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

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CHAPTER VICONCLUSIONSIn this study, new graphs were developed to replace MD SHA graphs for determining theallowable bearing capacity of shallow foundations, Policy and Procedures, Memorandum MemoNo. D-79-18-(4), March 29, 1979, relating the SPT N-value to the maximum advisablepresumptive bearing value. The new graphs consider the effect of depth, size and shape of thefooting, type of soil, factor of safety, and the location of the water table. The new graphs arebased on the AASHTO bearing capacity equations. By knowing the SPT N-value, the width ofthe footing B, the depth of the foundation, D, the engineer will be able by using the graphs tocame up with a quick estimation of the ultimate bearing capacity.The SPT should be used with discrete judgment when it is used to estimate the bearingcapacity of cohesive soils since silt and clay may be stiffened or softened depending on anincrease or decrease of their moisture contents. Additionally, the SPT number may bemisleading if large-size gravel is wedged into the split spoon sampler resulting in apparently highN-values.Although the goal of the present study is to produce charts providing quick estimates ofthe bearing capacity, one should not forget that settlement is a controlling mechanism infoundation design and was not addressed within the scope of this project.6-1
REFERENCESMcGregor, J.A. and Duncan, J.M., “Performance and Use of the Standard Penetration Test inGeotechnical Engineering Practice”, Center for Geotechnical Practice and Research, VirginiaPolytechnic Institute and State University, Blacksburg, VA, October 1998.NAVFAC DM-7.1, “Soil Mechanics,” Design Manual 7.1, Department of the Navy, May 1982.Peck, R.B., Hansen, W.E., and Thornburn, T.H. Foundation Engineering, 2 nd ed., Wiley, NewYork, 1953.Shioi, Y. and Fukui, J “Application of N-value to Design of Foundations in Japan,” 2 nd EuropeanSymposium of Penetration Testing, Vol. 1, 1982 pp 159 – 164.Wolff, T.F., “Pile Capacity Prediction Using Parameter Functions,” ASCE Geotechnical SpecialPublications No. 23, 1989, pp. 96-1067-1
Page 1: UPDATING BEARING CAPACITY - SPT GRA
Page 4 and 5: SUMMARYThe graphs used by the Maryl
Page 6: 90x1 and x2 factors x1 and x2 facto
Page 9 and 10: LIST OF TABLESTablePage2.1 Angle of
Page 11 and 12: CHAPTER IINTRODUCTION1.1 General Ov
Page 13 and 14: Fig. 1.2Maryland SHA graphs for cla
Page 15 and 16: CHAPTER IISOIL PROPERTIES FROM SPT
Page 17 and 18: Fig. 2.1Correlation between frictio
Page 19 and 20: The Japanese “Road Bridge Specifi
Page 21 and 22: Fig. 2.3Relationship between SPT N-
Page 23 and 24: CHAPTER IIIAVAILABLE BEARING CAPACI
Page 25 and 26: q ult(AASHTO 4.4.7.1-1)= cNc+ 0.5γ
Page 27 and 28: TABLE 3.3 AASHTO Expressions for Fo
Page 29 and 30: 90807060Wall Footing on Granular So
Page 31 and 32: x1 and x2 factors180160140120100806
Page 33 and 34: q ult= γ 1x 1D + γ 2x 2Bwhere γ
Page 35 and 36: Presumptive Ultimate Bearing Capaci
Page 37 and 38: = 466N psfFigure 4.5 and Table 4.4
Page 39 and 40: CHAPTER VAPPLICATIONS OF CURRENT AN
Page 41 and 42: Fig. 5.1 Comparison between the cur
Page 43: Fig. 5.2 Comparison between the cur
Page 47 and 48: A.1. x 1 and x 2 factors as a funct
Page 49: APPENDIX BShear Strength vs. SPT-va

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