I want to ask you how to classify this site for seismic design ?

[Chunil]

How can you classify this site for seismic desing?
This is the profile of vertical shaft excavation for "Power outlet".
The basement is embedded in hard rock.
This structure can be designed as site class "A" ?
I think this structure is seated on Hard Rock and then can be classified as site class "A"!
[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1623825295/tips/2021-06-16_%EC%98%A4%ED%9B%84_3-18-56_t4hcip.bmp[/url]

 

[HTURKAK]

Is this an inverted siphon structure? Apparently the left chamber partially supported on sand..

What is your plan for seismic design?

Will you post more details to get better responds ?..

 

[MTNClimber]

How are you deciphering between Seismic Site Class A and B? Did you have someone do shear wave velocity tests?

Looks like your structure isn’t just sitting on rock either. I’m not sure how you justify A or B.

 

[Chunil]

There are no other tests are conducted. Only SPT is conducted.
Wish you classify this site with method B(N bar method).
SPT was conducted at every 1 meter.
And that structure is for POWER OUTLET.
The left chamber partially supported on the sand but connected to the main structure strongly.

 

[HTURKAK]

The main structure is supported on hard rock but will experience the seismic active - passive pressure of the above sand and gravel layers..

What is the applicable standard?

 

[Chunil]

Thank you for your interest in this thread HTURKAK~
Wish you judge site class if you do this project according to the AASHTO.
And what if you ignore the left chamber?
Do I should account for the left chamber also?

 

[theCorkster]

You have a bit of complexity. The structure founded on "rock" will respond differently that those with the soil over rock configuration (upper left side of structure). Retaining walls above rock will experience soil response.

 

[HTURKAK]

I do not look to web every time and just see your post.

Let me explain my thought;

If the structure were not buried and supported on the rock, site class could be A or B..

But the structure buried and the surrounding soil is sand and gravel..

I will suggest you to analize the whole system with ELF and add the active seismic soil loading . You may calculate the active and passive seismic soil loading with Mononabe Okabe or with similar approach.

I advise also you to look NCHRP REPORT 611 ,Seismic Analysis and Design of Retaining Walls, Buried Structures, Slopes,
and Embankments.

Does this respond answer to your questions?