Lecture 1 introduction & properties of soil

Download Lecture 1  introduction & properties of soil

Post on 14-Jan-2017

171 views

Category:

Engineering

7 download

TRANSCRIPT

<ul><li><p>INTERNATIONAL UNIVERSITY FOR SCIENCE &amp; TECHNOLOGY </p><p>CIVIL ENGINEERING AND </p><p>ENVIRONMENTAL DEPARTMENT </p><p>303322: Soil Mechanics </p><p>Introduction &amp;Properties of Soil </p><p>Dr. Abdulmannan Orabi</p><p>Lecture</p><p>1</p></li><li><p>Das, B., M. (2014), Principles of geotechnical Engineering Eighth Edition, CENGAGE Learning, ISBN-13: 978-1-133-10867-2.</p><p>Knappett, J. A. and Craig R. F. (2012), Craigs Soil Mechanics Eighth Edition, Spon Press, ISBN: 978-0-415-56125-9.</p><p>References</p><p>2Dr. Abdulmannan Orabi IUST</p></li><li><p>Dr. Abdulmannan Orabi IUST 3</p><p>Introduction </p><p>Definition of Soil</p><p>The term soil according to engineering point of view is defined as the material, by means of which and upon which engineers build their structures. The term soil includes entire thickness of the earths crust (from ground surface to bed rock), which is accessible and feasible for practical utilization as foundation support </p><p>or construction material. It is composed of loosely bound mineral particles of various sizes and shapes formed due to weathering of rocks.</p></li><li><p>Soil Mechanics is a discipline of Civil Engineering involving the study properties of soil, behavior of soil </p><p>masses subjected to various types of forces, and its application as an engineering material.</p><p>Introduction </p><p>4Dr. Abdulmannan Orabi IUST</p><p>Definition of Soil Mechanics</p></li><li><p>Soil Mechanics is the application of laws of mechanics and hydraulics to engineering problems dealing with sediments and other unconsolidated accumulations of solid particles, which are produced by the mechanical and chemical disintegration of rocks, regardless of whether or not they contain an admixture of organic constituents.</p><p>According to Terzaghi (1948):</p><p>Introduction </p><p>5Dr. Abdulmannan Orabi IUST</p><p>Definition of Soil Mechanics</p></li><li><p>Why do you need to learn about soils?</p><p>Almost all structures are either constructed of soil, supported on soil, or both.</p><p>Introduction </p><p>6Dr. Abdulmannan Orabi IUST</p></li><li><p>1. Foundation to support Structures and Embankments</p><p>2. Construction Material3. Slopes and Landslides4. Earth Retaining Structures5. Special Problems</p><p>Various reasons to study the properties of Soil:</p><p>Introduction </p><p>Why do you need to learn about soils</p><p>7Dr. Abdulmannan Orabi IUST</p></li><li><p>Who must be concerned with soils?</p><p>Civil engineers (structural, environmental and geotechnical) must have basic understanding of the soil properties in order to use them effectively in construction.</p><p>Introduction </p><p>8Dr. Abdulmannan Orabi IUST</p></li><li><p>Problems in Geotechnical Engineering </p><p> Al-naser ) Dome)</p><p>9Dr. Abdulmannan Orabi IUST</p></li><li><p>Shear Failure-Loads have exceeded shear strength capacity of soil!</p><p>Problems in Geotechnical Engineering </p><p>Transcosna Grain Elevator, Canada Oct. 18, 1913</p><p>10Dr. Abdulmannan Orabi IUST</p></li><li><p>Shear Failure-Loads have exceeded shear strength capacity of soil!</p><p>Problems in Geotechnical Engineering </p><p>11Dr. Abdulmannan Orabi IUST</p></li><li><p>Problems in Geotechnical Engineering </p><p> Shear Failure-Loads have exceeded shear strength capacity of soil!</p><p>12Dr. Abdulmannan Orabi IUST</p></li><li><p>Problems in Geotechnical Engineering </p><p> Shear Failure-Loads have exceeded shear strength capacity of soil!</p><p>13Dr. Abdulmannan Orabi IUST</p></li><li><p> Settlement</p><p>Problems in Geotechnical Engineering </p><p>Leaning Tower, Pisa14Dr. Abdulmannan Orabi IUST</p></li><li><p> Seepage Problems</p><p>Problems in Geotechnical Engineering </p><p>15Dr. Abdulmannan Orabi IUST</p></li><li><p>Teton Dam Failure </p><p>Dam Failure - Seepage </p><p>Problems in Geotechnical Engineering </p><p>16Dr. Abdulmannan Orabi IUST</p></li><li><p>Problems in Geotechnical Engineering </p><p>Dr. Abdulmannan Orabi IUST 17</p><p>Soil subjected to dynamic load </p></li><li><p>All soils originate, directly or indirectly, from different rock types.</p><p>Soil Formation</p><p>Soils are formed from the physical and chemical weathering of rocks. </p><p>18Dr. Abdulmannan Orabi IUST</p><p>Soil is generally formed by disintegration and decomposition (weathering) of rocks through the action of physical (or mechanical) and chemical agents which break them into smaller and smaller particles.</p></li><li><p>Soil Formation</p><p>Physical weathering Involves reduction of size without any change in the</p><p>original composition of the parent rock. The main</p><p>agents responsible for this process are exfoliation,</p><p>erosion, freezing, and thawing. </p><p>Physical or mechanical processes taking place on the earth's surface include the actions of water, frost, temperature changes, wind and ice. They cause disintegration and the products are mainly coarse soils.</p><p>19Dr. Abdulmannan Orabi IUST</p></li><li><p>Dr. Abdulmannan Orabi IUST 20</p><p>Soil Formation</p><p>Physical weathering </p></li><li><p>Soil Formation</p><p>Chemical weathering causes both reduction in size and chemical alteration of the original parent rock. The main agents responsible for chemical weathering are hydration, carbonation, and oxidation. Rain water that comes in contact with the rock surface reacts to form hydrated oxides, carbonates and sulphates. </p><p>The results of chemical weathering are generally fine soils with altered mineral grains.</p><p>21Dr. Abdulmannan Orabi IUST</p></li><li><p>Soil Formation</p><p>Chemical weathering</p><p>22Dr. Abdulmannan Orabi IUST</p></li><li><p>Soils as they are found in different regions can be classified into two broad categories:</p><p>(1) Residual soils</p><p>(2) Transported soils</p><p>Soil Types </p><p>23Dr. Abdulmannan Orabi IUST</p></li><li><p>Dr. Abdulmannan Orabi IUST 24</p><p>Residual SoilsResidual soils are found at the same location where they have been formed. Generally, the depth of residual soils varies from 5 to 20 m.Chemical weathering rate is greater in warm, humid regions than in cold, dry regions causing a faster breakdown of rocks. Accumulation of residual soils takes place as the rate of rock decomposition exceeds the rate of erosion or transportation of the weathered material. In humid regions, the presence of surface vegetation reduces the possibility of soil transportation.</p><p>Residual Soil</p></li><li><p>25</p><p>Residual SoilsAs leaching action due to percolating surface water decreases with depth, there is a corresponding decrease in the degree of chemical weathering from the ground surface downwards. This results in a gradual reduction of residual soil formation with depth, until unaltered rock is found.Residual soils comprise of a wide range of particle sizes, shapes and composition.</p><p>Residual Soil</p><p>Dr. Abdulmannan Orabi IUST</p></li><li><p>Transported SoilsWeathered rock materials can be moved from their original site to new locations by one or more of the transportation agencies to form transported soils. Transported soils are classified based on the mode of transportation and the final deposition environment.</p><p>Transported Soil</p><p>26Dr. Abdulmannan Orabi IUST</p></li><li><p>Transported Soil</p><p>Dr. Abdulmannan Orabi IUST 27</p><p>DESERT SOIL Contains soluble salts. Originated by Mechanical disintegration &amp; wind deposit. Porous and coarse. 90% sand &amp; 5% clay..</p></li><li><p>Transported Soil</p><p>DESERT SOIL Rich in Nitrates &amp; Phosphates. Poor in Nitrogen. </p><p>28Dr. Abdulmannan Orabi IUST</p></li><li><p>Transported SoilsTransported soils are classified based on the mode of transportation and the final deposition environment.(a) Soils that are carried and deposited by rivers are called alluvial deposits.(b) Soils that are deposited by flowing water or surface runoff while entering a lake are called lacustrine deposits. Alternate layers are formed in different seasons depending on flow rate.</p><p>Transported Soil</p><p>29Dr. Abdulmannan Orabi IUST</p></li><li><p>Transported Soils(c) If the deposits are made by rivers in sea water, they are called marine deposits. Marine deposits contain both particulate material brought from the shore as well as organic remnants of marine life forms.(d) Melting of a glacier causes the deposition of all the materials scoured by it leading to formation of glacial deposits.(e) Soil particles carried by wind and subsequently deposited are known as Aeolian deposits.</p><p>Transported Soil</p><p>30Dr. Abdulmannan Orabi IUST</p></li><li><p>Gravity Soils Gravity can transport materials only for a short distance.Gravity soils are termed as talus these soilsare generally loose and porous.</p><p>Transported Soil</p><p>31Dr. Abdulmannan Orabi IUST</p></li><li><p>Soil is not a coherent solid material like steel and concrete, but is a particulate material. Soils, as they exist in nature, consist of solid particles (mineral grains, rock fragments) with water and air in the voids between the particles. The water and air contents are readily changed by changes in ambient conditions and location.</p><p>Phases System of Soils</p><p>32Dr. Abdulmannan Orabi IUST</p></li><li><p>As the relative proportions of the three phases vary in any soil deposit, it is useful to consider a soil model which will represent these phases distinctly and properly quantify the amount of each phase. A schematic diagram of the three-phase system is shown in terms of weight and volume symbols respectively for soil solids, water, and air. The weight of air can be neglected.</p><p>Phases System of Soils</p><p>33Dr. Abdulmannan Orabi IUST</p></li><li><p>Phases System of Soils</p><p>Ground surface </p><p>Voids</p><p>Air</p><p>Water</p><p>Solids</p><p>The compositions of natural soils may include diverse components which may be classified into three large groups:</p><p>1. Solid phase ( minerals, cementations and organic materials)</p><p>2. Liquid phase (water with dissolved salts)</p><p>3. Gaseous phase (air or other some gas)</p><p>34Dr. Abdulmannan Orabi IUST</p></li><li><p>Phases System of Soils</p><p>Ground surface </p><p>Voids</p><p>Air</p><p>Water</p><p>Solids</p><p>The spaces between the solids ( solid particles) are called voids. Water is often the predominant liquid and air is the predominant gas.We will use the terms water and air instead of liquid and gases.</p><p>35Dr. Abdulmannan Orabi IUST</p></li><li><p>Soils can be partially saturated (with both air and water present), or be fully saturated (no air content) or be perfectly dry (no water content).</p><p>In a saturated soil or a dry soil, the three-phase system thus reduces to two phases only, as shown.</p><p>Three Phases System</p><p>36Dr. Abdulmannan Orabi IUST</p></li><li><p>Three Phases System</p><p>Partially saturated soil</p><p>Solid Particles</p><p>Voids (air or water)</p><p>Idealization:Three Phases Diagram</p><p>Water</p><p>Air</p><p>Solid Particles</p><p>37Dr. Abdulmannan Orabi IUST</p></li><li><p>Two - Phases System</p><p>Fully saturated soil</p><p>Solid Particles</p><p>Idealization:Two Phases Diagram</p><p>Water</p><p>38Dr. Abdulmannan Orabi IUST</p></li><li><p>Two - Phases System</p><p>Dry soil</p><p>Idealization:Two Phases Diagram</p><p>Air</p><p>Solid Particles</p><p>39Dr. Abdulmannan Orabi IUST</p></li><li><p>The soil model is given dimensional values for the solid, water and air components.</p><p>Weight Symbols Volume Symbols </p><p>Va</p><p>VS</p><p>VT</p><p>VW</p><p>VV</p><p>WT</p><p>WS</p><p>WW</p><p>Wa </p><p> 0</p><p>Phase Relations of Soils</p><p>Water</p><p>Air</p><p>Solid Particles</p><p>40Dr. Abdulmannan Orabi IUST</p></li><li><p>For the purpose of engineering analysis and design, it is necessary to express relations between the weights and the volumes of the three phases.</p><p>The various relations can be grouped into:Weight relationsVolume relationsInter-relations</p><p>Three - Phases System</p><p>41Dr. Abdulmannan Orabi IUST</p></li><li><p>WT</p><p>WS</p><p>WW</p><p>Wa </p><p> 0</p><p>Water</p><p>Air</p><p>Solid Particles</p><p>Weight Relations </p><p> = +</p><p>where,</p><p>(1-1)</p><p> = </p><p> = </p><p> = </p><p> = 0</p><p>The following are the basic weight relations: water content or moisture content specific gravity (Gs)</p><p>42Dr. Abdulmannan Orabi IUST</p></li><li><p>Weight Relations </p><p>Water content </p><p>The ratio of the mass of water present to the mass of solid particles is called the water content ( ), or sometimes the moisture content.</p><p> % =</p><p> 100% (1-2)</p><p>The water content of a soil is found by weighing a sample of the soil and then placing it in an oven at until the weight of the sample remains constant , that is, all the absorbed water is driven out. </p><p>110 5 !</p><p>43Dr. Abdulmannan Orabi IUST</p></li><li><p>Weight Relations </p><p>Specific Gravity, </p><p>The mass of solid particles is usually expressed in terms of their particle unit weight or specific gravity (Gs) of the soil grain solids</p><p>The specific gravity of a solid substance is the ratio of the weight of a given volume of material to the </p><p>weight of an equal volume of water (at 20C).</p><p>" =</p><p>=</p><p>#$</p><p>#$=</p><p>#</p><p>#(1-3)</p><p># = %&amp; = 9.81*+</p><p>,</p><p>44Dr. Abdulmannan Orabi IUST</p></li><li><p>For most inorganic soils, the value of Gs lies between 2.60 and 2.80.The presence of organic material reduces the value of Gs.</p><p>Weight Relations </p><p>Specific Gravity, </p><p>45Dr. Abdulmannan Orabi IUST</p><p>The specific gravity of soil solids is often needed for various calculations in soil mechanics.</p></li><li><p>The following are the basic volume relations:</p><p>Volume Relations </p><p>1. Void ratio (e)</p><p>2. Porosity (n)</p><p>3. Degree of saturation (S)</p><p>4. Air content (a)</p><p>Volume Symbols </p><p>Va</p><p>VS</p><p>VT</p><p>VW</p><p>VV</p><p>Water</p><p>Air</p><p>Solid Particles$ = $ +$ + $ (1-4)</p><p>$- = $ + $</p><p>46Dr. Abdulmannan Orabi IUST</p></li><li><p>Void ratio (e) is the ratio of the volume of voids (Vv) to the volume of soil solids (Vs), and is expressed as a decimal.</p><p>Volume Relations </p><p>Void ratio (e) </p><p>The void ratio of real coarse grained soils vary between 0.3 and 1. Clay soils can have void ratio greater than one.</p><p> =$.</p><p>$(1-5)</p><p>47Dr. Abdulmannan Orabi IUST</p></li><li><p>Porosity (n) is the ratio of the volume of voids to the total volume of soil (Vt ), and is expressed as a percentage.</p><p>Volume Relations </p><p>Porosity (n) </p><p>The range of porosity is 0 %&lt; n &lt; 100%</p><p>&amp; 100% =$.</p><p>$ 100% (1-6)</p><p>48Dr. Abdulmannan Orabi IUST</p></li><li><p>Void ratio and porosity are inter-related to each oth...</p></li></ul>

Recommended

View more >