Excavation,
Trenching, and
Soil Mechanics
Subpart P
1
Call Before you dig!!!!!!!

Call One Call 72hrs.
Before any excavation
begins!!!!!!!!!!!!! It’s the
LAW!!!!!!!!!!!!!!!!!!!!!!!!!!
This Training!!!!

This training DOES NOT!!!!!! certify you as a
competent person. A competent person would
require specialized training in soil classification,
trenching and excavation and experience.

This training is for the individual involved with
excavation and trenching work and gives an
overview of their work to increase awareness with
trenching and excavation safety.
Points To Be Covered:

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!
4
DANGER!
5
Dangers of Excavation
and Trenching

Each year
- 70+ fatalities
- 1,000+ injuries
Related to excavation and trenching
operations
Fatal Facts!

An employee was installing a small
diameter pipe in a trench 3’ wide, 1215’ deep and 90 feel 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.
7

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 eightinch, 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.
8
1926.650
Scope and Application

“This subpart applies to all
open excavations made in
the earth’s surface.
Excavations are defined to
include trenches.”
9
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 are filled with water.
10
Weighing in on Soil…
Solid Rock weighs about 167 lbs. Per
cubic foot. Since a cubic foot of soil is
about ½ that 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 1
and ½ of a ton.
11
Conditions that Increase the
chances of a Cave In

Lack of, or to much moisture

Additional weight of
- spoil pile
- tools or equipment
Unsupported faces
Unsupported structures


Mechanics of a Cave-In

13
Diagram of a cave in
14
15
Look for Potential Problems






Fissures
Cracking
bulging or separation of soil
Surface water near excavation
Water accumulation in excavation
Soil that has been previously
disturbed
Protecting Employees in
Excavations




1926.652 (a)(1)
“Each employee in an excavation shall be
protected from a 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 4’ in depth
and examination of the ground by a
competent person provides no indication
of a potential cave-in.”
17
Protective Systems

“a method of protecting employees
from cave-ins, from material that
could fall or roll from an excavation
face or into and 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”
18
What are our Options?




Sloping, or Benching
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.
19
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.
20
Competent Person


“one who is capable of classifying soils,
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”
(Knowledge & Authority)
21
1926.651(k)(1)
Inspections
•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.
22
Access and Egress
1926.651 (c)(2)

“A stairway, ladder, ramp or other
safe means of egress shall be
located in trench excavations that
are 4’ or more in depth, and at a
distance to require no more than
25’ of lateral travel for employees
to use ladders or egress and is in
clear view of occupants at all
times.”
23
Soil Tests


1926 Subpart P appendix A, Soil
Classification (c)(3)
In order to classify a soil as Solid
Rock, A, B, or C at least one
visual and one manual test must
be performed by a competent
person.
24
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.”
25
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…
26
Thumb Penetration Test


1926 Subpart P Appendix A(2)(iii)
…type A soils with an unconfined
compressive strength of 1.5 tsf can be
readily identified 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.
27
SOLID ROCK

“Natural solid mineral matter that
can be excavated with vertical
sides and remain intact while
exposed”
28
Type A Soil


Cohesive soil with an
unconfined, compressive
strength of 1.5 Tsf
Examples of this type of soil
are: Clays, silt clay, sandy
clays, and clay loam.
29
A Soil is NOT type ‘A’ IF:





The soil is fissured
The soil is subject to vibration
The soil has been previously
disturbed
The material is subject to other
factors that would require it to
be classified as a less stable
material.
Water is present
30
Sources of Vibration






Traffic
Railroad Operations
Heavy Equipment
Operations
Jack Hammer Operations
Tamping Machine
Operations
Seismic activity
31
Type B Soil



Cohesive soil with an unconfined
compressive strength greater than
.5 Tsf
Granular cohesion less 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
32
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
33
Sloping Requirements
by Soil Type
Stable Rock
Maximum
Allowable Slope for
Excavations less
than 20’
Vertical (90 Deg.)
Type A
¾ to 1 (53 Deg.)
Type B
1 to 1 (45 Deg.)
Type C
1 ½ to 1 (34 Deg.)
Soil or Rock Type
34
Sloping in Type ‘A’ Soil
¾ to 1 (53 Deg.)
35
Sloping in Type ‘B’ Soil
1 1toto11(45
(45Deg.)
Deg.)
Sloping in Type ‘C’ Soil
1 ½ 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 or Shields may not
be modified, repaired unless
approved by a PE.
38
Trench Boxes or Shield
39
Is this allowable?
YES! If the Trench boxes are designed to
be stacked and are used in accordance
with their tabulated data.
40
Trench Boxes and
Sloping or Benching

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.
41
42
43
44
Shoring
(Shoring System)

“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.”
45
Hydraulic Shoring
46
Stacked Hydraulic
Shores
47
Whaler System
48
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
Curb and Gutter
Light poles
Utilities
Mailboxes
49
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…
50
Locates

Red = Power
Blue = Water
Orange = Communications
Yellow = Gas
51
Here's Your Sign!!!!!!!!!
Can an Excavation be a
Confined Space…?


Oxygen deficient atmospheres: less than 19.5% oxygen.
Potential for other gasses or Hazards to be present include
but not be limited to:
- Natural Gas from potential leaks or cut lines.
- Methane from decayed matter.
- welding/ cutting operations
- combustion engines
- Electrical utilities
- application of coatings, or paint
53
Other Hazards



Falls
- fall protection required when working with
unprotected areas that pose a fall of 6 ft or more
Overhead Power lines
- must maintain a minimum of 10ft clearance
Falling loads, equipment or tools, spoil pile
- Hard Hat
- maintain minimum of 2 ft. from excavation edge

Call before you dig.

Use at least one
visual and one
manual soil test to
determine soil type.
Summary



A Ladder is
required for access
and egress at 4’


The ladder must be
within 25’ lateral
travel at all times.

At 4’ 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.
55
Video
TEST
1. An additional hazard that can create the risk of Cave in is:
a.
Rain, snow
b.
Vibration
c.
Weight spoil pile, or equipment near trench wall
d.
All of the above
2. Which work operation when performed inside a trench has
the potential to create a Hazardous atmosphere?
a.
welding, cutting
b.
Application of coatings or paint
c.
Use of solvents
d.
Internal combustion engines
e.
All of the above
3. Ladders or access points should be located within
the excavation starting at what depth?
4. The weight of a cubic yard of soil (3’X3’X3’) can
equal approximately how many pounds?
5. Utilities that could be buried in your work area may
include?
a.
Electrical
b.
Fuel/oil/gas
c.
Water/Sewer
d.
all of the above
6. A worker within an excavation should have to walk
no further than _____ ft. in either direction to exit
the excavation.
7. The most unstable soil that you could work with is
classified as:
a.
Type A
b.
Type B
c.
Type C
d.
Solid Rock
8. A slope with the angle not steeper than 1.5
horizontal to 1 vertical is considered safe for which
type of soil?
a.
Type A
b.
Type B
c.
Type C
d.
All of the above
9. When using a trench box it should be at least ____
inches above the top of the vertical side, or soil
surface.
10. Who can order the evacuation of an excavation?