Phase relationship diagram:
In a mass of soil, there are three three physical components: components: solid, water, water, and air. A phase relationship diagram is normally used to represent the relationship as follows:
Definitions:
Volume: (ft3, m3)
Vt: Total volume Vs: Volume of solid Vv: Volume of void Vw: volume of water Va: Volume of air
Weights: (lbs, kg, kN)
Wt: total weight Ws: weight of solid Ww: weight of water Weight of air = 0
Phase Relationships:
Volume-volume relationship:
Void ratio (no unit):
Porosity (no unit):
Degree of saturation (%):
air content:
Weight-weight relationship:
Water (Moisture) content (%):
Moisture content at fully saturation is not 100%! 100% moisture content means the weight is equally divided into water and solid or in other words the weight of soil particles is equal to the weight of water. See: Solution of The Value of The Moisture When Fully Saturated
Weight-Volume relationship:
(Unit weight or density, lbs/ft3, g/cm3, kN/m3)
Moisture (total) unit weight:
Dry unit weight:
Solid unit weight: Saturated unit weight (when soil is completely saturated, S = 100%,V a=0):
Submerged (buoyant) unit weight (when soil is below ground water table, S = 100%):
Following relations are very handy in solving problems:
Unit weight to unit weight relationship
Specific gravity: (Unit weight of water = 62.4 lbs/ft 3 = 1 g/cm3 = 9.8 kN/m3) Average value of Gs for granular soils is 2.65, while the average value of Gs for cohesive soils is 2.80.
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Solved sample problems of Soil Phase Relationships:
Solution of Unit Weight and Its Conversion from Metric Units to SI and US Units Solution of Soil Compaction Check Via The Voids Ratio Solution of The Value of The Moisture When Fully Saturated
Example 1: Determine unit weights, water content, based on known volume and weight (English units)
Given: (English units)
Volume of soil mass: 1 ft3. Weight of soil mass at moist condition: 100 lbs Weight of soil after dried in oven: 80 lbs
Requirements:
Determine moist unit weight of soil, dry unit weight of soil, and water content.
Problem solving technique:
1. Moist unit weight gt= Wt / Vt (Wt = 100 lbs, Vt=1 ft3, are given) 2. Dry unit weight, gd = Ws / Vt (Weight of solid is weight of soil after dried in oven ,Ws = 80 lbs, V t=1 ft3, are given) 3. Water content, w (%) = Ww/Ws (Ws = 80 lbs , weight of water, W w not known) 4. Find weight of water, from phase relationship diagram, Ww = Wt – Ws. Solution:
1. 2. 3. 4.
Moist (total) unit weight, gt = Wt / Vt = 100/1 = 100 pcf (lbs/ft3) Dry unit weight, gd = Ws / Vt = 80/1= 80 pcf (lbs/ft3). Weight of water = 100-80=20 lbs Water (Moisture) content: w (%) = Ww/Ws ´ 100 (%) = 20/80x100% = 25%
Example 2: Determine unit weights, water content, based on known volume and weight (SI units)
Given: (SI units)
Volume of soil mass: 0.0283 m3.
Weight of soil mass at moist condition: 45.5 kg Weight of soil after dry in oven: 36.4 kg
Problem solving technique:
1. Moist unit weight gt = Wt / Vt (both value are given) 2. Dry unit weight, gd = Ws / Vt (both value are given) 3. Water content, w (%) = Ww/Ws (Weight of solid is weight of soil after dried in oven is given, weight of water not known) 4. Find weight of water, from phase relationship diagram, Ww = Wt – Ws. Requirements:
Determine moist unit weight of soil, dry unit weight of soil, and water content. Solution:
1. Moisture (total) unit weight, gt = Wt / Vt = 45.5/0.0283 = 1608 kg/m3 = 1.608 g/cm3 2. Dry unit weight, gd = Ws / Vt = 36.4/0.0283= 1286 kg/m 3=1.286 g/cm3 3. Weight of water = 45.5-36.4=9.1 lbs 4. Water (Moisture) content: w (%) = W w/Ws ´ 100 (%) = 9.1/36.4x100% = 25%
Example 3: Determine void ratio, porosity, and degree of saturation based on known volume, weight, and specific gravity (English units)
Given: (English units)
Volume of soil mass: 1 ft3. Weight of soil mass at moist condition: 125 lbs Weight of soil after dry in oven: 100 lbs Specific gravity of solid = 2.65
Requirements:
Determine void ratio, porosity, and degree of saturation Problem solving technique:
1. 2. 3. 4. 5. 6. 7. 8.
Void ratio, e = Vv/Vs (Vv, Vs, not given) Find Vs = Ws/gs (Ws = 100 lbs, gs is not given) Find gs = Gsgw (Gs is given, gw =62.4 lbs/ft3 is a know value) Find Vv = 1-Vs (e can be calculated) Porosity, n = Vv/Vt (Vv from step 4, Vs from step 2) Degree of saturation, S = Vw/Vv (Vv from step 4, need to find Vw) Vw =Ww/gw (Ww, not given, gw=62.4 lbs/ft3) Find Ww = Wt – Ws (Both Wt, Ww are given)
Solution:
1. 2. 3. 4. 5. 6. 7. 8.
Solid unit weight, gs = Gsgw=2.65*62.4=165.4 lbs/ft3 Volume of solid, Vs = Ws/gs = 100/165.4=0.6 ft 3 Volume of void = Vt – Vs = 1 –0.6=0.4 ft3 Void ratio, e = Vv/Vs = 0.4/0.6=0.66 Porosity, n = Vv/Vt = 0.4/1 = 0.4 Weight of water = 125-100=25 lbs Volume of water, Vw = Ww/gw = 25/62.4=0.4 ft3 Degree of saturation, S = Vw/Vv = 0.4/0.4x100% = 100%.
Example 4: Determine void ratio, porosity, and degree of saturation based on known volume, weight, and specific gravity (English units)
Given: (metric units)
Volume of soil mass: 0.0283 m3. Weight of soil mass at moist condition: 56.6 kg Weight of soil after dry in oven: 45.5 kg Specific gravity of solid = 2.65
Requirements:
Determine void ratio, porosity, and degree of saturation Problem solving technique:
1. 2. 3. 4.
Void ratio, e = Vv/Vs Find Vs = Ws/gs Find gs = Gsgw Find Vv = 1-Vs
(Vv, Vs, not given) (Ws = 45.5 kg, gs is not given) (Gs is given, gw =1 g/cm3 is a know value) (e can be calculated)
5. 6. 7. 8.
Porosity, n = Vv/Vt (Vv from step 4, Vs from step 2) Degree of saturation, S = Vw/Vv (Vv from step 4, need to find Vw) Vw =Ww/gw (Ww, not given, gw=62.4 lbs/ft3) Find Ww = Wt – Ws (Wt = 56.6 kg, Ws = 45.5 kg are given)
Solution:
1. 2. 3. 4. 5. 6. 7. 8.
Solid unit weight, gs = Gsgw=2.65*1=2.65 g/cm3 = 2650 kg/m3 Volume of solid, Vs = Ws/gs = 45.5/2650=0.0171 m 3 Volume of void = Vt – Vs = 0.0283 –0.0171=0.0112 m3 Void ratio, e = Vv/Vs = 0.0112/0.0171=0.65 Porosity, n = Vv/Vt = 0.0111/0.0283 = 0.39 Weight of water = 56.6-45.5=11.1 kg Volume of water, Vw = Ww/gw = 11.1 kg/1 g/cm3= 11100 cm3= 0.0111m3 Degree of saturation, S = Vw/Vv = 0.0111/0.0111x100% = 100%.
Question:
A contractor has compacted the base course for a new road and found that the mean value of the test samples shows w = 14.6%, Gs = 2.81, and γ = 18.2 kN/m3. The specifications require that e < 0.80. Has the contractor complied with the specifications?
Solution:
For formulas of soil phase relationships read Soil Phase Relationships article.
Thus
Yes, the contractor has complied. Question:
A cohesive soil sample was taken from an SPT and returned to the laboratory in a glass jar. It was found to weigh 140.5 grams. The sample was then placed in a container of V = 500 cm 3 and 423 cm3 of water were added to fill the container. From these data, what was the unit weight of the soil in kN/m 3 and pcf?
Solution:
For formulas of soil phase relationships read Soil Phase Relationships article. Notice that the 140.5 grams is a mass. Therefore, the ratio of mass to volume is the density rho
for conversion from SI units to US units:
Question:
1) Show that at saturation the moisture (water) content is
2) Show that at saturation the moisture (water) content is
Solution:
For formulas of soil phase relationships read Soil Phase Relationships article. (1) In a fully saturated soil the relation, Se=wGs e=wGs because S = 1
but
rearranging
or
therefore
becomes simply
(2) Again, in a fully saturated soil:
Thus
or
In Civil Engineering and more specifically Geotechnical Engineering there are many instances where the values of engineering parameters are cannot be obtained from the testings. Thus, typical values of these parameters will be used. In this article typical values and useful relationships of many important engineering parameters used in Civil Engineering and Geotechnical Engineering are given.
See the full table of typical values of cohesive intercept "C" of soils here See the full table of typical values of friction angle "φ" of soils here
Temperature
C / 100 = (F - 32) / 180 = (K - 273) / 100 = (R - 492) / 180 where C = F = K = R = Rankine scale
Celsius Fahrenheit Kelvin
degree degree degree
Water Pressure Gradient
0.1 kgf/cm2 / m = 0.433 psi/ft = 0.42 psi/m = 9.81 kPa/m
Acceleration of Gravity at Sea Level
9.806 m/s2 = 32.174 ft/s 2
Typical Values of Mass Density of Water
1000 kg/m3 = 1.0 kg/dm3 = 1.0 g/cm3 = 62.4 pcf = 8.34 lb/gal = 350 lb/bbl
Typical Values of Mass Density/Unit Weight of Soils
Sands: 115 ~ 135 pcf ( 18 ~ 21 kN/m 3 up to 22 kN/m3 with some gravel content) Clays: 90 ~ 120 pcf (14 ~ 19 kN/m3)
Typical Values of Void Ratios of Sands
emin = 0.38 ~ 0.5 emax = 0.75 ~ 1.0
Degree of Compaction versus Relative Density of Sands DR (%)
Qualitative assessment of degree of compactness
0 - 15
Very Loose
15 - 35
Loose
35 - 65
Medium
DR (%)
65 - 85
Qualitative assessment of degree of compactness
Dense
85 - 100 Very Dense
Typical Values of Coefficient of Lateral Earth Pressure at Rest
K0,NC = 0.38 ~ 0.5 in sands K0,NC = 0.5 ~ 0.75 in clays
Typical Values of Void Ratios of Clays
From e = 2 (extremely soft, weak clays) to e = 0.7 (very stiff clays). There are extreme examples of softer clays (with e as high as 5) and stiffer clays.
Typical Values of Critical-State Friction Angle
Silica sands: 28 ~ 36 Clays: 15 ~ 30
Typical Values of Residual Friction-Angle in Clays
As low as 5-7 degrees for smectites. For low confining stress levels and/or large sand content it can be as high as critical-state friction angle.
Typical Values of Poisson's Ratio
Drained: v = 0.1 ~ 0.3 Undrained: v = 0.5
Typical Values of Atterberg Indices
LL = Liquid Limit = 30% ~ 160% for clays PL = Plastic Limit = 20% ~ 50%
Typical Values of Recompression Index/Compression Index Ratio of Clays
Cs/Cc = 0.1 ~ 0.2
Typical Values of Coefficient of Consolidation for Clays
cv = 10-8 to 5 x 10-7 m2/s
Typical Values of Coefficient of Secondary Compression for Shale, Mudstone, Clay, and Peat
Ca/Cc = 0.02 ~ 0.07 (lower values for shale and mudstone; higher values for peat)
Typical Values of Hydraulic Conductivity of Soils Soil
K
Gravel 10-3 to 1 m/s Sand
10-7 to 10-2 m/s
Silt
10-9 to 10-5 m/s
Clay
10-13 to 10-9 ms
Cohesion Intercept of Soils + Typical Values
Courses > Soil Mechanics > Physical Properties of Soil > Cohesion Intercept of Soils + Typical Values
Introduction on Cohesion Intercept of Soils + Typical Values : The cohesion intercept is a term used in describing the shear strength soils. Its definition is mainly derived from the Mohr-Coulomb failure criterion and it is used to describe the non-frictional part of the shear resistance which is independent of the normal stress. In the stress plane of Shear stress-effective normal stress, the soil cohesion is the intercept on the shear axis of the MohrCoulomb shear resistance line.
Concepts and Formulas of Cohesion Intercept of Soils + Typical Values:
Difference between Cohesive and Granular soil
"Granular soil" means gravel, sand, or silt (coarse-grained soil) with little or no clay content. Granular soil has no cohesive strength. Some moist granular soils exhibit apparent cohesion. Granular soil cannot be molded when moist and crumbles easily when dry. "Cohesive soil" means clay (fine-grained soil), or soil with a high clay content, which has cohesive strength. Cohesive soil does not crumble, can be excavated with vertical sideslopes, and is plastic when moist. Cohesive soil is hard to break up when dry, and exhibits significant cohesion when submerged. Cohesive soils include clayey silt, sandy clay, silty clay, clay and organic clay.
Typical values of soil cohesion "C" for different soils
Some typical values of soil cohesion are given below for different soil types. The soil cohesion depends strongly on the consistence, packing, and saturation condition. The values given below correspond to normally consolidated condition unless otherwise stated. These values should be used only as a guideline for geotechnical problems; however, specific condition of each engineering problem often needs to be considered for an appropriate choice of geotechnical parameters. Cohesion [kPa] Description
USCS
min max
Specific value
Reference
Well graded gravel, sandy gravel, with little or no fines
GW
-
-
0
[1],[2],[3],
Poorly graded gravel, sandy gravel, with little or no fines
GP
-
-
0
[1],[2], [3],
Silty gravels, silty sandy gravels
GM
-
-
0
[1],
Clayey gravels, clayey sandy gravels
GC
-
-
20
[1],
Well graded sands, gravelly sands, with little or no fines
SW
-
-
0
[1],[2], [3],
Poorly graded sands, gravelly sands, with little or no fines
SP
-
-
0
[1],[2], [3],
Silty sands
SM
-
-
22
[1],
Silty sands - Saturated compacted
SM
-
-
50
[3],
Silty sands - Compacted
SM
-
-
20
[3],
Clayey sands
SC
-
-
5
[1],
Clayey sands - Compacted
SC
-
-
74
[3],
Clayey sands -Saturated compacted SC
-
-
11
[3],
Loamy sand, sandy clay Loam compacted
SM, SC
50
75
[2],
Loamy sand, sandy clay Loam saturated
SM, SC
10
20
[2],
Sand silt clay with slightly plastic fines - compacted
SM, SC
-
-
50
[3],
Sand silt clay with slightly plastic fines - saturated compacted
SM, SC
-
-
14
[3],
Inorganic silts, silty or clayey fine sands, with slight plasticity
ML
-
-
7
[1],
Inorganic silts and clayey silts compacted
ML
-
-
67
[3],
Inorganic silts and clayey silts saturated compacted
ML
-
-
9
[3],
Inorganic clays, silty clays, sandy clays of low plasticity
CL
-
-
4
[1],
Inorganic clays, silty clays, sandy clays of low plasticity - compacted
CL
-
-
86
[3],
Inorganic clays, silty clays, sandy clays of low plasticity - saturated compacted
CL
-
-
13
[3],
Mixture if inorganic silt and clay compacted
ML-CL
-
-
65
[3],
Mixture if inorganic silt and clay saturated compacted
ML-CL
-
-
22
[3],
Organic silts and organic silty clays of low plasticity
OL
-
-
5
[1],
Inorganic silts of high plasticity compactd
MH
-
-
10
[1],
Inorganic silts of high plasticity saturated compacted
MH
-
-
72
[3],
Inorganic silts of high plasticity
MH
-
-
20
[3],
Inorganic clays of high plasticity
CH
-
-
25
[1],
Inorganic clays of high plasticity compacted
CH
-
-
103
[3],
Inorganic clays of high plasticity satrated compacted
CH
-
-
11
[3],
Organic clays of high plasticity
OH
-
-
10
[1],
Loam - Compacted
ML, OL, MH, OH
60
90
[2],
Loam - Saturated
ML, OL, MH, OH
10
20
[2],
Silt Loam - Compacted
ML, OL, MH, OH
60
90
[2],
Silt Loam - Saturated
ML, OL, MH, OH
10
20
[2],
Clay Loam, Silty Clay Loam Compaced
ML, OL, CL, MH, OH, CH
60
105
[2],
Clay Loam, Silty Clay Loam Saturated
ML, OL, CL, MH, OH, CH
10
20
[2],
Silty clay, clay - compacted
OL, CL, OH, CH
90
105
[2],
Silty clay, clay - saturated
OL, CL, OH, CH
10
20
[2],
Peat and other highly organic soils
Pt
-
-
REFERENCES 1. Swiss Standard SN 670 010b, Characteristic Coefficients of soils, Association of Swiss Road and Traffic Engineers 2. Minnesota Department of Transportation, Pavement Design, 2007 3. NAVFAC Design Manual 7.2 - Foundations and Earth Structures, SN 0525-LP-300-7071, REVALIDATED BY CHANGE 1 SEPTEMBER 1986
What is Geotechnical Engineering? Subtopics, Salaries, Books, Journals, ... Articles > What is Geotechnical Engineering? Subtopics, Salaries, Books, Journals, ...
Geotechnical engineering is
the branch of civil engineering concerned with the engineering behavior of earth materials. Geotechnical engineering is important in civil engineering, but also has applications in military, mining, petroleum and other engineering disciplines that are concerned with construction occurring on the surface or within the ground. See the full list of civil engineering branches. A typical geotechnical engineering project begins with a review of project needs to define the required material properties. Then follows a site investigation of soil, rock, fault distribution and bedrock properties on and below an area of interest to determine their engineering properties including how they will interact with, on or in a proposed construction. Site investigations are needed to gain an understanding of the area in or on which the engineering will take place. Investigations can include the assessment of the risk to humans, property and the environment from natural hazards such as earthquakes, landslides, sinkholes, soil liquefaction, debris flows and rockfalls.
Practicing engineers:
Geotechnical engineers are typically graduates of a four-year civil engineering program and some hold a masters degree and/or PhD. In the USA, geotechnical engineers are typically licensed and regulated as Professional Engineers (PEs) in most states; currently only California and Oregon have licensed geotechnical engineering specialties. The Academy of GeoProfessionals (AGP) began issuing Diplomate, Geotechnical Engineering (D.GE) certification in 2008. State governments will typically license engineers who have graduated from an ABET accredited school, passed the "Fundamentals of Engineering" examination (FE), completed several years of
work experience under the supervision of a licensed Professional Engineer, and passed the Professional Engineering examination (PE).
Average geotechnical engineering salary:
Based on an investigation on 468 salaries, median pay for Geotechnical Engineers in the United States is around $65,000 annually (2017). Minimum: $55,000; Maximum: $92,000. (Low is the 10th percentile and High is the 90th percentile.)
Geotechnical engineering subtopics:
1. Soil mechanics Soil mechanics is a branch of soil physics and engineering mechanics that describes the behavior of soils. It differs from fluid mechanics and solid mechanics in the sense that soils consist of a heterogeneous mixture of fluids (usually air and water) and particles (usually clay, silt, sand, and gravel) but soil may also contain organic solids and other matter. investigation 2. Geotechnical Geotechnical engineers and engineering geologists perform geotechnical investigations to obtain information on the physical properties of soil and rock underlying (and sometimes adjacent to) a site to design earthworks and foundations for proposed structures, and for repair of distress to earthworks and structures caused by subsurface conditions. 3. Foundations A building's foundation transmits loads from buildings and other structures to the earth. Geotechnical engineers design foundations based on the load characteristics of the structure and the properties of the soils and/or bedrock at the site. earth support structures 4. Lateral A retaining wall is a structure that holds back earth. Retaining walls stabilize soil and rock from downslope movement or erosion and provide support for vertical or near-vertical grade changes. Cofferdams and bulkheads, structures to hold back water, are sometimes also considered retaining walls. 5. Earthworks Earthworks include excavation, filling, and compaction.
Improvement 6. Ground Ground Improvement is a technique that improves the engineering properties of the treated soil mass. Usually, the properties modified are shear strength, stiffness and permeability. Ground improvement has developed into a sophisticated tool to support foundations for a wide variety of structures. Properly applied, i.e. after giving due consideration to the nature of the ground being improved and the type and sensitivity of the structures being built, ground improvement often reduces direct costs and saves time. stabilization 7. Slope Slope stability is the potential of soil covered slopes to withstand and undergo movement. Stability is determined by the balance of shear stress and shear strength. geotechnical engineering 8. Offshore Offshore (or marine) geotechnical engineering is concerned with foundation design for human-made structures in the sea, away from the coastline (in opposition to onshore or nearshore). 9. Geosynthetics Geosynthetics are a type of plastic polymer products used in geotechnical engineering that improve engineering performance while reducing costs.
Most commonly used software in geotechnical engineering:
Plaxis 2D & 3D - finite element based FLAC 2D & 3D - finite difference based Abaqus - finite element based CSI SAFE - finite element based, commonly used for shallow foundation design
Most famous geotechnical engineering books:
Principles of Geotechnical Engineering, Braja M. Das Introduction to Geotechnical Engineering, Braja M. Das Foundation analysis and design, Joseph E. Bowles Soil mechanics in engineering practice, Karl Terzaghi Geotechnical Earthquake Engineering, Steven L. Kramer
Most famous (highest impact factor) geotechnical engineering journals:
The followings are almost the best geotehnical engineering journals, this list does not include all journals
Journal of Geotechnical and Geoenvironmental Engineering - ASCE International Journal of Geomechanics - ASCE Geotechnique Geotextiles and Geomembranes Canadian Geotechnical Journal Computers and Geotechnics International Journal for Numerical and Analytical Methods in Geomechanics Introduction on Effects of Water on Slope Stability : Very soft, saturated foundation soils or ground water generally play a prominent role in geotechnical failures in general. They are certainly major factors in cut slope stability and in the stability of fill slopes involving both “internal” and “external” slope failures. The effect of water on cut and
fill slope stability is briefly discussed below.
Concepts and Formulas of Effects of Water on Slope Stability:
Importance of Water:
Next to gravity, water is the most important factor in slope stability. The effect of gravity is known, therefore, water is the key factor in assessing slope stability.
Effect of Water on Cohesionless Soils:
In cohesionless soils, water does not affect the angle of internal friction (φ). The effect of water on cohesionless soils below the water table is to decrease the intergranular (effective) stress between soil grains (σ'n), which decreases the frictional shearing resistance (τ').
Effect of Water on Cohesive Soils:
Routine seasonal fluctuations in the ground water table do not usually influence either the amount of water in the pore spaces between soil grains or the cohesion. The attractive forces between soil particles prevent water absorption unless external forces such as pile driving, disrupt the grain structure. However, certain clay minerals do react to the presence of water and cause volume changes of the clay mass. An increase in absorbed moisture is a major factor in the decrease in strength of cohesive soils as shown schematically in Figure below. Water absorbed by clay minerals causes increased water contents that decrease the cohesion of clayey soils. These effects are amplified if the clay mineral happens to be expansive, e.g., montmorillonite.
Fills on Clays:
Excess pore water pressures are created when fills are placed on clay or silt. Provided the applied loads do not cause the undrained shear strength of the clay or silt to be exceeded, as the excess pore water pressure dissipates consolidation occurs, and the shear strength of the clay or silt increases with time. For this reason, the factor of safety increases with time under the load of the fill.
Cuts in Clay:
As a cut is made in clay the effective stress is reduced. This reduction will allow the clay to expand and absorb water, which will lead to a decrease in the clay strength with time. For this reason, the factor of safety of a cut
slope in clay may decrease with time. Cut slopes in clay should be designed by using effective strength parameters and the effective stresses that will exist in the soil after the cut is made.
Slaking - Shales, Claystones, Siltstones, etc.:
Sudden moisture increase in weak rocks can produce a pore pressure increase in trapped pore air accompanied by local expansion and strength decrease. The "slaking" or sudden disintegration of hard shales, claystones, and siltstones results from this mechanism. If placed as rock fill, these materials will tend to disintegrate into a clay soil if water is allowed to percolate through the fill. This transformation from rock to clay often leads to settlement and/or shear failure of the fill.
Friction Angle of Soils + Typical Values Courses > Soil Mechanics > Physical Properties of Soil > Friction Angle of Soils + Typical Values
Introduction on Friction Angle of Soils + Typical Values : Soil friction angle is a shear strength parameter of soils. Its definition is derived from the Mohr-Coulomb failure criterion and is used to describe the friction shear resistance of soils together with the normal effective stress. In the stress plane of Shear stress-effective normal stress, the soil friction angle is the angle of inclination with respect to the horizontal axis of the MohrCoulomb shear resistance line.
Concepts and Formulas of Friction Angle of Soils + Typical Values: Difference between Cohesive and Granular soil
"Granular soil" means gravel, sand, or silt (coarse-grained soil) with little or no clay content. Granular soil has no cohesive strength. Some moist granular soils exhibit apparent cohesion. Granular soil cannot be molded when moist and crumbles easily when dry. "Cohesive soil" means clay (fine-grained soil), or soil with a high clay content, which has cohesive strength. Cohesive soil does not crumble, can be excavated with vertical sideslopes, and is plastic when moist. Cohesive soil is hard to break up when dry, and exhibits significant cohesion when submerged. Cohesive soils include clayey silt, sandy clay, silty clay, clay and organic clay.
Typical values of soil friction angle for different soils according to USCS Soil friction angle [°] Description
USCS
min max
Specific value
Reference
Well graded gravel, sandy gravel, GW with little or no fines
33
40
[1],[2],
Poorly graded gravel, sandy gravel, with little or no fines
GP
32
44
[1],
Sandy gravels - Loose
(GW, GP)
35
[3 cited in 6]
Sandy gravels - Dense
(GW, GP)
50
[3 cited in 6]
Silty gravels, silty sandy gravels
GM
30
40
[1],
Clayey gravels, clayey sandy gravels
GC
28
35
[1],
Well graded sands, gravelly sands, with little or no fines
SW
33
43
[1],
Well-graded clean sand, gravelly sands - Compacted
SW
-
-
38
[3 cited in 6]
Well-graded sand, angular grains (SW) - Loose
33
[3 cited in 6]
Well-graded sand, angular grains (SW) - Dense
45
[3 cited in 6]
Poorly graded sands, gravelly sands, with little or no fines
SP
30
39
Poorly-garded clean sand Compacted
SP
-
-
Uniform sand, round grains Loose
[1], [2], 37
[3 cited in 6]
(SP)
27
[3 cited in 6]
Uniform sand, round grains Dense
(SP)
34
[3 cited in 6]
Sand
SW, SP
37
38
[7],
Loose sand
(SW, SP)
29
30
[5 cited in 6]
Medium sand
(SW, SP)
30
36
[5 cited in 6]
Dense sand
(SW, SP)
36
41
[5 cited in 6]
Silty sands
SM
32
35
[1],
Silty clays, sand-silt mix Compacted
SM
-
-
Silty sand - Loose
SM
27
33
[3 cited in 6]
Silty sand - Dense
SM
30
34
[3 cited in 6]
Clayey sands
SC
30
40
[1],
Calyey sands, sandy-clay mix compacted
SC
Loamy sand, sandy clay Loam
SM, SC
31
34
[7],
Inorganic silts, silty or clayey fine sands, with slight plasticity
ML
27
41
[1],
Inorganic silt - Loose
ML
27
30
[3 cited in 6]
Inorganic silt - Dense
ML
30
35
[3 cited in 6]
Inorganic clays, silty clays, sandy CL clays of low plasticity
27
35
[1],
34
31
[3 cited in 6]
[3 cited in 6]
Clays of low plasticity compacted
CL
Organic silts and organic silty clays of low plasticity
OL
22
32
[1],
Inorganic silts of high plasticity
MH
23
33
[1],
Clayey silts - compacted
MH
25
[3 cited in 6]
Silts and clayey silts - compacted ML
32
[3 cited in 6]
28
17
31
[3 cited in 6]
Inorganic clays of high plasticity
CH
[1],
Clays of high plasticity compacted
CH
Organic clays of high plasticity
OH
17
35
[1],
Loam
ML, OL, MH, OH
28
32
[7],
Silt Loam
ML, OL, MH, OH
25
32
[7],
Clay Loam, Silty Clay Loam
ML, OL, CL, MH, OH, CH
18
32
[7],
Silty clay
OL, CL, OH, CH
18
32
[7],
Clay
CL, CH, OH, OL
18
28
[7],
Peat and other highly organic soils
Pt
0
10
[2],
19
[3 cited in 6]
References: 1. Swiss Standard SN 670 010b, Characteristic Coefficients of soils, Association of Swiss Road and Traffic Engineers 2. JON W. KOLOSKI, SIGMUND D. SCHWARZ, and DONALD W. TUBBS, Geotechnical Properties of Geologic Materials, Engineering Geology in Washington, Volume 1, Washington Division of Geology and Earth Resources Bulletin 78, 1989, Link
3. Carter, M. and Bentley, S. (1991). Correlations of soil properties. Penetech Press Publishers, London. 4. Meyerhof, G. (1956). Penetration tests and bearing capacity of cohesionless soils. J Soils Mechanics and Foundation Division ASCE, 82(SM1). 5. Peck, R., Hanson,W., and Thornburn, T. (1974). Foundation Engineering Handbook. Wiley, London. 6. Obrzud R. & Truty, A.THE HARDENING SOIL MODEL - A PRACTICAL GUIDEBOOK Z Soil.PC 100701 report, revised 31.01.2012 7. Minnesota Department of Transportation, Pavement Design, 2007
Correlation between SPT-N value, friction angle, and relative density Correlation between SPT-N value and friction angle and Relative density (Meyerhoff 1956) SPT N3 Soi packing [Blows/0.3 m - 1 ft]
Relative Density [%]
Friction angle [°]
<4
Very loose
< 20
< 30
4 -10
Loose
20 - 40
30 - 35
10 - 30
Compact
40 - 60
35 - 40
30 - 50
Dense
60 - 80
40 - 45
> 50
Very Dense
> 80
> 45
Which test gives a better estimation of friction angle?
Usually, the economics of the project dictates the type of test you would use for determination of the friction angle. Nonetheless, the best test to determine the friction angle of soil is the one that is more analogous to the problem at hand. For example, if you are to determine bearing capacity of a square footing, triaxial test is the best one.
