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Chapter 7 – Geomechanics Chapter 7 GEOMECHANICS GEOTECHNICAL DESIGN MANUAL January 2019 Geotechnical Design Manual GEOMECHANICS Table of Contents Section Page 7.1 Introduction ....................................................................................................... 7-1 7.2 Geotechnical Design Approach......................................................................... 7-1 7.3 Geotechnical Engineering Quality Control ........................................................ 7-2 7.4 Development Of Subsurface Profiles ................................................................ 7-2 7.5 Site Variability ................................................................................................... 7-2 7.6 Preliminary Geotechnical Subsurface Exploration............................................. 7-3 7.7 Final Geotechnical Subsurface Exploration ...................................................... 7-4 7.8 Field Data Corrections and Normalization ......................................................... 7-4 7.8.1 SPT Corrections .................................................................................... 7-4 7.8.2 CPTu Corrections .................................................................................. 7-7 7.8.3 Correlations for Relative Density From SPT and CPTu ....................... 7-10 7.8.4 Dilatometer Correlation Parameters .................................................... 7-11 7.9 Soil Loading Conditions And Soil Shear Strength Selection ............................ 7-12 7.9.1 Soil Loading ........................................................................................ 7-12 7.9.2 Soil Response ..................................................................................... 7-13 7.9.3 Soil Strength Testing ........................................................................... 7-21 7.10 Total Stress .................................................................................................... 7-28 7.10.1 Sand-Like Soils ................................................................................... 7-28 7.10.2 Clay-Like Soils .................................................................................... 7-29 7.10.3 Transitional Soils ................................................................................. 7-35 7.10.4 Maximum Allowable Total Soil Shear Strengths .................................. 7-35 7.11 Effective Stress ............................................................................................... 7-35 7.11.1 Sand-Like Soils ................................................................................... 7-36 7.11.2 Clay-Like Soils .................................................................................... 7-39 7.11.3 Transitional Soils ................................................................................. 7-47 7.11.4 Maximum Allowable Effective Soil Shear Strength .............................. 7-47 7.12 Borrow Materials Soil Shear Strength Selection .............................................. 7-48 7.12.1 SCDOT Borrow Specifications ............................................................ 7-49 7.12.2 USDA Soil Survey Maps ..................................................................... 7-50 7.12.3 Compacted Soils Shear Strength Selection ......................................... 7-52 7.12.4 Allowable Soil Shear Strengths of Compacted Soils ............................ 7-53 7.13 Soil Settlement Parameters ............................................................................ 7-54 7.13.1 Elastic Parameters .............................................................................. 7-54 7.13.2 Consolidation Parameters ................................................................... 7-56 7.14 Rock Parameter Determination ....................................................................... 7-62 7.14.1 Shear Strength Parameters ................................................................. 7-62 7.14.2 Settlement Parameters........................................................................ 7-63 7.15 Scour .............................................................................................................. 7-64 7.15.1 Soil ...................................................................................................... 7-65 7.15.2 Rock .................................................................................................... 7-65 7.16 Dynamic Properties – General ........................................................................ 7-69 7.17 Soil Dynamic Properties.................................................................................. 7-70 7.17.1 Soil Consistency.................................................................................. 7-70 7.17.2 Shear Wave Velocity/Initial Shear Modulus ......................................... 7-71 7.17.3 Cyclic Stress-strain Behavior............................................................... 7-75 7.17.4 Cyclic Residual Shear Strength ........................................................... 7-85 7.18 Rock Dynamic Properties ............................................................................... 7-85 7.19 Electro-Chemical Properties ........................................................................... 7-85 7.20 References ..................................................................................................... 7-86 January 2019 7-i Geotechnical Design Manual GEOMECHANICS List of Tables Table Page Table 7-1, Site Variability Defined By COV ........................................................................... 7-3 Table 7-2, Assumed Energy Ratio by Hammer Type (CE) ....................................................... 7-5 Table 7-3, Rod Length Correction (CR) .................................................................................... 7-6 Table 7-4, Sampler Configuration Correction (CS) ................................................................... 7-6 Table 7-5, Borehole Diameter Correction (CB) ......................................................................... 7-6 Table 7-6, Soil Response Classification ................................................................................ 7-14 Table 7-7, OCR Values ......................................................................................................... 7-19 Table 7-8, Soil Shear Strength Selection Based on Strain Level ........................................... 7-21 Table 7-9, Bridge Foundation Soil Parameters ...................................................................... 7-22 Table 7-10, Earth Retaining Structures & Embankment Soil Parameters .............................. 7-23 Table 7-11, Laboratory Testing Soil Shear Strength Determination ....................................... 7-25 Table 7-12, In-Situ Testing - Soil Shear Strength Determination ........................................... 7-26 Table 7-13, Soil Suitability of In-Situ Testing Methods........................................................... 7-27 Table 7-14, Sensitivity of Cohesive Soils............................................................................... 7-33 Table 7-15, Residual Shear Strength Loss Factor (λτ) .......................................................... 7-34 Table 7-16, Maximum Allowable Total Soil Shear Strengths ................................................. 7-35 Table 7-17, Maximum Allowable Effective Soil Shear Strengths ........................................... 7-48 Table 7-18, Elastic Modulus Correlations For Soil Using SPT N-values ................................ 7-54 Table 7-19, Typical Elastic Modulus and Poisson Ratio Values for Soil ................................ 7-56 Table 7-20, Correction of the e-log p Curve for Disturbance.................................................. 7-57 Table 7-21, Correction of the ε-log p Curve for Disturbance .................................................. 7-58 Table 7-22, Constants m and s based on RMR ..................................................................... 7-63 Table 7-23, Values of Rock Mass Strength Parameter, Ms .................................................... 7-66 Table 7-24, Rock Joint Set Number Jn .................................................................................. 7-67 Table 7-25, Joint Roughness Number, Jr .............................................................................. 7-67 Table 7-26, Joint Alteration Number, Ja ................................................................................. 7-67 Table 7-27, Relative Orientation Parameter, Js ..................................................................... 7-69 Table 7-28, Typical Small-Strain Shear Wave Velocity and Initial Shear Modulus ................. 7-72 Table 7-29, Recommended Values γcr1, α, and k for SC Soils ............................................... 7-79 Table 7-30, Procedure for Computing G/Gmax ........................................................................ 7-80 Table 7-31, Recommended Value λmin1 (%) for SC Soils ....................................................... 7-81 Table 7-32, Procedure for Computing Damping Ratio ........................................................... 7-83 Table 7-33, Alternate Correlations for Determining Soil Stiffness Based on Gmax .................. 7-84 Table 7-34, Criteria for Substructure Environmental Classifications ...................................... 7-86 7-ii January 2019 Geotechnical Design Manual GEOMECHANICS List of Figures Figure Page
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