深基坑開挖土的力學行為實用教案

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頁/共45頁第一頁，共45頁。2.2 Grain-Size Distributiongrain-size distribution. sieve analysis. coarse-grained soil hydrometer analysis. fine-grained soil第2頁/共45頁第二頁，共45頁。sieve analysissieve analysis第3頁/共45頁第三頁，共45頁。第4頁/共45頁第四頁，共45頁。(

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頁/共45頁第五頁，共45頁。Hydrometer Analysis Hydrometer analysis is based on the princi

4、ple of sedimentation of soil particles in water.Stokes law,第6頁/共45頁第六頁，共45頁。第7頁/共45頁第七頁，共45頁。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頁/共45頁第八頁，共45頁。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頁/共45頁第九頁，共45頁。Example result第10頁/共45頁第十頁，共45頁。第11頁

7、/共45頁第十一頁，共45頁。12well-pulverized soil isCu、Cc。第12頁/共45頁第十二頁，共45頁。13particles/mm1055220.050.050.010.010.0050.005Content of group/g1016182422382025720tabletable第13頁/共45頁第十三頁，共45頁。14【solution】粒徑粒徑/mm1050.050.010.005小于某粒徑土小于某粒徑土占總土質(zhì)量的占總土質(zhì)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頁/共45頁第十四頁，共45頁。15第15頁/共45頁第十五頁，共45頁。16605030100.33,0.21,0.063,0.005dddd。60100.33660.005udCd223010600.0632.410.005 0.33cdCd d第16頁/共45頁第十六頁，共45頁。17665uC 12.413cC第17頁/共45頁第十七頁，共45頁。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頁/共45頁第十八頁，共45頁。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頁/共45頁第十九頁，共45頁。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頁/共45頁第二十頁，共45頁。Moist unit weight、Dry unit weight and The saturated unit wei

12、ght are:Vmsd=VVmwvssatawswsVVVmmVm+=wsatwssVVmBuoyant density : dsatdsatRelations:第21頁/共45頁第二十一頁，共45頁。22Relationship between the indexesRelationship between the indexes/11/(1)111vsssssssswswswssVVVVmeVVVmGmmGwmmmeeVVVVVVVVVnsvsvvsvv1/1/nnVVVVVVVVVevvvvsv1/1/第22頁/共45頁第二十二頁，共45頁。23()sswsvwsvwsatwmVmVV

13、VVV/() /1ssdsswsmmVmm mmmmw1wwwwsssrvvwvwswwrsVVmwmwwGSVVVeVeeSewG對飽和土，第23頁/共45頁第二十三頁，共45頁。241dwsatw(1)1swGe/() /(1)11sswsswswssvsswwswmVmVVVVVVVGGee 第24頁/共45頁第二十四頁，共45頁。第25頁/共45頁第二十五頁，共45頁。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頁/共45頁第二十六頁，共45頁。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頁/共4

15、5頁第二十七頁，共45頁。第28頁/共45頁第二十八頁，共45頁。第29頁/共45頁第二十九頁，共45頁。第30頁/共45頁第三十頁，共45頁。 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頁/共45頁第三十一頁，共45頁。第32頁/共45頁第三十二頁，共45頁。 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頁/共45頁第三十三頁，共45頁。 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頁/共45頁第三十四頁，共45頁。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頁/共45頁第三十五頁，共45頁。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頁/共45頁第三十六頁，共45頁。第37頁/共45頁第三十七頁，共45頁。3 Basic properties and mechanicalcharacteristics of

22、soils(2)第38頁/共45頁第三十八頁，共45頁。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頁/共45頁第三十九頁，共45頁。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頁/共45頁第四十頁，共45頁。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