FEATURE
The most stringent standard
restrictions on in-water pile
installations are in the current
it was noted that these same criteria will be added as a special
condition of the federal permit in other New England states if
the project site has potential for underwater noise issues, even
though it is not listed in the state General Permit conditions.
For smaller scale projects that can utilize timber piles, this
is not a major concern and underwater noise monitoring has
indicated noise levels are significantly below the regulatory limits.
The use of timber cushions with steel piles is not practical
as the cushion is unlikely to survive more than one blow. The
use of vibratory hammers can often be used for pile installation,
however, an impact hammer is necessary to finish pile driving
and establish a proven pile capacity. This was noted in the 2009
California DOT study, along with a risk of higher SEL values
from continuous use of a vibratory hammer. However, that was
not incorporated into the regulatory standards.
Higher capacity driven piles are still possible through permitting
with a full individual permit with the federal agencies if
the noise thresholds can be met at a given site or noise attenuating
methods are utilized, such as air bubble curtains, dewatered
surrounding casings or cofferdams. The air bubble curtain
method was attempted on a project in Maine with poor results
and issues that included the bubbles being swept away by the
current, sediment turbidity creation, a large compressor being
too small and some oil sheen in the water from the compressor
internal lubrication.
Pile driving noise was recently monitored for the temporary
construction access trestles on the Sarah Long Bridge replacement
project between Maine and New Hampshire4. This construction
access trestle was founded on 30-inch diameter driven
steel pipe piles using a diesel hammer selected with a heavy
hammer, but operated a low stroke (seven feet) which kept all
noise observations below the regulatory thresholds. This finding
was emphasized in the study as the existing general permit
conditions attempt to limit pile hammer weight, likely due to
a lack of understanding by regulators about driving piles to a
specified capacity.
On recent large bridge projects, both Maine DOT and New
Hampshire DOT have reacted to the underwater pile driving
noise requirements by designing the bridge foundations to use
eight to 10-foot diameter caissons drilled deep into the bedrock.
The regional regulatory agencies in Maine and New Hampshire
do not currently have underwater noise standards for drilled
caissons, however, the European studies are monitoring and
regulating this noise, and there are concerns the continuous and
prolonged nature of this noise is a significant issue with fish and
marine mammals.
VTL
Vertical Travel Leads
Precision Placement
Long Piles or Large Batters
Piling or Drilling
Rental or Purchase
600 Ferguson Avenue North
Hamilton, Ontario, Canada L8L 4Z9
Tel: 1.905.528.7924 Fax: 1.905.528.6187
Toll Free: 1.800.668.9432 (in Canada and USA)
www.berminghammer.com
Email: bfssales@berminghammer.com
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Maine General Permit.
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