FCE 311 - Geotechnical Engineering LECTURE NOTES FINAL2
University of NairobiDepartment of Civil and Construction EngineeringFCE 311GEOTECHNICAL ENGINEERING 1LECTURE NOTESDR. NYAMBANE OSANOsosano@uonbi.ac.ke2012
FCE 311 – GEOTECHNICAL ENGINEERING IOSN - Lecture NotesTABLE OF CONTENTS1OVERVIEW . 11.1COURSE DESCRIPTION11.2PREREQUISITE11.3STUDENT LEARNING OUTCOME11.4TEACHING METHODOLOGY AND TECHNIQUES11.5REQUIRED TEXT BOOKS12INTRODUCTION TO SOIL MECHANICS . 22.1DEFINITION OF SOIL22.2SOIL MECHANICS AND GEOTECHNICAL ENGINEERING23SOIL FORMATION . CTIONPHYSICAL WEATHERINGCHEMICAL WEATHERING44443.33.3.13.3.2RESIDUAL AND ALLUVIAL SOILSRESIDUAL SOILSALLUVIAL SOILS5554CLAY MINERALOGY. C AND MOLECULAR BONDSINTRODUCTIONIONIC BONDCOVALENT BONDHYDROGEN BONDVAN DER WAALS BONDS6667784.34.3.14.3.24.3.3BASIC STRUCTURAL UNITS OF CLAY MINERALSINTRODUCTIONSILICA UNITALUMINIUM (OR MAGNESIUM) OCTAHEDRAL UNIT999104.44.4.14.4.2TYPES OF CLAY MINERALSINTRODUCTIONKAOLINITE111111University of NairobiPage i
FCE 311 – GEOTECHNICAL ENGINEERING IOSN - Lecture 5.2SOIL STRUCTURESINTRODUCTIONTYPES OF SOIL STRUCTURES1313135BASIC PROPERTIES . 175.1SOME USEFUL TERMS AND ASSOCIATED .85.2.95.2.105.2.115.2.125.2.135.2.14PHASE RELATIONSHIPPHASE DIAGRAMVOID RATIO (E)MOISTURE CONTENT (WATER CONTENT) (W)POROSITY (N)SPECIFIC VOLUME (V)RELATIVE DENSITY (SPECIFIC GRAVITY) (GS)DEGREE OF SATURATION (SR)AIR CONTENT (A)DENSITY OF SOLIDS (ΡS)BULK DENSITY (Ρ)SATURATED DENSITY (ΡSAT)DRY DENSITY (ΡD)DRY UNIT WEIGHT (ΓDRY)SUBMERGED UNIT WEIGHT (ΓSUB)1818191919192020202121222223236CONSISTENCY AND PLASTICITY OF SOILS . 246.17STATE OF CONSISTENCY24DETERMINATION OF SOIL PROPERTIES BY LABORATORY TESTING. 277.17.1.17.1.2DETERMINATION OF LIQUID LIMITCASAGRANDE APPARATUSCONE PENETROMETER APPRATUS2727297.2DETERMINATION OF PLASTIC LIMIT307.3DETERMINATION OF SHRINKAGE LIMIT317.47.4.17.4.27.4.37.4.47.4.5ATTERBERG INDICESPLASTICITY INDEXFLOW INDEX, IFTOUGHNESS INDEXCONSISTENCY INDEXLIQUIDITY INDEX3232333333347.5USE OF CONSISTENCY LIMITS347.67.6.1WATER CONTENTOVEN-DRYING METHOD3535University of NairobiPage ii
FCE 311 – GEOTECHNICAL ENGINEERING IOSN - Lecture Notes7.6.27.6.3SAND BATH METHODOTHER METHODS35367.7SPECIFIC GRAVITY367.87.8.17.8.2DETERMINATION OF FIELD DENSITYCORE CUTTER METHODSAND REPLACEMENT IZE DISTRIBUTIONSIEVE ANALYSISPARTICLE-SIZE DISTRIBUTION CURVESSIEVE ANALYSIS TEST RESULTEXAMPLE PARTICLE SIZE DISTRIBUTION CURVESLIMITATIONS OF SIEVE ANALYSIS4041424344468SOIL DESCRIPTION AND CLASSIFICATION . 478.1INTRODUCTION478.2SOIL DESCRIPTION478.18.1.18.1.2SOIL CLASSIFICATION SYSTEMSPURPOSE OF SOIL CLASSIFICATIONSHORTCOMINGS OF THE CLASSIFICATION SYSTEMS4949549SOIL COMPACTION . 559.1INTRODUTION559.29.2.19.2.2THEORY OF COMPACTIONGENERALVARIATION IN COMPACTION CURVE5555579.3LABORATORY COMPACTION TESTS589.49.4.19.4.29.4.3FIELD COMPACTIONCOMPACTIONFIELD CONTROL OF COMPACTIONSPECIFICATION OF THE FIELD COMPACTED DENSITY59596061University of NairobiPage iii
FCE 311 – GEOTECHNICAL ENGINEERING I1OSN - Lecture NotesOVERVIEW1.1COURSE DESCRIPTIONThis course is an introductory part of Soil Mechanics, which focuses on soilformation, soil structures, physical properties of soils, soil classifications, soilcompaction and permeability.1.2PREREQUISITENone1.3STUDENT LEARNING OUTCOMEUpon successful completion of this course, the students should acquire the followingknowledge:a) Developed competence in the principles of soil mechanics and applicationin engineering practice.b) Ability to list the relevant engineering properties of soils and their characteristics anddescribe the factors which control these properties.c) Apply laboratory methods of determining the properties of soils.d) Ability to identify common situations when the soil becomes a factor in anengineering or environmental problem.e) Ability to apply basic analytical procedures to obtain the engineeringquantity desired and understand their limitations.1.4TEACHING METHODOLOGY AND TECHNIQUESThis course relies on lectures and Power Point presentation by the lecturer. Workedexamples will be offered. Students will then be required to contribute to discussionsbased on the explanations and will need to read the corresponding section in theassigned textbook.1.5REQUIRED TEXT BOOKSa) Modern Geotechnical Engineering, CBS Publishers & Distributors, New Dhelib) Geotechnical Engineering (Basics of Soil Mechanics), S. Chand & Company Ltd,New Dhelic) Foundation Engineering Handbook, CBS Publishers & Distributors, New Dheli.UNIVERSITY OF NAIROBIPage 1
FCE 311 – GEOTECHNICAL ENGINEERING I22.1OSN - Lecture NotesINTRODUCTION TO SOIL MECHANICSDEFINITION OF SOILSoil is the relatively loose mass of mineral and organic materials and sedimentsfound above the bedrock, which can be relatively easily broken down into itsconstituent mineral or organic particles.Fig. 2-1: Soil layersSoil consists of layers of minerals constituents of variable thickness, which differ fromthe parent materials in the morphological, physical, chemical and mineralogicalcharacteristics, as shown in Fig. 2-1. It is thus a natural product of weathering ofrocks and decomposition of organic matter. It is an accumulation of individualparticles that are bonded together by mechanical or attractive means, the strength ofthe bonds being a small fraction of the mineral particles. The particles may rangefrom colloidal size to small boulders.Soil can also be referred to as regolith, or loose rock material.2.2SOIL MECHANICS AND GEOTECHNICAL ENGINEERINGSoil mechanics is a branch of engineering mechanics that describes the behaviour ofsoils. Soil mechanics provide the theoretical basis for analysis in geotechnicalengineering.UNIVERSITY OF NAIROBIPage 2
FCE 311 – GEOTECHNICAL ENGINEERING IOSN - Lecture NotesGeotechnical Engineering is the branch of civil engineering concerned with theengineering behaviour of earth materials. It uses principles of soil mechanics, rockmechanics and engineering geology to investigate subsurface conditions andmaterials, determine the relevant physical/mechanical and chemical properties of thematerials, evaluate stability of natural slopes and man-made soil deposits, accessrisks posed by site conditions, design earthworks and structure foundations andmonitor site conditions, earthwork and foundation construction.A typical geotechnical engineering project begins with a review of project needs todefine the required material properties. Then follows a site investigation of soil,rock, fault distribution and bedrock properties on and below an area of interest todetermine their engineering properties.Site investigations are needed to gain an understanding of the area in or on whichthe engineering will take place. Investigations can include the assessment of the riskto humans, property and the environment from natural hazards such as earthquakes,landslides, soil liquefaction, debris flows and rock falls.A geotechnical engineer then determines and designs the type of foundations,earthworks and pavement subgrades required for the intended man-made structuresto be built. Foundations are designed and constructed for structures of various sizessuch as high-rise buildings, bridges, medium to large commercial buildings, andsmaller structures where the soil conditions do not allow code-based design.Foundations built for above-ground structures include shallow and deep foundations.Retaining structures include earth-filled dams and retaining walls. Earthworksinclude embankments, tunnels and sanitary landfills.Geotechnical engineering is also related to coastal and ocean engineering. Coastalengineering can involve the design and construction of wharves (structures on theshore of harbour where ships may dock to load and unload cargo or passengers) andjetties (structures that projects into a body of water to influence the current or tideor to protect a harbour or shoreline from storms or erosion).UNIVERSITY OF NAIROBIPage 3
FCE 311 – GEOTECHNICAL ENGINEERING I3OSN - Lecture NotesSOIL FORMATION3.1DEFINITIONSoil formation is the process by which soil is created. The formation of soil happensover a very long period of time. Soil is formed from the weathering of rocks ng is the process of breaking down rocks. Weathering occurs in situ or“with no movement”, and thus should not be confused with erosion, whichinvolves the movement of rocks and minerals by agents such as water, ice,wind, and gravity.Two important classifications of weathering processes exist – Physical andChemical Weathering3.2.2Physical weatheringInvolves the breakdown of rocks and soils through direct contact withatmospheric conditions, such as heat, water, ice and pressure, without anychange in chemical condition. The soil formed due to physical weathering willbe cohesionless (sand and gravel).In summary, the physical agencies causing mechanical weathering of rocks are;(i) Daily and seasonal temperature changes.(ii) Flowing water, glaciers and wind, which produce impact and abrasiveaction on rock.(iii) Splitting action of ice.(iv) Growth of roots of plants in rock fissures and to a minor degree burrowingactivities of small animals like earthworms.3.2.3Chemical weatheringChemical weathering changes the composition of rocks by decomposing theparent minerals, transforming them into new compounds such as clay silicaparticles, carbonates and iron oxides.The(i)(ii)(iii)(iv)decomposition of rock is the result of the following xidationWithin the weathering environment, oxidation of a variety of metals occurs. Themost commonly observed is the oxidation of Fe2 (iron) and combination withoxygen and water to form Fe3 hydroxides and oxides such as goethite, limoniteand hematite. This gives the affected rocks a reddish-brown coloration on theUNIVERSITY OF NAIROBIPage 4
FCE 311 – GEOTECHNICAL ENGINEERING Isurface which crumbles easily and weakens the rock.known as ‘rusting’.OSN - Lecture NotesThis process is betterii) CarbonationCarbonation of rock material is caused by carbon dioxide in the presence ofwater. Limestones are very much affected by carbonation.iii) HydrationMineral hydration is a form of chemical weathering that involves the rigidattachment of H and OH- ions to the atoms and molecules of a mineral. Whenrock minerals take up water, the increased volume creates physical stresseswithin the rock. For example iron oxides are converted to iron hydroxides andthe hydration of anhydrite forms gypsum. Another example of hydration is thechemical decomposition of mineral fieldspar in granite to form kaolite.iv) LeachingLeaching is the process in which percolating water washes out water-solublesalts from the soil.Soil produced by chemical weathering of rocks will be cohesive (silt and clay).3.3RESIDUAL AND ALLUVIAL SOILS3.3.1Residual soilsResidual soils are those which have remained over the parent rock from whichthey have been formed. They are relatively shallow in depth. They arecharacterized by a gradual transition from soil through partially weathered rocks,fractured and fissured rock, to bedrock.3.3.2Alluvial soilsAlluvial soils are the soils which have been transported and subsequentlydeposited by flowing water. An alluvial fan is formed when the velocity of a soilladen stream suddenly deceases due to abrupt decrease in gradient. Floodplains are formed on the sides of a stream due to overflowing of flood water. Adelta is formed just before a stream reaches the standing water of the sea.Alluvial soil deposits are usually stratified because of fluctuations in velocity offlowing water. The average particle size of alluvial deposits decreases withincreasing distance from the source of stream. The delta soils are soil depositsfarthest from the source of a stream and usually consist of silt and clay.Marine deposits are formed when fine-grained soils are carried beyond deltasinto the sea. Lacustrine soils are soils deposited at the bed of lakes.UNIVERSITY OF NAIROBIPage 5
FCE 311 – GEOTECHNICAL ENGINEERING I4OSN - Lecture NotesCLAY MINERALOGY4.1INTRODUCTIONA ‘mineral’ is an inorganic chemical compound formed in nature. As a solid, it mayoccur in an amorphous state or in a crystalline state. A ‘crystal’ is a homogenousbody bounded by smooth plane surfaces. Soil particles are largely composed ofmineral crystals. Molecules of minerals are composed of atoms of chemical elements.The atoms in a crystal are arranged in a definite orderly manner to form a threedimensional net-work, called a “lattice.” An atom consists of a small nucleus havinga positive electromagnetic charge around which a definite number of negativelycharged electrons rotate. The electrons rotate in orbits of different radii forming theso-called electron shells.Many compounds lose their identity, in solution, by separating into “ions.” The ionsconsist of only one element of the compound or of two or more elements which arenot electrically balanced. Atoms get transformed into ions by the gain or loss ofelectrons. The positively charged ions are called “cations” and the negativelycharged ions are called “anions”. On removal from solution the cations and anionswrite to form the original solid compound. Many elements do not form ions, yet theyunite to form compounds. Solutions of non-ion forming elements or compounds inwater are poor conductors of electric current.4.2ATOMIC AND MOLECULAR BONDS4.2.1IntroductionForces which bind atoms and molecules to build up the structure of substancesare primarily of electrical nature. They may be broadly classified into “primarybonds” and “secondary bonds.’ Primary bonds combine the atoms intomolecules. Secondary bonds link atoms in one molecular to atoms in another.They are much weaker than the primary bonds. Primary bonds are the ionicbond and the covalent bond. Secondary bonds are the hydrogen bond and theVan der Waals bond.4.2.2Ionic bondThe ionic bond is the simplest and strongest of the bonds which hold atomstogether. This bond is formed between oppositely charged ions by theexchange of electrons. Atoms held together by ionic bonds form “ioniccompounds”’, e.g. common salt (sodium chloride), and a majority of claymineral crystals fall into this group.Ionic bonding causes a separation between centres of positive and negativecharge in a molecule, which tends the molecule to orient in an electric fieldforming a “dipole”. Dipole is the arrangement of two equal electro-staticcharges of opposite sign. A dipolar molecule (Fig. 4-1) is one which is neutralbut in which the centres of positive and negative charges are separated suchthat the molecule behaves like a short bar magnet with positive and negativepoles.UNIVERSITY OF NAIROBIPage 6
FCE 311 – GEOTECHNICAL ENGINEERING IOSN - Lecture Notes -Fig. 4-1: Soil layers4.2.3Covalent bondThe covalent bond (Fig. 4-2) is formed when one or more bonding electrons areshared by two atoms so that they serve to complete the outer shell for eachatom.Fig. 4-2: Covalent bonding4.2.4Hydrogen bondA hydrogen bond is the attractive interaction of a hydrogen atom with anelectronegative atom, such as nitrogen, oxygen, or fluorine, that comes fromanother molecule.Thus when water molecules are close together, their positive and negativeregions are attracted to the oppositely-charged regions of nearby molecules.The force of attraction, shown in Fig. 4-3 below here as dotted line, is called ahydrogen bond. Each water molecule is hydrogen bonded to four others.UNIVERSITY OF NAIROBIPage 7
FCE 311 – GEOTECHNICAL ENGINEERING IOSN - Lecture NotesFig. 4-3: Covalent bondingHydrogen bond can link the oxygen from a water molecule to the oxygen on theclay particles surface. Hydrogen bonding between two oxygen atoms isresponsible for some of the weaker bonds between crystal layers for holdingwater at the clay surface and for bonding organic molecules to the clay surface.4.2.5Van der Waals bondsIt is the sum of the attractive or repulsive forces between molecules (orbetween parts of the same molecule) other than those due to covalent bonds orionic bond.The covalent bonds within the molecules are very strong and rupture only underextreme conditions. The bonds between the molecules that allow siding andrupture to occur are called Van der Waals forces.When ionic and covalent bonds are present, there is some imbalance in theelectrical charge of the molecule. The angle hydrogen atoms are bonded tooxygen atom in water produces a positive polarity at the hydrogen-rich end ofthe molecule and a negative polarity at the other end. As a result of this chargeimbalance the water molecules are attracted to each other. This is the force thatholds the molecules together in a drop of water, shown in Fig. 4-4.Fig. 4-4: Van der Waals BondingUNIVERSITY OF NAIROBIPage 8
FCE 311 – GEOTECHNICAL ENGINEERING IOSN - Lecture NotesHeat can be used to break the Van der Waal forces between the molecules andchange the form of the material from solid to liquid gas.4.3BASIC STRUCTURAL UNITS OF CLAY MINERALS4.3.1IntroductionThe clay minerals are a group of complex alumino-silicates, i.e., oxides ofaluminium and silicon with smaller amounts of metal ions substituted within thecrystal. The atomic structures of clay minerals are built up of two basic units;a) Silica tetrahedral units, andb) Aluminium (or magnesium) octahedral unit.These units are held together by ionic bonds.4.3.2Silica UnitThe silica unit (Fig. 4-5 and 4.6) consists of a silicon ion surrounded by fouroxygen ions arranged in the form of a tetrahedron. The basic units combine insuch a manner as to form a sheet.Fig. 4-5: Silicon TetrahedralUNIVERSITY OF NAIROBIPage 9
FCE 311 – GEOTECHNICAL ENGINEERING IOSN - Lecture NotesIn the silica sheet, the bases of the tetrahedrals are all in the same plane and thetips all point in the same direction. Each of the three oxygens at the base isshared by two silicons of adjacent units.Fig. 4-6: Silicon Tetrahedral SheetFor simplicity, the silica tetrahedral sheet is represented by the symbol below inFig. 4.5(c).4.3.3Aluminium (or Magnesium) Octahedral UnitThe octahedral unit (Fig. 4-7) has an aluminium ion or a magnesium ionendorsed by six hydroxyl radicals or oxygens arranged in the form of anoctahedron. In some cases, other cations (e.g. Fe) are present in place of Al andMg.Fig. 4-7: Aluminium or Magnesium OctahedralUNIVERSITY OF NAIROBIPage 10
FCE 311 – GEOTECHNICAL ENGINEERING IOSN - Lecture NotesCombination of octahedral units forms an Octahedral sheet, which is called a‘gibbsite” sheet if the central action of the unit is aluminum or a “brucite”sheet if the central cation is magnesium.4.4TYPES OF CLAY MINERALS4.4.1IntroductionThe variation in the stacking of the two basic sheet structures and nature ofbonding has given rise to over dozen clay minerals which have been identified.From an engineering point of view, three clay minerals of interest are kaolinite,montmorillonite and illite.4.4.2KaoliniteThis is the most common of the Kaolin group. Each structural unit of Kaolinite isa combination of two layers with apeces of a silica layer joined to one of agibbsite layer. The structural unit is represented by the symbol as shown in
FCE 311 – GEOTECHNICAL ENGINEERING I OSN - Lecture Notes UNIVERSITY OF NAIROBI Page 3 Geotechnical Engineering is the branch of civil engineering concerned with the engineering behaviour of earth materials. It uses principles of soil mechanics, rock mechanics and engineering
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