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Seismic Ground Response Parameters

  1. Apr 6, 2016 #1
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    Hey guys, recently I have do some self-study on the ground response parameters on cohesive and cohesionless soil.. I made some deduction but I cannot confirm if it is correct or not, thus needing the help from the PF community. The deduction is as follows;

    I need explanation for the occurrence of this phenomena..
    (1) As the thickness of the soil increases, the frequency will decrease. Why?
    (2) Amplification is higher in less dense/cohesive soil (e.g clay) than denser soil thus making cohesive soil to have a lower shear wave velocity, Vs. Why?
    (3) As thickness of the soil increases, the shear wave velocity will also increase. Why?
    (4) How does grain size affects the shear wave velocity?
    (5) How does density affect the shear wave velocity?
    (6) From the image, we can see that sand produce a steady amplification, and that amplification on clay is getting bigger and bigger..Why?

    Thanks for your help! If any statement is wrong above, please do let me know, thanks! :D
     

    Attached Files:

  2. jcsd
  3. Apr 13, 2016 #2
    Hello, let me start by saying I am not a soil guy, but have done some seismic work.
    On number (1) are you talking about the aggregate density of the soil?
    Also sound waves in mediums attenuate not amplify.
    From what I have seen, all soil types have a frequency that they will go plastic.
    I have heard this called the modulus of elasticity, and I think is defined by Young's modulus.
    http://www.geotechdata.info/parameter/soil-young's-modulus.html
    Vibroseis trucks generally sweep from 0 to about 110 hz,
    I had to find a video with the camera on a tripod to show you what I am talking about.

    At about the 38 second mark they pass the frequency where the greatest energy passes
    in that weathering layer. At that point the ground is going plastic under the tripod, so the tripod vibrates.
    Every combination of soil will have it's own frequency, but they all fall into that band.
    I understand that the attenuation above 110 hz in most soil types is greater than 3 db per octave.
    Within the very limited range of frequencies, many of the standard wave equations apply,
    except that "c" is the speed of sound in that medium.
    I hope this helps some!
     
  4. Apr 18, 2016 #3

    NascentOxygen

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    Staff: Mentor

    Homework-type exercise, requiring more member input than shown in opening post.

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