深基坑开挖土的力学行为实用教案

1、soilsoilSolid phaseSolid phasesoil mineral particlessoil mineral particlesLiquid phaseLiquid phaseusually usually waterwatervapor phasevapor phaseairair various components proportion of three phases will various components proportion of three phases will affect the engineering properties of soilaffe

2、ct the engineering properties of soilThree phases Three phases mixturemixture第1页/共45页第一页，共45页。2.2 Grain-Size Distributiongrain-size distribution. sieve analysis. coarse-grained soil hydrometer analysis. fine-grained soil第2页/共45页第二页，共45页。sieve analysissieve analysis第3页/共45页第三页，共45页。第4页/共45页第四页，共45页。(

3、1)the uniformity coefficient :Cu(2)the coefficient of gradation, coefficient of curvature:Cc1060ddCu6010230dddCc where ,D10、D30 and D60 are the diameters corresponding to percents finer than 10, 30, and 60%, respectively.第5页/共45页第五页，共45页。Hydrometer Analysis Hydrometer analysis is based on the princi

4、ple of sedimentation of soil particles in water.Stokes law,第6页/共45页第六页，共45页。第7页/共45页第七页，共45页。Curves of grain groupCurves of grain groupCurves of grain groupCurves of grain groupVertical coordinateVertical coordinate：percentage of particles by weight smaller than size shownpercentage of particles by

5、weight smaller than size shown。Horizontal coordinateHorizontal coordinate：grain diameter of soilgrain diameter of soil(semi-logarithmic(semi-logarithmic）。）。Low degree of slopeLow degree of slopenon-uniformnon-uniformwell- gradedwell- graded。8第8页/共45页第八页，共45页。Application of particle size distribution

6、 soilWell-graded:Poorly graded: C Cu u55；C Cc c=13=13If any one of the above terms can not be satisfied If any one of the above terms can not be satisfied with, the material is defined as poorly gradedwith, the material is defined as poorly graded第9页/共45页第九页，共45页。Example result第10页/共45页第十页，共45页。第11页

7、/共45页第十一页，共45页。12well-pulverized soil isCu、Cc。第12页/共45页第十二页，共45页。13particles/mm1055220.050.050.010.010.0050.005Content of group/g1016182422382025720tabletable第13页/共45页第十三页，共45页。14【solution】粒径粒径/mm1050.050.010.005小于某粒径土小于某粒径土占总土质量的占总土质量的百分比百分比/%1009587786655362613.51

8、0Cumulative mass of soil passing each sieveCumulative mass of soil passing each sieve第14页/共45页第十四页，共45页。15第15页/共45页第十五页，共45页。16605030100.33,0.21,0.063,0.005dddd。60100.33660.005udCd223010600.0632.410.005 0.33cdCd d第16页/共45页第十六页，共45页。17665uC 12.413cC第17页/共45页第十七页，共45页。Several organizations have attemp

9、ted to develop the size limits for gravel, sand, silt, and clay on the basis of the grain sizes present in soils.第18页/共45页第十八页，共45页。Basic physical indexes:1、bulk density of soil and unit weight 2、special gravity of soil particleairairwaterwaterparticleparticlem ms sm mw wm mV Vs sV Vw wV VV Va amass

10、massVolumeVolumeV Vv vawswsVVVmmVm+=g =44sssswwmGV3、water content of soil100%100%wsssmmmwmm第19页/共45页第十九页，共45页。Calculated physical indexes1、The void ratio, e, is the ratio of the volume of voids to the volume of soil solids in a given soil mass, or2、The porosity, n, is the ratio of the volume of void

11、s to the volume of the soil specimen, or3、 The degree of saturation, S, is the ratio of the volume of water in the void spaces to the volume of voids, generally expressed as a percentage, orsvVVe %=1 10 00 0VVnv%100vwrVVS第20页/共45页第二十页，共45页。Moist unit weight、Dry unit weight and The saturated unit wei

12、ght are:Vmsd=VVmwvssatawswsVVVmmVm+=wsatwssVVmBuoyant density : dsatdsatRelations:第21页/共45页第二十一页，共45页。22Relationship between the indexesRelationship between the indexes/11/(1)111vsssssssswswswssVVVVmeVVVmGmmGwmmmeeVVVVVVVVVnsvsvvsvv1/1/nnVVVVVVVVVevvvvsv1/1/第22页/共45页第二十二页，共45页。23()sswsvwsvwsatwmVmVV

13、VVV/() /1ssdsswsmmVmm mmmmw1wwwwsssrvvwvwswwrsVVmwmwwGSVVVeVeeSewG对饱和土，第23页/共45页第二十三页，共45页。241dwsatw(1)1swGe/() /(1)11sswsswswssvsswwswmVmVVVVVVVGGee 第24页/共45页第二十四页，共45页。第25页/共45页第二十五页，共45页。2.5 Relative Density In granular soils, the degree of compaction in the field can be measured according to the

14、 relative density, defined as:ddddddrD)()(minmaxmaxmin第26页/共45页第二十六页，共45页。D Dr r0.20.2Very looseVery loose0.330.33D Dr r0.670.67mediummedium0.670.67D Dr r11Very denseVery dense0.20.2r r0.330.33looseloose0.330.33D Dr r0.670.67M M0.670.67D Dr r11looselooseD Dr r0.30.3D DThe U.SThe U.SChinaChina第27页/共4

15、5页第二十七页，共45页。第28页/共45页第二十八页，共45页。第29页/共45页第二十九页，共45页。第30页/共45页第三十页，共45页。 The moisture content, in percent, at which the soil changes from a liquid to a plastic state is defined as the liquid limit liquid limit (LL). Similarly, the moisture content, in percent, at which the soil changes from a plasti

16、c to a semisolid state and from a semisolid to a solid state are defined as the the plastic limit (PL) plastic limit (PL) and the shrinkage limitthe shrinkage limit (SL), respectively. These limits are referred to as Atterberg Atterberg limitslimits第31页/共45页第三十一页，共45页。第32页/共45页第三十二页，共45页。 The differ

17、ence between the liquid limit and the plastic limit of a soil is defined as the plasticity index (PI), orThe plastic index indicates the water content range in which cohesive soil has the properties of a plastic material.第33页/共45页第三十三页，共45页。 The relative consistency of a cohesive soil in the natural

18、 state can be defined by a ratio called the liquidity index, which is given byIt indicates the stiff state of soilstatestateLILIrigidrigidRigid plasticRigid plasticwaxinesswaxinessplasticplasticliquidliquidI IL L000 0I IL L50.25I IL L0.750.750.750.75IL1IL1ILIL1 1第34页/共45页第三十四页，共45页。2.9 So

19、il Classification SystemsSoil classification systems divide soils into groups and subgroups based on common engineering properties such as the grain-size distribution, liquid limit, and plastic limit.(1)the American Association of State Highway and Transportation Officials (AASHTO) System and(not us

20、ed in foundation construction.)(2)the Unified Soil Classification System (also ASTM).第35页/共45页第三十五页，共45页。the Unified Soil Classification SystemIn the Unified System, the following symbols are used for identification:When classifying a soil be sure to provide the group name that generally describes t

21、he soil, along with the group symbol. Figures 2.6, 2.7, and 2.8 give flowcharts for obtaining the group names for coarse-grained soil, inorganic fine grained soil, and organic fine-grained soil, respectively.第36页/共45页第三十六页，共45页。第37页/共45页第三十七页，共45页。3 Basic properties and mechanicalcharacteristics of

22、soils(2)第38页/共45页第三十八页，共45页。3.1 Concept of effective stresses3.1 Concept of effective stressesThe principle of effective stress is one of the most important theories in soil mechanics since soil behaviors are highly related to it. In this book, drained/undrained shear strength, lateral earth pressur

23、e, and soil deformation are all explained in terms of effective stress. Considering its importance, this section will expound its basic concept though it is normally introduced in textbooks on soil mechanics. The total stress, which acts at a point O in soil, can be represented by the following equa

24、tion:where y = unit weight of soil above the groundwater table, ysat = saturated unit weight of soil.The above第39页/共45页第三十九页，共45页。Suppose the total area of the contact points is A and the area of the A and the area of the section of soil is A (Figure b), the area occupied by the porewater section of

25、 soil is A (Figure b), the area occupied by the porewater would then be A - A. Thus, the force acting on porewater would bewhere u = porewater pressure.Suppose F, F2,. . . are the intergranular contact forces (see Figure c), the resultant of the vertical components of the intergranular contact force

26、s on the wavy plane AB iswhere F1,v, F2,v. . . are the vertical components of F1, F2,. . . . Thus,第40页/共45页第四十页，共45页。where a is called the effective stress.where a is called the effective stress.Known from the above derivation, the effective stress represents, in theory, the average intergranular co

27、ntact stress on a unit cross-sectional area, which consists of solid areas and pore areassolid areas and pore areas.Suppose the porewater pressure is hydrostatic (e.g. there is no seepage or excess porewater pressure, etc.). The porewater pressure at a point 0 in Figure a iswhere yw = unit weight of

28、 water.yw = unit weight of water.Then the effective stress at 0 iswhere y = submerged unit weight of soil or the effective unit weight.Note: On the other hand, if the porewater pressure is not hydrostatic (i.e. when there exits seepage or excess porewater pressure), u has to be obtained through field mea