Updating Bearing Capacity – SPT Graphs - Maryland State Highway ...

CHAPTER IVDEVELOPMENT OF THE NEW GRAPHS4.1 Graphs for Footing on Granular Soils4.1.1 Wall FootingThe AASHTO equation:q 0+ qN s b iult= cNcscbcic+ .5γBNγsγbγiγqqq qwill have: i) c = 0 for granular soil; ii) s c = s q = s γ = 1 for L > 5B; iii) i c = i q = i γ = 1 for verticalload, and iv) b c = b q = b γ = 1 for horizontal base, thus the AASHTO equation will be:qult= γDN+ 0.5γBN= γ= γq[ DN + 0.5NB][ Dx + Bx ]1q2γγwhere x 1 = N q and x 2 = 0.5 N γFigure 4.1 and Table 4.1 show the values of x 1 and x 2 as a function of N 60 . Appendix A-1 showsthe determination of x 1 and x 2 as a function of ϕ.4.1.2 Square FootingThe AASHTO equation:q 0+ qN s b iult= cNcscbcic+ .5γBNγsγbγiγqqq qwill have: i) c = 0 for granular soil; ii) s q = 1 + tan ϕ, s γ = 0.6; iii) i c = i q = i γ = 1 for vertical load,and iv) b c = b q = b γ = 1 for horizontal base, thus the AASHTO equation will be:qultq( 1+tanφ)D( 1+tanφ) N[ Dx + Bx ]= γDN= γ= γ[ + 0.3NB]12+ 0.5γBNqγγ0.6where x 1 = (1 + tan φ) N q and x 2 = 0.3 N γ4-1