Includes significant points

1. GEOTECHNICAL ENGINEERING –
TESTING ASPECTS
Yogesh Bafna
PhD (Pursuing) Geo-tech
Assistant Professor
SVKM’s IOT Dhule

2. Outline
1. Introduction to soil
2. Field of Geotechnical Engineering
3. Various geotechnical parameters
4. Indian standard soil classification system (ISCS)
5. Various laboratory tests
6. Field tests
7. CNS
8. Record test
9. Test frequencies

3. Introduction
• Soil –
- Soil is a substance existing on the earth surface,
which grows and develops plant life
- Soil is the material in the relatively thin surface
zone within which roots occur and all of the rest
of the crust is grouped under the term rock
- Soil is the aggregated or uncemented deposit of
minerals and/or organic particles fragments
covering the large portion of the earth crust

4. • Soil Mechanics-
– Soil mechanics is the application of laws of mechanics and
hydraulics to engineering problems dealing with sediments
and other consolidated accumulations of the solid particles
produced by the mechanical and chemical disintegrations
of rocks regardless of whether or not they contain an
admixture of organic constituents.
• Formation of soil-
– Mechanical
• Physical agencies such as temperature changes,
flowing water, ice, wind, plant and animals.
– Chemical
• Oxidation, hydration, carbonation and leaching by
organic acid and water

5. Field of Geotechnical Engineering
1. Foundation design and construction:
– BC, Settlement, effect of water table and vibration
2. Pavement Design:
– Subsoil, strength, stability
3. Design of underground structures and earth
retaining structures:
– Lateral loading, stability, failure plane
4. Design of embankments and excavations:
– Strength parameters for slope stability, effect of seepage force
5. Design of earth dams:
– Index properties and physical properties

6. Geotechnical Properties
1. Water content
2. Specific gravity
3. Particle size distribution
4. Consistency limits
5. In-situ density
6. Density index
7. Permeability
8. Relative density
9. MDD and OMC

7. Indian Soil Classification System
• 1. Coarse Grained Soils
– More than 50% of total material by weight > 75μ
• 2. Fine Grained Soils
– More than 50% of total material by weight < 75μ
• 3. Highly Organic & other miscellaneous soils
– Contain large % of fibrous organic matter
– Peat, decomposed vegetation particles, shells,
cinders & other non-soil materials

8. • Coarse Grained Soils
– Gravels – more than 50% of coarse fraction > 4.75mm
– Sands – more than 50% of coarse fraction < 4.75mm
• Fine Grained Soils
– Silt & clays of :-
– Low compressibility (L) – Liquid limit < 35%
– Medium compressibility(I) – LL b/w 35% & 50%
– High compressibility(H) – LL > 50%

9. Groups
• Coarse grained soil – 8 groups
• Fine grained soil – 9 groups
• Highly organic and other miscellaneous soils
as separate group
TOTAL = 18 Groups
• Groups are designated by symbols

10. Classification of Coarse Grained Soils
• Gravel (G)
I. Clean Gravel – fines < 5%
1. Well Graded Gravel (GW) – all particle sizes (Cu > 4)
2. Poorly Graded Gravel (GP) – excess or absence of
intermediate particle sizes
II. Dirty Gravel – fines > 12%
1. Silty Gravel (GM) – little fine/no plasticity (Ip < 4)
2. Clayey Gravel (GC) – fines are of low to medium/high
plasticity (Ip > 7)
• Boundary classification – GM-GC (Ip b/w 4 & 7) &
GW-GM, GW-GC, GP-GM (fines 5-12%)

11. • Sand (S)
I. Clean Sand – fines < 5%
• Well graded sand (SW) – Cu > 6 & Cc b/w 1 & 3
• Poorly graded sand (SP)
II. Dirty Sand – fines > 12%
• Silty sand (SM) - Ip < 4
• Clayey sand (SC) - Ip > 7
• Boundary classification SM-SC (Ip b/w 4 & 7) &
SW-SM, SW-SC, SP-SM (fines 5-12%)
• Boundary classification b/w gravel & sand group
GW-SW, GP-SP, GM-SM, GC-SC

12. Classification of Fine Grained Soils
• Low Compressibility (L)
– ML – Inorganic silts of none to low plasticity
– Ip < 4 & Atterberg limits are below A-line
– CL – Inorganic clay of low plasticity
– Ip > 7 & Atterberg limits are above A-line
– OL – Organic silt of low plasticity
– Atterberg limits are below A-line
Ip b/w 4 & 7 : ML-CL

13. • Intermediate Compressibility (I)
– MI – Inorganic silts of medium plasticity
– Atterberg limits are below A-line
– CI – Inorganic clay of medium plasticity
– Atterberg limits are above A-line
– OI – Organic silt of medium plasticity
– Atterberg limits are below A-line

14. • High Compressibility (H)
– MH – Inorganic silts of high plasticity
– Atterberg limits are below A-line
– CH – Inorganic clay of high plasticity
– Atterberg limits are above A-line
– OH – Organic silt of high plasticity
– Atterberg limits are below A-line

15. High Organic Soil
• Peat & other highly organic soils
• Denoted as Pt
• Identified by
– Colour
– Odour
– Spongy feel
– Fibrous texture

16. Plasticity Chart

17. Geotechnical Laboratory tests
1. Moisture content –
2. Specific Gravity
3. Grain Size analysis
4. Atterberg’s limits- Liquid, Plastic and shrinkage
5. Field density
6. Permeability test
7. Compaction test
8. Relative density test
9. Consolidation test
10. Shear strength parameter test

18. Geotechnical field test
1. Placement moisture content test
2. Field permeability test
3. Standard penetration test

23. Moisture content
• Methods
1. Oven drying method
2. Sand bath method
3. Calcium carbide method
• Moisture content ,
• Significance:
• Dry density
• All limits

24. Minimum mass of moist material selected to be
representative of the total samples:

26. Specific Gravity
• Specific gravity, Gs, of soil solids is the ratio of
the density of the aggregate soil solids to the
density of water.
• The procedure employs Archimedes’s principle
“A body submerged in water will displace a volume of
water equal to its own volume.”

28. Recommended mass for test specimen
Expected Values of Gs
17 May 2020 28

29. Grain Size Analysis
– Mechanical Method : Dry and Wet
– Hydrometer method
• The knowledge of sizes of solid particles
comprising a certain soil type and their relative
proportion is useful because it is used in;
1. Soils classification
2. Soil filter design
3. Predictions the behavior of a soil with respect to
shear strength, settlement and permeability

30. • 4.75 mm, 2.36 mm,
1.18mm, 0.6mm, 0.425
mm, 0.300mm, 0.150
mm, 0.075 mm

32. Sieve Analysis
• D60 - the diameter corresponding to 60% finer
in the particle-size distribution curve
• D10 – effective size
• Cu – coefficient of gradation
– More than 4 - Well graded gravel
– More than 6 – Well graded sand
• Cc – coefficient of curvature
– Between 1 -3 : Well graded gravel and sand

36. Atterberg’s limits
• Atterberg Limits
– Liquid Limit, LL
– Plastic Limit, PL
– Shrinkage limits, SL
• Soil Classification
– Indian Soil Classification System (ISCS)
• The soil consistency is used as a practical and an
inexpensive way to distinguish between silts and clays
• Plasticity property is important because it describes
the response of a soil to change in moisture content

37. • Water Content Significantly affects properties
of Silty and Clayey soils (unlike sand and
gravel)
– Strength decreases as water content increases
– Soils swell-up when water content increases
– Fine-grained soils at very high water content
possess properties similar to liquids
– As the water content is reduced, the volume of
the soil decreases and the soils become plastic
– If the water content is further reduced, the soil
becomes semi-solid when the volume does not
change

38. Four states are used to describe the soil consistency;
solid, semi-solid, plastic and liquid

39. • Liquid Limit (LL) is defined as the moisture content at
which soil begins to behave as a liquid material and
begins to flow
– (Liquid limit of a fine-grained soil gives the moisture content
at which the shear strength of the soil is approximately
2.5kN/m2)
• Plastic Limit (PL) is defined as the moisture content at
which soil begins to behave as a plastic material
• Shrinkage Limit (SL) is defined as the moisture content
at which no further volume change occurs with further
reduction in moisture content.
– (SL represents the amount of water required to fully
saturate the soil (100% saturation))

40. Liquid Limit

41. .
The water content corresponding to 25 blows shows the liquid
limit.
• The liquid limit is
determined by
plotting the graph
on the semi-log
graph between the
number of blows
as abscissa on a
logarithmic and
water content as
ordinate

44. Plastic Limit (PL)
• The moisture content (%) at which the soil
when rolled into threads of 3.2mm (1/8 in) in
diameter, will crumble.
• Plastic limit is the lower limit of the plastic
stage of soil
• Plasticity Index (PI) is the difference between
the liquid limit and plastic limit of a soil

45. • Plasticity Index is the difference
between the liquid limit and
plastic limit of a soil
• PI = LL – PL
• After finding LL and PI use
plasticity chart to classify the
soil

48. Atterberg Indices
• Plasticity index, I p = WL - WP
• flow index,
• Toughness index, IT= IP/IF
• Consistency index, IC= (WL-W)/IP
• Liquidity index, IL= (W-WP)/IP

49. Field Density
Core Cutter Method

50. Sand Replacement Method

52. Sand Replacement Method
• Calibration of sand density
• Pit excavation
• Determination of volume of pit
• Determination of density

54. Permeability
• Permeability is the measure of the soil’s ability to
permit water to flow through its pores or voids
• The following applications illustrate the importance of
permeability in geotechnical design:
– Permeability influences the rate of settlement of a
saturated soil under load.
– The design of earth dams is very much based upon the
permeability of the soils used.
– The stability of slopes and retaining structures can be
greatly affected by the permeability of the soils involved.
– Filters made of soils are designed based upon their
permeability.

55. • Knowledge of the permeability properties of soil
is necessary to:
– Estimating the quantity of underground seepage
– Solving problems involving pumping seepage water
from construction excavation
– Stability analyses of earth structures and earth
retaining walls subjected to seepage forces
• k is determined in the lab using two methods:
– Constant-Head Test
– Falling-Head Test
• K is usually expressed in cm/sec
• Hydraulic conductivity is also known as the
coefficient or permeability

56. Permeability Test
Constant Head Test

57. Permeability Test
Falling Head Test

58. 17 May 2020 58

61. Compaction Test
• In construction of highway embankments, earth
dams and many other engineering structures, loose
soils must be compacted to improve their strength
by increasing their unit weight

62. • As compaction increases, the following occurs:
– Increase soil strength
– Increase bearing capacity
– Decrease potential for settlement
– Control undesirable volume changes
– Reduction in hydraulic conductivity

63. Compaction Curve
• Compaction curve plotted
dry density vs. water
content
• The peak of the curve is the
Maximum Compaction at
Optimum Moisture Content

64. Compaction - Lab Equipment

65. Compaction energy per unit volume
Standard Proctor Test
• 945 cc mould
• 2.6 kg hammer
• 300 mm drop
• 3 layers of soil
• 25 blows / layer
Modified Proctor Test
• 945 cc mould
• 4.89 kg hammer
• 450 mm drop
• 5 layers of soil
• 25 blows / layer

68. Relative density
• The ratio of difference between the void ratio
of the soil in its loosest state and its natural
void ratio to the difference between the void
ratios in the loosest and densest states:
ID=
𝑒 𝑚𝑎𝑥
−𝑒
𝑒 𝑚𝑎𝑥
−𝑒𝑚𝑖 𝑛

69. Measurement of Field Compaction
• Most common methods are
• Proctor needle method
• Sand Cone method
• Rubber Balloon method

71. Consolidation

72. Types of Consolidation
• There are three types of consolidation:
– Immediate consolidation; caused by elastic
deformation of dry soil or moist and saturated soil
without change in moisture content
– Primary consolidation; caused as a result of volume
change in saturated cohesive soils due to exclusion of
water occupied the void spaces
– Secondary consolidation; occurs in saturated cohesive
soils as a result of the plastic adjustment of soil fabrics

73. 1- D Consolidation Test
• The main purpose of consolidation tests is to obtain
soil data which is used in predicting the rate and
amount of settlement of structures founded on clay
• The four most important soil properties determined by
a consolidation test are:
– The pre-consolidation stress, This is the maximum stress
that the soil has “felt” in the past.
– The compression index, Cc , which indicates the
compressibility of a normally-consolidated soil.
– The recompression index, Cr , which indicates the
compressibility of an over-consolidated soil.
– The coefficient of consolidation, Cv , which indicates the
rate of compression under a load increment.

74. Consolidation Test
• Two types of
consolidometers
(oedometers)
commonly used:
– Floating-ring
– Fixed ring

75. 1. Place sample in ring
2. Apply load
3. Measure height change
4. Repeat for new load

76. • Determine the height of solids (Hs) of the specimen in
the mold
• Determine the change in height (∆H)
• Determine the final specimen height, Ht(f)
• Determine the height of voids (Hv)
• Determine the final void ratio
• Calculate the coefficient of consolidation (Cv) from t90
• Calculate the coefficient of consolidation (Cv) from t50
• Plot e-log p curve and find:
– бc, Cc, Cr
• Plot cv – log p curves

79. Shear Strength
• The strength of a material is the greatest
stress it can sustain
• The safety of any geotechnical structure is
dependent on the strength of the soil
• If the soil fails, the structure founded on it can
collapse

80. Slope Failure in Soils

81. Significance of Shear Strength
• Engineers must understand the nature of
shearing resistance in order to analyze soil
stability problems such as;
– Bearing capacity
– Slope stability
– Lateral earth pressure on earth-retaining
structures
– Pavement

82. • Soil derives its shear strength from two
sources:
– Cohesion between particles (stress independent
component)
• Cementation between sand grains
• Electrostatic attraction between clay particles
– Frictional resistance between particles (stress
dependent component)

83. • Mohr-Coulomb Failure Criteria
– This theory states that a material fails because of a
critical combination of normal stress and shear
stress, and not from their either maximum normal
or shear stress alone.
• The relationship between normal stress and
shear is given as

84. Direct Shear Test
• Direct shear test is Quick and Inexpensive
• Shortcoming is that it fails the soil on a
designated plane which may not be the
weakest one
• Used to determine the shear strength of both
cohesive as well as non-cohesive soils

91. Tri-axial Shear Test
• Advantages over DST
– More Versatile
– Drainage can be well controlled
– There is no rotation of the
principal stresses like the direct
shear test
– Also the failure plane can occur
anywhere
• The test is called "triaxial"
because the three principal
stresses are assumed to be
known and are controlled.

92. Soil Shear Strength under Drained and
Undrained Conditions
• Drained conditions occur when rate at which loads are
applied are slow compared to rates at which soil
material can drain (k - dependent)
• Sands drain fast; therefore under most loading
conditions drained conditions exist in sands
– Exceptions: pile driving, earthquake loading in fine sands
• In clays, drainage does not occur quickly; therefore
excess pore water pressure does not dissipate quickly
• Therefore, in clays the short-term shear strength may
correspond to undrained conditions
• Even in clays, long-term shear strength is estimated
assuming drained conditions

93. Types of Tests
• There are three types of tests:
– Unconsolidated-undrained (UU or Q) Test
– Consolidated-undrained (CU or R) Test
– Consolidated-drained (CD or S) Test
– Unconfined Compression (UC) Test

94. UU Test Results

95. Consolidated-undrained Test

96. Consolidated-drained Test

100. Unconfined Compression Test
• For clay soils
• Cylindrical Test
specimen
• No confining stress
• (i.e. б3 = 0)
• Axial stress, ∆б = б1

101. UC Test

104. Field Permeability- Pumping test

105. Confined aquifer

106. • When h0 > H0
• When h0 < H0

107. Sand Filter Criteria
• Stability criteria
• D15 Filter/ D 85 Base ≤ 5
• Permeability criteria
• D15 Filter/ D 15 Base ≤ 4 to 20
• Gradation criteria
• D50 Filter/ D 50 Base ≤ 25

108. • Cohesive non-swelling soil
– Kaolinite
– Halloysite
• Record Test-

109. Tests frequency
• Field density
– 1 test /300 Cum
• Compaction Test
– 1 test / 1500Cum

110. Thank you