Geotechnical Engineering with the Army

1. BASIC SOIL

2. LEARNING OBJECTIVES
•Why we test soils.
•Understand the role of project personnel.
•Awareness of applicable safety requirements:
•Radiation safety
•Excavation safety
•Working around earthmoving equipment
•Basic concepts.
•Obtain samples for laboratory testing.
2

3. LEARNING OBJECTIVES
(CONT’D)
•Basic familiarity with some laboratory tests.
•Introduction to soil classification (USCS).
•Interpret earthwork specifications and site
plans.
•Familiarity with compaction equipment and
proper use.
3

4. LEARNING OBJECTIVES
(CONT’D)
•Knows how to perform
field density and
moisture tests:
• Sand cone
• Nuclear gauge
4

5. BEFORE WE START…
•Safety is non-negotiable!
•Approved construction drawings
and specifications must be used!
5

6. WHY DO WE TEST SOILS?
•Foundation for most structures, and
we want to build on “Good Stuff.”
•Reduce potential
failures.
•Quality control.
6

7. SAFETY
• Hard hat is required at ALL TIMES.
• Safety glasses are required at ALL TIMES.
• Proper clothing is required at ALL TIMES.
• No shorts
• Shirts with sleeves on at ALL TIMES
• Avoid overexposure to the sun or cold.
7

8. SAFETY (CONT’D)
•Watch for moving
equipment:
• Announce your
presence
• Be visible
• Trench Safety
8

9. TRENCH SAFETY
SUMMARY
•No protective system needed
if:
• Entirely in stable rock, or
• Excavation less than 5 feet (4
feet in some jurisdictions),
and
• No indicators of potential
cave-in (“Competent
person”).
•Otherwise, don’t go in.
9

10. TRENCH SAFETY SUMMARY
(CONT’D)
• Reasonable exits within 25
feet if 4 foot deep or more:
• Stairs, ramps or ladders
• No soil or rock steps
• Hazardous atmosphere
check before entry if
problems could be
reasonably expected and if
more than 4 feet deep.
10

11. TRENCH SAFETY
SUMMARY (CONT’D)
•Material and equipment at
least 2 feet back from
edge.
•Competent person must
inspect daily.
•> 20 feet: designed by an
engineer.
•Trench boxes must extend
18 inches above edge.
11

12. TRENCH SAFETY
SUMMARY (CONT’D)
•Notify the site superintendent if you suspect
unsafe conditions.
•Document your observations in detail.
•Do not enter an unsafe trench!
•Never stay in a trench box when it’s moved.
12

13. RADIATION SAFETY
• Radiation safety:
• Wear dosimeter properly
• Gauge must be within your control at all
times (within 10’ when using).
• Do not expose the source.
• Wear reflective vest!
13

14. RADIATION SAFETY
(CONT’D)
•If an accident:
•Stop all activity near
incident
•Tape off area 15 feet
around the gauge
•Call the RSO
immediately
•Do not leave the area
14

15. LEARNING OBJECTIVES
•Why we test soils.
•Understand the role of project personnel.
•Awareness of applicable safety requirements:
• Radiation safety
• Excavation safety
• Working around earthmoving equipment
•Basic concepts.
•Obtain samples for laboratory testing.
15

16. ORGANIZATIONS
AND STANDARDS
•AASHTO: American
Association of State
Highway and
Transportation Officials.
•ASTM: American Society
for Testing and
Materials.
•State Transportation
Agencies:
• VDOT
• MHD
• TxDOT
• etc.
•USACE: U.S. Army Corps
of Engineers.
16

17. BASIC SOIL
CONCEPTS
•Soils/Rock form the foundation for virtually all
buildings, roads, and structures.
•Understanding of soil characteristics and how
they respond to structural loads is important in
design & construction.
•Soils formed naturally from weathering of rock.
17

18. SOIL MECHANICS
• Soils are defined or categorized by particle size and plasticity.
• Each category of soil or rock has different engineering characteristics.
• Moisture content significantly effects how soils behave.
• Compaction influences engineering characteristics.
18

19. PARTICLE SIZE
• Soil/rock categories based on particle sizes:
• Boulder
• Cobble
• Gravel
• Sand
• Silt/Clay
19

20. PARTICLE SIZE AND DENSITY OF
SOIL
• Rocks are more dense than soil.
• The larger the particles are in a given volume, the greater the
density.
20

21. GRAVEL
• Particle sizes smaller than 3
inches in diameter and retained
on No. 4 sieve.
21

22. SAND
• Pass No. 4 sieve, (4.75 mm) and
retained on No. 200 (75 µm)
sieve.
22

23. GRAVEL & SAND
• Good Structural fill material.
• Good for Drainage (pervious).
• Recommended for backfill of walls.
• Good roadway/slab subgrade material.
23

24. SILT AND CLAY
• Pass No. 200 (75 µm)
sieve.
24

25. SILT & CLAY
•Low permeability (less
pervious).
•Excellent for dam and
pond construction.
•Relatively weak for
road subgrades.
•Very sensitive to
moisture.
•Shrink/swell potential.
25

26. MOISTURE CONTENT (w)
• Influences ability to compact soils.
• Changes characteristics of silts and clays.
w = x 100
Weight of water = weight of wet soil – weight of dry soil
26
Weight of water
Weight of dry soil

27. COMPACTION
• Densification of soils by
mechanical means.
• Higher densities (dry density)
usually improve engineering
properties.
27

28. OBTAINING SAMPLES
• Determine where the sample should be taken:
• Sample the same that will be placed?
• What type of tests will be run?
• Proctor: sample from the source of the fill.
• CBR: sample from the subgrade.
28

29. OBTAINING SAMPLES (CONT’D)
•Must have enough to
run required tests:
• 35 lbs for standard
Proctor
• 65 lbs for CBR and
Proctor
• Ask if you are not sure!
29

30. COMMON LABORATORY TESTS
•Atterberg Limits Tests:
• Test the plasticity of the
soil.
• The higher the plasticity,
the worse the soil is for
structural backfill.
• Liquid Limit (LL) - Moisture
content at boundary of
plastic and semi-liquid
states.
30

31. COMMON LABORATORY TESTS
(CONT’D)
•Atterberg Limits Tests
(cont’d):
• Plastic Limit (PL) - Moisture
content at boundary of
plastic and semi-solid states.
• Plastic Index (PI) - Moisture
content range over which a
soil acts plastic. PI = LL – PL.
31

32. ATTERBERG LIMITS
AND SOIL STATES
32
Increasing W
Plastic State
Semi-Solid
State
Solid
State
Liquid
State
Plasticity Index
Plastic Limit Liquid
Limit
Plastic State
Semi-
Solid
State
Solid
State
Liquid
State
Plasticity Index

33. COMMON LABORATORY TESTS
(CONT’D)
• Grain-Size Analysis:
•Determines the % of different sizes of the soil particles
in a sample.
•Sample usually dried and sent through a series of
sieves.
•#4 sieve has 4 openings per inch.
•#10 sieve has 10 openings per inch.
•3/8-inch sieve has openings that are 3/8-inches wide.
•#200 has 200 openings per inch.
33

34. COMMON LABORATORY TESTS
(CONT’D)
•Grain-Size Analysis
(cont’d):
• % Retained.
• % Passing.
• Sample distribution
graphs at Tab II.
34

35. SAMPLE GRAIN SIZE
DISTRIBUTION GRAPH
35

36. COMMON LABORATORY TESTS
(CONT’D)
• Proctor Analysis / Moisture–Density Relationship:
•Density is the mass per unit of volume (lb/ft3
).
•Soil is made up of, air, water and particles.
•By adjusting the water content, we can obtain
different densities.
•By adjusting the compactive effort, we can obtain
different densities.
36

37. COMMON LABORATORY TESTS
(CONT’D)
• Oversize material is removed.
• Obtained by molding samples at different moisture contents
and a constant compactive effort.
• The top of the curve is the uncorrected or “as tested”
Maximum Dry Density.
• The corresponding moisture content is the uncorrected or
“as tested” Optimum Moisture Content.
• Sample Report at Tab II.
• What’s this zero air voids curve?
37

38. SAMPLE PROCTOR CURVE
38

39. PROCTOR METHODS
• Different procedures due to:
• Maximum particle size
• Desired compactive effort
• ASTM:
• D 698
• D 1557
• AASHTO:
• T99
• T180
• Others such as VTM-1.
• Watch what the specifications
say!
39

40. PROCTOR METHOD
(CONT’D)
•ASTM D 698
(“standard”):
• 5.5 pound hammer
• 3 equal layers
• 12 inch drop height
Method Mold
Diameter
(inches)
Oversize
Sieve
Blows
Per
Layer
A 4 #4 25
B 4 3/8” 25
C 6 ¾” 56
40

41. PROCTOR METHOD
(CONT’D)
•ASTM D 1557
(“modified”):
• 10 pound
hammer
• 5 equal layers
• 18 inch drop
height
Method Mold
Diameter
(inches)
Oversize
Sieve
Blows
Per
Layer
A 4 #4 25
B 4 3/8” 25
C 6 ¾” 56
41

42. PROCTOR METHOD
(CONT’D)
•Does laboratory test agree with specifications?
• ASTM D 698
• ASTM D 1557
• AASHTO T99
• AASHTO T180
• VTM-1
•Is oversize correction based on proper oversize
fraction?
• Type A
• Type B
• Type C
•Is as-tested oversize the same as field results?
42

43. LEARNING OBJECTIVES
(CONT’D)
•Basic familiarity with some laboratory tests.
•Introduction to soil classification (USCS).
•Interpret earthwork specifications and site
plans.
•Familiarity with compaction equipment and
proper use.
43

44. USCS CLASSIFICATION
• USCS: Unified Soils Classification System (ASTM D 2487). (Summary
at Tab III).
• Classifies soils based on Atterberg limits and grain-size analysis.
• USCS system breaks soil into 2 categories (No. 200 sieve):
•Coarse-grained: Gravel and Sand
•Fine-grained: Silt and Clay
44

45. USCS CLASSIFICATION
(CONT’D)
• S = Sand
• G = Gravel
• M = Silt
• C = Clay
• O = Organic
45
– Pt = Peat
– P = Poorly Graded
– W = Well Graded
– L = Lean Clay or Silt (low
compressibility)
– H = Fat Clay or Elastic Silt
(high compressibility)
• Then use a combination of letters to
classify soils:

46. USCS SUMMARY
46

47. PLASTICITY CHART
47

48. USCS
CLASSIFICATION #1
• Given:
• % passing #4 = 56.7%
• % passing #200 = 16.3 %
• Liquid limit = 48
• Plastic limit = 15
• Gravel is well graded
• Classification?
• See Tab III
48

49. COARSE–GRAINED
OR FINE–GRAINED?
49

50. 50
SAND OR GRAVEL?

51. 51
CLEAN GRAVEL OR
GRAVEL WITH FINES?

52. 52
ML/MH OR CL/CH?

53. GM OR GC?
53

54. USCS EXAMPLE
CLASSIFICATION #1
• Given:
• % passing #4 = 56.7%
• % passing #200 = 16.3 %
• Liquid limit = 48
• Plastic limit = 15
• Gravel is well graded
• Classification?
54• Answer: GC

55. USCS EXAMPLE CLASSIFICATION #2
• Given:
• % passing #4: 100%
• % passing #200: 75%
• Liquid limit: 52
• Plasticity Index: 12
• Classification?
55

56. USCS EXAMPLE CLASSIFICATION #3
• Given:
• % passing 3/4”: 100%
• % passing #4: 85%
• % passing #200: 36%
• Liquid limit: 29
• Plasticity Index: 10
• Classification?
56

57. USCS EXAMPLE CLASSIFICATION #4
• Given:
• % passing ¾”: 100%
• % passing #4: 72%
• % passing #200: 33%
• Liquid limit: 35
• Plasticity Index: 0 (not plastic)
• Classification?
57

58. USCS EXAMPLE CLASSIFICATION
ANSWERS
• #1: GC
• #2: MH
• #3: SC
• #4: SM
58

59. VISUAL CLASSIFICATION
•Not as accurate as laboratory
classification.
•Use ASTM D 2488 as guide.
•Always identify when classification is
by visual methods.
59

60. COMPACTION
EQUIPMENT
•Size
•Weight
•Types:
• Smooth drum
• Sheepsfoot
• Vibratory
• Rubber–tired
60

61. OPTIMUM COMPACTION
EQUIPMENT
GW or
GP
GM or
GC
SW or
SP
SM or
SC
Rubber-
tire or
steel-
wheel
Rubber-
tire or
sheeps
foot
Rubber-
tire
Rubber-
tire or
sheeps
foot
61

62. COMPACTION EQUIPMENT
(CONT’D)
62
Note: Operator’s PPE

63. COMPACTION
EQUIPMENT (CONT’D)
63

64. COMPACTION
EQUIPMENT (CONT’D)
64

65. COMPACTION
EQUIPMENT (CONT’D)
65

66. COMPACTION
EQUIPMENT (CONT’D)
66

67. SAND CONE
METHODOLOGY
•Wet weight of soil from hole.
•Volume of hole.
•Wet density of soil.
•Moisture content of soil.
•Dry density of soil.
•Does it pass specifications?
67

68. SAND CONE
•Tools Needed:
• Sand Cone
• Calibrated Sand
• Sand Cone Plate
• Empty Jar with air
tight lid
• Digging tools
• Digital scale
68

69. SAND CONE
(CONT’D)
•Step 1:
• Determine weight of sand
to fill cone.
•Step 2:
• Fill Sand Cone with
Calibrated sand and weigh.
• Weigh empty sample jar.
69

70. SAND CONE
(CONT’D)
• Step 3:
• Place sand cone plate on area to
be tested.
• Area must be level and smooth.
• Dig hole apprx 4-6” deep.
• Put all soil from hole in empty
jar and seal.
• Step 4:
• Place sand cone over hole on
plate.
70

71. SAND CONE
(CONT’D)
• Step 4 (cont’d):
• EQUIPMENT MUST STOP
WORK IN AREA.
• Carefully open the sand cone
valve and allow sand to fill
hole and cone.
• Once sand stops flowing,
carefully close valve.
• Step 5:
• Weigh Jar with soil.
• Weigh Sand Cone.
• Do not re-use sand
71

72. SAND CONE
EXAMPLE
•Weight of Sand Cone Before Test = 13.52 lbs.
•Weight of Empty Sample Jar = 2.52 lbs.
•Density of Sand (provided) = 99.20
lb/ft3
•Weight of Sand Cone After Test = 9.42 lbs.
•Weight of Full Sample Jar = 4.32 lbs.
•Weight of Sand to Fill the Cone = 2.73 lbs
•Weight of soil after drying = 1.57 lb
72

73. SAND CONE
EXAMPLE (CONT’D)
• Wet weight of soil:
(weight of full jar) – (weight of
empty jar): 4.32 lb – 2.52 lb =
1.80 lb
73

74. SAND CONE
EXAMPLE (CONT’D)
• Volume of hole:
(weight of full apparatus) – (weight after test)
– (weight of sand in cone)
density of sand
1 3.52 lb – 9.42 lb – 2.73 lb 1.37 lb
99.20 lb/ft3
99.20 lb/ft3
• Round volume to nearest 0.0001 ft3
74
= 0.0138 ft3
=

75. SAND CONE
EXAMPLE (CONT’D)
•Wet density of the soil (γw):
wet weight of soil from hole
volume of hole
Therefore:
1.8 lb
0.0138
75
WD or γ w = = 130.44 lb/ft3
=

76. SAND CONE
EXAMPLE (CONT’D)
•Compute moisture content of soil:
weight of water
weight of dry soil
weight of wet soil-weight of dry soil
weight of dry soil
1.80 – 1.57
1.57
= 14.7%
76
w = x 100
= x 100
= x 100

77. SAND CONE
EXAMPLE (CONT’D)
•Moisture content of
the soil:
•Methods:
• Microwave oven
• Laboratory
determination
• Field stove
77

78. SAND CONE
EXAMPLE (CONT’D)
•Dry density (γ d):
Wet density (γ w)
1 + (w/100)
130.44 130.44
1 + (14.3/100) 1.143
• Report 114.1 lb/ft3
78
=
= 114.12 lb/ft3
γ d =
=

79. BACKFILLING
UTILITY LINES
•Issues:
• Safety!!
• Nuclear Gauge Trench
Correction (more later)
• Thinner lifts
• Distorted gauge results
when close to pipes or
culverts
• Good judgment is essential
79

80. GEOTECHNICAL
REPORTS
80

81. STRIP CHECKS & PROOFROLLING
• Type of Testing:
• Strip Check:
• After site has been
cleared of trees, roots
and grass.
• Visual check that roots,
topsoil, organics, debris,
etc. removed.
81

82. STRIP CHECKS & PROOFROLLING
(CONT’D)
• Type of Testing (cont’d):
• Proofroll:
• After strip check,
proofroll area to receive
fill.
82

83. STRIP CHECKS & PROOFROLLING
(CONT’D)
• Proofroll (con’t):
• Use a LOADED dump.
• Look for signs of loose or soft soils…
PUMPING or RUTTING:
83

84. STRIP CHECK & PROOFROLLING
(CONT’D)
84
• When an area is pumping
or rutting you must inform
the the Project Engineer:
– Undercut?
– Bridge lifts?
– Geosynthetics?
• Only evaluates surface
material (2-3 feet).

85. CALIBRATION OF
FIELD EQUIPMENT
• Nuclear Gauge:
• Must be calibrated every 12 months
• Leak tested every 6 months (12 months in some instances).
• Standard counts (“standardization”) required each day used.
• Sand Cone:
• Must be calibrated every 12 months, not including the sand
• Sand must be calibrated every new bag
85

86. CALIBRATION OF
FIELD EQUIPMENT (CONT’D)
• Sand Cone (continued):
• Recalibrate sand if significant humidity changes.
• Recalibrate sand at intervals not exceeding 14 days
• One-Point Proctor Equipment:
• Calibrate annually
• Scale, mold, hammer, & sieve
86

87. QUESTIONS
&
REVIEW
87

88. SOILS DEFINITIONS
• Bridge Lift: a lift of soil to stabilize soft or unsuitable soil so additional
lifts of soil may be placed and compacted.
• Coarse Fraction: the portion of the sample that is larger than (retained
on) a #200 sieve, includes both soil and gravel.
88

89. SOILS DEFINITIONS
(CONT’D)
• Cohesive soils: soil that tends to adhere or stick to themselves (clay
and most silts). Can usually be rolled and shaped in your hand.
• Cohesionless soil: soil that falls apart or cannot be shaped in your
hand (sands, gravels, and some silts).
89

90. SOILS DEFINITIONS
(CONT’D)
• Compaction: the mechanical densification of soil.
• Density: the weight of a material per unit volume.
90

91. SOILS DEFINITIONS
(CONT’D)
• Engineered fill: fill that has been placed and monitored to ensure it meets
the minimum requirements for a specific project.
• Fill: man placed deposits of soil or material.
91

92. SOILS DEFINITIONS
(CONT’D)
• Fines: All material smaller than a #200 sieve. Includes silt and clay.
• Foundation: the portion of a structure that transmits the load to the
soil. Footing, caisson, pile, drilled pier, etc.
92

93. SOILS DEFINITIONS
(CONT’D)
• Gravel: All material Larger than a #4 sieve and less than 3 inches.
• Liquid Limit (LL): The w that defines the boundary between
liquid/semi-liquid and plastic states.
93

94. SOILS DEFINITIONS
(CONT’D)
•Maximum Dry Density: the highest dry density
obtained from the Proctor analysis.
•Moisture content (w): the ratio, expressed as a
percentage, of the weight of the water in a
given sample to the weight of the dry soil.
•w = X 100soildrytheofweight
waterofweight
94

95. SOILS DEFINITIONS
(CONT’D)
•Optimum Moisture Content: moisture content at
which the maximum dry density is reached for a
specified compactive effort.
•Percent Compaction: the ratio expressed as a
percentage of the dry density of the field tested soil
vs. the (corrected) maximum dry density of that soil
as determined in the laboratory by the Proctor test.
95

96. SOILS DEFINITIONS
(CONT’D)
• Plastic Limit (PL): The w that defines the boundary between plastic
and semi-solid states.
• Plasticity Index (PI): The numeric difference between the liquid limit
and the plastic limit.
96

97. SOILS DEFINITIONS
(CONT’D)
• Proctor Analysis: Laboratory test to determine the Maximum Dry
Density of a soil sample. Also known as the Moisture – Density
Relationship, (ASTM D 698,D 1557; AASHTO T-99,T-180).
• Proofroll: Field test of natural soil that indicates soft or wet soils. A
ten – ton single axle weight truck is driven across area to be tested.
97

98. SOILS DEFINITIONS
(CONT’D)
• Pumping: The soils will appear to be moving under the loading of the
truck. A wave like motion of the soil is often seen. Indicates wet or
soft soil below the surface.
• Rutting: Proofrolling leaves indentations from the truck tires.
Indicates soft or wet soils at the surface.
98

99. SOILS DEFINITIONS
(CONT’D)
• Sand: Material smaller than a #4 but larger than a #200 sieve.
• Sand Cone: a apparatus used in the field to determine the in–place
density of the soil.
99

100. SOILS DEFINITIONS
(CONT’D)
• Sheepsfoot Roller: equipment used for compacting cohesive soils, has
"feet" on the drum to knead the soil in place. (Silt and Clay).
• Smooth Drum Vibratory Roller: equipment that uses weight and vibration
to compact the soil, used for cohesionless soils. (Sand and Gravel).
100

101. SOILS DEFINITIONS
(CONT’D)
• Specific Gravity (SG): The ratio of the weight of the unit volume of a
solid to the same volume of water.
• Subgrade: the prepared or compacted soil that will support a structure
or pavement section. Soil under footing, slab, pavement.
101

102. SOILS DEFINITIONS
(CONT’D)
• USCS: Unified Soil Classification System, used to classify soil based
on laboratory tests (uses Atterberg Limits and Grain Size Analysis).
• Zero Air Voids Curve”: A curve showing the zero air voids unit
weight as a function of water content.
102

103. BASIC RELATIONSHIPS
•1 gallon = 8.33 pounds of water
•1 ft3
= 7.49 gallons
•Unit wgt of Material/ Unit wgt of water =
Specific Gravity
•1 oz = 28.35 g
•1 lb = 454 g
•1 ft3
of water = 62.4 lb
•1 meter = 3.281 feet
103

104. BASIC RELATIONSHIPS
(CONT’D)
•3 ft = 1 yard
•1 yard = 0.9144 m
•1 ft3
= .02832 cubic meters
•1 in = 2.54 cm
• 1 yd3
= 27 ft3
• 1 cubic meter = 1.31 yd3
104