Vibration question

[kxa]

What is a good resource/reference for diesel engine vibration. I am investigating the effects on pile supported residential house. What are the noise lvibration frequency.

 

[a2mfk]

We have this book in our office and its pretty comprehensive, though not sure if it has specific reference to diesel engines there are lots of different types of construction equipment that are addressed.

Construction Vibrations (2nd ed) [Hardcover]
Charles H. Dowding (Author)

 

[Ron]

kxa...agree with a2mfk that Dowding's book is a good reference. The California Department of Transportation (CALTRANS) also has some good info in its publication, Technical Advisory TAV-02-01-R601 "Transportation Related Earthborne Vibrations" as well as the US Federal Transit Administration "Transit Noise and Vibration Impact Assessment" dated May 2006.

A diesel engine obviously produces vibration, but its affect on structures is dictated by how the vibration is transmitted. For a diesel engine running on rubber tires (truck, tractor, front-end loader, etc.), the vibration is significantly attenuated even before it goes into the ground for lateral transmission. If the diesel engine is running in something with a more direct ground transfer, the effect is quite a bit greater (diesel locomotive, tracked construction equipment, etc.)

We recently measured the vibration produced by a diesel locomotive at various distances from the source. At about 80 feet from the source, the vibration was about 0.043 in/sec or about twice the perception range...in short, you could feel the vibration, but it wasn't enough to damage a structure, even a very sensitive structure such as a historical building. (soil conditions were generally loose to medium dense fine sands and silty fine sands)

Buildings bearing on pile foundations are generally less susceptible to vibrations than those that are bearing directly on the ground.

I have attached the CALTRANS document for your use.
I have also attached a conference paper done by Amick and Gendreau in 2000.

 

[Ron]

Well...here's the CALTRANS document...it didn't go the first attempt....

 

[kxa]

Thanks Ron for the information and the link. The investigation is related to a power plant generator and the possible effects on the houses nearby that are supported on timber piles.

I read long time ago that low frequency vibration and noise can cause damage. The vibration could also reduce the skin friction between the soil and the piles resulting in settlement. I also thought that I came across an article that said vibration can increase the soil density and hence increase the friction. Maybe both events can occur and maybe in the order I just mentioned as long as we won’t have liquefaction.

 

[Ron]

Liquifaction is not likely. The other issues you mentioned can and do occur in the presence of vibration.

Low frequency noise and vibration can cause damage, depending on the natural frequency of the structure and the amplitude of the noise/vibration. If you think of it, thunder is a low frequency noise/vibration. It doesn't often cause structural damage, but it could.

The stationary generator would be somewhat like a diesel locomotive sitting on a side track and idling. That is exactly one of the conditions we tested for a court case last year. While vibration can cause compaction in sandy soils, the moisture conditions would have to be close to optimum for even a small increase in compaction under the loads imposed by a structure. Since vibration attenuates rather well in sands, loss of skin friction is not, in my opinion, a big concern.

I would suggest that you measure the vibrations with distance from the generator while running and while not running. This will give you hard data that is defensible.

 

[kxa]

If ground vibration can result in reducing the coefficient of external friction of soil, the skin friction can also be Reduced allowing some slippage. Anyway, this house is by the bay with ground water 10' below. Soil is sandy. There are large settlement cracks and the case is in court.

 

[Ron]

It would be better if you could get some hard data. With the data, you can predict the vibrations that the piles and structure would feel. Further, with a few soil test borings, you could get some hard data for better prediction of both the vibrations and the settlement issues.

The settlement might have nothing to do with vibration. It could simply be poor design of the foundation system.

Is the structural damage greater on the side of the vibration source? Is there a clear differential settlement condition across the structure? How old is the structure and how old are the cracks? How long has the vibration source been there? Is it an intermittent operating generator or does it run full time? What is the mass of the generator foundation?

 

[a2mfk]

Ron is giving you some great advice. There are two types of damage related to vibration that you are discussing that are important to separate: direct vibration damage to a structure, and subsidence that may be indirectly or directly related to vibration activities.

You will find that research and case studies have shown that humans perceive vibrations at very low levels. I can tell you when a big truck rolls by our office for example. And research has shown this (mostly with mine blasting effects on residential structures), and that book drives that point home. The ground may vibrate, windows may rattle, dishes may shake, etc. but at these levels they rarely are responsible for even cosmetic damage.

Completely agree with Ron, you will have to do on-site testing for the actual vibration level. And it sounds like its not such a simple problem since you have timber piles which means you had some bad soils to research also. If you don't have a geotech or geologist then I would get one involved in this case with you, and I would think you will want some deep SPTs to find out what the exact soil composition is at the site. This whole subject is its own field and there are some experts out there, so you want your ducks in a row...