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1、Chapter4TheformationofsoilanditsengineeringpropertiesSoilsaretheresultsofnaturalgeologicalhistory,atthesametimesoilsarealsothemostcommonmaterialsdistributedonthegroundsurfaceoftheearthcrust.Theengineeringpropertiesofsoilshavecloselyrelationswiththeengineeringactivitiesofhumanbeing.B
2、ecauseofcomplexitiesofsoils,manyengineershavebeenpaidmuchattentiontothestudyonsoils.Insomesense,thecomplexitiesofsoilsaremainlyfromthecomplexityofformationprocessofsoilsandthecomplexitiesofsoilsconstitution.Inthischapter,Wearemainlyconcernedwiththeformation,constitutionofsoils,thecl
3、assificationofsoilsbasedonthedifferentformation,sinceothersaspectsaboutsoilswillbediscussedinsoilsmechanics・§4-1SoilformationSoilsareporousnaturalmaterialscomposedofinorganicandorganicmatter,soilsaretheendproductfromweatheringrocks.(Alsowecanmerelytakeitasastageinthegiganticcycleofm
4、ineralrecyclingbythemovementoftectonicplates)Weatheringtakesavitalimportantroleintheprocessofsoilsformation.Undertheinfluenceofphysicalfactorslikedeformationbyheatandcold,assaultbywind,rain,hailandice,andtheenormousleveringforcesofwaterexpandingintoice,solidrockisshatteredintosmalle
5、rpieces(seepicture).Buthoweversmallthesefragments,theystillhavethesamepropertiesastheparentrock.Factorsinsoilformation:parentmaterialtimeclimateatmosphericcompositiontopographyorganismssilicaeoussiltheatcoldfineparentmaterial.sand/quartzwindrainfrosthailiceparentmaterialoxidesofiron
6、&aluminaminerals,nutrientsionsinsolution2-Iayerclayarable,3-layerclayweak,moist,swells,~~topicalclogs,bogs,temperate§4-2ThemaintypesofsoilsbasedontheformationprocessGenerallyspeaking,theengineeringpropertiesofsoilsaremuchinflueneedbythevarietiesofformationprocess.Sointhisaspect,itis
7、importsntforacivilengineertoknowthesoilstypesbasedonformationprocess.1Eluvialsoils（残积土）Theeluvialsoils（residualsoils）arethedirectproductsofweathering,theyareformedintheplacewheretheirmotherrocksarelocated.Thecompositionofeluvialsoilsaredeterminedbytheirbedrocks,and・-solublematerials
8、havebeencarriedaway
