Lecture 1 introduction & properties of soil

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  • INTERNATIONAL UNIVERSITY FOR SCIENCE & TECHNOLOGY

    CIVIL ENGINEERING AND

    ENVIRONMENTAL DEPARTMENT

    303322: Soil Mechanics

    Introduction &Properties of Soil

    Dr. Abdulmannan Orabi

    Lecture

    1

  • Das, B., M. (2014), Principles of geotechnical Engineering Eighth Edition, CENGAGE Learning, ISBN-13: 978-1-133-10867-2.

    Knappett, J. A. and Craig R. F. (2012), Craigs Soil Mechanics Eighth Edition, Spon Press, ISBN: 978-0-415-56125-9.

    References

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  • Dr. Abdulmannan Orabi IUST 3

    Introduction

    Definition of Soil

    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

    or construction material. It is composed of loosely bound mineral particles of various sizes and shapes formed due to weathering of rocks.

  • Soil Mechanics is a discipline of Civil Engineering involving the study properties of soil, behavior of soil

    masses subjected to various types of forces, and its application as an engineering material.

    Introduction

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    Definition of Soil Mechanics

  • 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.

    According to Terzaghi (1948):

    Introduction

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    Definition of Soil Mechanics

  • Why do you need to learn about soils?

    Almost all structures are either constructed of soil, supported on soil, or both.

    Introduction

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  • 1. Foundation to support Structures and Embankments

    2. Construction Material3. Slopes and Landslides4. Earth Retaining Structures5. Special Problems

    Various reasons to study the properties of Soil:

    Introduction

    Why do you need to learn about soils

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  • Who must be concerned with soils?

    Civil engineers (structural, environmental and geotechnical) must have basic understanding of the soil properties in order to use them effectively in construction.

    Introduction

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  • Problems in Geotechnical Engineering

    Al-naser ) Dome)

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  • Shear Failure-Loads have exceeded shear strength capacity of soil!

    Problems in Geotechnical Engineering

    Transcosna Grain Elevator, Canada Oct. 18, 1913

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  • Shear Failure-Loads have exceeded shear strength capacity of soil!

    Problems in Geotechnical Engineering

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  • Problems in Geotechnical Engineering

    Shear Failure-Loads have exceeded shear strength capacity of soil!

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  • Problems in Geotechnical Engineering

    Shear Failure-Loads have exceeded shear strength capacity of soil!

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  • Settlement

    Problems in Geotechnical Engineering

    Leaning Tower, Pisa14Dr. Abdulmannan Orabi IUST

  • Seepage Problems

    Problems in Geotechnical Engineering

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  • Teton Dam Failure

    Dam Failure - Seepage

    Problems in Geotechnical Engineering

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  • Problems in Geotechnical Engineering

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    Soil subjected to dynamic load

  • All soils originate, directly or indirectly, from different rock types.

    Soil Formation

    Soils are formed from the physical and chemical weathering of rocks.

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    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.

  • Soil Formation

    Physical weathering Involves reduction of size without any change in the

    original composition of the parent rock. The main

    agents responsible for this process are exfoliation,

    erosion, freezing, and thawing.

    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.

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    Soil Formation

    Physical weathering

  • Soil Formation

    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.

    The results of chemical weathering are generally fine soils with altered mineral grains.

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  • Soil Formation

    Chemical weathering

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  • Soils as they are found in different regions can be classified into two broad categories:

    (1) Residual soils

    (2) Transported soils

    Soil Types

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    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.

    Residual Soil

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    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.

    Residual Soil

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  • 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.

    Transported Soil

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  • Transported Soil

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    DESERT SOIL Contains soluble salts. Originated by Mechanical disintegration & wind deposit. Porous and coarse. 90% sand & 5% clay..

  • Transported Soil

    DESERT SOIL Rich in Nitrates & Phosphates. Poor in Nitrogen.

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  • 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.

    Transported Soil

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  • 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.

    Transported Soil

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