地质学基础岩石的工程性质Word文档格式.docx
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地质学基础岩石的工程性质Word文档格式.docx
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Theratiobetweentheweightofwaterandtheweightofsolid.
3Bulkspecificgravity:
Theratiobetweenthetotalweightandthetotalvolumeofrock
Mostsilicatemineralshavedensitiesbetween26
and32
.Becauseofthismostigneousandmetamorphicrockshavedensitiesbetween26
.
Limestoneandothersedimentaryrocksusuallyhavesomewhatlowerdensities(20to26
)becausetheyhavesignificantporosity.
Sedimentsgenerallyhavedensitiessimilartothisorlower.
4Porosity(
Theratiobetweenthevolumeofvoidspace(containingliquidsandorgases)andtotalvolume.
5Absorbability(吸水性)
(常压下)
6Softness(软化性)
Changeconditioninstrengthwhensaturatedwithwater
7Anti-frozenability
decliningdegreeofcompressingstrength
8Permeability(
Themeasurementoftherateatwhichfluidswillflowthroughasaturatedmaterials.WewilldiscussthemeasurementsofpermeabilitylaterinthelectureofGroundwater.
3-2Mechanicspropertiesofrock
一Theconceptofstressandstrainofrocks
Stressisdefinedasforceperunitarea.TheunitsofstressarePascals.Soilstressesaretypicallyinthekilopascalrange(kPa).RockstressesareusuallymeasuredinMegapascals(MPa).
Aloadappliedtoamaterialresultsinastressatanypointwithinit.Stressesmaybe:
CompressiveorsqueezingTensileorstretchingShearortearing.
Strainisdefinedaschangeinlengthperunitlength(normalstrain)orchangeinanglebetweenlinesinadeformingbody(shearstrain).Strainisdimensionless.
二MechanicalBehavior
Themechanicalbehaviorsofrocksbehaveinanelasticandplasticmanner,orsometimesinaplasticmanner.Itdependsonmanyfactorssuchasthepressure,temperatureandstrain-rate.
Mostrocksbehaveinelasticmanneratrapidstrain-ratesandlowtemperaturesandpressures,Aspringiselasticmannerasimplemechanicalanalogue.Allstrainisrecoveredwhentheloadisremoved.Theslopeofthestress:
straincurveistheelasticmodulusoftherock.
Rocksbehaveinaplasticmanneratlowerstrain-ratesandelevatedtemperaturesandpressures,showinglargedeformationsatstressesbeyondacriticalstresslevelcalledtheyieldstress.Strainisnotrecoverable,deformationispermanent.Ablockslidingonaplaneisasimplemechanicalanalogue.
Sometimesthedeformationofrocksbecomessimilartothatofaflowingfluid.Therateofdeformationorstrain-rateisdevelopedwiththeappliedstress.Suchbehavioriscalledviscous.Theslopeofthestressvstrain-ratecurveisthefluidviscosity.Adashpot(缓冲筒)isasimplemechanicalanalogue.Strainisnotrecovered.Viscouselementsareintroducedintomodelsofrockbehaviourtoincorporatetime-dependency.
Theelastic-plasticmodelofmaterialbehaviorisoftenusedtocharacterizerocks.Itcombineselasticandplasticaspectsofstress-strainbehavior.Ablockonaplaneattachedtoaspringisthemechanicalanalogue.Strainisonlyrecoveredfortheelasticpartofthedeformation.
Poisson'
sratio(u)-theratiooflateralstraintotheaxialstrain.Forelasticmaterialsitisaconstant.Iftherewerenochangeinvolumeunderstressthevaluewouldbe0.5.Forrocksitvariesbetween0.25and0.33.
三StrengthofRock
Rocksfailindifferentwaysdependingonthetemperatureandpressure.Atlowtemperaturesandhighstrainratesrocksarebrittle-elastic.Theydeformelasticallyatstressesuptoabout70%oftheirstrengththencrackpropagationbecomesdominantandeventuallytherockfailsascrackscoalesce(结合)toformalargefractureorfailuresurface.
Thedeformationpropertiesofrockcanbeshowedfromstress:
straincurve(seediagram),whichisfromtheUniaxialUnconfinedCompressionTest.Thedeformationprocessofrockcanbedividedintothreestages:
1OA—thestageofcrackcompaction
2AB—thestageofelasticdeformation,linerrelationshipbetweenstressandstrain.
3BC—thestageofplasticdeformationorcrackexpending,Strainisnotrecoverable,ordeformationispermanent.
***diagram**
Inpractice,atlowconfiningpressuresverticalsplitting
(1)istheusualfailuremodeshallowdepthsorneargroundsurface.Athigherconfiningpressures(deeper)asingleshearplanedevelops
(2).Atevenhigherconfiningpressures,anetworkofinclinedshearsdevelops(3).
Atlowstrain-rates,elevatedtemperaturesandveryhighconfiningpressuresthestressstraincurvedoesnothaveadistinctmaximumtoindicatefailure.Samplesshowthecontinuousdeformationunderload
characteristicofductile-plasticmaterials.Failedcoreshaveacharacteristic"
barrel"
shape.Thetransitionfrombrittle-elasticbehaviourtoductile-plasticbehaviourisfavouredby:
increasingpressure
increasingtemperature
increasingfluid(pore)pressure
Thechangeinbehaviouriscalledthebrittle-to-ductiletransition.Formostrocksitoccursattemperaturesandpressuresoutsidethenormalrangeofengineering.However,someshales,finegrainedlimestones(chalk)andmostevaporites(rocksalt,potash(钾碱),gypsumetc)showductilebehaviourinnear-surface,low-temperatureenvironments.
Rockstrengthismeasuredbylaboratorytesting.Strengthsareverydifferentdependingonthestressfieldappliedtotherock.Allrocksaremuchstrongerincompressionthanintension.
1Compressivestrength(
)
Thisiscompressivestressrequiredforfailuretooccur.Forrocksthisvaluevariesfrom1to300MPa,
ThecompressivestrengthofrockareusuallydeterminedbythetestofUniaxialUnconfinedCompressionTest-Acylindricalrockcoreisloadedaxiallyuntilitfails.
3Tensilestrength(
Theamountoftensilestrengthrequiredfortherocktofailundertension.Formostrocksthisvariesfrom1-25MPa.Usuallyrockshaveacompressivestrengthabout10to100timesthatoftheirtensilestress.
Thereareavarietyofteststodeterminethetensilestrengthofrock:
DirectPullTest-Acylindricalrockcoresampleisanchoredatbothends
Allthetestsmentionedsofarareusedtodeterminethepropertiesofintactrock.Suchpropertiesarerarelyrepresentativeofrockmassbehaviourbecauseofthepresenceofnumerousdiscontinuities(fractures,joints,faults,etc)invirtuallyallrocksclosetotheEarth'
ssurface.
3Shearstrength
Fordesignofundergroundstructure(suchastunnels,mining,wasterepository),weneedtotakeintoaccountoftheconfiningpressureatdepth.Thisisdoneatlaboratorybyso-calledtriaxialcompressiontest.ThefailurecurveconstructedusingMohr'
scircleafteraseriesoftestsgivestheshearstrength(cohesion)andinternalfriction(angleofshearingresistance)oftherock(orsoil)sample.ThiswillbefurtherdiscussedonMohr-CoulombfailurecriterioninthenextlectureonSoilMechanics.
四Engineeringclassificationofintactrocks
Intactrockisinternallycontinuous,intact,andfreefromweaknessplanessuchasjointing,bedding,andshearing.Theengineeringclassificationofintactrocksisbasedontheuniaxialcompressivestrengthandweatheringcondition.
1Thehardnessclassificationofintackrock
Rocksaresubdividedintofivestrengthcategories(seetablebelow):
常见岩石抗压强度和抗拉强度
岩石名称
rockname
granite
Shale
Rhyolite
Clayrock
Diorite
Limestone
Dacite(安山岩)
Dolomite
pyroxenire
板岩slate
辉绿岩
片岩schist
basalt
片麻岩gneiss
Conglomerate
quartize
sandstone
Marble
>
60
60~30
30~15
15~5
<
5
hardness
Veryhard
hard
Mediumhard
soft
VerySoft
2Theclassificationofrockbasedonweatheringcondition
3-4theengineeringpropertyofrockmass
一、Thedefinitionofrockmass
Thestrengthanddeformationpropertiesofintactrockscannotbedirectlyappliedtotheoverallrockmassinthefieldsituation.Thestrengthandbehaviorofarockmassarelargelycontrolledbythenatureofitsdiscontinuitiesorweaknessplanes.Discontinuitiesacttolowerthestrengthoftherockmass.Therockmasstendstofailalongexistingweaknessplanesratherthandevelopnewfracturewithinintactsolidrocks.Theconceptofrockmasscanberegardedasthecombinationofstructuralbodyandstructuralplanes.
二、Theanalysesofrockbodystructure
1Structuralplane
(1)Themaintypeofstructuralplanes
Thediscontinuitiesofrockmassincludeprimarystructuralplanes,structuralplanesandthesecondarystructuralplanes.
Theprimarystructuralplanesareformedintheinitialstageofrockformation,suchasbeddingplanes,sedimentarystructuremudcracks,ripplemarks,crossbeds(insedimentaryrock);
coolingjoints,flowcontacts,intrusivecontacts,dikes,sills(inigneousrock);
foliation(inmetamorphicrock).
Thetectonicplanesaretheresultsofrockstresscausedbythecrust
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- 关 键 词:
- 地质学 基础 岩石 工程 性质