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Dear Brian,
At AES it is our desire to keep our valued clients
and associates informed with up to date environmental, geologic,
remediation, land development, energy conservation and other useful
information. We hope you find this newsletter helpful, and we
look forward to hearing from you soon.
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The
Importance of Geotechnical Studies
By
Elizabeth Cushman
Preliminary geotechnical studies play a crucial role in all
land development projects. The need to investigate the
engineering properties of subsurface materials is of key
importance before any construction work takes place, and the
failure to carry out adequate geotechnical investigations can
have expensive consequences on development projects. It is
recommended that builders and designers consult the findings of
a geotechnical study and take into account recommended design
requirements and identified potential problems. Adjusting
construction plans to suit the characteristics of the
underlying soil and geologic formations can eliminate any
related problems and the liabilities that can arise with them.
Generally, the cost of a proper geotechnical study is
insignificant when compared to the cost of foundation repair.
A typical geotechnical engineering project evaluates the
subsurface conditions at the site and provides recommendations
regarding the design of foundations and earthwork for the
development project. The study begins with a review of project
needs and preliminary construction plans to define the required
material properties, followed by four major tasks:
- Subsurface
Exploration
- Soil Laboratory
Testing
- Site
Reconnaissance and Field Engineering
- Geotechnical
Engineering Study
Subsurface exploration involves the advancement of a number of
test borings in the area of the proposed construction. The
boring depths may vary depending on subsurface conditions
encountered. Data collected from the test borings is included
in the site investigation of soil, bedrock, fault distribution
and bedrock properties on and below an area of interest to
determine their engineering properties.
A detailed site reconnaissance is typically performed by a
geotechnical engineer to identify conditions influencing
construction. The engineer will also document and compile all
field information along with the test boring logs, containing
descriptions of the major soil strata encountered and measured
groundwater elevations. Site investigations are needed to gain
an understanding of the area in or on which the engineering
will take place, and can include the assessment of the risk to
humans, property and the environment from natural hazards such
as earthquakes, landslides, sinkholes, soil liquefaction,
debris flows and rock falls.
Following the completion of test borings, a limited laboratory
analysis may be performed to determine engineering properties
of the site's underlying soils pertinent to evaluating the
load-carrying capabilities and stability of the proposed
foundation, and in some cases, soil is evaluated for stormwater
drainage systems. The soil conditions may play an important
role in determining both the viability and type of foundation
and/or stormwater drainage system best suited for the site,
which will be known only after the site-specific geotechnical
report is available. Because this information may not be
available in the initial preliminary design phase, it is
important to evaluate the new data as the project progresses.
The finalized geotechnical engineering study includes the evaluation
of boring, geological, soil test, and related structural data
to develop foundation requirements for support of the proposed
construction, including a recommended allowable soil bearing
pressure, bearing grades and estimated total and differential settlements
for shallow spread footings. Estimated subsurface conditions,
including groundwater levels in the area of concern are also
included, as well as recommendations for floor slab support,
lateral earth pressures, subdrainage, and backfill requirements
for retaining walls. A discussion of pertinent design and
construction considerations, including requirements for
foundation installation, the need for and the methods of rock
removal, parameters for earthwork and compaction, and any
geotechnical engineering services necessary during construction
are also provided with the geotechnical study.
It is extremely valuable for builders and designers of any
construction project to include a geotechnical study in their
project schedule, and to take the information and
recommendations into consideration during further planning
stages, as well as during construction, in order to prevent
costly consequences and liabilities.
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The
Methods of Geotechnical Evaluation
By
Bridget Shadler
If the land you are developing is underlain by karst geology,
there are many different methods that can be utilized to
determine how likely these issues are to arise. Initially, a
desktop study should be performed, which consists of the review
of karst geology literature and maps, aerial photographs, along
with a site reconnaissance. However, this may only provide you
a cursory view of your site. Geophysical and geotechnical
surveys will help to provide valuable information regarding
karst features and necessary engineering data.
Geophysical surveys are non-intrusive and typically less
expensive. There are multiple geophysical surveys that can be
completed to help determine the location and extent of karst
features on your property. Ground penetrating radar (GPR),
electrical resistivity (ER), and electromagnetic (EM) are all
appropriate and popular methods for karst environment surveys.
Ground penetrating radar uses a high frequency radio
signal that is transmitted into the ground where it reflects
and returns to a receiver where the data is stored. A computer
will measure the time it takes for a pulse to travel to and
from its' reflection point which will indicate its' location
and depth. GPR is best applied in dry and sandy soils. Although
it will work in clay based soils, the depth the radar can
penetrate will be limited.
Electrical resistivity is a method that introduces a
current into the ground surface by a pair of surface
electrodes. The resistivity can then be calculated from the
electrode separation, applied current, and the measure voltage.
This method works well with clays and other soil types that are
conducive to electrical currents. Sandy soils typically produce
such high resistivity values that the data cannot be used.
Lastly, Electromagnetic surveys use the principle of
induction to measure the electrical conductivity of the
subsurface. EM units contain two sets of coils which will
determine the depth of penetration. One set of coils will
transmit a magnetic field which will induce a secondary current
in the subsurface while the second set of coils will receive
the magnetic field and log the information.
The potential negative effects of karst features are frequently
overlooked; however, these environments can often cause
expensive damages that could have been foreseen or prevented
with the completion of a geophysical investigation.
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Early
Misconceptions About Groundwater
By Peter
Voci
Prior to my life as a Project Scientist for Alternative
Environmental Solutions, I was an 8th grade science teacher.
One of the units that I taught focused on groundwater
contamination, and the topic began with a group discussion on
what the class "knew" regarding groundwater: What is
it? How does it get there? What happens to it? and How do we
get it back? I led the discussion with some of those questions.
One thing that was strikingly obvious to me as my students
listed what they "knew" about our groundwater supply
was the number of the misconceptions that they held. Consequently,
if school-age children are never taught the truth about this
subject, then how many adults will continue to carry these
misunderstandings with them throughout their life because they
never learned what is actually true about our groundwater
supply?
Above all, the biggest misconception that my students held was
that the water located underneath the surface of the Earth
flows in rivers. While it is true that a fraction of the
groundwater flows in channels, the vast majority of it either
moves between the small spaces located between the soil
particles or through fractures found between layers of rock.
Another common misconception is that once in the ground, the
water located there is lost to us, never able to be used again.
I quickly learned that because my students lived most of their
lives in an urban environment, where water simply flows out of
a faucet, there is little reason for them to understand how
water supply wells are dug and constructed and how, literally
millions of people throughout the world obtain their water used
for drinking, cooking, and bathing from groundwater collected
by a well. It seemed that my students thought the water that
ran into their houses or other buildings they occupied
originated from somewhere other than the ground. Some students
even seemed to be bothered by the idea that people would
actually put water into their mouths that came from the ground.
A large challenge in teaching students about groundwater was
how it is part a huge, Earth-wide system that moves water
around the planet, either called The Water Cycle or the
Hydrogeologic Cycle. The total amount of water, located on the
surface and underground, remains constant, and the only thing
that changes are the individual amounts found in different
locations. In protest of this fact, my students would exclaim,
"But there is a drought in Kansas!" for example, and
they would fail to realize that because there is a lack of
water in one location that does not mean the total supply of
water found on the planet has decreased.
Groundwater is a precious resource, proven by the effects of
pollution, contamination, and its scarcity in some areas. A
lack of usable groundwater can reduce crop yields and thus,
will raise the price of those crops because of a reduced
supply. It is acceptable that young people, who have never been
taught the truth about a certain subject, may hold many
misconceptions regarding groundwater but, that begs the
question, "How many adults hold the same misconceptions
and do these misconceptions affect their beliefs and decision
making with respect to public policy?"
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Seeking
Employment?
By Brian J. Beahan, P.G., President
We are always looking for qualified professionals to join our
team. We appreciate your referrals of business and now are seeking
your referrals for qualified environmental and geologic
consulting professionals. If you know of anyone who is seeking
a change and a challenging new direction in their career, where
creativity and solutions-oriented thinking really make a
difference, please pass on our contact information.
Find out more....
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Our customers have approached us with problems,
we've understood what needed to be done and we've provided
appropriate solutions. Our mission statement, indeed our company
as a whole, is centered on meeting this objective. May we put our
quality, client-centered environmental solutions to work for you
too?
On behalf of the staff of Alternative Environmental
Solutions, Inc., I invite you to experience the value we add to
your business.
Sincerely,
Brian J. Beahan
Alternative Environmental Solutions
email: aes1@altenv.com
phone: 717-517-5000
fax: 717-517-5004
web: http://www.altenv.com
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