Engineering Properties of Soil by Prof.E.Saibaba Reddy & Eadala Rakesh Reddy

1. ENGINEERING PROPERTIES OF SOIL
Prof. E.Saibaba Reddy (esreddy1101@gmail.com)
B.Tech, M.E.(Hons) Roorkee, Ph.D (Nottingham, UK)
Post Doc,(Halifax Canada), Post Doc (Birmingham UK)
&
Eadala Rakesh Reddy (rakesh.eeecs2020@gmail.com)
B.Tech (JNTUH), M.Tech (VSSUT-Gold Medal),
(Ph.D)- Andhra University-DST-Inspire Fellow
Chief Consultant- EE Engineering Construction Services
1

2. PERMEABILITY OF SOIL
 Permeability is defined as the property of a porous material which
permits the passage or seepage of water through its interconnecting
voids. A material having continuous voids is called permeable.
 Gravels are highly permeable while stiff clay is the least permeable,
and hence clay may be termed impermeable for all the practical
purposes.
2

3. IMPORTANCE OF PERMEABILITY
 The study of seepage of water through soil is important for the following
engineering problems:
 Determination of rate of settlement of a saturated compressible soil layer.
 Calculation of seepage through the body of earth dams and stability of slopes.
 Calculation of uplift pressure under hydraulic structure and their safety
against piping.
 Ground water flow towards wells and drainage of soil.
3

4. FACTORS AFFECTING PERMEABILITY OF SOIL
 The following factors affect the permeability of soils:
1. Particle Size
2. Void ratio of soil
3. Properties of pore fluid
4. Shape of particles
5. Structure of soil mass
6. Degree of Saturation
7. Absorbed water
8. Entrapped air and organic impurities in water.
9. Temperature
10. Stratification of Soil
4

5. FACTORS AFFECTING PERMEABILITY OF SOIL
5

6. FACTORS AFFECTING PERMEABILITY OF
SOILS
1. Particle Size: The Permeability varies approximately as the square
of grain size. It depends on the effective Diameter of the grain size
(D 10).
2. Void Ratio: Increase in the void ratio increases the area available
for flow hence permeability increases for critical conditions.
3. Properties of Pore Fluid: Pore fluids are fluids that occupy pore
spaces in a soil or rock. Permeability is directly proportional to the
unit weight of pore fluid and inversely proportional to viscosity of
pore fluid.
4. Shape of Particles: Permeability is inversely proportional to specific
surface e.g as angular soil have more specific surface area
compared to the round soil therefore, the soil with angular particles
is less permeable than soil of rounded particles. 6

7. FACTORS AFFECTING PERMEABILITY OF
SOILS
5. Structure of Soil Mass: For same void ratio the permeability is more
for flocculent structure as compared to the dispended structure.
6. Degree of Saturation: The permeability of partially saturated soil is
less than that of fully saturated soil.
7

8. FACTORS AFFECTING PERMEABILITY OF
SOILS
7. Absorbed water means a thin microscopic film of water surrounding
individual soil grains. This water is not free to move and hence,
reduces the effective pore space and thus decreases coefficient of
permeability.
8. Entrapped Air and Organic Impurities: The organic impurities and
entrapped air obstruct the flow and coefficient of permeability.
8

9. FACTORS AFFECTING PERMEABILITY OF
SOILS
9. Temperature: As the viscosity of the pore fluid decrease with the
temperature, permeability increases with temperature, as unit weight
of pore fluid does not change much with change in temperature.
10. Stratification of Soil: Stratified soils are those soils which are formed
by layer upon layer of the earth or dust deposited on each other. If
the flow is parallel to the layers of stratification the permeability is
maximum while the flow in perpendicular direction occurs with
minimum permeability.
9

10. DARCY’S LAW
 Darcy's law states that there is a linear relationship between flow
velocity (v) and hydraulic gradient (i) for any given saturated soil under
steady laminar flow conditions.
 If the rate of flow is q (volume/time) through cross-sectional area (A) of
the soil mass, Darcy's Law can be expressed as
10

11. DARCY’S LAW
 The flow velocity (v) is also called the Darcian velocity or
the superficial velocity. It is different from the actual velocity inside
the soil pores, which is known as the seepage velocity, vS. At the
particulate level, the water follows a tortuous path through the pores.
Seepage velocity is always greater than the superficial velocity, and it
is expressed as:
 where AV = Area of voids on a cross section normal to the direction of
flow
 n = porosity of the soil
11

12. HYDRAULIC CONDUCTIVITY
12

13. THE VALUE OF HYDRAULIC CONDUCTIVITY
 Typical value for saturated soils are given in the following
table:
13

14. EMPIRICAL RELATION FOR K
14

15. EMPIRICAL RELATION FOR K
15

16. DETERMINATION OF COEFFICIENT OF
PERMEABILITY
 Constant Head Flow
Constant head permeameter is recommended for coarse-grained soils only
since for such soils, flow rate is measurable with adequate precision. As water
flows through a sample of cross-section area A, steady total head drop h is
measured across length L.
 Permeability k is obtained from:
16

17. DETERMINATION OF COEFFICIENT OF
PERMEABILITY
17

18. DETERMINATION OF COEFFICIENT OF
PERMEABILITY
18

19. DETERMINATION OF COEFFICIENT OF
PERMEABILITY
19

20. DETERMINATION OF COEFFICIENT OF
PERMEABILITY
20

21. DETERMINATION OF COEFFICIENT OF
PERMEABILITY
21

22. DETERMINATION OF COEFFICIENT OF
PERMEABILITY
22

23. FIELD TESTS FOR PERMEABILITY
 Field or in-situ measurement of permeability avoids the difficulties
involved in obtaining and setting up undisturbed samples in a
permeameter. It also provides information about bulk permeability,
rather than merely the permeability of a small sample.
 A field permeability test consists of pumping out water from a main
well and observing the resulting drawdown surface of the original
horizontal water table from at least two observation wells. When a
steady state of flow is reached, the flow quantity and the levels in the
observation wells are noted.
23

24. FIELD TESTS FOR PERMEABILITY
24

25. FIELD TESTS FOR PERMEABILITY
25

26. FIELD TESTS FOR PERMEABILITY
26

27. FIELD TESTS FOR PERMEABILITY
27

28. PERMEABILITY IN STRATIFIED SOILS
 When a soil deposit consists of a number of horizontal layers having
different permeabilities, the average value of permeability can be
obtained separately for both vertical flow and horizontal flow,
as kVand kH respectively.
 Consider a stratified soil having horizontal layers of
thickness H1, H2, H3, etc. with coefficients of permeability k1, k2, k3,
etc.
28

29. PERMEABILITY IN STRATIFIED SOILS
29

30. PERMEABILITY IN STRATIFIED SOILS
30

31. PERMEABILITY – PROBLEMS
31

32. PERMEABILITY – PROBLEMS
32

33. PERMEABILITY – PROBLEMS
33

34. SHEAR STRENGTH OF SOIL
34

35. SHEAR FAILURE OF SOILS
35

36. SHEAR FAILURE MECHANISM
36

37. SHEAR FAILURE MECHANISM
37

38. MOHR COULOMB FAILURE CRITERIA
(TOTAL STRESSES)
38

39. MOHR COULOMB FAILURE CRITERIA
(EFFECTIVE STRESSES)
39

40. MOHR COULOMB FAILURE CRITERIA
40

41. MOHR CIRCLE OF STRESS
41

42. MOHR CIRCLE OF STRESS
42

43. MOHR CIRCLE OF STRESS
43

44. MOHR CIRCLES & FAILURE ENVELOPE
44

45. MOHR CIRCLES & FAILURE ENVELOPE
45

46. MOHR CIRCLES & FAILURE ENVELOPE
46

47. ORIENTATION OF FAILURE PLANE
47

48. MOHR CIRCLES IN TERMS OF TOTAL AND
EFFECTIVE STRESSES
48

49. MOHR CIRCLES IN TERMS OF TOTAL AND
EFFECTIVE STRESSES
49

50. MOHR COULOMB FAILURE CRITERION WITH
MOHR STRESS CIRCLE
50

51. MOHR COULOMB FAILURE CRITERION WITH
MOHR STRESS CIRCLE
51

52. DETERMINATION OF SHEAR STRENGTH
52

53. LABORATORY TESTS
53

54. DIRECT SHEAR STRENGTH
54

55. DIRECT SHEAR STRENGTH
55

56. DIRECT SHEAR STRENGTH
56

57. DIRECT SHEAR TEST PROCEDURE
57

58. ANALYSIS OF TEST RESULTS
58

59. DIRECT SHEAR TEST ON SANDS
STRESS-STRAIN RELATIONSHIPS
59

60. DIRECT SHEAR TEST ON SANDS
60

61. DIRECT SHEAR TESTS ON CLAYS
61

62. INTERFACE TESTS ON DIRECT SHEAR
APPARATUS
62

63. TRIAXIAL SHEAR TEST
63

64. TRIAXIAL SHEAR TEST
64

65. TRIAXIAL SHEAR TEST
65

66. TRIAXIAL SHEAR TEST
66

67. TRIAXIAL SHEAR TEST
67

68. TYPES OF TRIAXIAL TESTS
68

69. TYPES OF TRIAXIAL TESTS
69

70. CONSOLIDATED-DRAINED TEST (CD TEST)
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71. CONSOLIDATED-DRAINED TEST (CD TEST)
71

72. CONSOLIDATED-DRAINED TEST (CD TEST)
72

73. CONSOLIDATED-DRAINED TEST (CD TEST)
73

74. CONSOLIDATED-DRAINED TEST (CD TEST)
74

75. CONSOLIDATED-DRAINED TEST
FAILURE ENVELOPES
75

76. CONSOLIDATED-DRAINED TEST
FAILURE ENVELOPES
76

77. CONSOLIDATED-UNDRAINED TEST (CU TEST)
77

78. CONSOLIDATED-UNDRAINED TEST (CU TEST)
78

79. CONSOLIDATED-UNDRAINED TEST (CU TEST)
79

80. CONSOLIDATED-UNDRAINED TEST (CU TEST)
80

81. CONSOLIDATED-UNDRAINED TEST
FAILURE ENVELOPES
81

82. UNCONSOLIDATED-UNDRAINED TEST (UU
TEST)
82

83. UNCONSOLIDATED-UNDRAINED TEST (UU
TEST)
83

84. UNCONSOLIDATED-UNDRAINED TEST (UU
TEST)
84

85. UNCONSOLIDATED-UNDRAINED TEST (UU
TEST)
85

86. UNCONSOLIDATED-UNDRAINED TEST (UU
TEST)
86

87. UNCONSOLIDATED-UNDRAINED TEST (UU
TEST)
87

88. UNCONSOLIDATED-UNDRAINED TEST (UU
TEST)
88

89. UNCONSOLIDATED-UNDRAINED TEST (UU
TEST)
89

90. UNCONFINED COMPRESSION TEST (UC
TEST)
90

91. UNCONFINED COMPRESSION TEST (UC
TEST)
91

92. VARIOUS CORRELATIONS FOR SHEAR
STRENGTH
92

93. SHEAR STRENGTH OF PARTIALLY SATURATED
SOILS
93

94. SHEAR STRENGTH OF PARTIALLY SATURATED
SOILS
94

95. SHEAR STRENGTH OF PARTIALLY SATURATED
SOILS
95

96. 96

97. TERMINOLOGY
97

98. COMPRESSIBILITY OF SOIL
98

99. COMPRESSIBILITY
99

100. COMPRESSIBILITY
100

101. CONSOLIDATION
101

102. CONSOLIDATION
102

103. CONSOLIDATION
103

104. CONSOLIDATION
104

105. CONSOLIDATION VS COMPACTION
105

106. CONSOLIDATION SETTLEMENT
106

107. CONSOLIDATION SETTLEMENT
107

108. CONSOLIDATION SETTLEMENT
108

109. SPRING CYLINDER MODEL
109

110. SPRING CYLINDER MODEL
110

111. SPRING CYLINDER MODEL
111

112. SPRING CYLINDER MODEL
112

113. SPRING CYLINDER MODEL
113

114. SPRING CYLINDER MODEL
114

115. SPRING CYLINDER MODEL
115

116. SPRING CYLINDER MODEL
116

117. LABORATORY CONSOLIDATION TEST
117

118. LABORATORY CONSOLIDATION TEST
118

119. LABORATORY CONSOLIDATION TEST
119

120. LABORATORY CONSOLIDATION TEST
120

121. CONSOLIDATION TEST
121

122. CONSOLIDATION TEST
122

123. CONSOLIDATION TEST
123

124. CONSOLIDATION TEST
124

125. COMPRESSIBILITY PARAMETERS
125

126. COMPRESSIBILITY PARAMETERS
126

127. COMPRESSIBILITY PARAMETERS
127

128. PRECONSOLIDATION PRESSURE
128

129. PRECONSOLIDATION PRESSURE
129

130. PRECONSOLIDATION PRESSURE
130

131. COEFFICIENT OF CONSOLIDATION
131

132. PRIMARY CONSOLIDATION
132

133. PRIMARY CONSOLIDATION
133

134. SECONDARY CONSOLIDATION
134

135. SECONDARY CONSOLIDATION
135

136. SECONDARY CONSOLIDATION
136

137. SECONDARY CONSOLIDATION
137

138. TIME RATE OF CONSOLIDATION
138

139. TIME RATE OF CONSOLIDATION
139

140. TIME RATE OF CONSOLIDATION
140

141. EXAMPLE PROBLEMS
141

142. EXAMPLE PROBLEMS
142

143. EXAMPLE PROBLEMS
143

144. COMPACTION OF SOIL
144

145. PRINCIPLES OF COMPACTION
145

146. COMPACTION CURVE
146

147. OPTIMUM MOISTURE CONTENT
147

148. ZERO AIR VOIDS CURVE
148

149. FACTORS AFFECTING COMPACTION
149

150. GENERAL COMPACTION METHODS
150

151. LABORATORY COMPACTION TESTS
151

152. STANDARD PROCTOR COMPACTION TEST
152

153. STANDARD PROCTOR COMPACTION TEST
153

154. STANDARD PROCTOR COMPACTION TEST
154

155. STANDARD PROCTOR COMPACTION TEST
155

156. MODIFIED PROCTOR COMPACTION TEST
156

157. COMPARISON CURVES
157

158. DETERMINATION OF FIELD UNIT WEIGHT OF
COMPACTION
158

159. SAND CONE METHOD
159

160. DETERMINATION OF FIELD UNIT WEIGHT OF
COMPACTION
160

161. VERTICAL STRESS IN SOIL DUE TO APPLIED
LOADS
161

162. VERTICAL STRESS IN SOIL DUE TO APPLIED
LOADS
162

163. VERTICAL STRESS IN SOIL DUE TO APPLIED
LOADS
163

164. 164

165. 165

166. 166