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1、Chapter 4 The formation of soil and its engineering propertiesSoils are the results of natural geological history, at the same time soils are also the most comm on materials distributed on the ground surface of the earth crust. The engineering properties of soils have closely relations with the engi
2、neering activities of human being. Because of complexities of soils, many engineers have been paid much attention to the study on soils. In some sense, the complexities of soils are mainly from the complexity of formation process of soils and the complexities of soils constitution. In this chapter,
3、We are mainly concerned with the formation, constitution of soils, the classification of soils based on the different formation, since others aspects about soils will be discussed in soils mechanics 4-1 Soil formationSoils are porous natural materials composed of inorganic and organic matter, soils
4、are the end product from weathering rocks.(Also we can merely take it as a stage in the gigantic cycle of mineral recycling by the movement of tectonic plates)Weathering takes a vital important role in the process of soils formation. Under the influence of physical factors like deformation by heat a
5、nd cold, assault by wind, rain, hail and ice, and the enormous levering forces of water expanding into ice, solid rock is shattered into smaller pieces (see picture). But however small these fragments, they still have the same properties as the parent rock.Factors in soil formation:parent material t
6、imeclimateatmospheric compositiontopography orga nismssilicaeoussiltheat coldfine parent material.sand/ quartzwind rain frost hail iceparent materialoxides of iron & aluminaminerals, nutrientsions in solution2-I ay er clay arable,3-layer clay weak, moist,swells,topical clogs,bogs, temperate 4-2 The
7、main types of soils based on the formation processGen erally speaki ng, the engi neeri ng properties of soils are much influe need by the varieties of formati on process. So in this aspect, it is imports nt for a civil engin eer to know the soils types based on formation process.1 Eluvial soils（残积土）
8、The eluvial soils （residual soils） are the direct products of weathering, they are formed in the place where their mother rocks are located. The composition of eluvial soils are determined by their bedrocks, and-soluble materials have been carried away-the composition has the relation with the mothe
9、r rock-di什erent particle size-obvious edge and comer-thickness change greatly-lower psephicity silisiti2 Slope deposits（坡积物）Qd,the slope deposits are formed from erosion of surface flow along the mountain slope surface . after being carried to the foot of hill by surface flow, where the speed of flo
10、w will slow down and the slack sediments will deposit there.3 Pluvial deposits （洪积物）QplThe pluvial deposits are more comm only distributed along the conn ecti on zones between the mountainous areas and plain areas. The flood water caused by heavy rain or snow dissolved when temperature rise up , is
11、the dynamic resource.According to the features of hydrogeology and engineering of deposits, The pluvial deposits can be divided into three zones, they are:I : the zone for groundwater level deeply buriedthe size of soils grain are the largestlower compressive factor and Higher bearing capacity middl
12、e psephicityII: Zone for ground water overflowing sandy soils and clay are deposited alter natively the groundwater shallowly buriedIII: Zone for periodic dry and damp conditionteiraceeriver bed faces: coarse sand, gravel, boulderwell psephicityflood land faces: upper partfine sandlower part-driver
13、bed facesoxbow lake faces: swamp d0.005mmooze: high water contenthigh porosity, lower strength, high compressive5.Lake deposits (QL)6 Sea deposits (Qm)coastal areala nd slope areashallow sea- deep seaFour zone can be divided7 Wind deposits (Qeo1)wind sand, windloessf collapsible soil niform, homogen
14、eous-porous, scattered structure8 Glacial deposits (Qgl) 4-3 Mineral composition in soilPrimary m泊eralsSecondary minerals (unsolvable with water)Soluble salt and decomposed mineralsOrganic materials一.primary mineralsquartz -feldspar- mica -amphibolegeneral feature:Stable in chemical propertiesweathe
15、ring resista neeGood performanee of engineering PropertiesZl.secondary mineralsclay minerals: Kaolinitemontomorillonite- micaceous* SiO2, AI2O3, Fe2O3： colloidal state* Oxidized materialThe mineral described above is very important to the engineering properties of soilReas on:mineral particle surfac
16、e-*surface power absorbing water affinity（亲和力）That depend on the characteristics of crystallized structure .especially montmorillinate is most obvious then water mica last kaolinitesoluble salt and decomposed mineralsoluble salt: NaCI, Caso4.2H20（石膏），CaCO3（calcium carbonate）,salt salinized soil （盐 ）U
