| |
It is our privilege and
pleasure to complain about governments, politicians, today's music,
kids not related to us, and especially regulations and rules made
by people in a distant city who know nothing about the reality of
our everyday hard work. Even in our sports watching, many of us
seem more interested in logging the conduct of the referees than
in the skills of the players. If there is one sector of the construction
industry where rules and regulations are vital to everybody's safety
and success, it is excavation and trenching. The statistics on accidents
from cave-ins show that we are still too complacent or careless,
because it is not a lack of affordable solutions that prevents improvement.
 |
| The
worker is checking the security of his ladder at this lift station
site. |
Cave-ins aren't the only
threat to workers. They are the best-known hazards because they
seem the most likely to cause fatalities, but other perils - such
as workers falling, objects falling on workers, and a hazardous
working atmosphere - should also be considered. How reliable is
that ladder? If much of your work is on foundations or house basements,
some of the Occupational Safety & Health Administration rules
do not apply, but workers should be aware of the dangers. A simple
rule would be: Keep workers out of the excavation as much as possible,
and place your soil loads as far back as possible.
"Accidents always happen
to those other guys who don't know what they're doing" might be
the thinking that causes most problems. Recently I met a neighbor
limping along the sidewalk. Dave is not a professional contractor
like you. Now in his fifties, he "does jobs" for people - he fixes
things, charges less, and takes more chances to make sure the profit
is right. He is - or was, until four weeks previously - an unusually
strong barrel of a man. He was working alone in a trench and had
taken none of those precautions you hear about; the concrete culvert
broke and collapsed because Dave was trying to solve the problem
with sheer physical strength. He fell 10 ft.; the concrete followed.
It was several minutes before a passer-by noticed his predicament.
He broke one shoulder, several ribs, and one foot.
"I can move my left hand
now, Paul," he smiled. "You should have seen me a month ago! I was
lucky nothing hit my head." His smile included a large measure of
pain and, yes, even fear. If he continues to do jobs that
involve trenches and ditches for people, he might wear a hardhat
even when nobody is looking and might make sure there is somebody
else with him for dangerous work. When I mentioned OSHA to Dave,
he grinned and said the safety rules apply to employees, not owners,
so he could not be blamed. From talking to other contractors, I
deduce that attitude is not as rare as one would hope. There is
a story of four men who refused to shore their excavation or shield
themselves because they were all "part-owners" of the company. They
had just been warned that a cave-in had killed a man a few blocks
away in exactly the same kind of soil and excavation, but they still
refused to shore their trench.
Planning Is Better
Than Correcting
 |
| Some
sites require enormous supports that make the workers look tiny. |
You would assume that
anybody who digs would check for underground obstacles, especially
since there are instruments available that can tell the precise
location of water mains, sewer pipes, telecommunications lines,
and all those entanglements that can not only disrupt the bucket's
progress but cause horribly expensive damage to property and people.
In the detective stories of the '40s and '50s, the crooks would
case the joint before barging into the bank or jewelry store. That's
what an excavation contractor does before making the first hole.
He or she has a virtual
map of the ground and communicates the information to the workers.
"We thought it was just another excavation with no obstacles," says
a young backhoe operator about some recent work at a Midwestern
hospital, where the fourth powerful scoop fractured two utility
lines. Yes, the problems caused were critical. (We'll keep names
and locations out of this true story to protect the not-so-innocent.)
"The boss didn't tell us what was there." The boss said any fool
would know what was there. How right he was! Somebody did know but
was foolish enough not to pass the information along to the employees.
It cost him a lot.
It's a shame that most
thinking about trench safety and shoring equipment stems from negative
ideas when there are several positive reasons - many of them
financial - for planning your excavations and trenches. With modular
shoring and shields readily available, installation at the site
is usually fast and accurate. By taking the guesswork out of protective
equipment you can avoid the costs of onsite welding and cutting.
By removing any anxiety about existing utility lines or other underground
obstacles, you will have your workers achieving good speed in the
trenches. Imagine how smoothly the job will proceed with planned
protection rather than worrying about how expensive it will be if
you cut utility lines or damage existing infrastructure.
Here's an advantage you
might not have considered but will understand immediately. A trench
or an excavation that is shored or shielded is much smaller than
one that is sloped - as much as six or seven times smaller. Think
of the amount of soil that you won't have to remove and then replace.
Did somebody mention compaction time? Today's cost of disposal of
debris and soil?
Your rate for workers'
compensation might depend on the history of safety for your company.
If there is an accident - or, worse still, a fatality - in your
recent history (reckon on three years as "recent"), your premiums
could be doubled. That cost is one that puts you at a disadvantage
in bidding against your competitors. The good name of your company
is also vulnerable when you have an accident, especially one considered
avoidable. You may not be told you are a risk your customers can't
afford; when contracts are not awarded, you'll find out.
Thorough planning before
the excavation means you'll know how to go around hidden obstacles.
It means you will profit from a safe operation, profit from not
having to pay for repairs to buried cables and pipe, profit from
not facing huge bills for repairs to structures or equipment. Even
if it takes several hours to shore a trench or shield the workers,
how will that compare with the cost of an accident? Hospital bills?
Lifting out an excavator or loader that has fallen in? Repairing
the machine? Replacing injured workers? This is serious business.
One careless trench incident could ruin your company.
What Do You Look
for in Shoring Equipment?
 |
| Winter
does not stop the need, for efficiency of, good shoring. |
According to Allied Construction
Products, makers of the Tren-Shore hydraulic shoring units, "One
person can install and remove the Tren-Shore System, all from above
the trench." Trenches can be braced up to 12 ft. wide and 20 ft.
deep with the system. That statement addresses some of the questions
contractors have with shoring systems. What are the hidden costs?
How many workers will be used to install them? Are they so heavy
they require additional lifting equipment? How can you install
a shoring system in a trench if you're not allowed in the trench
before a shoring system is installed? How many workers will
be needed when the shoring needs to be removed at the end of the
job? "The Tren-Shore fold-flat design allows quick installation
without having to enter an unsecured trench," notes Greg Smith of
Allied Construction Products, which has produced more than 100,000
units in the last 30 years. "We also offer three levels of strength
[medium, heavy, and extra heavy duty] and features like safety finger
guards to protect against the scissor action of the folding shores
and protective coil jacking at the cylinder end of the hydraulic
hoses."
The shoring system itself
must be safe as well as offer protection to the workers in its strength.
When Allied Construction Products talks of medium and heavy duty
for its aluminum rails (6061-T6 Ally), it means that medium duty
exceeds all applicable OSHA specifications and the others are even
better. Part of your planning for trench and excavation safety is
to learn the advantages (or disadvantages) of any shoring system
recommended to you. Who has used the system? Don't be afraid to
ask manufacturers for names of satisfied customers. Safety and strength
seem to be the keywords, but ease of installation and removal makes
better profits too.
Dispelling Some Myths
 |
| The
rules are different for small trenches, but the level of care
should be the same. |
 |
| The
design of Allied shields protects workers inside the trenches. |
G.H. Ross Contractors
of Williamston, MI, has adopted Efficiency Production's Slide Rail
System as its usual means of shielding big excavations. Dispelling
the myths generally associated with slide-rail systems, Ross effectively
has used the Slide Rail on many recent projects. Common misconceptions
contractors have about a slide-rail system include: it is too difficult
to install, it comes out of the ground too hard, it takes too long
to learn how to use, it's left to the contractors to figure out,
it's applicable only to limited types of jobs, it's less cost-effective
than sheet piling, it doesn't work around utilities, it's not accepted
by engineers, and it's not productive. Successful projects have
proved those fears to be unfounded.
The first Ross project
was the $1.83 million construction of a new 3,100-ft.2
iron-removal facility in Hartland, MI; it provides 1.72 million
gal. of water per day to the community. The scope included installation
of two 8-ft. green sand filters, a precast backwash holding tank,
a grinder pump station, 1,500-lin.-ft. high-density polyethylene
(HDPE) pipe, and all related site work at the water treatment plant
and elevated storage-tank sites. Ross used Efficiency Production's
ClearSpan Slide Rail System to facilitate the installation of the
backwash holding tank by shielding the deep (24-ft.) open pit with
panels, posts, and walers, without interfering cross-braces. The
ClearSpan configuration allowed close access to the excavation for
installations of cast-in-place and precast concrete. That eliminated
the need for concrete pumping and large hoisting equipment. "It
was easy to figure out," remarks Mike Ross, project manager. "Assembly
was quicker than we expected for our first-time use." Efficiency's
Research and Development Director Doug Austin and Slide Rail installer
Troy Serrells were on-site to assist the crew with the entire installation
and removal process. The system also saved time and money since
it was less expensive and less labor intensive than tight sheeting.
"It's faster and safer than other options, and it's easier to bid
bedding and backfill material since the dimensions of the excavation
are constrained to the size of the slide-rail dimensions," explains
Ross.
Greg
Ross, project safety inspector, states, "The system is very sound.
Assembly is limited primarily to machine work, which limits exposure
to personnel. It's a safe system during the installation and at
the completion of the excavation."
Another
project was a $350,000 sewer system expansion in Howell, MI, where
a precast 12- x16-ft. wet well was installed in a 21- x 27-ft. footing.
The job began in January while weather conditions in the North were
at their worst. The soil consisted of frozen upper layers, silt
and clay, and slurrylike soil at 14 ft. below grade with a water
table at 10 ft. Ross Contractors had to install a wellpoint system
to dewater and consolidate the soil. It used the ClearSpan Slide
Rail again to maintain the unstable excavation and limit the size
for an already large wet well base. "Soil conditions were unknown
and changing during the excavation," notes Mike Ross. "The slide
rail allowed a safe excavation to stand while equipment was installed
to handle unworkable soil." As a bonus the Ross crew was able to
use the slide rail as an excellent mount for the header pipe. After
the structure was finished the modular shielding system's components
were removed easily from the frozen ground with a Caterpillar 235
excavator, while a Cat 950 loader backfilled until the entire system
was out and the pit was topped off. "It's very cost-effective,"
Mike Ross exclaims. "No cranes or special equipment is needed, and
there is no lost time since the system is installed while digging
and extracted while backfilling - all with less disturbance of the
site."
Special Applications
 |
| Once
a trench is 5 ft. deep, you should consider shoring or shields
if workers will go inside. |
Earlier this year, Independence
Excavating started the second phase of construction on an interchange
for West 3rd and State Route in Cleveland, OH, a two-year
project. The interchange is located adjacent to the Cleveland Browns's
stadium, and the modifications are designed to facilitate access
into the port. The project includes a new bridge on West 3rd and
a new bridge to get onto the shoreway heading eastbound. For this
project, the owner representative is Skip Jacobsen of the Cleveland
Cuyahoga County Port Authority. Tim Sopenski is the representative
for engineering consultants HNTB, and Steve Goodreau is the engineer
of record with Parsons Brinckerhoff.
One
of the interesting portions of this job includes the tangent pile
walls. These walls include 278 drilled concrete caissons (each 3
ft. in diameter). Some of the caissons located at the West 3rd
bridge area are up to 140 ft. long. The caissons are drilled on
3-ft. centers so that they touch each other and when complete will
act as a retaining wall. The installation of the two parallel walls
enables the soil between them to be excavated without adversely
affecting the adjacent stadium or the Regional Transit Authority
station. The new road between these walls will allow the public
to go under the West 3rd bridge. Kundel Industries, a
manufacturer of safety equipment for all kinds of trenches and excavations,
supplied engineering and equipment for the waler system that held
the piles in place. The products included t.e.d. (trench engineering
division of Kundel) 8-in. screw spreaders, and a jacking frame for
preset pressure on the piling.
Krings
International, a manufacturer of all kinds of standard shoring and
shielding with sales worldwide and a specialist in trenches used
for laying pipe and duct, produces shoring machines that have been
successful for duct pipe laying between existing buildings, in narrow
lanes, in difficult geological conditions, and in specially protected
environments. "Press shoring is preferred as a no-vibration method
of digging trenches in densely built-up areas and on poorly grounded
building foundations," observes Alain Matos, export manager of Krings.
He adds that there is a low operation noise that makes it popular
in residential areas. As a temporary excavation pit, press shoring
minimizes the annoyance to traffic. It provides optimum safety for
trench workers and has been demonstrated as more economical than
alternative solutions. The hydraulic system is controlled by a radio
remote control that combines all the required functions. Krings
also supplies the piling frame. "You can combine this with large-area
shoring, wherever a small number of crossing lines alternates with
long distances of no crossing lines at all," notes Matos. "It may
be integrated both as an individual element in parallel shoring
and as an independent shoring for trenches."
Shielding Individual
Workers
 |
| If
you have to compact the soil inside a trench, remotely controlled
machines could be practical. |
 |
| A current
job in New Orleans that requires a lot of working room (clearance). |
My first acquaintance
with an aluminum trench shield was some years ago at a site where
a shield - I remember it as a Griswold Machine and Engineering (GME)
model - totally protected a worker when a trench collapsed. The
shield did not look especially strong, but it withstood pressure
that would have crushed the man. It saved his life. Similar to shoring
and culverts, the value of the trench shield is in its engineering
and design. Some are steel, others are aluminum. The metal you choose
will depend on the strength and weight that are most appropriate
to your applications. Concerning aluminum shields, manufacturer
GME says, "Contractors working on jobs with moderate cuts and lighter-weight
machines will find our 2 AEX and 4 AEX series fit the bill. They
offer protection in the trenches but weigh as little as half of
some similar-size shields. We recommend them especially for those
contractors using today's small excavators or rubber-tire backhoes."
Makers of aluminum trench
shields will provide you with complete specifications and advice
about suitable depths for each size (which will depend on the soil
type, so you should know the characteristics of the ground where
you are digging). By reading what features are standard or optional
you usually can tell what other contractors are requesting - such
items as lifting eyes and bridles, pull bars, no-knife edges, standard
lengths, and availability of special sizes.
In
the information from PRO-TEC Equipment, the easy, quick assembly
of its modular trench shields is emphasized. Two workers can unload
the lightweight aluminum panels from a pickup truck (in which they
stack flat), and assembly follows a simple routine. On PRO-TEC ModSeries
shields, the user can choose panels or adjustable spreaders and
install a two-, three- or four-sided shield. The panels are filled
with foam, are tongue-and-groove design, and keep the dirt and moisture
out. By having flanged ends, the panels last longer and are easier
to handle.
A
honeycomb inner structure is a feature stressed by ShoreTec Inc.
for its steel trench shields, available with 3-, 4-, 6-, and 8-in.
walls. According to the company, "Our standard line is anything
but standard in quality and performance. It contains features common
to all our steel trench shields and is a good starting point for
your build-your-own shield. We offer options that make shields adaptable
to specific job conditions and contractor needs." Among those options
are adjustable collars, bottom stacking tubes, a height adapter,
a floating collar assembly, or a four-sided pit kit. When you don't
know the benefit of a particular feature of a trench shield or shoring
system ask.
Paul
Hull is a frequent contributor to Grading & Excavation Contractor.
GEC
- September/October 2003
|
|
