Lecture_02 Soil and its constituents, type of rock, type of soil. (Last update 6-Nov-2021).pptx

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2. Soil and its constituents, Weathering of Rocks and Types of soil Dr. Muhammad Safdar , PhD. (Professional Geotechnical Engineer) Assistant Professor, Earthquake Engineering Center, Department of Civil Engineering, UET Peshawar, KP, Pakistan. E-mail: [email protected] CE-209: Geotechnical Engineering-I . Lecture-2

3. Lecture Contents Geotechnical Engineering-1 Course Instructor Dr. M. Safdar, EEC UET Peshawar. Origin of soil What is rock ? Types of Rock (Igneous, Sedimentary, Metamorphic) Weathering (i.e. Mechanical and Chemical) Soil Mass Types of Soil O n the basis of moisture content On the basis of mode of transportation and deposition On the basis of texture On the basis of particle size Soil fabrics Clay minerals Inter-particle forces Water Content 3

4. The term ‘soil’ in civil engineering is defined as the uncemented aggregate of mineral grains and decayed organic matter with liquid and gas in the empty spaces between the solid particles. Generally, soils are formed due to weathering (disintegration) of rocks. Thus the mineral grains that form the solid phase of a soil aggregate are the product of rock weathering . Hence we can simply say that the physical properties of soil are dictated primarily by the minerals that constitute the soil particle and the rock from which it is derived . Many of the physical properties of soil are dictated by the size, shape and chemical compositions of the grains. To better understand these factors, one must be familiar with the basic types of the rock that forms the earth’s crust. 4 Geotechnical Engineering-1 Course Instructor Dr. M. Safdar, EEC UET Peshawar. Origin of Soil

5. 5 Geologist define rock as aggregates or mass, composed of one or more commonly, several of minerals . While Engineers (or contractor) define rock to be a “ hard, durable material that can’t be excavated without blasting .” Geotechnical Engineering-1 Course Instructor Dr. M. Safdar, EEC UET Peshawar. What is Rock ? Blasting of Rock

6. 6 On the basis of mode of origin , rocks can be divided into the following three types: Igneous Rock Sedimentary Rock Metamorphic Rock Geotechnical Engineering-1 Course Instructor Dr. M. Safdar, EEC UET Peshawar. Rocks types

7. 7 Igneous Rock Igneous rocks are formed by the solidification and cooling of molten magma/lava . Solidification is the process when a molten liquid becomes a solid. Magma/lava is a viscous solution of silicates and non silicates minerals . Rock in liquid form inside the earth crust/ mantle is called magma , while when this molten rock come to earth surface then it is known as lava. The types of Igneous rock formed depend on Composition of the magma. Rate of cooling of Molten Magma. Mode of occurrence Geotechnical Engineering-1 Course Instructor Dr. M. Safdar, EEC UET Peshawar. Rocks types

8. 8 Igneous Rock Based on mode of occurrence, Igneous Rocks are divided into : Intrusive Igneous rocks Extrusive Igneous rocks Intrusive Igneous rocks Crystallize below Earth's surface Slow cooling allow large crystals to form. Examples : diorite, gabbro, granite, pegmatite, and peridotite. Extrusive Igneous rocks Molten Magma erupt onto the earth surface Cool quickly to form small crystals. Some cool so quickly that they form an amorphous (i.e. formless, shapeless) glass. Examples: andesite, basalt, obsidian, pumice. Granite Basalt Geotechnical Engineering-1 Course Instructor Dr. M. Safdar, EEC UET Peshawar. Rocks types

9. 9 Sedimentary Rock Sedimentary rocks are formed from particles of sand, shells, pebbles, and other fragments of material. Together, all these particles are called sediment. Gradually, the sediment accumulates in layers and over a long period of time hardens into rock . Generally, sedimentary rock is fairly soft and may break apart or crumble easily. You can often see sand, pebbles, or stones in the rock, and it is usually the only type that contains fossils. Examples of this rock type include conglomerate and limestone. Geotechnical Engineering-1 Course Instructor Dr. M. Safdar, EEC UET Peshawar. Rocks types

10. 10 Metamorphic Rock Metamorphic rocks are formed under the surface of the earth from the metamorphosis. The rocks that result from these processes often have ribbon like layers and may have shiny crystals, formed by minerals growing slowly over time, on their surface. Examples of this rock type include slate, Quartzite, Gneiss, Phyllite and marble. Metamorphism is the process of changing the composition and texture of rocks by heat and pressure (without melting). Geotechnical Engineering-1 Course Instructor Dr. M. Safdar, EEC UET Peshawar. Rocks types

11. 11 Geotechnical Engineering-1 Course Instructor Dr. M. Safdar, EEC UET Peshawar. Rock Cycle Rock Cycle

12. 12 The destructive process of breaking down rocks by mechanical and chemical processes into smaller pieces to form soil particles is known as weathering. Mechanical or physical weathering Chemical weathering Geotechnical Engineering-1 Course Instructor Dr. M. Safdar, EEC UET Peshawar. Weathering Weathering

13. 13 Mechanical or physical weathering Mechanical weathering break rocks into smaller pieces without changing their composition . The resultant soil particles retain the same properties as that of the parent rock. Expansion and contraction of rocks by continuous gain and loss of heat , due to which cracks are produced . Water seeps into the pores and existing cracks in rocks. When Temperature drops , the water freezes and expands. On expansion, pressure exerted by ice on rock. Other physical agents are glacier ice, wind, the running water of streams and rivers . Geotechnical Engineering-1 Course Instructor Dr. M. Safdar, EEC UET Peshawar. Weathering

14. Mechanical or physical weathering Particles of this type are indicated by terms such as angular, rounded, flat and elongated . The particles occur in a wide range of sizes , from boulders down to the fine rock flour formed by the grinding action of glaciers. The structural arrangement of bulky particles is described as single grain , each particle being in direct contact with adjoining particles without there being any bond between them. The state of the particles can be described as dense, medium dense or loose, depending on how they are packed together. 14 Single grain structure Geotechnical Engineering-1 Course Instructor Dr. M. Safdar, EEC UET Peshawar. Weathering

15. 15 Geotechnical Engineering-1 Course Instructor Dr. M. Safdar, EEC UET Peshawar. Weathering Mechanical Weathering

16. 16 Chemical weathering The type of weathering in which original rock minerals are transformed into new minerals by chemical reaction . Water and carbon dioxide from the atmosphere form carbonic acid , which Reacts with the existing rock minerals to form new minerals and soluble salts. Chemical weathering results in the formation of groups of crystalline particles of colloidal size (<0.002 mm) known as clay minerals . For example: The clay mineral kaolinite , is formed by the breakdown of feldspar by the action of water and carbon dioxide. Geotechnical Engineering-1 Course Instructor Dr. M. Safdar, EEC UET Peshawar. Weathering

17. 17 Chemical weathering Geotechnical Engineering-1 Course Instructor Dr. M. Safdar, EEC UET Peshawar. Weathering

18. 18 Soil Mass is generally a three-phase system. It consists of: Solid Particles ( ) Water particles ( ) Air Geotechnical Engineering-1 Course Instructor Dr. M. Safdar, EEC UET Peshawar. Soil Mass Soil Mass

19. 19 On the Bases of Moisture Content in Soil mass, soil are of three types Dry Soil Saturated Soil Partially Saturated Soil (Unsaturated soil) Geotechnical Engineering-1 Course Instructor Dr. M. Safdar, EEC UET Peshawar. Types of Soil Saturated Soil Partially Saturated Soil Dry Soil

20. 20 Geotechnical Engineering-1 Course Instructor Dr. M. Safdar, EEC UET Peshawar. Types of Soil

21. 21 On the basis of mode of transportation and deposition soil are of the following types : Glacial soils formed by transportation and deposition of glaciers Alluvial soils transported by running water and deposited along streams Lacustrine soils formed by deposition in quiet lakes Marine soils formed by deposition in the seas Aeolian soils transported and deposited by wind Colluvial soils formed by movement of soil from its original place by gravity, such as during landslides Geotechnical Engineering-1 Course Instructor Dr. M. Safdar, EEC UET Peshawar. Type of Soil

22. Based on the texture or ‘feel’ , soil are of two types; Fine grained soils: Soils whose properties are influenced mainly by clay and silt size particles are referred to as fine grained soils. Individual particles are not visible by the naked eye. It is divided into silt and clay. Fine-grained soils have 50% or more material passing the No. 200 sieve . It feels smooth, greasy and sticky when touched by hand. Coarse grained soils: Soils whose properties are influenced mainly by sand and gravel size particles are referred to as coarse grained soils. Individual particles are visible by naked eye. It is divided into two classes sand and gravel. Coarse-grained soils have 50% or less material passing the No. 200 sieve . Coarse-grained soil feels gritty when touched by hand. 22 Geotechnical Engineering-1 Course Instructor Dr. M. Safdar, EEC UET Peshawar. Types of Soil

23. 23 Based on the particle size , soil types are: Clay, Silt, Sand and Gravel . Geotechnical Engineering-1 Course Instructor Dr. M. Safdar, EEC UET Peshawar. Types of Soil The above soil classification systems (AASHTO & USCS ) will be discussed in detail in lecture-6

24. Clay minerals Geotechnical Engineering-1 Course Instructor Dr. M. Safdar, EEC UET Peshawar. 24 Particles classified as clay on the basis of their size may not necessarily contain clay minerals . Clays have been defined as those particles “ which develop plasticity when mixed with a limited amount of water ” (Grim, 1953). Clay minerals are the characteristics minerals on the earth found near planetary surface. Clay minerals are complex aluminum silicates composed of two basic units: Silica tetrahedron Alumina octahedron Sometimes magnesium replaces the aluminum atoms in the octahedral units. Some of the common clay minerals are Kaolinite Illite montmorillonite They are commonly found in fine grained sedimentary rocks such as shale, mudstone and siltstone.

25. Soil fabrics Geotechnical Engineering-1 Course Instructor Dr. M. Safdar, EEC UET Peshawar. 25 The geometrical arrangement of individual particles in a soil, including the geometrical distribution of pore spaces is known as soil fabrics. Soil fabric may be used to describe the particle arrangement in both cohesive soils such as clays and granular soils such as silts, sands, and gravels. Types of soil fabric Single grained structure – in case of coarse grained soil deposits (sand) Honeycomb structure – in the case of silt deposits Flocculated structure – in the case of clay deposits Dispersed structure – in the case of clay deposits Coarse grained skeleton structure – in the case of composite soils Cohesive matrix structure – in the case of composite soils Soil structure is same as that of Soil fabric , except that interparticle forces are considered in soil structure.

26. Soil fabrics Geotechnical Engineering-1 Course Instructor Dr. M. Safdar, EEC UET Peshawar. 26 Coarse grained skeleton structure Single grained structure Honeycomb structure Flocculated structure Dispersed structure Cohesive matrix structure

27. Inter-particle forces Geotechnical Engineering-1 Course Instructor Dr. M. Safdar, EEC UET Peshawar. 27 The behaviour of individual soil particles and their interaction with other particles is influenced by the following forces: • Weight of the particle ( ) • Particle surface forces ) Weight of the particle is the result of gravitational forces and is function of volume of the particle. Particle surface forces are of electric nature. They are caused by unsatisfied electrical charges in the particle's crystalline structure. Surface forces are directly proportional to the surface area. For large particle sizes, which include soil particles in the coarse fraction ( 0.075 mm), the weight of the particle is predominant over the surface forces. While for small particles the surface forces are predominate. This accounts for the cohesive nature of most fine-grained soils.  

28. 28 The Water content is defined as ratio of weight of water to weight of Soil Solids. The water content of the fine-grained soils is generally more than that of the coarse grained soils. The water content of some of the fine-grained soils may be even more than 100%, which indicates that more than 50% of the total mass is that of water. x 100 Geotechnical Engineering-1 Course Instructor Dr. M. Safdar, EEC UET Peshawar. Water content (Absorbed water) A b sorbed Water: Water that fills the voids of a soil. A d sorbed Water: Water that is held in a film on the surface of soil particles.

29. Geotechnical Engineering-1 Course Instructor Dr. M. Safdar, EEC UET Peshawar. 29 Problem: Determine water content within a soil sample as a percentage, by drying the soil in the oven at 105 C for 24 hours. The total mass of the soil sample is 30.2 g, while dry mass of the soil sample is 23.3 g. Solution: First finding the weight of water content ( ) = total mass dry mass = 30.2 g 23.3 g = 6.9 g Now water content = = = 29.6 %   Water content (Problem)

30. Geotechnical Engineering-1 Course Instructor Dr. M. Safdar, EEC UET Peshawar. Thank You Any Question(s) ? 30