Excavation and Trenching

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1. Slide 1

   EXCAVATION AND TRENCHING

   • OSHA - SUSAN HARWOOD TRAINING GRANT
2. Slide 2

   WELCOME

   • Please sign the attendance sheet
   • Take one handout
   • Answer the pre-test
3. Slide 3

   LOCATION

   • Emergency Exits
   • Emergency Stairs
   • Location of restrooms
   • Location of water fountains
4. Slide 4

   DISCLAIMER

   • This material was produced under grant number SH-16582-SH7 (2007) from the Occupational Safety and Health Administration, U.S. Department of Labor. It does not necessarily reflect the views or policies of the U. S. Department of Labor, nor does mention of trade names, commercial products, or organizations imply endorsement by the U. S. Government.
   • Revisions were made to this material under grant number SH-05120-SH9 from the Occupational Safety and Health Administration, U.S. Department of Labor.
5. Slide 5

   AGENDA

   • Welcome
   • Introduction to OSHA
   • Worker’s rights
   • Introduction to Trenching and Excavation Hazards
   • What is trenching?
   • Preventing excavation hazard
   • Common Trenching and Excavation Hazards
   • Soil Classifications
   • Exercises
   • Certificates
6. Slide 6

   INTRODUCTION

   • TO
   • OSHA
   • Overview of anti-retaliation provisions, employee rights, employer responsibilities, whistleblower laws, and OSHA’s complaint investigation procedures
7. Slide 7

   WHY IS OSHA IMPORTANT TO YOU?

   • OSHA began because, until 1970, there were no national laws for safety and health hazards.
   • On average, 14 workers die every day from job injuries
   • Worker deaths in America are down–on average, from about 38 worker deaths a day in 1970 to 14 a day in 2017
   • WORKER FATALITIES
   • 5,147 workers died at the job in 2017, 971(20.7%) worked in construction
   • Excavation — an average of 19 death per year, from a low of 10 death in 2014 to a high of 33 death in 2016
   • (Source: BLS 2018)
8. Slide 8

   DISCUSSION QUESTIONS

   • When, during your work experience, did you first hear about OSHA?
   • What did you think about OSHA then?
   • What do you think OSHA’s job is?
9. Slide 9

   HISTORY OF OSHA

   • OSHA stands for the Occupational Safety and Health Administration, an agency of the U.S. Department of Labor
   • OSHA’s responsibility is worker safety and health protection
   • On December 29, 1970, President Nixon signed the OSH Act
   • This Act created OSHA, the agency, which formally came into being on April 28, 1971
10. Slide 10

    OSHA’S MISSION

    • To save lives
    • To prevent injuries
    • To protect
    • America’s workers
11. Slide 11

    STRATEGIES TO REDUCE INJURIES AND DEATHS

    • Strong, fair, and effective enforcement.
    • Outreach, education, and compliance assistance.
    • Partnerships and other cooperative programs.
12. Slide 12

    HCS PICTOGRAMS AND HAZARDS

    • Labels for hazardous substances in your workplace
13. Slide 13

    OSHA INSPECTIONS

    • The OSH Act authorizes OSHA compliance safety and health officers (CSHOs) to conduct workplace inspections at reasonable times.
    • OSHA conducts inspections without advance notice, except in rare circumstances (e.g. Imminent Danger)
    • In fact, anyone who tells an employer about an OSHA inspection in advance can receive fines and a jail term.
14. Slide 14

    INSPECTIONS PROCESS

    • A typical OSHA on-site inspection includes four stages:
    • 1. Presentation of inspector credentials.
    • 2. An opening conference.
    • 3. An inspection walk-around.
    • 4. A closing conference.
15. Slide 15

    OSHA’S INSPECTION PRIORITIES

    • Priority
    • 1st
    • 2nd
    • 3rd
    • 4th
    • Category of Inspection
    • Imminent Danger:
    • Reasonable certainty an immediate danger exists
    • Fatality/Catastrophe:
    • Reported to OSHA; inspected ASAP Complaints/Referrals:
    • Worker or worker representative can file a complaint about a safety or health hazard Programmed Inspections:
    • Cover industries and employers with high injury and illness rates, specific hazards, or other exposures.
16. Slide 16

    OSHA’S COMPLAINT INVESTIGATIONS

    • OSHA evaluates each complaint to determine how it can be handled best--an off-site investigation or an on-site inspection
    • Before beginning an inspection, OSHA staff must be able to determine from the complaint that there are reasonable grounds to believe that a violation of an OSHA standard or a safety or health hazard exists.
    • If OSHA has information indicating the employer is aware of the hazard and is correcting it, the agency may not conduct an inspection after obtaining the necessary documentation from the employer.
17. Slide 17

    CONT.

    • Employee may file a complain with OSHA under Section 11(c) if your employer retaliates against you by taking unfavorable personnel action because you engaged in protected activity relating to workplace safety and health.
    • OSHA requires that complaints must be filed within 30 days after the alleged retaliation.
18. Slide 18

    RIGHTS AS A WHISTLEBLOWER

    • Your employer may be found to have retaliated against you if your protected activity was a contributing or motivating factor in its decision to take unfavorable personnel action against you. Such actions may include:
    • Firing or laying off
    • Blacklisting
    • Denying overtime or promotion
    • Disciplining
    • Denying benefits
    • Failing to hire or rehire
    • Intimidation
    • Reassignment affecting promotion prospects
    • Reducing pay or hour
19. Slide 19

    QUESTIONS ABOUT

    • OSHA?
20. Slide 20

    DEFINITIONS

    • Excavation
    • Any man-made cavity or depression in the earth’s surface (including its walls, floor and lip) formed by earth removal. For rescue purposes an excavation is wider than it is deep.
21. Slide 21

    DEFINITIONS

    • Trench
    • A narrow excavation which is deeper than it is wide, with a maximum width of fifteen (15) feet measured at the floor (bottom).
22. Slide 22

    EXCAVATIONS OVERVIEW / MAIN POINTS

    • Excavation laws, regulations, standards
    • Soil classification
    • Soil testing
    • Competent person responsibilities
    • Hazards associated with trenches
    • Protective systems
23. Slide 23

    TRAGIC FACTS

    • Excavating is recognized as one of the most hazardous construction operations
    • 97 Workers were killed on Excavation/Trenching jobs from 2013-2017.
    • From a low of 10 deaths in 2014 to a high of 33 in 2016.
    • Cave-ins are more likely than other excavation related accidents to result in worker fatalities.
    • (Source: BLS 2018, www.osha.gov)
24. Slide 24

    TRAGIC FACTS

    • 60% of related deaths are rescuers
    • Civilians
    • Fire dept personnel
    • Co-workers
    • Cave-ins can happen without warning
    • All of the fatalities and injuries could have been prevented
25. Slide 25

    COLLAPSE FORCES

    • 24 inches of soil on a person’s chest weighs 750-1000 lb.
    • 18 inches of soil covering a body weighs 1800-3000 lb.
26. Slide 26

    SOIL WEIGHT EXAMPLE

    • 20 cubic feet = 2,000 lbs.
    • How tall are you? This example is 4ft deep Do you think you can get out?
    • © ACR Publications Used By Permission
27. Slide 27

    COLLAPSE FORCE

    • Shear wall collapse speed is 45 mph
    • 1 cubic foot of soil can weigh from 100 to 125 lb.
28. Slide 28

    SPEED OF COLLAPSING DIRT

    • Imagine this coming down on top of you….
    • Weight of a Volkswagen
    • Weight of one cubic yard of soil
    • 2,785 Pounds
    • 2,700 Pounds
29. Slide 29

    EFFECTS ON THE BODY

    • Respiratory distress
    • Crush syndrome
    • Total body impact
30. Slide 30

    TRENCH COLLAPSE

31. Slide 31

    THE SEVEN TRENCHING HAZARDS

    • 1. Cave–ins
    • 2. Electric Line Contact
    • Overhead
    • Buried
    • 3. Falls into Excavations
    • 4. Equipment Falling into Excavations
    • 5. Explosion / Fire / Electrocution
    • 6. Hazardous Atmosphere
    • 7. Drowning
32. Slide 32

    UNSAFE ATTITUDES

    • “I Know what I’m doing.”
    • “It can’t happen to me.”
    • “I’ve been doing it that way for years.”
    • “I’d sleep in that hole!”
    • “Don’t worry, we’ll watch the walls and tell you if you need to get out.”
33. Slide 33

    MOST COMMON CAUSES OF CAVE-INS:

    • Poor Planning
    • Misjudgment of soil type.
    • Inadequate, or incorrect installation of protective devices.
    • Defective protective devices.
    • Failure to adjust for changing conditions
34. Slide 34

    LEGAL ASPECTS

    • OSHA [29 CFR 1926.650 - 652]
    • Excavation standard applies to all open excavations made in the earth’s surfaces including
    • trenches, all
    • surface
    • encumbrances that would create a hazard, and protective systems
35. Slide 35

    WHAT’S IN THE STANDARD?

    • Scope, application and definitions
    • Job Site Hazard Listing
    • Requirements for Protective Systems
    • Appendixes that detail:
    • Soil Classification
    • Sloping and Benching
    • Timber and Aluminum Hydraulic Shoring
    • Protective System Selection Decision Tree
36. Slide 36

    GENERAL REQUIREMENTS

    • 1926.651
    • (a) Surface encumbrances
    • (b) Underground installations
    • (c) Access & egress
    • (d) Exposure to vehicle traffic
    • (e) Exposure to falling loads
    • (f) Warning systems for mobile equipment
37. Slide 37

    GENERAL REQUIREMENTS ( CONT.)

    • 1926.651
    • (g) Hazardous atmospheres
    • (h) Protection from hazards associated with water accumulation
    • (i) Stability of adjacent structures
    • (j) Protection from loose rock or soil
    • (k) Inspections
    • (l) Fall protection
38. Slide 38

    SURFACE ENCUMBRANCES

    • All surfaces encumbrances that are located so as to create a hazard to employees shall be removed or supported as necessary to safeguard employees
39. Slide 39

    UNDERGROUND INSTALLATIONS

    • Utility companies shall be contacted with in established local response times
    • Advised of proposed work
    • Asked to establish location of utility
    • When request cannot be met, employer may proceed with caution with detection equipment of an acceptable means to locate utility
40. Slide 40

    UNDERGROUND INSTALLATIONS ( CONT.)

    • While
    • the excavation
    • is open, underground installations shall be protected, supported or removed as necessary to safeguard employees
41. Slide 41

    ACCESS & EGRESS

    • Structural ramps
    • Used by employees shall be designed by a competent person
    • When used for equipment shall be designed competent person qualified in structural design
    • Stairway, ladder, ramp or other safe means of egress require no more than 25 ft of lateral travel for employees in excavations that are 4 feet or more in depth
    • Ladders must be secured and extend a minimum of 36 inches above the landing
42. Slide 42

    EXPOSURE TO VEHICLE TRAFFIC

    • Employees exposed to public vehicle traffic shall be provided with and wear warning vests or other suitable garments
    • Marked or made with reflectorized or highly visible material
    • Requiring a designated, trained flag person along with signs, signals, and barricades when necessary
43. Slide 43

    EXPOSURE TO FALLING LOADS

    • No
    • employee
    • shall
    • be permitted
    • underneath loads handled by digging or lifting equipment
    • Stand away from vehicle being loaded or unloaded to avoid being struck
    • Operators may remain in cabs when vehicles are equipped in accordance with 1926.601
44. Slide 44

    STUCK-IN

45. Slide 45

    WARNING SYSTEMS FOR MOBILE EQUIPMENT

    • When operator does not have clear view of edge of excavation
    • Warning system shall be utilized
    • Barricades
    • Hand or mechanical signals
    • Stop logs
46. Slide 48

    HAZARDOUS ATMOSPHERES

    • Testing and controls
    • To prevent harmful levels of atmospheric contaminants
    • Less than 19.5% or more than 23.5% oxygen
    • Atmosphere tested before entry
    • Adequate precautions shall be taken
    • Ventilation
    • Proper respiratory protection
    • Testing done often as necessary
47. Slide 49

    EXPOSED TO HAZARDOUS ATMOSPHERE

48. Slide 50

    EMPLOYEES EXPOSED TO HAZARDOUS ATMOSPHERE

49. Slide 51

    MONITORIN

50. Slide 52

    VENTILATION BLOWERS

51. Slide 53

    EMERGENCY RESCUE EQUIPMENT

    • Rescue equipment
    • Breathing equipment
    • Safety harness and line or basket stretcher
    • Must be readily available
    • Must be attended
    • Bell-bottom pier holes, deep and confined footing excavation shall wear a harness with a lifeline securely attached to it
52. Slide 54

    BELL BOTTOM PIER HOLE

    • A tubular shaft with a wider bell shaped cross-section at it’s base for support. Created for foundations and footer construction.
53. Slide 55

    WATER ACCUMULATION

54. Slide 56

    WATER ACCUMULATION (CONT.)

    • Employees shall not work in excavations where there is accumulated water, or where water is accumulating, unless adequate precautions have been taken, to protect employees.
    • Must take adequate precautions to protect employees
    • Accumulating water
    • Varies with each situation
    • Removal monitored by competent person
    • Run off from heavy rains requires inspection by competent person
55. Slide 57

    WATER REMOVAL FROM TRENCH

56. Slide 58

    WATER REMOVAL EQUIPMENT

57. Slide 59

    STABILITY OF ADJACENT STRUCTURES

    • Where stability is endangered by excavation operations
    • Support systems such as shoring, bracing or underpinning shall be provided
    • Sidewalks, pavement and appurtenant structures shall not be undermined unless support systems are used to protect employees
58. Slide 60

    NO SUPPORT PROVIDED TO PREVENT

    • STRUCTURAL FAILURE
59. Slide 62

    PROTECTION FROM LOOSE ROCK AND SOIL

    • Hazard from falling or rolling from excavation face
    • Scaling to remove loose materials
    • Installation of protective barricades
    • Other means (retaining devices)
    • 2 feet from edge of excavation
60. Slide 64

    WHAT’S GOOD?

    • WHAT’S NOT SO GOOD?
61. Slide 65

    WHO IS COMPETENT PERSON

    • One who is capable of identifying existing or predictable hazards in the surroundings which are unsanitary, hazardous or dangerous to employees & who has authorization to take prompt corrective measures
62. Slide 66

    COMPETENT PERSON

    • Has specific training in and be knowledgeable about soil analysis, use of protective systems and the requirements of the standard
63. Slide 67

    COMPETENT PERSON MUST BE AWARE OF:

    • Falling loads or equipment
    • Hazardous atmospheres
    • Weather conditions and forecast
    • Stability of adjacent structures.
64. Slide 68

    THE COMPETENT PERSON MUST BE AWARE OF:

    • Surface and overhead encumbrances
    • Underground utilities
    • Access and egress
    • Vehicular traffic
    • Continuation of trade activity
65. Slide 69

    INSPECTIONS

    • Daily and before start of work
    • As needed throughout the shift
    • After snowstorms, windstorms, thaw, earthquake
    • Soil classification
    • Any hazard increasing occurrence
    • Employees shall be removed until precautions have been taken
66. Slide 70

    INSPECTIONS ( CONT.)

    • When fissures, tension cracks, sloughing undercutting, water seepage, bulging at the bottom
    • Change in size, location or placement of the spoil pile
    • Indication of movement in adjacent structures
67. Slide 71

    HAZARD

68. Slide 72

    TRAINING, KNOWLEDGE AND EXPERIENCE AS DEMONSTRATED

    • THROUGH RESPONSIBLE ACTION
    • MAKES A PERSON “COMPETENT.”
69. Slide 73

    FALL PROTECTION

    • If walkway provided
    • Where employees permitted to cross, guard rails provided where 6 feet or more above lower levels
    • Fall protection standard
70. Slide 74

    REQUIREMENTS OF PROTECTIVE SYSTEMS

    • 1926.652
    • Employees shall be protected from cave-in by an adequate protective system except;
    • Entirely in stable rock
    • Less than 5 feet in depth with no indication of cave-in
71. Slide 75

    NO PROPER PROTECTION

72. Slide 76

    PROPER SHORING

73. Slide 77

    DESIGNS USING MANUFACTURERS DATA

    • Deviation will only be allowed after manufacturer issues specific written approval
    • Written form at the job site during construction
74. Slide 78

    MATERIALS AND EQUIPMENT

    • Free of damage and defects
    • Maintain in manner consistent with manufactures data
    • Examined by competent person & evaluated for continued use
    • Removed from service until approved by registered professional engineer
75. Slide 79

    TRENCH BOX

76. Slide 80

    TRENCH BOXES

77. Slide 81

    INSTALLATION & REMOVAL

    • Members securely connected
    • Prevent sliding, falling, kick outs
    • Other predictable failure
    • Members shall not subjected to loads exceeding those which were designed
    • Members removed from bottom first
    • Back fill with removal of support system
78. Slide 82

    INSTALLATION & REMOVAL (CONT.)

    • Excavate to no greater than 2 feet below – only if system is rated at full depth and there are no indications of a loss of soil from behind or below the support system
    • Employees are not permitted to work below other employees unless adequately protected from falling, rolling, sliding material
    • Employees are not allowed in shields when installed, removed or moved vertically
79. Slide 83

    REMOVAL OF TRENCH BOX

80. Slide 84

    PICTURE OF TRENCH

81. Slide 85

    PROPER TRENCH BOX

82. Slide 86

    SHIELD TESTING

83. Slide 87

    SHIELD TESTING BY COMPETENT PERSON

84. Slide 88

    WHAT’S GOOD?

    • WHAT’S NOT SO GOOD?
85. Slide 89

    SHIELD USED WITH SLOPING

86. Slide 90

    HORIZONTAL SHORING DIMENSIONS

    • © ACR Publications Used By Permission
87. Slide 91

    VERTICAL SHORING DIMENSIONS

    • © ACR Publications Used By Permission
88. Slide 92

    PNEUMATIC SYSTEMS

89. Slide 93

    SHIELD USAGE AND SAFETY

    • SHIELDS ARE USED TO PROTECT WORKERS FROM CAVE-INS, NOT TO PROVIDE SUPPORT FOR THE TRENCH.
    • Manufacturer’s Data must be present at work site.
    • Top of the shield must extend to the top of the trench.
    • If used with sloping, top of shield must extend 18 inches above vertical trench walls.
    • Shields may be stacked, provided the bottom one is rated for the total depth of the trench.
    • The trench may be dug 2 feet lower than the shield bottom, but the shield must be rated for that depth.
    • Backfill around the box to prevent lateral movement.
90. Slide 94

    SOIL CLASSIFICATION

    • 1926 SUBPART P APP A
    • Cemented soil
    • Cohesive soil
    • Dry soil
    • Fissured
    • Granular soil
    • Layered system
    • Moist soil
    • Plastic
    • Saturated soil
    • Soil classification system
    • Stable rock
    • Submerged soil
    • Unconfined compressive strength
    • Wet soil
91. Slide 95

    SOIL CATEGORY: STABLE ROCK

    • Natural solid mineral material that can be excavated with vertical sides and remain intact while exposed. Examples are granite and sandstone.
    • Determining whether a deposit is stable rock may be difficult unless it is known whether cracks exist and whether or not the cracks run into or away from the excavation.
92. Slide 96

    SOIL CLASSIFICATIONS

    • Stable rock
    • Type A
    • Cohesive soils with an unconfined compressive strength of 1.5 tons per square foot [tsf]
    • Examples: Clay, silty clay, sandy clay
93. Slide 97

    SOIL CLASSIFICATIONS (CONT.)

    • No soil is type A if;
    • Fissured
    • Subject to vibration
    • Previously disturbed
    • Seeping water
    • Part of a sloped or layered system of four horizontal to one vertical
94. Slide 98

    SOIL FISSURING

95. Slide 99

    TO MUCH WATER?

96. Slide 100

    WEIGHT AND VIBRATION

97. Slide 101

    SOIL TYPES

    • Type B
    • Cohesive soils with an unconfined compressive strength greater than 0.5 tsf but less than 1.5 tsf
    • Silt, silt loam, angular gravel
    • Soils that are fissured, or subject to vibration
98. Slide 102

    SOIL CLASSIFICATION

    • Type C
    • Cohesive soils with a unconfined compressive strength of 0.5 tsf or less.
    • Gravel, sand, loamy sand, submerged soil, soil from which water is freely seeping
99. Slide 103

    SOIL STRENGTH MEASURE UNCONFINED COMPRESSIVE STRENGTH (UCS)

    • The amount of pressure in tons per square foot (tsf) required to cause the soil to fail in compression.
    • OSHA Soil Classification is based on the UCS of the soil.
100. Slide 104

     BASIS OF CLASSIFICATION

     • The classification of deposits shall be made based on the results of at least one visual and one manual analysis conducted by a competent person
101. Slide 105

     ACCEPTABLE VISUAL TEST

     • Determine qualitative information on site in general
     • Soil adjacent to excavation
     • Soil forming the sides of the open excavation
     • Soil taken as samples from excavated material
     • Estimate range of particle sizes
102. Slide 106

     ACCEPTABLE VISUAL TEST CONT.

     • Observe evidence of surface water
     • Water seeping from the sides
     • Location of the level of the water table
     • Sources of vibration that may affect stability
     • Evidence of previously disturbed soil
103. Slide 107

     ACCEPTABLE MANUAL TEST

     • Plasticity
     • Ribbon and thread test
     • Dry strength test
     • Thumb penetration test
     • Other strength test
     • Pocket pentrometer
     • Hand-operated shearvane
104. Slide 108

     FIELD SEDIMENTATION TEST

     • Flat bottom container - at least 7 inches high (old olive jar)
     • One 1/2 to 2 inches of soil
     • Place soil in the glass jar
     • 5 inches of water on top of soil
105. Slide 109

     FIELD SEDIMENTATION TEST (CONT.)

     • After 30 seconds granular sand
     • After 3 minutes silt type material type material settles at the bottom settles on top of the sand
106. Slide 110

     CLAY, SAND AND SLIT

107. Slide 111

     THE RIBBON TEST

     • STEP 1
     • Mix soil + water to make into plastic mass
     • Roll mass into cylindrical shape 1/2 to 3/4 inch diameter
     • Lay across palm of hand
     • Press between thumb and second joint of index finger
108. Slide 112

     THE RIBBON TESTS STEP 2

     • Pass through thumb
     • Squeeze until it takes the shape of a 1/8 to 1/4 inch thick strip
     • Allow to hang freely from hand
109. Slide 113

     THE RIBBON TEST (CONT.)

     • Clay loam will barely ribbon and break easily
     • Clay = relatively long ribbon 6” to 8” or more
     • More clay = longer and stronger ribbon
     • Silt has tendency to produce short ribbon with broken appearance
110. Slide 114

     PENCILING

     • If a 2 inch or longer thread can be held without breaking, the soil is cohesive.
111. Slide 115

     SHEAR VANE / TORVANE

     • Measures Soil’s Shear Strength
112. Slide 116

     SHEAR VANE / TORVANE

     • Select fresh clod or block of undisturbed soil from spoil pile
     • Cut a smooth surface on the clod
     • Insert vanes of device into the soil
     • Retract vanes to show foot imprint
     • Set indicator at zero device
     • firmly
     • Hold
     • against soil and twist in clockwise manner until soil fails in shear
113. Slide 117

     POCKET PENETROMETER TEST

     • Device is designed to work on saturated clay soil
     • Measures unconfined compressive strength of soil
     • Twice the value of shear strength of same soil
     • Note machine ring
114. Slide 118

     POCKET PENETROMETER

115. Slide 119

     POCKET PENETROMETER TEST

     • To begin test, remove red protective cap, push ring against body so that low side reads “O”
     • Slowly insert piston until engraved mark is level with soil
116. Slide 120

     POCKET PENETROMETER TEST

     • (CONT.)
     • Read strength in tons/sq ft using low side of ring (side closest to the piston end). Record reading and repeat step #1.
     • For weak soils, use 1” adaptor foot, multiply by 0.0625
117. Slide 121

     THUMB PENETRATION TEST

     • The thumb penetration procedure involves an attempt to press the thumb firmly into the soil in question.
118. Slide 122

     THUMB PENETRATION TEST (CONT.)

     • If the thumb makes an indentation in the soil only with great difficulty, the soil is probably Type A.
     • If the thumb penetrates no further then the length of the thumb nail, it is probably Type B soil.
     • If the thumb penetrates the full length of the thumb it is Type C soil.
     • The thumb test is subjective and is therefore the least accurate of the tests.
119. Slide 123

     SOIL CLASSIFICATIONS.

     • Layered Geological Strata
     • where soils are configured in layers
     • must be classified on the basis of the weakest soil
     • each layer may be classified individually if a more stable layer lies below a less stable layer
     • Type C soil rests on top of stable rock
120. Slide 124

     CLASSIFICATION

     • Look for the following conditions
     • Particle size
     • Primarily fine grained=cohesive material
     • Primarily coarse-grained sand or gravel
     • Granular material
     • Cohesion
     • Remains in clumps=cohesive
121. Slide 125

     SOIL STRENGTH IS DEPENDENT UPON:

     • Type of Soil.
     • Amount of Moisture in the Soil.
     • Whether the Soil Has Been Previously Disturbed.
122. Slide 126

     IF WATER IS ADDED

     • It Brings Additional Weight
     • Hydrostatic Pressure
     • It Erodes the Trench Wall
     • Water movement typically moves soil
     • It Can Freeze and Thaw
     • Resulting in cracks & false cohesion
     • REMOVAL OF GROUND WATER IS CRITICAL
123. Slide 127

     SOIL COMPONENTS

     • Clay:
     • Composed of mineral particles less than 0.002 mm in diameter
     • Silt:
     • Individual mineral fragments that range from 0.002 to 0.05 mm in diameter.
     • Sand:
     • Individual rock or mineral fragments that range in diameter from 0.05 to 2.0 mm in diameter.
     • Gravel:
     • Can be either angular or rounded.
124. Slide 128

     COHESIVE SOIL

     • Soil with a high clay content which has cohesive strength.
     • It does not crumble.
     • It can be excavated with vertical side slopes.
     • It is hard to break up when dry.
     • It can be molded.
     • It exhibits significant cohesion even when submerged.
125. Slide 129

     GRANULAR SOIL

     • Soils that include gravel, sand, silt.
     • Very low clay content.
     • It has no cohesive strength.
     • Some moist granular soils exhibit apparent cohesion.
     • It cannot be molded when moist and crumbles easily when dry.
126. Slide 130

     SOIL MECHANICS

     • Toppling occurs when the trench’s vertical face shears along the tension crack line and topples into the excavation
127. Slide 131

     TOPPLING

128. Slide 132

     SUBSIDENCE

     • Subsidence and bulging occurs when an unsupported excavation can create an unbalanced stress in the soil which causes subsidence at the surface and bulging of the vertical face
129. Slide 133

     UNSUPPORTED EXCAVATION

130. Slide 134

     BULGING

131. Slide 135

     SOIL MECHANIC

     • Heaving or squeezing is caused by the downward pressure created by the weight of adjoining soil or equipment
     • Can occur even when shoring or shielding has been properly installed
132. Slide 136

     FORCES ACTING ON A TRENCH

     • © ACR Publications Used By Permission
133. Slide 137

     BOILING

     • Boiling is evidenced by an upward water flow into the bottom of the cut
     • High water table is one cause
     • Boiling produces a quick condition even when trench boxes are used
134. Slide 138

     TRENCH BOILING

135. Slide 139

     TRENCH CRACK

     • Tension cracks usually form at a horizontal distance of 0.5 to .75 times the depth of the trench
     • Tension Crack
136. Slide 140

     SLIDING

     • Sliding or sloughing may occur as a result of tension cracks
     • Sliding
137. Slide 141

     SLOPING AND BENCHING

     • 1926 SUBPART P APP B
     • Actual slope
     • Distress
     • Maximum allowable slope
     • Short term exposure
     • Stable rock
     • Type A soil
     • Type B soil
     • Type C soil
138. Slide 142

     DESIGN OF SLOPING AND BENCHING

     • Allowable configurations and slopes
     • Not steeper than 11/2 horizontal to 1 vertical
     • Designs using other tabulated data
     • Shall be in written form
     • Must identify limits of use of the data
     • Identify the registered professional engineer who approved
139. Slide 143

     IMPROPER DESIGN

140. Slide 144

     IMPROPER SLOPING

141. Slide 145

     ALLOWABLE SLOPES

     • Soil Type
     • Height/ Depth
     • Slope angle
     • Stable Rock
     • Vertical
     • 90 Degree
     • Type A
     • ¾ to 1
     • 53 Degree
     • Type B
     • 1 to 1
     • 45 Degree
     • Type C
     • 34 Degree
     • Type A Short term
     • ½ to 1 height/depth and 63 degree slope
     • Max excavation depth 12 ft
142. Slide 146

     EXAMPLES OF SLOPING FOR DIFFERENT SOILS

143. Slide 147

     BENCHING

     • Only to be used on soil types A and B
     • Type A
     • Type B
144. Slide 148

     SOIL TYPE A

     • Type A soil
     • Supported of shielded vertically sided lower portion
     • ¾ to 1
     • 20 feet max depth
     • Shield 18 inches above to prevent rollover
145. Slide 149

     SOIL TYPE B

     • Type B soil
     • Supported of shielded vertically sided lower portion
     • 1 to 1 sloped
     • 18 inches minimum at top of shield to prevent rollover
     • Type B
     • Soil Supported of shielded vertically sided lower portion
146. Slide 150

     SOIL TYPE C

     • Type C soil supported of shielded vertically sided lower portion
     • 1 ½ to 1
     • 20 feet max depth
     • 18 inches above to prevent rollover