Cover
Title Page
Preface
Acknowledgements
List of Symbols
List of Property Values and Correlations in the Tables and Figures
1 Commonly Measured Properties
1. 1.1 Moisture Content
2. 1.2 Grading
3. 1.3 Plasticity
4. 1.4 Specific Gravity of Soil Particles
5. 1.5 Soil Density
6. 1.6 Permeability
7. 1.7 Consolidation
8. 1.8 Shear Strength
9. 1.9 Standard Compaction Test
10. 1.10 California Bearing Ratio
11. 1.11 Other Properties
12. References
2 Grading and Plasticity
1. 2.1 Grading
2. 2.2 Plasticity
3. References
3 Density
1. 3.1 Density in the Context of Soils
2. 3.2 Compacted Density
3. 3.3 Relative Density
4. References
4 Permeability
1. 4.1 Effects of Soil Macro‐Structure
2. 4.2 Typical Values
3. 4.3 Permeability and Grading
4. References
5 Consolidation and Settlement
1. 5.1 Compressibility of Clays
2. 5.2 Rate of Consolidation of Clays
3. 5.3 Secondary Compression
4. 5.4 Settlement of Sands and Gravels
5. 5.5 Assessment of Settlement Parameters from Static Cone Penetration Testing
6. References
6 Shear Strength
1. 6.1 Stresses Within a Material
2. 6.2 Shear Strength in Soils
3. 6.3 The Choice of Total or Effective Stress Analysis
4. 6.4 Peak, Residual and Constant‐Volume Shear Strength
5. 6.5 Undrained Shear Strength of Clays
6. 6.6 Drained and Effective Shear Strength of Clays
7. 6.7 Shear Strength of Granular Soils
8. References
7 California Bearing Ratio
1. 7.1 Correlations with Soil Classification Tests
2. 7.2 Correlations with Soil Classification Systems
3. 7.3 CBR and Undrained Shear Strength
4. 7.4 An Alternative to CBR Testing
5. References
8 Shrinkage and Swelling Characteristics
1. 8.1 Identification
2. 8.2 Swelling Potential
3. 8.3 Swelling Pressure
4. References
9 Frost Susceptibility
1. 9.1 Ice Segregation
2. 9.2 Direct Measurement of Frost Susceptibility
3. 9.3 Indirect Assessment of Frost Susceptibility
4. 9.4 Choosing a Suitable Method of Evaluating Frost Susceptibility
5. References
10 Susceptibility to Combustion
1. Reference
11 Soil-Structure Interfaces
1. 11.1 Lateral Pressures in a Soil Mass
2. 11.2 Friction and Adhesion at Interfaces
3. References
Appendix A: Soil Classification Systems
1. A.1 Systems Based on the Casagrande System
2. A.2 The AASHTO System
3. A.3 Comparison of the Unified, AASHTO and BS Systems
4. References
Appendix B: Sampling Methods
1. B.1 Pits and Borings
2. B.2 Sampling and Samplers
3. B.3 Probes
4. Reference
Index
End User License Agreement

List of Tables

Chapter 03
1. Table 3.1 Typical values of natural density.
2. Table 3.2 Typical compacted densities and optimum moisture contents for soil types using the Unified soil classification system. Adapted from Al‐Hussaini and Townsend (1975).
3. Table 3.3 Typical compacted densities and optimum moisture contents for soil types using the AASHTO soil classification system. Adapted from Gregg (1960).
4. Table 3.4 Relative density descriptions and correlation with SPT N‐values in sands and gravels.
5. Table 3.5 Summary of published SPT correction factors for overburden pressure.
6. Table 3.6 Summary of rod energy ratios for standard penetration tests. Adapted from Skempton (1986).
7. Table 3.7 Approximate corrections A to measured SPT N‐values. Adapted from BS (2011).
Chapter 04
1. Table 4.1 Typical values of permeability. Adapted from Krebs and Walker (1971).
Chapter 05
1. Table 5.1 Typical values of the coefficient of volume compressibility m_v and the descriptive terms used.
2. Table 5.2 Some published correlations for compression index C_c. Reproduced from Azzouz et al. (1976).
3. Table 5.3 Typical values of the coefficient of consolidation c_v. Adapted from Holtz & Kovacs (1981).
4. Table 5.4 Typical values of the ratio of secondary compression index to compression index. Adapted from Mesri and Godlewski (1977).
5. Table 5.5 Typical values of coefficient α used to estimate m_v values from static cone penetration testing. Reproduced from Meigh (1987).
Chapter 06
1. Table 6.1 Typical values of the undrained shear strength of compacted soils.
2. Table 6.2 Values of undrained shear strength based on consistency descriptions.
3. Table 6.3 Typical values of the effective angle of shearing resistance of compacted clays.
4. Table 6.4 Typical values of the angle of shearing resistance of cohesionless soils.
5. Table 6.5 Typical values of the angle of shearing resistance of compacted sands and gravels.
Chapter 07
1. Table 7.1 Some variations that can affect CBR test results.
2. Table 7.2 Estimated CBR values for British soils compacted at the natural moisture content. Adapted from TRRL (1970).
Chapter 08
1. Table 8.1 Free swelling data for clay minerals.
2. Table 8.2 Typical Atterberg limit values for common clay minerals.
3. Table 8.3 Descriptive terms for swelling potential.
4. Table 8.4 Identification of swelling soils based on plasticity index.
5. Table 8.5 Suggested guide to the determination of potential for expansion using shrinkage limit and linear shrinkage. Adapted from Altmeyer (1955).
6. Table 8.6 Estimation of potential volume changes of clays. Adapted from Holtz and Gibbs (1956). Reproduced with permission of American Society of Civil Engineers.
7. Table 8.7 Estimating probable swelling pressure. Adapted from Chen (1988). Reproduced with permission of Elsevier.
Chapter 09
1. Table 9.1 Preliminary identification of frost susceptible soils. Adapted from TRRL (1970).
2. Table 9.2 Frost susceptibility of soils related to soil classification. Adapted from US Army Corps of Engineers (1965).
Chapter 11
1. Table 11.1 Typical values of friction and adhesion at interfaces. Adapted from US Naval Publications and Forms Center, US Navy (1982).
2. Table 11.2 Values of K_s and δ for driven piles. Adapted from Broms (1979).
Appendix A
1. Table A1 The Unified soil classification system.
2. Table A2 The Unified soil classification system. Extended soil groupings for coarse‐grained soils defined by specific laboratory test values, as used in ASTM D2487.
3. Table A3 The Unified soil classification system. Extended soil groupings for fine‐grained soils defined by specific laboratory test values as used in ASTM D2487.
4. Table A4 The British Standard soil classification system.
5. Table A5 Description of soil types in the AASHTO soil classification system.Classification of materials in the various groups applies only to the fraction passing the 75 mm sieve. The proportions of boulder‐ and cobble‐sized particles should be recorded separately and any specification regarding the use or A‐1, A‐2 or A‐3 materials in construction should state whether boulders are permitted.
6. Table A6 The AASHTO soil classification system.
7. Table A7 Comparison of soil groups in the Unified and British Standard soil classification systems.
8. Table A8 Comparison of soil groups in the Unified and AASHTO soil classification systems.
Appendix B
1. Table B1 Standard cone sizes and attributes.

List of Illustrations

Chapter 01
1. Figure 1.1 Nested sieves.
2. Figure 1.2 Casagrande liquid limit apparatus.
3. Figure 1.3 Cone penetrometer liquid limit apparatus.
4. Figure 1.4 Specific gravity determination jars: (a) gas jar with stopper and glass plate; (b) pkynometer; and (c) specific gravity bottle.
5. Figure 1.5 Sand replacement method equipment.
6. Figure 1.6 Nuclear density meter modes of operation: (a) direct transmission mode; and (b) backscatter mode.
7. Figure 1.7 Basic layout of the falling head permeameter.
8. Figure 1.8 Basic layout of the constant head permeameter.
9. Figure 1.9 Consolidation test equipment.
10. Figure 1.10 Triaxial test equipment.
11. Figure 1.11 Example of a Mohr circle plot.
12. Figure 1.12 Schematic arrangement of a shear box.
13. Figure 1.13 Shear test types and typical uses.
14. Figure 1.14 Standard compaction test equipment.
15. Figure 1.15 Test arrangement for CBR.
Chapter 02
1. Figure 2.1 Some common definitions of soils, classified by particle size.
2. Figure 2.2 Principal features of a grading chart.
3. Figure 2.3 Electrochemical bonding between clay mineral particles and the resulting microstructures: (a) electrochemical charges within a clay; (b) semi‐orientated (or dispersed) structure; and (c) flocculated structure.
4. Figure 2.4 Consistency limits: (a) change from liquid to solid as a soil dries out; and (b) volume and consistency changes with water content change.
5. Figure 2.5 Plasticity chart.
Chapter 03
1. Figure 3.1 Theoretical relationships between density, porosity, voids ratio and moisture content.
2. Figure 3.2 Relationship between dry density, moisture content and percentage of air voids.
3. Figure 3.3 Type of density–moisture relationship obtained in the standard compaction test with some sands.
4. Figure 3.4 Relationships between optimum moisture content, maximum dry density and plastic limit for red tropical soils.
5. Figure 3.5 Typical moisture–density curves for rapid determination of maximum dry density and optimum moisture content.
6. Figure 3.6 Plots of SPT correction factors for overburden depth.
7. Figure 3.7 Relationships between cone resistance and vertical effective stress for different relative densities D_r.
8. Figure 3.8 CPT–SPT correlation with grain size.
Chapter 04
1. Figure 4.1 Typical permeability values for soils.
2. Figure 4.2 Permeability of sands and gravels.
Chapter 05
1. Figure 5.1 Basic features of plots of compressibility test results.
2. Figure 5.2 The compression process in terms of the model soil sample.
3. Figure 5.3 Correlation of coefficient of volume compressibility m_v with plasticity index and SPT N‐value.
4. Figure 5.4 Typical values of factor μ for a foundation of width b on a compressible layer of thickness H.
5. Figure 5.5 Typical values of consolidation factor μ for various types of soil.
6. Figure 5.6 Typical values of time factor T_V.
7. Figure 5.7 Approximate correlations between the coefficient of consolidation and liquid limit.
8. Figure 5.8 Plotting and calculation of secondary compression.
9. Figure 5.9 Correlation between modified secondary compression index and natural moisture content.
10. Figure 5.10 Approximate correlation between moisture content and the modified coefficient of secondary compression.
11. Figure 5.11 Chart for estimating allowable bearing pressures on sand from standard penetration test results.
12. Figure 5.12 Chart for estimating allowable bearing pressures on sand from standard penetration test results based on recommendations by Bowles (1982).
13. Figure 5.13 Correlation between influence factor I_c and SPT N‐value for estimating settlements on sand using the method of Burland and Burbridge (1985).
14. Figure 5.14 Correlation between deformation modulus M and SPT N‐value for granular soils based on recommendations by Menzenbach (1967).
15. Figure 5.15 (a) Estimation of coefficient of consolidation from piezocone values. (b) Estimation of rigidity index for use in chart (a).
Chapter 06
1. Figure 6.1 Stresses within a material and the Mohr circle construction: (a) stresses on a block of material; (b) resolution of stresses in relation to a sloping plane; (c) geometry of a circle in Cartesian co‐ordinates; and (d) the Mohr circle representation of stresses.
2. Figure 6.2 Examples of the principal stresses: (a) next to a smooth cantilever retaining wall; and (b) in a triaxial test specimen.
3. Figure 6.3 Mohr diagram representations of stress and failure criteria: (a) a generalised c‐φ soil; (b) a purely frictional soil; and (c) a purely cohesive soil.
4. Figure 6.4 Correlations between remoulded shear strength and liquidity index.
5. Figure 6.5 Correlation between sensitivity and liquidity index.
6. Figure 6.6 Relationship between the ratio of undrained shear strength to effective overburden pressure and plasticity index for normally consolidated clays.
7. Figure 6.7 Correlations between shear strength and liquidity index.
8. Figure 6.8 Correction factor for field vane test results depending on plasticity index, based on back‐analysis of embankment failures.
9. Figure 6.9 Approximate correlations between undrained shear strength and SPT N‐values.
10. Figure 6.10 Correlation between undrained shear strength, SPT N‐value and plasticity index for overconsolidated clays.
11. Figure 6.11 Correlations between effective angle of shearing resistance and plasticity index.
12. Figure 6.12 Typical values of density and angle of shearing resistance for cohesionless soils.
13. Figure 6.13 Estimation of the angle of shearing resistance of granular soils from standard penetration test results.
14. Figure 6.14 Examples of relationships between relative density and angle of shearing resistance.
Chapter 07
1. Figure 7.1 Relationship between CBR and plasticity index for various consistency index values.
2. Figure 7.2 Correction of CBR values for partial saturation.
3. Figure 7.3 Relationship between suitability index and soaked CBR values.
4. Figure 7.4 Relationship between the ratio of maximum dry density to plasticity index and CBR for laterite–quartz gravels.
5. Figure 7.5 Correlations of plasticity index, maximum dry density and optimum moisture content with CBR.
6. Figure 7.6 Approximate relationships between Unified soil classes and CBR values.
7. Figure 7.7 Approximate relationships between AASHTO soil classes and CBR values.
8. Figure 7.8 Relationship between California Bearing Ratio and modulus of subgrade reaction.
Chapter 08
1. Figure 8.1 A comparison of various correlations between swelling potential and plasticity index.
2. Figure 8.2 Classification chart for swelling potential.
3. Figure 8.3 Simplified relationship between plasticity index and clay content.
4. Figure 8.4 Relationships between volume change and colloid content, plasticity index and shrinkage limit, for air‐dry to saturated conditions under a load of 6.9 kPa.
5. Figure 8.5 Relationship between swell index and swelling pressure for a range of liquid limits.
Chapter 09
1. Figure 9.1 Mechanisms of ice lens formation.
2. Figure 9.2 The influence of permeability and capillary action on frost susceptibility of soils.
3. Figure 9.3 Relationship between the average rate of frost heave and the percentage of soil particles finer than 20 μm.
4. Figure 9.4 A selection of proposed limits of frost susceptibility based on grading according to (a) Beskow (1935) for Denmark, Greenland and Sweden; (b) Armstrong and Csathy (1963) for Canada; and (c) Croney (1949) for UK.
5. Figure 9.5 Average rate of heave plotted against percentage finer than 20 μm from laboratory tests of a range of natural soils.
Chapter 10
1. Figure 10.1 Correlation between calorific value and mass loss on ignition.
Chapter 11
1. Figure 11.1 Correlation between coefficient of earth pressure at rest and angle of shearing resistance for normally consolidated sands.
2. Figure 11.2 Correlation between coefficient of earth pressure at rest and angle of shearing resistance for normally consolidated clays.
3. Figure 11.3 Correlations between coefficient of earth pressure at rest and plasticity index.
4. Figure 11.4 Correlation between the coefficient of earth pressure at rest and overconsolidation ratio for clays of various plasticity indices.
Appendix A
1. Figure A1 Plasticity chart for the Unified/ASTM soil classification system.
2. Figure A2 Plasticity chart for the British Standard soil classification system.
Appendix B
1. Figure B1 Light cable percussive rig and tools.
2. Figure B2 Portable rotary power auger.
3. Figure B3 Schematics of open drive samplers.
4. Figure B4 Principles of the piston sampler.
5. Figure B5 Split spoon sampler and cone attachment.
6. Figure B6 Schematic arrangement of standard penetration test equipment in borehole.
7. Figure B7 Principal features of a static cone.
8. Figure B8 Soil identification based on cone resistance and friction ratio of static cone tests.

This edition first published 2016
© 2016 John Wiley & Sons, Ltd

First Edition published in 1991

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Library of Congress Cataloging‐in‐Publication Data

Names: Carter, Michael, author. | Bentley, Stephen P., author.
Title: Soil properties and their correlations / Michael Carter and Stephen P. Bentley, Cardiff University, UK.
Description: Second edition. | Chichester, West Sussex, United Kingdom : John Wiley & Sons, Inc., 2016. | Includes bibliographical references and index.
Identifiers: LCCN 2016013755 (print) | LCCN 2016014304 (ebook) | ISBN 9781119130871 (cloth) | ISBN 9781119130901 (pdf) | ISBN 9781119130895 (epub)
Subjects: LCSH: Soil mechanics.
Classification: LCC TA710 .B4285 2016 (print) | LCC TA710 (ebook) | DDC 624.1/5136–dc23
LC record available at http://lccn.loc.gov/2016013755

A catalogue record for this book is available from the British Library.

Preface

The aims of this book are to provide a summary and discussion of commonly used soil engineering properties and to give correlations of various engineering properties.

The book includes:

a compendium of published correlations;
discussions of the reliability, accuracy and usefulness of the various correlations;
practical advice on how soil properties are used in the assessment and design of geotechnical problems, including basic concepts, and limitations on their use that need to be considered; and
descriptions of the measurement of soil properties, and how results are affected by the method of measurement and the expertise of technicians carrying out the testing.

A consideration in describing the various properties has been an awareness by the authors that many geotechnical engineers and engineering geologists have little, if any, hands‐on experience of laboratory testing, and are often unaware of the procedures used to obtain the various soil properties and of the effects of poor or inappropriate practice.

The properties are also described in relation to their use in geotechnical analysis, in a way that we hope will give students and younger engineers an in‐depth appreciation of the appropriate use of each property and the pitfalls to avoid, and should also provide a useful reminder to more experienced professionals.

Many soil correlations were established in the early decades of soil mechanics, with there being no need to repeat the work once correlations had been established and verified by sufficient researchers. As a consequence, the correlations given in this book span a wide range of time, a few as far back as the 1930s, but we have also presented more recent work where this adds useful information. However, our intention in selecting correlations is to present those that will be of wide practical application, and the book is not intended as a research review. To aid their use in spreadsheet calculations, we have derived mathematical expressions to fit many of the correlations that were originally given only graphically. We have also tried to keep the work independent of national design codes, but it inevitably contains references to practices that are more prevalent in the English‐speaking world. Where references are made to classification systems and associated codes we have, where possible, included references to both UK and US practice.

We envisage and recommend that correlations be used in two ways: firstly, to obtain values of a property that has not been measured; and secondly, to provide additional values where some direct measurements of the property have been made. In the first case, where no values of a particular property have been directly measured, the values obtained from correlations should be viewed with caution and treated as preliminary, especially where the property value is critical to the predicted performance of a design. Where correlations are used in combination with direct measurements to provide supplementary values, the accuracy and reliability of the correlations can usually be verified, fine‐tuning the correlation if necessary, which may allow the values obtained by correlation to be viewed with more confidence.

While every care has been taken in the preparation of this book, with the very large amount of information that has been assembled it is possible that some errors have occurred; users should satisfy themselves that the information presented is correct. The authors can take no responsibility for consequences resulting from any errors in the book. The views expressed about the reliability and accuracy of correlations, typical values and other published information are based on the authors’ own experience and may not accord with those of other geotechnical specialists.

List of Symbols

Symbol	Name of variable	Typical units (SI)*
α	A scaling factor for estimating footing settlements from plate bearing test results.	D
α	A factor for estimating values of coefficient of volume compressibility from static cone test results.	D
α	Adhesion factor, for pile calculations.	D
α	A factor used to estimate the pull‐out resistance of a soil reinforcement grid.	D
Δp	A distance above or below the A‐line on a standard plasticity chart.	%
θ	Angle of a plane, from the direction of maximum principle stress, on which stresses act.	Degrees
μ	Viscosity of permeant for general seepage calculations.	kN.s/m²
ν	Poisson's ratio.	D
π	Ratio of the circumference of a circle to its diameter (≈3.14159).	D
ρ	Settlement.	m, mm
σ	Direct stress.	kPa (kN/m²)
σ'	Effective direct stress.	kPa (kN/m²)
σ₁, σ₂, σ₃	Maximum, intermediate and minimum principal stresses.	kPa (kN/m²)
σ_n	Effective earth pressure, used in soil nail calculations.	kPa (kN/m²)
σ_v, σ'_v	Vertical stress, or overburden pressure, in total and effective stress terms, respectively.	kPa (kN/m²)
τ	Shear stress.	kPa (kN/m²)
γ	Bulk density of soil.	kN/m³
γ_d	Dry density of soil.	kN/m³
γ_dmax	Maximum dry density, for relative density calculations.	kN/m³
γ_dmin	Minimum dry density, for relative density calculations.	kN/m³
γ_p	Density of permeant for general seepage equation.	kN/m⁴
γ_sub	Submerged density of soil.	kN/m³
γ_w	Density of water.	kN/m³
ϕ	Angle of shearing resistance (general, or in total stress terms).	Degrees
ϕ'	Effective stress angle of shearing resistance.	Degrees
ϕ_d	Drained angle of shearing resistance.	Degrees
ϕ_r	Residual angle of shearing resistance (general).	Degrees
a	Air voids content of soil.	%
a	Component of influence factor I_c for estimating settlements of footings on sands.	D
A	Area (nominal) of soil water flow.	m²
A	A correction factor for rod energy ratio in the standard penetration test.	D
A	Percentage passing a 2.4 mm sieve, used in the calculation of suitability index.	%
A	A constant used in the estimation of swelling potential from plasticity index.	D
A_c	Activity value (of a clay).	D
A_p	End area of penetration cone in a 1standard penetration test.	mm²
A_s	End area of penetration cone in a dynamic probe.	mm²
a_v	Coefficient of compressibility. (See also m_v, coefficient of volume compressibility.)	m²/MN
b	Component of influence factor I_c for estimating settlements of footings on sands.	D
B	Footing width.	m
B	A constant used in the estimation of swelling potential from plasticity index.	D
c	Shape factor in general seepage calculations.	D
c	Cohesion.	kPa (kN/m²)
C	Percentage finer than 0.002 mm, used in the calculation of activity for a clay.	D
c'	Effective stress cohesion.	kPa (kN/m²)
C₁	Constant used in Hazen's formula to estimate the coefficient of permeability.	D
CBR	California Bearing Ratio.	%
C_c	Coefficient of curvature (coefficient of grading).	D
C_c, C_r	Compression index, recompression index, respectively.	D
c_d	Drained cohesion.	kPa (kN/m²)
CI	Consistency index.	%
C_N	Correction factor for overburden pressure, applied to SPT N‐values.	D
c_u	Undrained cohesion, shear strength.	kPa (kN/m²)
C_u	Coefficient of uniformity.	D
c_v	Coefficient of consolidation.	cm²/s, m²/year
C_α	Secondary compression index.	(log₁₀ time)^–1
C_αε , C'	Modified secondary compression index (sometimes referred to simply as the secondary compression index).	(log₁₀ time)^–1
d	Maximum length of drainage path in consolidation calculations.	m
D	Depth of foundation (when calculating allowable bearing pressures on sands).	m
D₁₀	The 10% particle size, also called the effective size.	mm (or μm)
D₃₀, D₆₀	The 30% and 60% particle sizes, respectively.	mm (or μm)
D_n	The particle size at which n% of the material is finer. See also D₁₀, D₃₀, D₆₀.	mm (or μm)
D_r	Relative density (of granular soils).	D
D_s	An effective particle size for permeability estimates, usually taken as D₁₀.	mm
e	Voids ratio.	D
e	The natural number, approximately 2.718.	D
E	Young's modulus (also called the elastic modulus).	kPa, MPa
e₁, e₂	Initial and final voids ratios in consolidation testing.	D
E_d	Deformation modulus (also called the constrained modulus).	kPa, MPa
e_max	Maximum voids ratio, for relative density calculations.	D
e_min	Minimum voids ratio, for relative density calculations.	D
ER_r	Rod energy ratio in standard penetration test.	D
F	The percentage passing the 75 μm sieve, used in the calculation of AASHTO classification group index.	%
f_l, f_s, f_t	Shape, layer thicknes and time factors, respectively, for estimating settlements of footings on sands.	D
F_p	Drop distance of monkey (falling hammer) in a dynamic probe.	mm
F_s	Drop distance of monkey (falling hammer) in a standard penetration test.	mm
G	Shear modulus.	kPa, MPa
G_s	Specific gravity of soil solids	D
h	Thickness of specimen in consolidation testing.	mm
H	Thickness of a compressible layer in consolidation testing.	m
i	Hydraulic gradient in soil water flow.	D
I_c	Influence factor for estimation of settlements of footings on sands.	D
I_r	Rigidity index, used in rate‐of‐settlement estimates based on static piezocone test results.	D
I_r	Swell index, used in the estimation of swelling pressure.	D
k	Coefficient of permeability.	m/s, m/year
K	A constant used in the estimation of swelling potential from plasticity index.	D
K₀	Coefficient of earth pressure at rest.	D
K_d	Depth factor for allowable bearing pressures on sands.	D
K_s	Earth pressure coefficient use in driven pile calculations.	D
L	Footing length.	m
LI	Liquidity index.	%
LL	Liquid limit.	%
m	Moisture (water) content of soil.	%
M_p	Mass of monkey (falling hammer) in a dynamic probe.	kg
M_s	Mass of monkey (falling hammer) in a standard penetration test.	kg
m_v	Coefficient of volume compressibility. (See also a_v, coefficient of compressibility.)	m²/MN
n	Porosity of soil.	D
n	A factor used to estimate undrained shear strength from consistency index or liquidity index.	D
N	SPT N‐value; blows of standard hammer to drive the SPT sampler or cone 300 mm.	Blows
N₁	SPT N‐value corrected for overburden pressure.	Blows
N₁₍₆₀₎	SPT N‐value corrected for overburden pressure and to a rod energy ratio of 60%.	Blows
N₆₀	SPT N‐value corrected for rod energy ratio, ER_r. (the “60” refers to standardisation to 60% rod energy.)	Blows
N_corrected	SPT N‐value corrected for silts and fine sands below the groundwater table.	Blows
N_k	A factor used in the estimation of undrained shear strength from static cone tip resistance.	D
O₄₀, O₈₀	Pore diameters at which 40% and 80% of the pores are finer	mm, μm
OCR	Overconsolidation ratio.	D
p	Previous maximum overburden pressure, used in estimating settlements of footings on sands.	D
p₁, p₂	Initial and final pressures used in a stage of consolidation testing.	kPa (kN/m²)
PI	Plasticity index.	%
PL	Plastic limit.	%
PM	Plasticity modulus.	%
P_p	Penetration for each blow count in a dynamic probe.	mm
P_s	Penetration for each blow count in a standard penetration test.	mm
q	Quantity of flow of water through soil per unit time.	m³/s, m³/year
q	Bearing pressure.	kPa (kN/m²)
q_a	Allowable bearing pressure.	MPa (MN/m²)
q_c	Measured cone resistance (pressure) in static cone tests.	kPa (kN/m²)
q_u	Ultimate bearing capacity.	kPa (kN/m²)
R	Component of influence factor f_t for estimating settlements of footings on sands.	D
S	Degree of saturation.	%
S	Swelling potential.	%
s, s_u	Undrained shear strength.	kPa (kN/m²)
S_t	Sensitivity	D
SL	Shrinkage limit.	%
t	Time, used in calculations or rates of consolidation and secondary compression.	s, years
t₁, t₂	Start and end times for secondary compression calculations.	s, years
T_v	Basic time factor, used in calculations or rates of consolidation.	D
u	Pore water pressure.	kPa (kN/m²)
U	Degree of consolidation.	D
v	Nominal velocity of flow of water through soil.	m/s, m/year
v_t	True velocity of flow of water through soil.	m/s, m/year
W_LW	Weighted liquid limit, used in the estimation of swelling potential.	%
W_w	Weight of water (in the model soil sample).	g
Y	Rate of frost heave.	mm/day

* D = dimensionless; % values are also essentially dimensionless.