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

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LIST OF FIGURESFigurePageFig. 1.1 Maryland SHA graphs for granular soils 1-2Fig. 1.2 Maryland SHA graphs for clays and mixed soils 1-3Fig. 2.1 Correlation between friction angle and SPT N-value (from Peck, 2-3Hanson and Thornburn, 1953)Fig. 2.2 Relationship between SPT N-value and undrained shear strength 2-6(Sowers, 1979)Fig. 2.3 Relationship between SPT N-value and unconfined compressive strength 2-7(from NAVFAC 1982)Fig. 4.1 x 1 and x 2 factors as a function of N-value for a wall footing 4-2Fig. 4.2 x 1 and x 2 factors as a function of N-value for a square footing 4-4Fig. 4.3 Water Table Level 4-5Fig. 4.4 Ultimate bearing capacity as a function of N-value for a wall footing 4-8Fig. 4.5 Ultimate bearing capacity as a function of N-value for a square footing 4-11Fig. 5.1 Comparison between the current and new graphs for example 1 5-3Fig. 5.2 Comparison between the current and new graphs for example 2 5-5viii
CHAPTER IINTRODUCTION1.1 General OverviewThe graphs used by the Maryland State Highway Administration (MD SHA) fordetermining the allowable bearing capacity of shallow foundations are presented in Policy andProcedure Memorandum Memo No. D-79-18-(4), March 29, 1979. The graphs were originallypublished in Basic Soils Engineering by B.K. Hough, published by the Roland Press Company,1957. The graphs, Fig. 1.1 and Fig 1.2, related the Standard Penetration Test (SPT) in blows/ftto the maximum advisable presumptive bearing value. The major drawbacks to the use of thesegraphs are that they do not consider the effects of the depth, shape and the size of the footing, thelocation of the water table, or the factor of safety considered. They are also very conservative,which suggests that they do not provide accurate, cost effective designs, and in the case of a highwater table they provide unsafe values, however, their main advantage is that they are simple touse.1.2 Objective of the StudyThe objective of the study is to develop new graphs that relate the SPT N-value to thebearing pressure. The new graphs are to use the American Association of State Highway andTransportation Officials (AASHTO) bearing capacity equations. The new graphs will thusconsider the effects of the depth, shape and size of the footing, soil properties, factor of safety,and location of the water table. The challenge here is to have the new graphs as simple to use asthe current ones.1-1
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: LIST OF TABLESTablePage2.1 Angle of
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 and 44: Fig. 5.2 Comparison between the cur
Page 45 and 46: REFERENCESMcGregor, J.A. and Duncan
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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