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Publication 293 Geotechnical Engineering Manual Chapter 5 PUBLICATION 293 GEOTECHNICAL ENGINEERING MANUAL CHAPTER 5 – SOIL AND ROCK PARAMETER SELECTION SEPTEMBER 2016 1 Table of Contents CHAPTER 1 – GEOTECHNICAL WORK PROCESS, TASKS AND REPORTS CHAPTER 2 – RECONNAISSANCE IN GEOTECHNICAL ENGINEERING CHAPTER 3 – SUBSURFACE EXPLORATIONS CHAPTER 4 – LABORATORY TESTING CHAPTER 5 – SOIL AND ROCK PARAMETER SELECTION 5.1 INTRODUCTION .............................................................................................................. 3 5.1.1 Purpose ......................................................................................................................... 3 5.1.2 Approach to Selecting Parameters ................................................................................ 4 5.1.2.1 Determining the Necessary Geotechnical Soil and Rock Parameters ................... 5 5.1.2.2 Finalizing/Updating the Subsurface Profile .......................................................... 5 5.1.2.3 Selecting Soil and Rock Parameters and Performing Analyses/Design ............... 6 5.2 UNDERSTANDING SOIL CONDITIONS ....................................................................... 6 5.2.1 Regional Soil Conditions .............................................................................................. 6 5.2.2 Special Problem Soils ................................................................................................... 8 5.2.2.1 Micaceous Soils..................................................................................................... 8 5.2.2.2 Pyritic Soils ........................................................................................................... 8 5.2.2.3 Peats ...................................................................................................................... 8 5.2.2.4 Non-plastic Silts .................................................................................................... 9 5.2.2.5 Slag ........................................................................................................................ 9 5.2.3 Compacted Soils ........................................................................................................... 9 5.3 STANDARD PENETRATION TEST (SPT) AND N-VALUE ......................................... 9 5.3.1 Soil Type/Gradation ................................................................................................... 10 5.3.2 Importance of Standardization for Standard Penetration Testing .............................. 10 5.3.3 SPT Hammer Efficiency Correction........................................................................... 11 5.3.4 SPT Depth/Overburden Pressure Correction .............................................................. 12 5.4 ROCK CORE DRILLING ................................................................................................ 13 5.5 ESTIMATING ENGINEERING PROPERTIES OF SOIL AND ROCK ........................ 13 5.5.1 Selecting Soil and Rock Parameters from Correlations ............................................. 14 5.5.2 Selecting Soil and Rock Parameters Directly from Lab. and/or Field Test Data ....... 14 5.5.3 Engineering Properties of Soil .................................................................................... 16 5.5.3.1 Soil Shear Strength .............................................................................................. 16 5.5.3.2 Soil Unit Weight.................................................................................................. 26 5.5.3.3 Soil Settlement .................................................................................................... 28 5.5.3.4 Soil and Rock Shrink/Swell Factors.................................................................... 31 i 5.5.3.5 Soil Hydraulic Conductivity ............................................................................... 33 5.5.3.6 Frost Susceptibility .............................................................................................. 35 5.5.4 Selecting Rock Parameters ......................................................................................... 35 5.5.4.1 Rock Unconfined Compressive Strength ............................................................ 38 5.5.4.2 Rock Mass Shear Strength .................................................................................. 38 5.5.4.3 Rock Joint Friction .............................................................................................. 39 5.5.4.4 Rock Elastic Modulus ......................................................................................... 39 5.5.4.5 Slake Durability................................................................................................... 40 5.6 FINAL SELECTION OF DESIGN VALUES ................................................................. 41 CHAPTER 6 - SOIL SLOPE STABILITY CHAPTER 7 - SETTLEMENT CHAPTER 8 - ROCK CUT SLOPE DESIGN CHAPTER 9 - COMPACTION CHAPTER 10 - ACID BEARING ROCK CHAPTER 11 - GEOSYNTHETIC REINFORCED SOIL SLOPES CHAPTER 12 - GEOCELL CHAPTER 13 - GEOFOAM CHAPTER 14 - GEOSYNTHETICS USE GUIDELINES Appendix A - INSTRUMENTATION FIELD (IN-SITU) TESTING Appendix B - IMPERVIOUS LINERS Appendix C - ROCK SLAKE DURABILITY Appendix D - CLAY LINERS Appendix E - COMPACTION GROUTING Appendix F - ROCK MASS RATING (RMR) Appendix G - DESIGN/CONSTRUCTION IN KARST Appendix H - GROUND MODIFICATION Appendix I – SUBSIDENCE ii PUBLICATION 293 – GEOTECHNICAL ENGINEERING MANUAL CHAPTER 5 – SOIL AND ROCK PARAMETER SELECTION 5.1 INTRODUCTION This chapter of the publication provides guidelines, recommendations, and considerations for selecting soil and rock parameters using the results from the subsurface exploration and laboratory testing programs. The soil and rock parameters selected to be used in geotechnical analyses (e.g., bearing resistance, settlement, slope stability, etc.) are fundamental to the final geotechnical recommendations. Therefore, it is imperative that sufficient and good quality subsurface information be obtained so that these parameters can be estimated as accurately as possible. Geotechnical engineering analyses are meaningless if the soil and/or rock parameters used in the analyses are not representative of the project subsurface conditions. Additionally, resistance/safety factors prescribed in design manuals are based on the assumption that soil/rock parameters have been estimated from good quality data. 5.1.1 Purpose The purpose of this chapter is to identify appropriate methods for assessing soil and rock properties and describing how to use soil and rock property data to establish the final soil and rock parameters to be used in geotechnical analyses. Soil parameters needed for geotechnical design on roadway and bridge projects include unit weight, soil strength, soil deformation (i.e., settlement), hydraulic conductivity (i.e., permeability), and many others. Table 5.1.1-1 provides information on soil and rock parameters typically used on roadway and bridge projects. Table 5.1.1-1 Summary of Soil and Rock Parameters Applicable Correlation Direct Geotechnical Parameter Symbol Unit Material Estimate Estimate Analyses Cohesionless Soil Angle of Internal Classification, – Granular Friction of ϕ (phi) degree SPT, including and Drained Soil CPT Direct Shear, Non-Plastic Silt Triaxial Bearing Drained ϕ’ degree Cohesive Soil – Shear1 Resistance, (Effective) Shear Clay and Plastic None Friction Strength of c’ ksf Silt Pile/Drilled Cohesive Soils Shaft in Soil Triaxial Resistance, Shear, (CU or Undrained Slope Stability, Cohesive Soil – UU) (Total) Shear Sliding c, s ksf Clay and Plastic None Field Strength of u Resistance, Silt Torvane, Cohesive Soils2 Lateral Earth Pocket Pressure Penetrometer Classification, Unit Weight Unit Weight γ kcf All Soils SPT, Test3 CPT 3 Applicable Correlation Direct Geotechnical Parameter Symbol Unit Material Estimate Estimate Analyses Compression Consolidation Cc dim Cohesive Soil – Index Consolidation (long term) Clay and Plastic None Recompression Test Primary C dim Silt Index r Settlement Coefficient of Consolidation c ft2/year Cohesive Soil – Consolidation v (long term) Clay and Plastic Primary Void Ratio e dim Silt o Consolidation Settlement None Test Consolidation Secondary Organic Cohesive (long term) Compression C dim Soil – Clay and α Secondary Index Plastic Silt Settlement Young’s Classification, Modulus (Elastic E ksi SPT, s Elastic Modulus) CPT, PMT, (immediate) Field Torvane, DMT Settlement Poisson’s Ratio ν dim Pocket Penetrometer All Soils Dewatering Permeability Design, Permeability Length/ Test, Classification Drainage/Filter (Hydraulic k time Field Gradation design, Conductivity) (cm/sec) Infiltration Stormwater Test Design Point Load Foundation Rock Stress Test, Field Unconfined Design, Unconfined q (ksf, psi, Rock Description Compressive Excavation Compressive u etc.) (rock type and Strength Test (rippability, Strength condition) blasting) GSI4, Hoek Passive Rock Mass τ ksf Rock Brown Failure None Resistance of Shear Strength Criterion Soldier Piles Notes: 1. CU with pore pressure measurements 2. Cohesion (c) = Undrained Shear Strength (su)/2 3. Cohesive soil at in-situ moisture content 4. Geologic Strength Index for Jointed Rocks 5.1.2 Approach to Selecting Parameters After the subsurface exploration and laboratory testing programs are complete, soil and/or rock parameters need to be selected in order to perform the necessary geotechnical design calculations/analyses. Selecting these parameters must be done using a logical, systematic
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