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

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Prior to developing the graphs, the correlation between the SPT N-Value and the soilstrength parameters based on current research were developed. This is because soil strengthparameters are the needed input into the bearing capacity equation.1.3 Organization of the ReportThis report is divided into six chapters. Chapter II presents the relationships between thesoil properties and the SPT N values. Chapter III summarizes the available bearing capacityequations, and Chapter IV presents the development of the new graphs. Chapter V shows theapplication of both the current and new graphs in several examples, and Chapter VI presents theconclusion of the study.1-4
CHAPTER IISOIL PROPERTIES FROM SPT VALUES2.1 OverviewTo determine the bearing capacity using the bearing capacity equations, the soilproperties should be known. Laboratory testing should be performed as necessary to determineengineering properties including unit weight, shear strength, compressive strength andcomparisonability. If laboratory testing is not performed, the soil strength parameters for bothgranular and cohesive soils as a function of the SPT N-value will be needed. In this chapter thecorrelation between the SPT N-value and the soil strength parameters is presented. As discussedby McGregor and Duncan (1998) the existing correlations generally use the uncorrected SPTblow count, N. However, hammers delivering 60% of the theoretical energy have been the mostcommonly used hammers for SPT tests, and it seems likely that the data on which thesecorrelations were based was obtained primarily from tests with such hammers. It, therefore,seems logical to use N 60 with these correlations.2.2 SPT N-Value CorrectionThe adoption of the 60% standard energy requires the SPT N-value obtained using anyhammer to be corrected. The correction is done in accordance with the following equation:N= N f⋅ ER60 f( / 60)whereN 60 = SPT N-value corrected to 60% of the theoretical free fall hammer energyN f= SPT N-value obtained in the fieldER f = Energy ratio for hammer used in the investigation (measured)2-1
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: Fig. 1.2Maryland SHA graphs for cla
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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