Construction Safety and Soil Mechanics Overview
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Excavation, Trenching,
and Soil Mechanics
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OSHA Regulations
1926.650: Scope and Application
1926.651: Specific Excavation Requirements
1926.652: Requirements for Protective Systems
1926 Subpart P Appendix A: Soil Classification
Other Appendix and Tabulated Data
Most Frequently Cited Serious Violations in
Construction FY 2020
Most Frequently Cited Serious Violations in
Excavation FY 2020
Scope and Application
Fatal Facts
An employee was installing a small diameter
pipe in a trench 3’ wide, 12-15’ deep and 90
feet long. The trench was not sloped or
shored nor was there a box or shield to protect
the employee. Further, there was evidence of
a previous cave-in. The employee apparently
reentered the trench, and a second cave-in
occurred, burying him. He was found face
down in the bottom of the trench.
Fatal Facts
Four employees of a mechanical contractor were laying
a lateral sewer line at a building site. The foreman, a
plumber by trade, and a laborer were laying an eight-
inch, 20-foot-long plastic sewer pipe in the bottom of a
trench 36 inches wide, nine feet deep, and
approximately 50 feet long. The trench was neither
sloped nor shored, and there was water entering it
along a shale seam near the bottom. The west side of
the trench caved in near the bottom, burying one
employee to his chest and completely covering the
other. Rescue operations took two and five hours - too
late to save the men.
What is Soil?
A soil is a mixture of rock, water, air and a
variety of other substances.
Soil is made up of rock in the form of small
particles and spaces called voids. Normally
some part of these voids is filled with water.
Weighing in on Soil…
Mechanics of a Cave-In
Diagram of a Cave-In
Diagram of a Cave-In
Protecting Employees
1926.652 (a)(1)
“Each employee in an excavation shall be
protected from cave-ins by an adequate
protective system designed in accordance
with paragraph (b) or (c) of this section except
when:
(i) Excavations are made in entirely stable rock;
or
(ii) Excavations are less than 5’ in depth and
examination of the ground by a competent
person provides no indication of a potential
cave-in.”
Protective Systems
“a method of protecting employees from cave-
ins, from material that could fall or roll from an
excavation face or into an excavation, or from
the collapse of adjacent structures. Protective
systems include support systems, sloping and
benching systems, shield systems, and other
systems that provide the necessary protection”
Options for Protection
Use a Registered Professional Engineer to
design a sloping or benching system.
Use support systems in accordance with
requirements set forth in the standard.
Purchase an engineered system, (example..a
trench box or shield.)
Have a PE design a shielding or shoring system
specific to your task.
Protective Reqiurements
29 CFR 1926.652(b)(4)(i)
Design by a registered professional engineer.
Any system not found within the guidelines set forth
in the standard, or within the tabulated data tables
in the standard requires use of a Professional
Engineer.
No where in the standard or tabulated data does it
allow for excavations deeper than 20 feet.
Knowledgeable Employee
Inspections
1926.651(k)(1)
Daily Inspection of excavations shall
be conducted by a ‘competent
person’ prior to the start of work and
as needed throughout the shift.
Inspections shall also be conducted
after every rainstorm or other hazard
increasing occurrence.
Access and Egress
“A stairway, ladder, ramp
or other safe means of
egress shall be located in
a trench excavations that
are 4’ or more in depth so
as to require no more
than 25’ of lateral travel
for employees.”
1926.651 (c)(2)
Soil Tests
Visual Test
“Visual analysis is conducted to determine the qualitative
information regarding the excavation site in general, the
soil adjacent to the excavation, the soil forming the sides
of the open excavation, and the soil taken as samples
from the excavated materials.”
Manual Tests
“Manual analysis of soil samples is conducted to
determine quantitative as well as qualitative
properties of soil to provide more information in
order to classify soil properly.”
Examples: Thumb penetration, Pocket
penetrometers, Drying tests, Sedimentation…
Thumb Test
1926 Subpart P Appendix A(2)(iii)
Type A soils with an unconfined compressive strength of
1.5 tsf can be readily indented by the thumb; however,
they can only be penetrated by the thumb only with
great effort
Type C soils with an unconfined compressive strength of
.5 tsf can be easily penetrated several inches by the
thumb and can be molded by light finger pressure.
Solid Rock
“Natural solid mineral matter that can
be excavated with vertical sides and
remain intact while exposed
Type A Soil
Cohesive soil with an unconfined, compressive
strength of 1.5 Tsf.
Examples of this type of soil are:
Clays
Silty clay
Sandy clays
Clay loam.
Sources of Vibration
Traffic
Railroad Operations
Heavy Equipment Operations
Jack Hammer Operations
Tamping Machine Operations
Thumping Car Stereos that make you want to pull your
hair out and to…never mind…
Type B Soil
Cohesive soil with an unconfined compressive
strength greater than .5 Tsf
Granular cohesionless soils including; silt, silt loam,
sandy loam, and some sandy clay loam
Previously disturbed soils except those which would
otherwise be classified as Type ‘C’ soil
Type C Soil
Cohesive soils with an unconfined compressive
strength of 0.5 Tsf or less
Granular soils including gravel, sand, and loamy sand
Submerged soil, or soil from which water is freely
seeping
Soil Requirments by Slope Type
Sloping in Type A Soil
Sloping in Type B Soil
Sloping in Type C Soil
Trench Boxes or Shield Systems
“A structure that is able to withstand the forces
imposed on it by a cave-in and thereby protect
employees.”
Trench boxes are generally
used in open areas, but they
may also be used in
combination with sloping and
benching. The box should
extend at least 18 inches
above the surrounding area if
there is sloping toward the
excavation.
Is this Allowable?
YES! If the Trench boxes are
designed to be stacked and
are used in accordance
with their tabulated data.
Type of Soil with Trench Box
Shoring Systems
“A structure such as metal hydraulic, mechanical or
timber shoring system that supports the sides of an
excavation and which is designed to prevent cave-ins.”
Hydraulic Shoring
Stacked Hydraulic Shoring
Whaler System
Surface Encumbrances
1926.651 (a)
“All surface encumbrances that are located
so as to create a hazard to employees shall
be removed or supported as necessary to
safeguard employees”
Utilities
1926.651(b)
The estimated location of utility installations, such
as sewer, telephone, fuel, electric, …that
reasonably may be expected to be encountered
during excavation work, shall be determined prior
to opening an excavation…
Can an Excavation be
a Confined Space…?
Oxygen deficient atmospheres: less than 19.5% oxygen
Potential for other gases to be present include but not be
limited to:
Natural Gas from potential leaks or cut lines.
Methane from decayed matter.
Summary
Call before you dig.
Use at least one visual and one manual soil test to determine
soil type.
A ladder is required for access and egress at 4’.
The ladder must be within 25’ lateral travel at all times.
At 5’ depth some type of ‘protective system is required’.
Treat all soil as Type ‘C’ and slope at 1 ½ : 1 and you are
covered.
If not: Use some type of shoring or shielding to protect your
employees.
Excavations over 20’ require the use of a P.E.
This content provides valuable information on excavation, trenching, soil mechanics, OSHA regulations, common violations in construction and excavation, fatal incidents, soil composition, and soil weight calculations. It emphasizes the importance of following safety protocols in construction work related to excavations, highlighting the risks and consequences of non-compliance with regulations. The data presented sheds light on the significance of understanding soil behavior and implementing protective measures to prevent accidents and ensure worker safety.
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Presentation Transcript
Excavation, Trenching, and Soil Mechanics
OSHA Regulations 1926.650: Scope and Application 1926.651: Specific Excavation Requirements 1926.652: Requirements for Protective Systems 1926 Subpart P Appendix A: Soil Classification Other Appendix and Tabulated Data
Most Frequently Cited Serious Violations in Construction FY 2020
Most Frequently Cited Serious Violations in Excavation FY 2020
Scope and Application This subpart applies to all open excavations made in the earth s surface. Excavations are defined to include trenches. 1926.650
Fatal Facts An employee was installing a small diameter pipe in a trench 3 wide, 12-15 deep and 90 feet long. The trench was not sloped or shored nor was there a box or shield to protect the employee. Further, there was evidence of a previous cave-in. The employee apparently reentered the trench, and a second cave-in occurred, burying him. He was found face down in the bottom of the trench.
Fatal Facts Four employees of a mechanical contractor were laying a lateral sewer line at a building site. The foreman, a plumber by trade, and a laborer were laying an eight- inch, 20-foot-long plastic sewer pipe in the bottom of a trench 36 inches wide, nine feet deep, and approximately 50 feet long. The trench was neither sloped nor shored, and there was water entering it along a shale seam near the bottom. The west side of the trench caved in near the bottom, burying one employee to his chest and completely covering the other. Rescue operations took two and five hours - too late to save the men.
What is Soil? A soil is a mixture of rock, water, air and a variety of other substances. Soil is made up of rock in the form of small particles and spaces called voids. Normally some part of these voids is filled with water.
Weighing in on Soil Solid Rock weighs about 167 lbs. Per cubic foot. Since a cubic foot of soil is about rock it will weigh about 83 lbs. Add in water and the weight begins to rise to around 114 lbs. (if saturated). Do the math and a simple cubic yard of soil can weigh over 3000 lbs! That is a ton and a !
Protecting Employees 1926.652 (a)(1) Each employee in an excavation shall be protected from cave-ins by an adequate protective system designed in accordance with paragraph (b) or (c) of this section except when: (i) Excavations are made in entirely stable rock; or (ii) Excavations are less than 5 in depth and examination of the ground by a competent person provides no indication of a potential cave-in.
Protective Systems a method of protecting employees from cave- ins, from material that could fall or roll from an excavation face or into an excavation, or from the collapse of adjacent structures. Protective systems include support systems, sloping and benching systems, shield systems, and other systems that provide the necessary protection
Options for Protection Use a Registered Professional Engineer to design a sloping or benching system. Use support systems in accordance with requirements set forth in the standard. Purchase an engineered system, (example..a trench box or shield.) Have a PE design a shielding or shoring system specific to your task.
Protective Reqiurements 29 CFR 1926.652(b)(4)(i) Design by a registered professional engineer. Any system not found within the guidelines set forth in the standard, or within the tabulated data tables in the standard requires use of a Professional Engineer. No where in the standard or tabulated data does it allow for excavations deeper than 20 feet.
Knowledgeable Employee One who is capable of identifying existing and predictable hazards in the surroundings, or working conditions which are unsanitary, hazardous, or dangerous to employees, and who has the authorization to take prompt corrective measures to eliminate them
Inspections Daily Inspection of excavations shall be conducted by a competent person prior to the start of work and as needed throughout the shift. 1926.651(k)(1) Inspections shall also be conducted after every rainstorm or other hazard increasing occurrence.
Access and Egress 1926.651 (c)(2) A stairway, ladder, ramp or other safe means of egress shall be located in a trench excavations that are 4 or more in depth so as to require no more than 25 of lateral travel for employees.
Soil Tests 1926 Subpart P Appendix A, Soil Classification (c)(3) In order to classify a soil A, B, or C at least one visual and one manual test must be performed by a competent person.
Visual Test Visual analysis is conducted to determine the qualitative information regarding the excavation site in general, the soil adjacent to the excavation, the soil forming the sides of the open excavation, and the soil taken as samples from the excavated materials.
Manual Tests Manual analysis of soil samples is conducted to determine quantitative as well as qualitative properties of soil to provide more information in order to classify soil properly. Examples: Thumb penetration, Pocket penetrometers, Drying tests, Sedimentation
Thumb Test 1926 Subpart P Appendix A(2)(iii) Type A soils with an unconfined compressive strength of 1.5 tsf can be readily indented by the thumb; however, they can only be penetrated by the thumb only with great effort Type C soils with an unconfined compressive strength of .5 tsf can be easily penetrated several inches by the thumb and can be molded by light finger pressure.
Solid Rock Natural solid mineral matter that can be excavated with vertical sides and remain intact while exposed
Type A Soil Cohesive soil with an unconfined, compressive strength of 1.5 Tsf. Examples of this type of soil are: Clays Silty clay Sandy clays Clay loam.
Soil is NOT Type A if: The material is subject to other factors that would require it to be classified as a less stable material. The soil has been previously disturbed. The soil is subject to vibration. The soil is fissured. Water is present.
Sources of Vibration Traffic Railroad Operations Heavy Equipment Operations Jack Hammer Operations Tamping Machine Operations Thumping Car Stereos that make you want to pull your hair out and to never mind
Type B Soil Cohesive soil with an unconfined compressive strength greater than .5 Tsf Granular cohesionless soils including; silt, silt loam, sandy loam, and some sandy clay loam Previously disturbed soils except those which would otherwise be classified as Type C soil
Type C Soil Cohesive soils with an unconfined compressive strength of 0.5 Tsf or less Granular soils including gravel, sand, and loamy sand Submerged soil, or soil from which water is freely seeping
Soil Requirments by Slope Type Maximum Allowable Slope for Excavations less than 20 Vertical (90 Deg.) Soil or Rock Type Stable Rock Type A to 1 (53 Deg.) Type B 1 to 1 (45 Deg.) Type C 1 to 1 (34 Deg.)
Trench Boxes or Shield Systems A structure that is able to withstand the forces imposed on it by a cave-in and thereby protect employees. Trench boxes are generally used in open areas, but they may also be used in combination with sloping and benching. The box should extend at least 18 inches above the surrounding area if there is sloping toward the excavation.
Is this Allowable? YES! If the Trench boxes are designed to be stacked and are used in accordance with their tabulated data.
Shoring Systems A structure such as metal hydraulic, mechanical or timber shoring system that supports the sides of an excavation and which is designed to prevent cave-ins.
Surface Encumbrances 1926.651 (a) All surface encumbrances that are located so as to create a hazard to employees shall be removed or supported as necessary to safeguard employees Adjacent Structures Roads and/ or Sidewalks Mailboxes Curb and Gutter Utilities Light poles
Utilities 1926.651(b) The estimated location of utility installations, such as sewer, telephone, fuel, electric, that reasonably may be expected to be encountered during excavation work, shall be determined prior to opening an excavation
Can an Excavation be a Confined Space ? Oxygen deficient atmospheres: less than 19.5% oxygen Potential for other gases to be present include but not be limited to: Natural Gas from potential leaks or cut lines. Methane from decayed matter.
Summary Call before you dig. Use at least one visual and one manual soil test to determine soil type. A ladder is required for access and egress at 4 . The ladder must be within 25 lateral travel at all times. At 5 depth some type of protective system is required . Treat all soil as Type C and slope at 1 : 1 and you are covered. If not: Use some type of shoring or shielding to protect your employees. Excavations over 20 require the use of a P.E.
