VAI ALLA PRIMA PAGINA


	------------------------------

I do not disagree with Dr Muller's general discussion on wave impact
induced vibrations, but on one aspect I must make a correction.

The Admiralty Breakwater at Alderney is indeed generally founded on a
rubble mound, larger towards the outer end, but there are two places
where it crosses rock outcrops, especially along the landward side.
These points have been termed the 'hinges', and were of particular
interest to the team led by Coode & Partners in the early 1990s when
they analysed long-term movements of the breakwater wall. If I recall
correctly, most upward or downward movements of the wall occurred either
side of these 'hinges'.

I therefore conclude that there probably is less damping or dynamic
de-coupling than Dr Muller suspects, at least at those points. Coupled
with the propensity of this breakwater to attract violent wave impacts,
it is not surprising that the last major failure of the breakwater wall
was reported as being heard across the island.

with best regards,

N. William H. Allsop
Technical Director, Maritime Structures
HR Wallingford
Howbery Park
Wallingford, OX10 8BA
Tel: +44 (0)1491 82 22 30
Fax: +44 (0)1491 83 22 33

-----------------------------

Dear Prof. Carratelli,

Been a structural engineer as well as a coastal one, thought that your problem is very interesting.

I have never experienced something like that. Due to the fact that you feel the vibrations (that is to say they are in the human perception spectrum), suggests that they are of periods of the order of sub-second. This is somehow large period compared to solid rock periods (not the seismic waves). So, I think there might be some cavity(s) somewhere underneath the nearby housing area, which due to fluxuating water pressures (as well as due to nearby breaking wave dynamics), through which the pressure waves are transmitted to the above soil layers. The exact geology of the region in 3-dimensional space might give the answer to the mobility of the strata. That might be potentially dangerous. All depends on the strata thicknesses, the materials involved, the water table, the easiness of water movement below (probably like a piston up and down), forcing the strata to vibrate.

I hope that might be an idea of the phenomenon's mechanics. I shall be very interested to hear other ideas as well.

We have been working on the seismic signature of surf. There are several mechanisms for generating seismic vibrations from waves. The vibrations experiences there may be caused directly by the breaking waves or they could be caused by long-period, standing waves further from shore. In either case the water table is likely to play an important role in the vibrations being felt on land. Do the foundations of these buildings penetrate the water table? Is the foundation substrate consolidated or unconsolidated?

I would like to learn more about this situation and I’d be delighted to help if I can. Had you gotten other responses?

> > Prof. Ing. Eugenio Pugliese Carratelli
> >
> > A few years ago I was retained by a city here in Canada to investigate and
> > remediate a similar situation.
> >
> > We set up a monitoring/data collection program and confirmed that in
> > fact there
> > was a direct correlation between vibrations experienced in nearby
> residences
> > and the occurence of storm waves and their breaking on the shoreline. The
> > problem was successfully resolved with some innovative coastal
> > engineering and
> > everyone is very satisfied with the results.
> >
> > I don't know if the setting and metocean conditions are the same as yours
> but
> > they sound similar.
> >
> > At the moment I am offshore and have limited comms. I would be pleased to
> > provide more information on my return to terra firma sometime in November.
> >
> > Best Regards
> > John Readshaw, P. Eng.
> > Manager, Coastal and Ocean Engineering.
John Readshaw <jreadshaw@sandwell.com>:

> John,
> yours is the most interesting (and intriguing) answer I got so far; I
> do not have time to conduct a proper investigation so the only option
> I was thinking of was to reduce the impact itself by
> A)locating a(submerged ) wave barrier as far as possible from the
> shoreline and B) byreconstructing the beach with the mildest possible
> slope.
> can you advice me about other possibilities, even before you go back
> ashore? (By the way, where are you??)
> Thank you, and best regards
> eugenio

I am currently offshore on the Sea of Okhotsk.

The situation I was describing was caused largely by the construction of a
small, approximately 2 m high, stepped concrete seawall - this overlaid on an
80 year old recurved seawall that had worked without a problem for many years.

Beach erosion had also been a problem over the last 20 years.

We eventually constructed a gravel - rock headland beach system after a full
scale test program (Phase 1) and a physical model test program to design Phase
2.

The gravel beach has developed into a very popular recreational feature for the
City. Now the biggest problem is a lack of parking in the area!

Best Regards
John

------------------------------

"Goshow, Christopher" <cgoshow@islandglobalyachting.com>:

> Is the area in a diffracted zone? Are the wave heights and periods
> rather large during the storms? Without getting into the technical
> details, I would first think a clean diffracted (swell-like) wave
> propagating at a nearly constant wave period would generate such a
> phenomenon at breaking. I have experienced this rhythmic "thumping"
> when I lived on the beach in Florida. Summertime swell would always be
> very clean small waves breaking on a steep beach. So rhythmic that it
> would keep me awake!
>
> Sounds like something above interacting with the ground water table
> could cause a shock effect??
>
>
>
> Christopher K. Goshow, P.E.
>
> Island Global Yachting
>
> Shatha Tower 40th Floor, Office 4002
>
> P.O. Box 211592, Dubai, UAE
>
> Tel: +971-4-363-1500
>
> Fax: +971-4-368-8218
>
> Mob: +971-50-451-6405
>
> www.islandglobalyachting.com <http://www.islandglobalyachting.com>

Chris,

In other words, waves are noisy... What I wonder, when and why does
this noise turn into proper shocks? It is probably due to the impact
on the vertical wall at the end of the beach, or on the subaerial
beach itself. And the water table may or may not have to do with the
transmission of the shock itself. Unfotunately we don't have time to
conduct a proper investigation so the only option is probably to
reduce the impact itself by A) locating the (submarged ) wave barrier
as far as possible from the shoreline and B) by reconstructing the
beach with the mildest possible slope. Do you have any experience or
idea?
Best regards
Eugenio

------------------------------

>

I work in a building in New Orleans that is perhaps 20-25 metes from a railroad track that carries slow moving freight trains. When ever a train passes, there is considerable vibration in the building. I have attributed this to the soils – mostly silts and clays with a high water content. Our building is pile supported.

Perhaps there are fine soils with a high water content underneath the sand beach and the pounding of the waves is thus transmitted to the foundation of the apartment buildings close to the beach.

Please include me with any interesting responses.

thanks

Winer, Harley S MVN

Harley S.Winer, Ph.D, P.E.

Chief, Coastal Engineering Section

New Orleans District, Corps of Engineers

(504) 862-2454

Harley.S.Winer@mvn02.usace.army.mil

------------------------------

Dear Eugenio,

I saw an article in the new scientist which might be of interest and may give you some leads. The article talked about a seismic hum generated by waves hitting the shoreline during hurricane Katrina. These waves were felt nearly 3000 kilometres away in southern California. The link below should take you to the the article.

http://www.newscientist.com/channel/earth/dn10140-hurricane-katrinas-waves-felt-in-california.html

A colleague tells me there was a prof. in Australia who was investigating the phenomena 10 years ago, but my colleague can not remember the prof. name.

Regards,

John

j.alderson@hrwallingford.co.uk

------------------------------

Harley S.Winer, Ph.D, P.E.

Chief, Coastal Engineering Section

New Orleans District, Corps of Engineers

(504) 862-2454

------------------------------

Prof, My research into causes of beach erosion along the

North Carolina, USA coastline suggests that the Buildings

themselves collect the rain, particularly during strong winds

on the sides of the buildings and concentrate the storm water

under the foundations. this elevates the Beach water table

exit point resulting in erosion during a falling tide. During a

Hurricane, with 15-20 ft waves, you can feel the waves over

a mile inland. Of considerable interest to me is the presence

of standing waves within the Surf Zone, waves reflected off

the beach interact with incoming waves and form very large

standing waves, but they don't "Break" they collapse.

Its important also, that any other source of water, such as

Septic Tanks, will also contribute to the Erosion.

By comparing uninhabited Islands with inhabited islands

that were subjected to the same Storms, it became apparent

that the cause of our beach erosion is an elevated beach

water table due to the Buildings on the nearshore.

I would be pleased to share our research with you if interested

rsp DB

Prof, I forgot to reply to your most important question, " does it

lead to a particular choice of breakwater?" Yes Sir, I believe that

it suggests that a breakwater might not be the solution, Wave

Run-up may be "pumping up" the beach, but its more likely that

the elevated water table is caused ashore. Rsp, Denny

Dennison Breese

seadozer@starfishnet.com

Dear Prof. Ing. Eugenio Pugliese Carratelli,

Did you check the geological maps of the area?

Did this happen before (did you check past history of
the area)?

What material is between the foundations of the
buildings and the shore?

Check how the foundations made?

Sand is not such strong material, therefore there will
be an erosion as you said probably much more if there
were gravel at these location. Therefore, there is a
case that the material of the area to be collapsed
(the beach to be eroded and the water to come further
to the land). In this case, maybe the distance between
the foundations of the buildings that the the people
living and the shore to be decreased. Consequently,
the force that generating by the waves will have an
impact on the foundations of the buildings.

AS far as the type of breakwaters to be used, the
submerged breakwaters and especially contained by
gravel or reef will be have great impact at the storm
waves and especially if there are long. However, you
must find first the root of the problem and then
decide if you need to use breakwaters or not, because
instead to do something good maybe will make it worst.

I hope my proposals to be helpful. Please, inform me
if you find the problem and the solution of your
problem.

Kind Regards,

Christos

christos antoniadis <feugatos1@yahoo.com>

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Data: Tue, 24 Oct 2006 15:38:33 -0700
Da: "Moritz, Heidi P NWP" <Heidi.P.Moritz@nwp01.usace.army.mil>
Rispondi-A:"Moritz, Heidi P NWP" <Heidi.P.Moritz@nwp01.usace.army.mil>

I am sure that there is someone at OSU or who used to work there who knows
more about this interesting data collection system than I do. However, I did
include the microseismometer data that Dr. Miller refers to below in an
extremal analysis of wave heights along the Oregon Coast. Period of record
for the mircroseismometer gage at that time was 1971 to 2000. Water depth
(approximate) of measurement was 20 m, calibrated to deep water. For the
period of analysis used in my study (1991 to 2000) the seismometer gage
recorded 15 events with a wave height greater than 6m, compared to 55 to 121
events measured by the NDBC buoys. The data measured may have interesting
applications for a variety of purposes, however, it was determined that the
microseismometer gage did not record a sufficient number of significant
storms to be representative of the extremal wave climate.

Heidi Moritz, P.E.

Coastal Engineer U.S. Army Corps of Engineers Portland District (CENWP-EC-HY)

P.O. Box 2946 Portland, OR 97208 (503)808-4893

IS THERE A WAY TO DESIGN BREAKWATERS - SUBMERGED OR NOT - IN ORDER TO MINIMIZE VIBRATIONS IS SUCH A SITUATION? I HAVE THE FEELING THAT

B) THEY SHOULD BE LONG RATHER THAN SHALLOW. I.E., KEEP THEM DEEP WITH A LONG BERM

I WILL BE GLAD TO RECEIVE AND POST ANY OTHER COMMENT, EITHER THROUGH THE COASTAL LIST OR DIRECTLY TO EPC@UNISA.IT

Scott Mackenzie -San Francisco 1967