphic agent in the arid region. The desert floors being dry and barren heat up very fast. They heat up the air directly above them resulting in upward movements in the hot light air with turbulence, and any obstruction in its path sets up whirlwinds, eddies, downdrafts and updrafts. Winds also move along the desert floors with great speed and the obstruction on their path results in turbulence. There are also storm winds which are very destructive. Winds cause deflation, abrasion and impact. Deflation involves the lifting and removal of dust and smaller particles from the surface of rocks. In the transportation process, sand and silt act as effective tools to abrade the land surface. The impact is the sheer force of momentum which occurs when sand is blown into or against a rock surface. The rainfall is scarce in arid regions, however, torrential rains come down in a short period of time. The desert rocks which are devoid of any vegetation get exposed to chemical and mechanical  weathering  due to drastic diurnal changes in temperature, decay faster and the torrential rains remove the weathered debris easily. Thus the weathered materials in the deserts are moved not only by wind but also by rain (sheet wash). The general mass erosion is carried mainly by sheet floods and the wind moves fine particles. Wind 

18. Erosional Landforms due to Wind   Pediplains  – When the high relief structures in desserts are reduced to low featureless plains by the activities of wind, they are called as pediplains . Mushroom, Table and Pedestal rocks  – In deserts, a greater amount of sand and rock particles are transported close to the ground by the winds which cause more erosion in the lower part of the rock than the top. These results in the formation of rock pillars shaped like a mushroom with narrow pillars with broad top surfaces. Sometimes, the top surface is broad like a tabla top and quite often, the remnants stand out like pedestals. Deflation hollows  – When deflation causes a shallow depression by persistent movement of winds, they are called deflation hollows. Playas  – In basins with mountains and hills around and along, the drainage is towards the centre of the basin and due to gradual deposition of sediment from basin margins a nearly level plain forms at the centre of the basin. When there is sufficient water, this plain is covered up by a shallow water body and such types of shallow lakes are termed “playas”. In playas, water is retained for a short duration only (evaporation) and quite often the playas contain a good deposition of salts. The playa plain covered up by salts is called alkali flats.

19. Depositional Landforms due to Wind Sand Dunes – Dry hot deserts are good places for sand dune formation. According to the shape of a sand dune, there are varieties of sand forms: Barchans  – Barchans are one of the classic desert landforms. These are crescent shaped dunes with points or wings directed away from the wind direction. Parabolic dunes  – These are reversed barchans with wind direction being the same. These are formed when sand surfaces are partially covered with vegetation. Seif dunes  – These are similar to barchans but have only one wing or point. These are formed when there is a shift in wind conditions. The long wings of seif can grow very long and high. Longitudinal dunes  – These appear as long ridges of considerable length but are low in height. These are found when the supply of sand is poor and wind direction is constant. Transverse dunes  – These dunes are formed when the wind direction is constant and the source of sand is an elongated feature at right angles to the wind direction.

20. Groundwater The result of the work of groundwater cannot be seen in all types of rocks. Physical or mechanical removal of materials by moving groundwater is insignificant in developing landforms. In rocks like dolomite, limestone which are rich in calcium carbonate, the groundwater as well as surface water through the chemical action of solution and precipitation deposition form varieties of landforms. The processes of solution and deposition are active on limestones or dolomites which occur either exclusively or interbedded with other rocks. Any limestone, dolomite or gypsum region showing typical landforms produced by the action of groundwater through the process of solution and deposition is called  Karst topography  after the typical topography developed in the limestone rock of the Karst region in the Balkans adjacent to the Adriatic sea. The Karst topography is characterised by erosional and depositional landforms.

21. Erosional Landforms due to Groundwater The following are the erosional landforms formed due to the action of groundwater – Sinkhole  – A sinkhole is an opening more or less circular at the top and funnel-shaped towards the bottom. The area of these sinkholes may vary from a few square metres to a hectare and the depth ranges from less than half a metre to thirty metres or more. When a sinkhole is formed solely through the process of solution, it is called a solution sink. Quite often, sinkholes are covered up with soil mantle and appear as shallow water pools. Doline /Collapse sinks  – When the bottom of the sinkhole forms the roof of a void or cave underground, it might collapse leaving a large hole opening into a void or a cave below which is called collapse sinks. The term doline is sometimes used for collapse sinks. Uvala   – When a series of smaller sinkholes coalesce into a compound sinkhole, it is called uvala or valley sinks. Lappies  – These are irregular grooves and ridges formed when most of the surfaces of limestone are removed by a solution process. Caves  – Caves normally have an opening through which streams are discharged. Caves having an opening at both ends are called tunnel caves. Cave formation is prominent in areas where there are alternating beds of rocks (sandstone, shales , quartzite) with dolomites or limestone in between or in areas where limestones are massive, dense and occur as thick beds.

22. Depositional Landforms due to Groundwater The following are the depositional landforms formed within the limestone caves: Stalactite  – Stalactites are calcium carbonate deposits hanging as icicles. They are usually broad at the base and taper towards the free ends. The stalactites that stretch towards the sides are known as helactites . Stalagmite  – Stalagmites are calcium carbonate deposits that grow upwards from the cave floor. Stalagmites may take the shape of a column, a disc with either a smooth, rounded building end or a miniature crater-like depression. The stalactite and stalagmite eventually fuse to give rise to columns and pillars of varying diameters.

23. Waves and Currents Coastal processes are the most dynamic and therefore, most destructive.   The changes along the coasts are mainly due to waves. When waves break, the water is thrown with great force onto the shore which results in great churning of sediments on the sea bottom. The constant impact of breaking waves drastically affects the coasts. Tsunami waves and storm waves cause far-reaching changes in a short span of time than normal breaking waves. The coastal landforms also depend upon: the configuration of land and seafloor. whether the coast is advancing (emerging) or retreating (submerging) landward. Types of Coasts Assuming the sea level to be constant, two types of coasts are considered to explain the concept of evolution of coastal landforms: High rocky coasts – submerged coasts Low, smooth and gently sloping sedimentary coasts – emerged coasts

24. High Rocky Coasts Along the high rocky coasts, erosion features dominate and shores don’t show any depositional landform initially. The rivers appear to have been drowned with a highly irregular coastline. The coastline is highly indented with the extension of water into land where glacial valleys (fjords) are present. The hillsides drop off sharply into the water. Along high coasts, waves break with high force against the land, shaping the hillsides into cliffs. With constant hitting by waves, the cliffs recede leaving a wave-cut platform in front of the sea cliff. The materials which fall off from the cliff, gradually break into smaller fragments and become rounded. These fragments get deposited in the off-shore. After a considerable period of time, with more addition of material to this deposit in the off-shore, a wave built terrace would develop in front of the wave-cut terrace. As the erosion along the coast takes place, a good supply of material becomes available to longshore currents and waves to deposit them as beaches and as bars, which are long ridges of sand and/or shingle parallel to the coast in the nearshore zone. Bars are submerged and when they emerge above water, they are called barrier bars. A barrier bar that gets keyed up to the headland of a bay is called a spit. When the barrier bars and spits form at the mouth of a bay and block it, a lagoon is formed. These lagoons get gradually filled up by sediments from the land giving rise to a coastal plain.

25. Low Sedimentary Coasts Along low sedimentary coasts, the rivers appear to extend their length by building coastal plains and deltas. The coastline appears smooth with occasional incursions of water in the form of lagoons and tidal creeks. Depositional features dominate over erosional ones. When waves break over a low sedimentary coast, the sediments in the bottom get churned and move readily to build bars, spits, barrier bars and lagoons. Lagoons would eventually turn into swamps which would subsequently turn into coastal plains. Tsunami waves and storms cause drastic changes irrespective of the supply of sediments. Large rivers that carry huge sediments build deltas along low sedimentary coasts. The east coast of India is a low sedimentary coast and depositional forms dominate the east coast. The west coast is a high rocky retreating coast and erosional forms dominate the west coast.

26. Erosional Landforms When erosion is the dominant shore process, wave-cut cliffs and terraces are two forms that are usually found. At the foot of the cliffs, there may be a gentle sloping or flat platform covered by rock debris. Such platforms which occur at elevations above the average height of waves are called wave-cut terraces.  The lashing of the waves against the base of the cliff and the rock debris that gets hit against the cliff along with lashing waves create hollows and these hollows deepen and widen to form sea caves. A 90 m long sea cave is found on the Loliem beach in Canacona in Goa. The world’s most extensive cave is the 1.5 km long Matainaka cave in New Zealand.  The resistant masses of rock that appear as rocks standing isolated as small islands just off the shore, originally parts of a cliff or hill, are called sea stacks.  All the above features are temporary and eventually disappear because of wave erosion giving rise to narrow coastal plains, and with a rush of deposits from over the land behind may get covered up by alluvium or may get covered up by shingle or sand to form a wide beach.

27. Depositional Landforms Beach It is an elongated stretch of sand, pebbles, gravels, etc. deposited along the coast. Most of the sediments making up the beaches comes from land carried by the streams and rivers or from wave erosion. The sandy beach which appears so permanent may be reduced to a very narrow strip of coarse pebbles in some other season, so these beaches are temporary features. Praia da Casino beach in Brazil is the world’s longest beach. Marina beach, Chennai is the second longest beach in the world. Bars  – The bar is a stretch of sand deposition off the shoreline. Barrier Bar  – The further addition of sand to the off-shore bar results in a barrier bar. Spits  – When the barrier bars get keyed up to one end of the bay, spits are formed. Spits may also get attached to headlands/hills. Lagoon  – The bars, barriers and spits formed at the mouth of the bay gradually extend leaving only a small opening of the bay into the sea and the bay eventually develop into a lagoon. The lagoon is eventually replaced by a wide coastal plain. These lagoons get filled up gradually by sediments coming from the land or from the beach itself (aided by wind). Tombolo  – A tombolo is a bar connecting an island with the coast.

28. UNIT II Minerology Physical properties of minerals Quartz group, Feldspar group, Pyroxene hypersthenes and augite , Amphibole hornblende, Mica muscovite and biotite , Calcite, Gypsum and Clay minerals.

29. Mineralogy is a branch of geology that deals with the formation, physical, chemical, optical and engineering properties of minerals. They have specific sub branches such as Crystallography Optical mineralogy Descriptive mineralogy A naturally occurring inorganic solid that has a definite chemical composition and / or crystal structure. It is more or less homogeneous defined chemical composition and definite atomic structure. Naturally forming solid. Inorganically formed. E.g.:- i . Ice is a mineral but water is not. → Solid ii. Mercury and petroleum. → liquid More than 2500 minerals on earth crust.

30. States of Mineral:- Crystal Crystalline Amorphous Their colour , streak, hardness, cleavage, crystal form, specific gravity and lust generally identify minerals. The symmetry elements are: Plane of symmetry ii) Axis of symmetry iii) Centre of Symmetry Formation and Composition • Minerals come from cooled magma • 2500 kinds of minerals; some are easy to find and others are rare. Formation of Minerals:- Minerals are formed by anyone of the following processes. Solidification→ cooling from hot and molten material. Solidification → from gases state. Metamorphism → change of composition due to temperature, chemical. Precipitation and evaporation → under favorable temperature

31. Physical Properties of Minerals:- These are diagnostic from identification in the fields. Colour Streak Lusture Hardness Cleavage Fracture Tenacity Special gravity Form/Structure Odour Fluorescence . Phosphorescence Magnetism Habit

32. 1. Colour :- • Colour of the mineral is due to the absorption and reflection of light. • Any minerals that appear white will absorb and reflect all the seven colours of the light. • Any minerals that appear black will absorb all colours , but reflect none of the colours of light. 2. Streak:- • The colour of mineral powder is called as streak. • The streak may or may not be the same as that of the mineral’s colour • Color of powder scraped off when it is rubbed against a hard, rough surface • Streak may be a different color than the mineral itself. 3. Lusture :- Lusture is defined as the shining efficiency of a mineral, due to the intensity of light from its surface. • The natural reflection of surface. • The light absorption capacity of mineral. • The refractive index of minerals. • The way a mineral reflects light from its surface Non-metallic luster: – Don’t have much of a reflection; known as glassy, pearly, and dull