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As a small boy on a sandy,
chilly beach on the other side of the Atlantic, I discovered how
independent and obstinate water could be. However many cities of
sand and carefully engineered channels I dug, built, and barricaded,
the water went where it wanted to go. One of the first gems of scientific
wisdom I learned was that water seeks its own level. Overfilling
a glass onto a clean tablecloth caused this parental comment. In
many construction projects involving excavation, the resting place
water seems to prefer is at the bottom of your trench to a depth
just above your boots, or hiding in the ground under your machine.
In some parts of this country, especially where new streets have
been built over old streams, the ground can be downright jelloish
or like a wet sponge just a few feet below yesterday's asphalt.
Mats are often essential for the stability of loaders, excavators,
trucks, and dozers on such terrain; sitting in a working excavator
can feel like standing on a sidewalk in an earthquake. When the
water table is just below the surface (and Florida is by no means
the only place where that occurs), the ground is sure to be less
stable and friendly to earthmoving machinery than sites where the
top several feet of soil are dry and solid.
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| Tracks
handle wet, soft conditions well. You can have steel tracks
over standard wheels to achieve a similar result. |
When water finds its
preferred level, it usually stays there until an attractive new
level is presented. It seldom goes away quickly by itself. There
were several incidents last year - one of the most publicized was
near Cincinnati, OH - where abandoned excavation sites filled with
water that quickly became stagnant. There was a public outcry against
the contractors who neglected to handle the situation correctly.
One of the greatest dangers of waterholes such as those is that
they are attractive to children (for throwing and skipping stones,
wading in to find underwater treasures, and even trying to imitate
Huckleberry Finn on discarded plywood). They are too often unfenced,
easy-to-reach playgrounds for unsuspecting youngsters. Although
the worst cases seem to have occurred when projects were halted
or abandoned for financial reasons, with nobody accepting
responsibility for any site condition, it is wise to check that
the site where you have just finished your excavation or grading
does not offer similar hazards.
Water can be the contractor's friend too when air pollution
and excessive dust cause impaired vision in work areas. Water sprayed
accurately from trucks helps control those problems, and its cost
is generally at a special, lower construction rate, such as the
water used for earthfill, drainfill, and rockfill. Measurement and
payment will vary from state to state. Your first contact for the
correct information could be your Natural Resources Conservation
Service. Some contractors - those who work in these conditions constantly - prefer
to use their own water trucks and drivers, but others like to use
the services of local companies whose expertise is in dust control
at construction sites.
Water Often Attacks
Below the Surface
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| Having
the right-size pumps available at the right time has solved
many emergency and temporary water problems. |
It always seems easier
to combat the enemy you can see rather than the one you can't. Ask
those contractors who regularly dig trenches. Even ground that looks
dry and stable can cave in, with terrible results for people and
property, and that is why regulations for shoring and shielding
are so strict (and welcome). When the ground is wet, it seems to
be more unstable, more inclined to fill any hole you care to excavate.
(That is, after all, water's mission in life - to fill holes. What
else is an ocean?) In many of the state regulations we saw, there
was emphasis on the presence of a competent person where
there was excavation and trenching. Such a person should understand
how soils are classified and be able to judge the slope required
for a trench or the most appropriate form of cave-in protection.
Usually there is no protection required if the trench is less than
5 ft. deep or if the excavation is being made in stable rock. If
shielding or shoring is mandated, it should be the right size. Does
that sound obvious? Installing inadequate protection would be similar
to securing the expensive equipment in your yard with a wet paper
fence.
The
competent person is also responsible for daily inspections of the
site and inspection after a rainstorm. It is his/her responsibility
to ensure that there is no accumulated water in excavations or trenches
where there will be people working. The competent person will also
be aware of the water table and natural drainage and know if there
has been any change in the moisture content of the soil. Moisture,
water, and runoff are threats below the surface that are too easy
to ignore. Perhaps the most important regulation (in California
and others states) concerning trenches and excavations is that nobody
works in a trench without a lookout standing by. One of the observations
made by researchers into the disposal of nuclear waste was that
water tended to seep into some trenches used for burial of wastes
at a greater rate than out of them. This is known as the "bathtub
effect." It does not happen at every site, but it does emphasize
the importance of knowing the soil conditions at every site where
you excavate, trench, or grade.
Heavy rain is an obvious threat to trench work. Trenches
should be inspected by a competent person after each rain before
employees are permitted to go back into them. Many contractors say
they take their workers out of the trenches during a rainstorm because
it's just not known how quickly the walls will collapse. Controlling
water on the surface might help prevent problems below. Benching,
sloping, shielding, and shoring can help. What you use will depend
on the type of soil. Benching, for example, cannot be used in most
places if the soil is Type C. In a crude test with your finger,
Type C soil would allow your finger to penetrate easily. It often
indicates that the soil is wet or that it shifts easily when wet.
Soil testing sounds like something expensive and even academic,
but it isn't - it's something that your competent person should be
able to do. You will come across such terms as cohesive, noncohesive,
and granular. You will find out the characteristics (especially
as they are affected by water) of clay, silty clay, sandy clay,
angular gravel, silt, silt loam, gravel sand, and loamy sand.
We must put a paragraph in here about the water that
runs off construction sites, especially from excavated ground. There
have been many instances of contractors being sued for causing pollution
with the construction water that ran into lakes and streams. It
is an aspect of excavation and construction that you cannot afford
to ignore.
Pumps: Simple Solutions
to Water Problems
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| For
regular wetland excavation, excavators can be given amphibious
undercarriages. |
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| This
tracked excavator has a PowerTilt bucket to cope with the particular
problems of ditch work |
The simplest way to keep
water out of excavated holes is to pump it out. Remember that this
water is seldom clean, and the pumps that work best are those designed
to handle dirty water or water with contaminants (bits and pieces,
twigs, stones, gravel, silt, and sand) in it. They are even called
"contractors' pumps" by some manufacturers. You see them categorized
as trash or diaphragm pumps; both types expect to handle solids
in the water. Manufacturer names mentioned frequently by contractors
were Gorman-Rupp, Honda, Flygt, Grindex, Chicago Pump, Bowie, Grundfos,
and Tsurumi. In our conversations nationwide, comments made on pumping
systems tended to be related to styles rather than brand names,
with almost every interviewed person agreeing that there are many
excellent pump manufacturers out there. Popular trash pumps will
pass solids of 1 in. or so, and you can expect them to pump out
around 100 gpm - more if you have a larger engine, such as the WT40X
from Honda with an 11-hp overhead valve engine; that model will
pump more than 500 gpm when there is a low head, as there often
is in everyday excavation work. If you have to move huge amounts
of water, 16-in. pumps from Crisafulli will discharge 10,000 gpm;
they have successfully handled floods and could claim to have outpumped
the Mississippi River on several occasions. Most were powered by
tractors because the surging water was threatening farmland by the
river, but options for electrical and diesel power have become popular
too.
Shortcuts do not work with pumping systems. With most,
there are three components that must match: the pump itself, the
inlet hose, and the discharge hose. "A smaller-than-necessary inlet
hose will seriously affect the system's performance," warns Kip
Rohr, an experienced professional with Pump Systems Inc., in Dickinson,
ND. The company sells, rents, and services several brands that would
be appropriate to contractor work. "When users complain about the
wrong pressure or too little volume, it is too often because they
have tried to go around the recommended setup." Pumps are carefully
engineered products; the prolific amount of performance curves published
(and readily available from distributors) will show that there is
probably a pump for every application. "If a contractor who has
regular excavation and trenching projects has a 4- or 6-inch pump,
he will find he can do almost any job," adds Rohr. He counsels that
smaller sizes can be suitable for many applications, but the bread-and-butter
models for companies involved in frequent excavation are the 4-
and 6-in. sizes. An observation made by several users was that the
solidly constructed discharge hose, rather than the lay-flat variety,
has shown more efficiency and stability for construction-related
applications.
A word that seems to occur frequently when talking of
water problems is "bypass," and that is because many water-related
problems are caused by broken or malfunctioning pipe. Much of the
pipe in the United States is older than most of us, installed when
our grandparents were young. It has served well but, like us, develops
faults and frailties. When the sewer pipe on Main Street breaks - a
sewer carries very dirty water - the repairs must be done, if possible,
without disturbing the flow of the pipe. It sounds impossible, but
it's what customers want. Repairs usually involve precise excavation;
it can't be done efficiently if sewage is flowing over the excavator
bucket. The contractor makes a temporary link where the pipe is
broken so that the flow can continue while repairs are done. Pumps
that do this are in constant demand, and they must work without
interruption. Many contractors expressed high regard for the distributors
and rental yards that supplied their pumping systems. Manufacturers
insist on the highest service standards from their own staff and
their distributors because most of the situations are genuine emergencies.
The Right Equipment
at the Right Time
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| Special
long-reach booms can improve the versatility of excavators in
projects where water is involved. |
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| Tracked
loaders have low ground pressure that enables them to work on
soft terrain and avoid damage to sensitive ground. |
In Massachusetts, a 96-in.
sewer and an 18-in. force main had to be relocated in a road construction
project, and the interstate had to be kept open and construction
access maintained to help build a new bridge pier. The main contractor
used Godwin pumps, 26 of the 12-in. DPC300 Dri-Prime models, with
almost 1.5 mi. of pipe. Eight of the same pumps helped authorities
in Philadelphia control up to 35 million gpd to complete sewer work
with no damage to historic and environmentally sensitive areas.
Similar to many others, Godwin pumps often are rented for emergency
situations; renting is a solution you should consider if your water
problem is not permanent or unlikely to be frequent. Contractors
who work in areas subject to regular but not frequent flooding also
rent the pumps. Godwin offers a Regional Re-rental Program that
gives distributors the opportunity to rent from Godwin at a discount
from national rental rates. Kieger Enterprises in Hugo, MN, is a
contractor working with the Federal Emergency Management Agency.
When the Mississippi crested at a dangerous level, Kieger needed
pumps immediately. "Because of the nature of their business, the
Kieger people expect an answer within five minutes," notes Dave
Lillquist, operations manager for Ziegler Rental, a Godwin distributor.
"We responded to calls from seven states," adds Pat Iwan, general
manager at Kieger Enterprises. "We had pumps on the road within
an hour of receiving them, thanks to the quick turnaround at Ziegler
and Godwin. It wasn't only the Mississippi that was giving trouble,
but the St. Croix, Red, and Minnesota too."
The right equipment for handling problems caused by water
might include an excavator. The Cobra Cutterhead, engineered and
manufactured by pump company Crisafulli, can have an excavator mounting
system that makes it a powerful solution for coping with water problems
where the water might be full of weeds and silt. This system has
been successful for smallish projects, such as golf course pond,
and for much bigger challenges. In Hawaii, at the Oahu National
Wildlife Refuge, there were severe problems with silt in the drinking-water
lagoons. It could build up to a depth of 30 ft., and because of
the disturbance caused by straightforward excavation, a method was
required that would be as effective but with much less disturbance
of the water supply. The Cobra Cutterhead on an excavator cut away
the mud bottom and discharged it through flexible pipeline, proving
to be an acceptable and affordable solution. Wetland Equipment Company,
based in Thibodaux, LA, was involved in that Hawaiian project and
has produced many amphibious undercarriages for similar work with
excavators. The low-ground-pressure, 100% amphibious excavator carrier
works with excavators from Kobelco, Volvo, Case, Caterpillar, Daewoo,
Hitachi, John Deere, Hyundai, Komatsu, Link-Belt, and New Holland.
Wetland Equipment also makes an amphibious backhoe carrier. "We
have our machines working in more than 30 countries," states Jim
Atkinson, general manager. "So far, however, we have not found anything
that will compare with our Louisiana coastal marsh, and we work
our machines in, out, and across that every day. We are tooling
up to provide 100% amphibious excavators and supply buggies for
a project along the coast here that may take 15 or 16 years to complete."
If water threatening your excavation or grading is more
mud than water, tracks can be more efficient than wheels. Some contractors
have tracks that they substitute for their standard wheels on such
machines as skid-steer loaders. In northern states, having tracks
for use on muddy or even icy ground has enabled contractors to extend
their working season into the late fall and winter. Tracks give
lower ground pressure and better traction. Bobcat offers tracks
for some of its machines, and ASV (a Cat affiliate) specializes
in the design and production of tracked loaders for soft ground
conditions.
Being Prepared
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| Crisafulli
has designed a cutterhead/pump system that mounts on an excavator
for dredging silts that are full of weeds or other plants. |
Prompt delivery and easy
setup apply to shoring protection too. One of the reasons that aluminum
hydraulic shoring seems to be more popular now than timber shoring
is that it is lightweight - often light enough to be installed by
one worker - and the installer does not have to be in an unprotected
trench to install the protection. Aluminum shoring is installed
from the top down, with the top hydraulic cylinder recommended to
be no more than 18 in. below the top of your excavation. There are
other regulations regarding the bottom of the cylinder and the number
of shores to be used. Manufacturers of shoring know these rules;
they might be your best source of information and advice.
Shielding is different from shoring. Shoring supports
the face of the trench; shielding protects workers by putting them
in a safe box. To prevent movement of the box, the space between
it and the wall of the excavation should be backfilled. "Protecting
workers is the main goal of shielding," asserts Diane Beckerman
of Comcore Utility Products in Falls Church, VA. "Shields are not
intended to support the trench walls you have excavated but to guard
the people inside against cave-ins." There are many types and brands
of shoring and shielding available. Comcore aims to provide equal
strength with less weight in its fiberglass composite products and
has designed a "Crossing Service shield" that comprises an array
of vertical and horizontal shoring panels to accommodate distribution
lines and crossing services, at random heights and angles, as well
as those other obstructions that always seem to exist in the trench
you need. Another helpful point for those who are excavating to
install pipe comes from Gordie Schmitt, who has years of experience
with Montana Dakota Utilities. "Make sure that the open end of the
pipe is out of any water. If water can't get into the pipe or what
the pipe contains, it won't cause future problems."
Water does not warn you when it is about to break into
your trench or excavated site. It arrives quietly, often in a seeping,
creeping mode, and holds its ground until you force it away. If
you know the soils in which you are working - are they Type A, B,
or C? - you can be prepared for problems. For Type C soils, water
invasion is much more likely. You can be prepared, too, by ensuring
that your workers know about the hazards of water at their work
sites. The training required is neither lengthy nor complicated.
An excavator operator need not be a soils engineer, and an installer
of utilities in trenches need not be a professor of hydraulics,
but everybody should know what can happen, what to do if something
dangerous does happen, and how to make the job site safe for themselves
and their colleagues. It's a training program that is simple; you
yourself can probably be the teacher. As with all simple programs,
it is easy to neglect or assume that everybody knows all the answers
without your checking.
We
must have water. Most construction work requires water at some stage,
for some technique of the project, for jobs as diverse as mixing
concrete or cleaning tools and equipment. When it is creeping, seeping,
or gushing where we don't want it, it becomes a problem. Good preparation
will avoid damage and delay from water for most excavation and grading
work. If one piece of advice was much more popular than any other
from the contractors with whom we spoke, it was know the soils where
you are going to work before you start the work.
Frequent contributor
Paul Hull writes on construction and environmental topics for several
international magazines.
GEC
- May/June 2003
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