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Sorl,s <br />Table 9.10 <br />Typical Strength Chazacteristics <br /> cohesion eAective <br /> (as tom- cohesion stress <br />group patted) (saturated) envelope <br />symbol psf psf degrees <br /> C Csaf 95 <br />G W 0 0 > 38 <br />GP 0 0 > 37 <br />GM - - > 34 <br />GC - - > 31 <br />SW 0 0 38 <br />SP 0 0 37 <br />SM 1050 420 34 <br />SM-SC 1050 300 33 <br />SC 1550 230 31 <br />ML 1400 190 32 <br />ML-CL 1350 960 32 <br />CL 1800 270 28 <br />OL - - - <br />MH 1500 420 25 <br />CH 2150 230 19 <br />OH - - - <br />Ezample 9.7 <br />A sample of dry sand is taken and a triaxial test per- <br />formed. The added axial stress causing failure was 5.43 <br />tons/ft2 when the radial stress was l.5 tons/ft~. What <br />i=_ the angle of internal friction? What is the angle of <br />the failure plane? <br />Sus <br />~ = 40° <br />B = 45° + 2(40) = 65° <br />For any given radial pressure, astress-strain curve can <br />be plotted. This is illustrated in figure 9.14. The strain <br />is volumetric strain due to the axial load only. The <br />stress is the difference between the axial and radial <br />stresses. The ultimate compressive stress (S„r) can be <br />read directly from the chart. S„a is usually taken as the <br />s-17 <br />stress difference for which the strain is 20%. The initial <br />slope of the line is the elwtit modulus. <br />°uc I_ _ _ _ _ _ ]~ Suc <br />O ~ loose o <br />I ~ I <br />o ~ o <br />0.2 Ev <br />Figure 9.14 Stress Strain Curves <br />K. CALIFORNIA BEARING RATIO TEST: <br />SHEARING RESISTANCEII <br />The Cnlifornia Bearing Ratio (CBR) test consists of <br />measuring the relative load required to cause a stand- <br />ard (3 square inches) plunger to penetrate awater- <br />saturated soil specimen at a specific rate to a specific <br />depth. The word `relative' is used because the actual <br />load is compared to a standard load derived from a sam- <br />ple of crushed stone. The ratio is multiplied by 100 and <br />the percent omitted. <br />The resulting data will be in the fo: m of inches of pene- <br />tration versus load. This data can be plotted as shown <br />in figure 9.15. if the plot is concave upward (curve B), <br />the steepest. slope is extended downward to the x-a+ds. <br />This point is taken as the zero penetration point and <br />all penetration values adjusted accordingly. <br />load <br />(psi) <br />Figure 9.15 Plotting CBR Test Data <br />Standard loads for crushed stone are given in table 9.11. <br />For a plunger of 3 square inches, the CBR is the ratio <br />of the load fora 0.1 inch penetration divided by 1000 <br />psi. The CBR for 0.2 inches should also be calculated. <br />tl California's Department of T1'ansportation was the first to <br />make use o! the CHR teat. However, other etatee and the Corps <br />o! Engineers have adopted CBR teeting terbniques. These etat® <br />have, generally, retained the California Bearing Ratio name. <br />PROFESSIONAL PUBLICATIONS INC. ~ P.O. Box 799, San Carlos, CA 94070 <br />penetration <br />(inches) <br />-r - max e <br />