Highway Bridge Abutment Spread Footing Design

[nmporter]

For abutment spread footings located near or on slope fill, AASHTO 4.4.7.1.1.4 provides an ultimate bearing capacity formula which contains a modified bearing capacity factor (Ngamaq). Depending on the soil parameters and geometric conditions, this modified bearing factor can be odtained from Figure 4.4.7.1.1.4B. However, if the soil parameters and geometric conditions are not consistent with the plotted variables (i.e. phi=34 deg, j=26 deg, Df/B = 0.5), it becomes your best guess interpretation of what the true Ngamaq values are using linear interpolation. Are there tables available or equations which clearly define what the true modified bearing capacity factors are for any given condition?

 

[KAM_imported]

I looked in several textbooks, and all reference the graph by Meyerhof you mentioned. Das makes reference to a paper that may have the original equation, but I am not sure. The reference is:

Graham, J., Andrews, M., and Shields,D.H. (1988). "Stress Characteristics for Shallow Footing in Cohesionless Slopes," Canadian Geotechnical Journal, Vol. 25, No. 2, 238-249.

 

[ishvaaag]

In any case there are formulations for such situation (bearing capacity besides a slope) in foundation engineering texts, like Bowles'.