Liquefaction risks 1

[YandoGinger]

I am designing a school which is expected to be built very close to the sea-----the soil there is predominantly sandy, with a water table about 1 meter below ground level---what options do I have in terms of foundation design, recent constructions near by had raft foundations---does this help the situation?

 

[dik]

Check with your Geotekkie... it should not likely be an issue... and, raft foundations work very well.

If it were something like the Millenium Tower in SanFran... I'd be a bit more concerned.

Dik

 

[YandoGinger]

Thanks

 

[YandoGinger]

What if the site lies within an earthquake zone, exposed to potential liquefaction?

 

[EireChch]

If liquefaction is an issue then you need to undertaken a liquefaction assessment.

I would follow the below statement (which i copied and pasted from the link:

https://www.dot.ny.gov/divisions/en...es/technical-services-repository/GDP-9b.pdf).

You kind of sound like you already have concluded that liquefaction is an issue.

A method for constructing liquefaction potential maps was developed by Youd and Perkins (1978), relating geological age, origin of sediments and site distance to the potential earthquake epicenter. The proposed criteria are widely used for general assessment of regional liquefaction hazards

You should then undertake a liquefaction analysis, using SPT or CPT data and your design Peak Ground Acceleration (it was 0.35g for ULS case in NZ from memory). There are a number of methods available from Robertson, Idris and Boulanger etc. for liquefaction analysis.

You will then determine an amount of liquefaction induced settlement. Depending on how large it is, a raft may be fine or you may need to pile, excavate and replace, ground improve etc. All depends.

 

[dik]

With a high water table and a sandy soil (low cohesiveness) liquifaction is a real possibility and your Geotekkie should be able to provide you with the info you require.

Dik

 

[YandoGinger]

Thanks All

 

[Okiryu]

Is the sand dense or loose? What are the blow counts?

Also, near to the sea? if liquefaction is an issue, then lateral spreading should be considered as well.

If this is a new school, perhaps the playgrounds can be close to the seawall while the building can be more "inland". This may alleviate the lateral spreading issues (if you really have it).

Is this a seismic zone? any historical liquefaction issues in previous earthquakes?

 

[fattdad]

blow counts, soil classification, Seed and Idriss come to mind.

Just need longitude and latitude.

f-d

ípapß gordo ainÆt no madre flaca!

 

[BigH]

Just to keep in mind - building that close to the sea - you may need to have a system in place so that potential scour of the beach during an ungodly storm doesn't undermine your foundations. Atlantic City NJ comes to mind as to a coded depth of foundation - usually built with an underground wall - but can't remember the details off the top of my head.