Ihab Saad – Excavations
AI: Summary ©
The safe practices for excavation are discussed, including the definition of " guaranteed person" and the importance of proper construction and protection of surrounding infrastructure. The safety distance for excavation operations is also emphasized, with proper safety measures and surface protection measures being essential. Different types of tests and soil stabilization are used, including visual, hardware, and manual tests, and the importance of knowing the type of surface protection is emphasized. The process of classifying soil using various tests and assessments is discussed, including the use of particle side, pocket cup, and manual tests. The soil must be stable, not type A, and is not currently classified as " type A."
AI: Summary ©
Music. Welcome to another safety class, and today we're going to
start talking about subpart p, which is excavations. Definitely.
Excavations take place on most construction sites, and this is
one of the most hazardous areas, and that's why OSHA has designated
excavations as one of the focus four areas of inspections which
has the hazard of cabing ins or being
stranded in a ditch, for example, with the size of the ditch
collapsing and so on, so caught in between, which is one of the focus
four applies particularly to excavations and ditches. So today,
we're going to learn about what are the safe practices when doing
excavation, and what are the different types of soils that
we're going to be exposed to, and what kind of precautions have to
be taken with these different types of soils.
Some of the most frequently cited violations when it comes to
excavation are the protection from cave ins, which is the focus of
the of the issue here, means of egress provided, which is how to
get out of the trench in case cave ins start to happen. Daily
inspections by a competent person. We're going to learn what's a
competent person, and why do we have to perform daily inspections?
Because weather conditions might change, there might be freezing
and thawing, or there might be some rain, which would loosen the
soil and make it more susceptible to cave ins and collapse
protection from things falling into the excavation. If you have
equipment at the side of the excavation, or if you have labor
standing at the edge of the excavation. There's a Fall issue
here, and a competent person inspection employees removed from
hazard. Again, these are the most frequently cited issues when it
comes to excavation, and we can see these in our code book.
First of all, a quick refresher on what you have learned in your
soils class, or what you learn in the soils class,
to think to know exactly what's the magnitude of hazard when it
comes to excavation. The density of dry soil is 85 pounds per cubic
foot. Once it gets wet with water filling the voids of that soil, it
becomes heavier. So it becomes the weight becomes around 120 pounds
per cubic foot. So if you are standing in a trench that's 10
foot deep, a 10 foot column of dirt could weigh up to 1200
pounds. So imagine if 1200 pounds collapse on a person that can
easily kill that person. That's why the big hazard when it comes
to excavation.
So how do these cave ins happen? Basically, the hazard is
unsupported. Excavations can slide into the hole. There's going to be
lack of friction so that these are going to slide the layers of the
soil are going to slide on top of another layer, and it's going to
fill that void. So this is basically what's going to be the
big hazard there.
Another hazard is what's called boiling water, rising up or
boiling from the bottom of the trench, which can undermine the
stability of the surrounding soil. Again, if you have granular soil,
like sandy soil, for example, with upward water pressure, that can
definitely cause that boiling and can cause the collapse of that
soil. That's another big hazard. That's why water in ditches or in
excavation is a very risky issue. We're going to talk about that
little bit later.
The third hazard is heaving, which is a downward pressure of
adjoining soil which pushes the trench bottom upwards. So the
weight of the wet soil masses, basically pushes the bottom
upwards, and that causes also a collapse, and this particularly
happens in wet clay soil, where you have the particles very close
together, and they're going to form lumps, and that can cause
this heaving.
So today we're going to talk about a competent person. What is a
competent person? OSHA has three definitions. In fact, it has a
definition for something called an authorized person, a qualified
person and a competent person. And I'm going to read from the OSHA
definition here, an authorized person is a person who is
authorized by the employer to perform a task. So any laborer,
for example, working inside The Trench, in this case, is going to
be an authorized person because they have been authorized to work
inside the trench. However, there's another layer, which is
called a qualified person. A qualified person is a person who
has the knowledge to perform that task through education, schooling,
training or experience. So that's a higher level than authorized
person. And then the highest level is going to be the competent
person, which is going to be, by the way, and a qualified person
working a trench.
If someone is working inside The Trench, you're going to provide a
lifeline, which is a form of personal protective equipment. So
even if that person loses consciousness, then you can pull
them out of that trench. Water in the ditch, as we mentioned,
always, water in the ditch is a very hazardous issue, especially
if you're going to be operating electrical equipment inside that
ditch as well. Water and electricity are always a bad
combination. Fall Protection from the people outside of that trench.
They might fall in the trench, cave in protection. We're going to
talk about different types of soil. We classify them under OSHA
standards as type A, type B and type C. We're going to talk about
these in more details, allowable side slopes. We're going to learn
about these and the use of trench boxes. How should they be
installed? We're going to talk about that as well as we just
mentioned, deep excavations require a PE design was the
definition of a deep excavation, any excavation 20 feet or more,
protective systems,
if not installed properly, that might cause a hazard by itself, so
they have to be installed in the proper way.
Surface encumbrances include telephone, utility poles,
sidewalks, buildings, roadways, etc. They must be supported or
removed if they pose a hazard to employees. It happens sometimes
when you excavate, especially for mass excavation and deep
excavation, that you might find that the adjacent buildings or
structures are starting to crack or tilt or even in except
excessive cases, collapse. Why? Because the stress distribution
goes in something called the stress bulb, which goes as a at a
something like a 45 degree angle. So even if you're not digging
directly underneath the building, the stress coming from the
foundations of the building exists in the soil that you have removed.
So by removing that soil, this building, the load from the
building is not distributed properly anymore, so that causes
the building to lean or even to collapse. So this is definitely a
danger. That's why you have to support the sides of the
excavation to carry the load from the adjacent buildings.
Structures must be supported if near the excavation and
excavations must not undermine sidewalks unless properly
supported. So we're going to provide the proper support,
whether it's in the form of sheet piles, for example, that's one of
the common ways of supporting the excavation,
undercutting existing foundations. Do not excavate below existing
footings of or of structures, unless either a support system has
been provided, or excavation is in stable rock where the load
distribution is vertical, or you have a PE professional engineer
approving that excavation, because they would know exactly how the
stress is distributed and whether it's safe or unsafe to excavate
under these foundations.
In case of underground utilities, you must locate all underground
utilities. They might exist from existing maps that you might find
them through existing maps, old maps of that site, or you call the
utility company if they have any knowledge about these, the routes
of these different cables, pipes, etc. So prior to any excavation,
you have to locate the underground utilities. And the underground
utilities must be protected, either supported, removed or
guarded while the excavation is open, if they are still active, so
that they would not interfere with the excavation operations.
Call before you did. There's usually a an 800 number, in case
you are doubting whether they are. There are utilities or not, call
that number and they're gonna give you some
some information. So contact utility company locator prior to
excavating if no response within 24 hours, if you don't get an
immediate response from them, or if they cannot establish utility
location, if they don't have existing maps, then the employer
may proceed with caution, because you may find you may hit a cable,
especially if it's a live cable that can cause electrocution.
Employer must use detection equipment or other acceptable
means used to locate utilities. Now we have a new technology,
relatively new. It's been around for the past maybe 10 years or so,
which is called GPR. GPR stands for ground penetrating radar that
enables you by sending radar waves, ultrasound waves, it
enables you to draw a to get a 3d view of what's embedded underneath
your soil before digging. So it would show you there are pipes or
there are cables, and what are their directions and what are
their volumes, etc. So you'd know before excavation where these
exist, and you can either avoid them or deactivate them before the
excavation.
Of
loose material is always a hazard, so protect workers from loose
material that may fall from the excavation phase. How do you do
that? Again, we're going to talk about either sloping or benching,
and what is the safe distance to keep away from the edge of the
excavation and the use of trench boxes as well.
So spoil piles must be at least two feet from the excavation and
or use retaining devices to prevent material from rolling into
excavation. Again. One of these retaining devices is what's called
sheet piles. In case you haven't seen sheet piles, they are
something like a C section, steel
element that's driven vertically in the soil, and that's going to
take the lateral load of that soil so that the excavation doesn't
cave in, and that's usually used in deep excavation. Keep equipment
away from the edge of excavation, because, again, if they get too
close to the side, they might destabilize the soil and fall into
that trench. So the minimum distance is going to be two feet.
And here's a graph showing, for example, if this is a backhoe or
an excavator at the edge of the excavation, the spoiled pile must
be at least two feet from the edge, and material storage and
equipment must be at least two feet from the edge. So the minimum
safe distance is going to be two feet from the top of the edge of
the excavation, as you can see here. Now we have we can see that
it's sloped, and that sloping follows what's called the angle of
repose of the soil, which is a natural angle that the soil forms,
if left naturally, without any external support, that would be a
safe way to support that soil.
Operating equipment, too close hazard of operating equipment too
close to excavations. You have to watch for vibrations, clear view
to the rear, especially if that equipment is backing up. So if
it's backing up, you must have someone a monitor, or you have you
must have some mirrors, or any way to know whether you're too close
to the edge of the excavation or not. And the moisture content of
the soil, again, that can change the characteristics of the soil,
making it more collapsible. So use barricades or other warning
systems. Either you're gonna have cones or barricades, or you're
gonna have a flagger, someone with a flag who's going to notify the
equipment operator stop. You're getting too close to the edge of
the excavation,
access and egress. Remember these numbers here. Trenches four feet
or deeper, must have a means of egress, ladders, stairways, ramps
or others.
Travel distance, the maximum travel distance that the person
inside the ditch or the trench has to move to get out of the trench
to get to an egress or access means like a ladder is 25 feet, no
more than 25 feet. Quick question here, if we have a trench that's
49 feet long,
okay, how many ladders do we need for that trench?
Think for a second. How many ladders? Remember the maximum
distance is 25 feet. So the trench is 49 feet long. How many ladders
do we need? Some of you may have said two. Some of you may have
said three. The correct answer is one. Why is it one? If you locate
that ladder in exactly in the middle, from the farthest point on
either side, the distance is going to be 24 and a half feet, which
satisfies the code.
You would like maybe to have some redundancy so that people are not
rushing to get out of the trench. So you may say, Okay, I'm going to
install two but by the code, you're going to be fine. You're
not going to be violated if you install only one ladder for that
49 foot trench. But remember, the maximum horizontal distance that
people have to travel is 25 feet.
So the two numbers that you have to remember from the slides is for
trenches, for the four feet or deeper, if the trench is less than
four feet, you don't need that, because they can jump, jump over
the side of the trench, and the 25 feet the horizontal distance.
When it comes to loads, stand away from overhead loads, whether they
are buckets, clamshells or other from equipment excavating that
soil, the hull truck operators may remain in the cab for overhead
protection during loading. So if they are in the cab, they are
already protected by the roof of that cab stand away from vehicles
being loaded, because, again, sometimes the operator might not
pay attention, and a person might get hit by that equipment.
Hazardous atmospheres. Check excavation for hazardous
atmospheres. Mesh.
Or other gasses, sulfur dioxide or oxygen deficiencies. Again, if
there's not enough oxygen getting inside that trench, where these
conditions might exist. Again, use a sniffer to do this. There's a
mechanical sniffer that's a device that determines and measures the
oxygen content and analyzes the gasses inside the trench to decide
whether they are there are any noxious gasses or poisonous gasses
and things like that, and you have to have proper aeration or
ventilation of the trench. In this case,
rescue equipment is going to be needed if hazardous atmospheres
exist. So if someone is going to be working at in a trench that has
this hazardous atmosphere, you might need a breathing apparatus
so that they do not directly breathe the air inside The Trench,
which is poisonous or hazardous and a safety hardness and line.
Again, if something happens and they cannot move on their own, you
can pull them out and a basket stretcher. So if someone is
totally out of it and you cannot bring them out, you're going to
load them on the stretcher, and you're going to lift that
stretcher out of the trench to save them
lifelines in deep end, or confined space excavations, we have a
special lecture on confined spaces, so we're going to learn
later on what's a confined space and what are the conditions of
working in a confined space. Employees must wear a harness with
Lifeline attached, again, because if they cannot rescue themselves,
then someone else can rescue them. The lifeline must be separate from
any other line, so that it doesn't get entangled with any other line,
and it must be individually attended at all times when
employee is in the excavation. So we're gonna have an attendant
waiting outside doing nothing but watching the people inside the
excavation and monitoring their performance, and keeping a voice
contact and or an eye contact with them to notice any change in their
conditions which might necessitate taking them out of the excavation.
Water in a ditch, as we mentioned before, water in a ditch is not
good. We try to avoid that as much as possible. So do not work in
excavations that contain water unless special precautions are
taken. What kind of precautions are we talking about? First of
which is going to be dewatering. We're going to try to suck this
water out by dewatering through a well point system or a sump pump
or something like that, special shielding. So again, water is
going to destabilize the soil, so we might require special
shielding, and third use of the hardness and lifeline, just in
case there's a cave in then you can extract these workers out.
Dewatering operations if used, must be continually monitored by a
competent person, because, again, if it's going to be a sump pump,
for example, when that sump pump stops, water is going to start
accumulating again. So you want to keep a constant watch on the sump
pump. Same thing for a well point system again. It keeps absorbing
this water and expelling it out. So you want to make sure that it
keeps working continuously so that water does not accumulate.
Fault protection, walkways over excavation six foot deep or more,
must have guard rails where employees or equipment cross over
excavations. If you're gonna have something like a bridge over the
excavation and the excavation six foot deep or more, then you must
have the proper guardrails, as we're gonna learn about them. In
Fall Protection, they have special specifications that we're going to
learn about. So you must install these guard rails to prevent
people or equipment from falling into the excavation or something
falling on top of the people who are working inside the trench.
The Cave in protection is required, except one. So the only
cases when you do not need cave in protection is excavation is
entirely in stable rock. What is stable rock we're going to talk
about that? Or the other case where you do not need cave in
protection is if the excavation is less than five foot deep and has
been inspected by a competent person who says it is safe to work
inside that trench and it does not require cave in production.
What is stable drug? Again, stable rock is non fissure drug, solid
rock with no cracks in it. So note, if blessing was done, if the
method of excavation to that truck was blasting blessing, by default,
is going to create cracks in the remaining rock that has not been
excavated. So now it is not stable rock anymore because it has
fissures or cracks. So it does not become a stable rock. So it must
require some side protection. Rock with sand seams is not stable.
Rocky.
There. So if you find some sand seams inside the rock, which are
basically filling these fissures or these cracks, it is not stable
rock anymore.
What kind of protective systems are we going to use? We're going
to need side slopes. The steepest, the steepest is going to be 1.5
to one, which is rise over run,
slope or bench per soil type
and application. Like for example, we're going to look at type B of
soils shoring systems
like trench boxes, etc, timber or hydraulic shorting
for as as for per appendices C and D, as we're going to see in the
book. And it's designed, has to be designed by a professional
engineer. So these are basically the some of the protective systems
that we're going to use into excavation.
So when we talk about the different types of soil, A, B and
C, we have either rock, stable rock, which is not fissure drug,
which does not require any lateral support, or if it's not fissure
drug, if it's not stable rock, then it's going to be either type
A, B or C. And we're going to see what what kind of precautions do
we need to make soil classifications. How are we going
to classify the soil? It must be made on the basis of at least one
visual and one Manual Test. This is something that you have to
remember very carefully what you're going to need two different
tests to classify the soil, one visual and one manual. The visual
tests include the particle side, which size, which you can you
which you can visually inspect, spalling and fissures, cracks and
scaling and water presence you can see clearly with your naked eye
whether there's water inside the trench or not. So these are visual
tests. The other types of tests, which include the manual tests,
which are the pocket penetrometer test, they're all tests for
cohesiveness. This is something that you're going to learn about
in soils and the sedimentation test. So these are manual tests.
So again, we're going to need at least one visual and one Manual
Test to classify the soil.
For soil testing. Never enter an excavation to get a soil sample,
because, again, if you don't know what kind of soil it is, you don't
know what kind of support it's going to need, so do not enter
you're going to use some device to extract that soil. Watch how the
freshly excavated soil falls from the bucket in the next two slides.
Does the soil stick together in large, cohesive clumps, or does it
fall apart like granular soil? So if you hold a handful of soil and
let it fall naturally, is it going to form a cone, like in case of
sand, granular soil, and that cone is going to follow that angle of
repose, or is going to fall in chunks or in clumps, if it's
sticky soil with the particles sticking together.
So the first type is, which is type a soil?
This is the best after stable rock. So when we classify the
soil, depending on how good the soil is for the purpose of
excavation and the minimum amount of required support. The best one
is going to be stable rock, which does not require any electric
support. The next one is going to be type a soil, which is generally
a clay soil, where the soil particles are going to be sticking
together, which is a cohesive, cohesive soil sticks together. You
can't make mud without clay. So in this case, that's basically what
mud is. It has an unconfined compressive strength of one point
time, 1.5 tons per square foot or greater. So that's a mechanical
test that you can perform on the soil, which is at the unconfined
compressive strength. It includes clay, silty clay or cemented
soils. These are different types of soils that you can read about
in the soils report clay, silty clay or cemented soil. So that's
going to be the type a soil. Okay, how are we going to work in type a
soil?
Soil is not type A. If it is unstable dry rock, it is not type
A anymore. If it has been previously disturbed, this is not
type A. If it's fissured, it's not type A. And if it's subject to
vibration, it is not type A anymore. So again, in this case,
it might be either B or C
in case of Type A soil. And again here, if we have 20 foot maximum,
because beyond that, you're going to need a PE
you're going to have the soil self support through the slope of three
quarters to one three quarters horizontal to one vertical. So the
angle here is going to be more than 45 degrees.
Is
so in trench boxes, again, the maximum space between the bottom
of the trench box and the of the excavation the trench box is going
to be two feet. And here we have the minimum is going to be it's
not maximum, it's minimum. This is the typo. The minimum
height difference between the edge of the trench box and the edge of
the excavation is going to be 18 inches.
No employees should be standing inside while installing the trench
boxes. They're going to be installed mechanically by a piece
of equipment. Employees are not allowed in shields when installed,
moved or removed, because the soil. Why are we installing these
trench boxes in the first place? Because the soil is unstable. So
if you allow someone to be standing inside The Trench while
the soil is unstable, it can cave in at that time, do not over
excavate a round box. That's another issue. Do not leave a big
distance between the edge of the box or the wall of the box and the
edge of the excavation, because it might cause sudden lateral loads
to be applied and someone might be caught in between the trench box
and the wall of the excavations. Again, we are going to need
ladders for access and egress. It must be within the shield system.
Again, the distance is going to be no more than 25 feet apart.
Now we have reached the final part of this presentation, and we're
going to have a quick review over what we have gone over, ladders or
other means of access are required at what depth in a trench?
Remember where? Remember on that slide where we had two numbers, we
had four feet of depth and we had 25 feet of distance. So the answer
to the first question is, four feet, how far back from the edge
of the trench must spoil piles be? Whether it's spoil piles or
equipment that's going to be operating, the minimum safe
distance is going to be two feet. What two types of tests must be
done to classify soils? We mentioned that we're going to have
two groups of tests. We must have one of each group, which is a
visual test and a manual test,
at what depth must trenches be either sloped or short? At what
depth must trenches be either sloped or short, five feet, at
least anything above five feet, and a competent person judges that
there's no danger. How often must the excavation competent person
inspect trenches? Remember, we talked about that with the
different conditions that might affect the
situation inside The Trench. It must be inspected daily, at the
shift start and during the shift and at other times when the
conditions might change after rainstorms, for example, or
earthquakes, or if heavy equipment is operating close by, and so on.
So this is our review of subpart P related to excavation. Again,
remember that this is one of the focus four, and we have to be very
cautious when we're working near or inside ditches or trenches. I
hope you have learned about this sub part, and I'll be glad to
receive any of your questions online. You.