dirt-nerd
Geotechnical
- Feb 12, 2023
- 5
I'm not interested in calculating the liquefaction induced settlement in each liquefiable layer. My interest is in predicting/estimating how much that cumulative settlement will be manifested at the surface. Intuition tells me that some of the non-liquefiable material (or crust) will bridge over the settlement or absorb some of the settlement in increased volume in said layer. That would result in less settlement at the ground surface (or BOF elevation) than the cumulative amount in each liquefiable layer. However, I'm struggling with reasonably estimating this.
Ishihara (1985) seems to intend for “surface manifestation” to refer to sand boils, ground fissures, etc. and for “surface manifestation” to not refer to ground surface settlement. Essentially, no surface manifestation =/= no ground surface settlement.
Rateria (2021) expanded on Ishihara’s model with thousands of data points from recent New Zealand earthquakes; this paper states:
Here, Rateria seems to reiterate that the H1-H2 model is not applicable to ground surface settlement but rather the H1-H2 model is intended to predict surface manifestation (sand boils, ground fissures, ejecta, etc.). However, later in the document, it states:
The way geotechnical engineers use the H1-H2 seems to be inconsistent. I've seen some not use this method to reduce the settlement at ground surface and seen others use this method to reduce the settlement at the ground surface.
How do people employ the H1-H2 model and how do you estimate the reduction in settlement at the ground surface from the cumulative settlement from each liquefiable layer? Interpret the H1-H2 model as exclude ground surface settlement if the H1-H2 model shows no surface manifestation? Or that you cannot use the H1-H2 model to predict ground surface settlement? Are there other methods that are better or clear standard of practice? I'm familiar with a Bray (2017) method to estimate liquefaction-induced building settlement but I've never seen it been used in practice.
Thank you in advance.
Ishihara (1985) seems to intend for “surface manifestation” to refer to sand boils, ground fissures, etc. and for “surface manifestation” to not refer to ground surface settlement. Essentially, no surface manifestation =/= no ground surface settlement.
Rateria (2021) expanded on Ishihara’s model with thousands of data points from recent New Zealand earthquakes; this paper states:
…placed emphasis on compiling case histories from free-field level-ground sites, with the occurrence and severity of liquefaction defined primarily by liquefaction ejecta and ground cracking. Sites with other indications of liquefaction, such as foundation settlements or evidence from ground motions, were not considered. The definition of ‘‘surface manifestation” adopted herein is thus generally consistent with that used by Ishihara (1985) to develop the H1–H2 model.
Here, Rateria seems to reiterate that the H1-H2 model is not applicable to ground surface settlement but rather the H1-H2 model is intended to predict surface manifestation (sand boils, ground fissures, ejecta, etc.). However, later in the document, it states:
It should be emphasized that ‘‘surface manifestation” – the prediction target of the analyses presented herein – refers to free field surface ejecta, settlement, and cracking on ground that is generally level, consistent with the definition adopted by Ishihara (1985).
The way geotechnical engineers use the H1-H2 seems to be inconsistent. I've seen some not use this method to reduce the settlement at ground surface and seen others use this method to reduce the settlement at the ground surface.
How do people employ the H1-H2 model and how do you estimate the reduction in settlement at the ground surface from the cumulative settlement from each liquefiable layer? Interpret the H1-H2 model as exclude ground surface settlement if the H1-H2 model shows no surface manifestation? Or that you cannot use the H1-H2 model to predict ground surface settlement? Are there other methods that are better or clear standard of practice? I'm familiar with a Bray (2017) method to estimate liquefaction-induced building settlement but I've never seen it been used in practice.
Thank you in advance.
