Integrated Buildings & Structures

Hi Everyone,

I am currently working on a foundation (a single CIDH) design under liquefaction and spreading for a railroad bridge project. The design PGA is very low, less than 0.1g. Do you have experience or reference on how much is liquefaction triggered due to the low PGA? It seems ODOT does not require liquefaction analysis if a PGA is less than 0.1g.

 

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Lee Keun Ph.D., P.E., M.ASCE
JACOBS
Denver CO
(720)934-3151
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Caveat: I am a student who has taken one *single* class on liquefaction and settlement analysis.  What I am about to say may be super-basic knowledge you already have, or it may be incorrect.

Lateral displacement and settlement are factors of 1) soil type, 2) effective intergranular stress, 3) EQ magnitude, and 4) PGA.  If I plug some numbers into my handy spreadsheet created using "Soil Liquefaction During Earthquakes" (Idriss & Boulanger, 2008), I see that a M9.0 EQ at 0.1 PGA can cause significant liquefaction effects if the soil (sand) is weak.  Failure is dependent upon the number of loading cycles as well as the peak value of each cycle.

Short answer: talk to a geotech in your area...

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Kathleen Mitchell
Student Member, ASCE
Portland, OR
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Thanks for sharing your thought. Our geotech is figuring out an extent of liquefaction impact. She mentioned liquefaction extent for higher and lower PGAs is not much different. I am thinking there will be some difference on residual strength though.  

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Lee Keun Ph.D., P.E., M.ASCE
JACOBS
Denver CO
(720)934-3151
------------------------------

Original Message:
Sent: 02-24-2017 12:41
From: Kathleen Mitchell
Subject: Liquefaction induced by low PGA

Caveat: I am a student who has taken one *single* class on liquefaction and settlement analysis.  What I am about to say may be super-basic knowledge you already have, or it may be incorrect.

Lateral displacement and settlement are factors of 1) soil type, 2) effective intergranular stress, 3) EQ magnitude, and 4) PGA.  If I plug some numbers into my handy spreadsheet created using "Soil Liquefaction During Earthquakes" (Idriss & Boulanger, 2008), I see that a M9.0 EQ at 0.1 PGA can cause significant liquefaction effects if the soil (sand) is weak.  Failure is dependent upon the number of loading cycles as well as the peak value of each cycle.

Short answer: talk to a geotech in your area...

------------------------------
Kathleen Mitchell
Student Member, ASCE
Portland, OR
------------------------------