Structural Foundations for Bridges

2. ? New Legal Load

12. A Limit State is a defined condition beyond which a structural component, ceases to satisfy the provisions for which it is designed. Resistance is a quantifiable value that defines the point beyond which the particular limit state under investigation for a particular component will be exceeded.

15. Strength Limit State

16. Extreme Event Limit State

17. Service Limit State

18. Service Limit State

20.  i  i Q i ≤ R r =  R n f(  ,  ) Q n R n Q R  Q n  R n Q or R Probability of Occurrence 

22. 10.4 SOIL AND ROCK PROPERTIES 10.4.1 Informational Needs 10.4.2 Subsurface Exploration 10.4.3 Laboratory Tests 10.4.3.1 Soil Tests 10.4.3.2 Rock Tests 10.4.4 In-situ Tests 10.4.5 Geophysical Tests 10.4.6 Selection of Design Properties 10.4.6.1 Soil Strength 10.4.6.1.1 Undrained strength of Cohesive Soils 10.4.6.1.2 Drained Strength of Cohesive Soils 10.4.6.1.3 Drained strength of Granular Soils 10.4.6.2 Soil Deformation 10.4.6.3 Rock Mass Strength 10.4.6.4 Rock Mass Deformation 10.4.6.5 erodibility of rock

26. % Finer by Weight Uniform Well Graded Gravel Sand Silt Clay Grain Diameter (mm) 100 100 10 1 0.1 0.01 0.001 US Standard Sieves 3” 2” 1” 3/4 ” 3/8” 4 6 10 20 40 60 100 200 80 60 40 20 0

29. Soil Shear Strength  ’ = c’ +  n ’ tan  f ’  ’ a  ’ a  ’ r  ’ r  ’  ’ n  ’  ’ n  ’ f  ’  ’ c’ Strength envelope

30. Undrained Strength of Cohesive Soils, s u Unconfined Compression s u = q u /2 Vane Shear Test s u  q u  =0 Typical Values s u = 250 - 4000 psf

31. Drained Strength of Cohesive Soils, c’ and  ’ f Triaxial Compression CU Test Typical Values c’ = 100 - 500 psf  ’ f = 20 o - 35 o

32. Drained Strength of Cohesionless Soils,  ’ f Standard Penetration Test (SPT) Typical Values  ’ f = 25 o - 45 o Friction angle is correlated to SPT results.  ’ f  ’ q’ c=0

34. Guided Walk Through For N 1 60 = 10, select  ’ f = 30 o (modified after Bowles, 1977) N 1 60  f <4 25-30 4 27-32 10 30-35 30 35-40 50 38-43

35. Soil Deformation 0 -2 -4 -6 -8 -10 -12 1 10 100 1000 10000 Time (days) Settlement (in) Initial elastic settlement (all soils) Primary consolidation Secondary consolidation Fine-grained (cohesive) soils

36. Consolidation Properties Log 10  v ’ Void Ratio (e)  p ’ = Preconsolidation Stress C s C r C c 0.1 1 10 100 0.5 1 e o

37. One log cycle  e=C  =0.06 0.1 1 10 100 1000 10000 Elapsed Time (min) Void ratio (e) 2.65 2.6 2.55 2.5 2.45 2.4 2.35 2.3 2.25 Stress Range, 40 – 80 kPa t p

38. Typical Consolidation Properties Property Typical Value C c 0.1 to 1.0 C r 10 % of C c C s Approximately C r C  4% to 6% of C c C v 0.01 to 1.0 ft 2 /day

41. Intact Rock Strength Point Load Test Unconfined Compression, q u Typical Values q u = 1500 - 50000 psi

42. Rock Quality Length, L 0.8 ft 0.7 ft 0.8 ft 0.6 ft 0.2 ft 0.7 ft Sound Not sound, highly weathered Not sound, centerline pieces < 4 inches, highly weathered Sound Not sound Sound Core Run Total = 4 ft CR = 95% RQD = 53%

44. Rock Mass Strength C 1 ’ Shear stress,  Effective Normal Stress,  ’  tm  3  1    ’ i  = (cot  ’ i – cos  ’ i )mq u /8  ’ i = tan -1 (4 h cos 2 [30+0.33sin -1 (h -3/2 )]-1) -1/2 h = 1 + 16(m  ’ n +sq u )/(3m 2 q u )

47. Rock Mass Deformation E  = 2 RMR - 100 90 70 50 30 10 In situ modulus of deformation, E M (GPa) 10 30 50 70 90 12 10 8 6 4 2 (psi x 10 6 ) Rock mass rating RMR

48. Read More About It GEC 5 FHWA-IF-02-034

49. Jerry A. DiMaggio P. E. Principal Bridge Engineer TEL: (202) 366-1569 FAX: (202) 366-3077 The best Geotechnical web site in town! www.fhwa.dot.gov/bridge WOW! FREE STUFF FROM THE FEDERAL GOVERNMENT!