×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Are you an
Engineering professional?
Join Eng-Tips Forums!
• Talk With Other Members
• Be Notified Of Responses
• Keyword Search
Favorite Forums
• Automated Signatures
• Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Full Stack Settlement

Full Stack Settlement

(OP)
Engineers,

I am involved on a project which consist of development of a landfill.

The idea is to store Ash up to a height of about 60 feet from grade (surcharge ~ 7200 psf). The length of the area is 1000 feet by 900 feet.

Somehow client is concern about any potential settlements at the base of the landfill. Soils are SP and SC in the top 20 ft, N from 5 to 20. We did 1 boring 100 feet deep and N values were on average 30 down to 60 feet. Then found a 5 foot layer of SP, with N = 2 and again, SP with N between 10 and 20, down to 100 ft. Rock was not found.

Having a width of 1000 feet, I think that 100 feet deep boring will not provide all information needed for settlement analyses of this landfill area (load ~ 7200 psf). It is not economical to drill 1000 ft borings either.

In that case, how would you perform a settlement analyses?

By using schmertmann, having a L/B ~ 1, means that my analysis will end at 2 B, which is something out of proportion.

At the same time, I think all these methods for stress distribution are for footings and small structures, I don't think they are effective for LARge structures such as a 1000 ft landfill.

Please le me know what you think.

RE: Full Stack Settlement

We think in terms of modulus for each layer, but. . .

Modulus does vary by confinement. Hyperbolic parameters can be considered to show that soil modulus really goes high at these various depths!

Also, the seat of settlement is typically taken to the depth where the delta sigma H is less than 10 percent of the in-situ (i.e., pre-placement) stress. A delta sigma v of 7200 psf would then extend to the depth where the confinement is 72,000 psf and that's 600 ft. Then again, you'll have some attenuation from the original load.

good luck in this? I'm not completely sure how I'd handle this problem, 'cause I don't know where the project is located. Glacial terrain? Coastal Plain? Depth to bedrock?

f-d

ípapß gordo ainÆt no madre flaca!

RE: Full Stack Settlement

(OP)
Thanks.

Per geologic publications, the rock is about 150 feet from the ground surface.

Yes, I know this is not a typical settlement analyses since the area is so large. Job location is in Florida.

I know that the recognized settlement analyses do not consider such large areas.

RE: Full Stack Settlement

Just playing devil's advocate, but hear me out. Say the allowable bearing capacity is 3000 psf and 1" of settlement is expected (pretty typical). You're at 7200 psf, so say your settlement doubles to 2". First, how would he/she notice a settlement of 2" on a pile 60' high? Second, why would he/she care?......its a landfill. Seems like an academic exercise.

RE: Full Stack Settlement

Quote (pelelo)

Somehow client is concern about any potential settlements at the base of the landfill.

What is the source of the ash? Maybe municipal waste... or coal?
Since the project is in Florida, how far below the surface of the existing ground to the water table?

Keeping the bottom of an ash disposal area above the water table is important for environmental reasons. That is probably why the settlement prediction is needed.

RE: Full Stack Settlement

This isn't all that hard.

Drill to rock so you know where it, not just from maps.

Ignore settlement in the rock.

Calculate the settlements based on standard settlement theory based on your materials. Looks like there is no clay to speak of, therefore no consolidation settlement to worry about. All elastic. Can't get much easier.

If you want to get fancy, use something like Settle3D or just do it by hand.

Mike Lambert

RE: Full Stack Settlement

Don't worry about "seat of settlement" for such a wide area. There ain't any significant spread. Luckily the SP will hardly settle due to small range from loose to dense. You might run a trial "settlement" on firm samples of SC to estimate deflection under different pressures and go with that. It likely would be on the generous side.

RE: Full Stack Settlement

Rather than settlements (you are not adding any structure on top of the fill, correct?), I would be more worried about the slope stability at the edges of the fill. 60 feet is quite high and if you have structures around you should also look at slope stability.

Also, I am not in the US but I heard that in some areas of Florida there is karst geology. Any concerns about cavities/sinkholes?

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Resources

eBook - Manufacturing the Cars of Tomorrow
In this ebook, we'll explore how additive manufacturing is going to transform the way cars are made. This includes commentary from thought leaders such as Ford's CTO, Ken Washington, Customer case studies of ways 3D printing is being used today, and a variety of part examples where 3D printing is already impacting how automobiles are made. Download Now
White Paper - Smart Manufacturing for Semiconductor
New technologies and approaches present great opportunities for semiconductor manufacturers to achieve high levels of innovation, yield and improvement. This white paper explores some of these cutting-edge technologies and how they can be applied effectively in the semiconductor industry. Read about how Smart Manufacturing is transforming the semiconductor industry. Download Now
White Paper - Analysis and Simulation in Aircraft Structure Certification
Organizations using simulation and analysis tools effectively see the benefits in their ability to achieve certification faster and with drastically less total cost than those who do not maximize these tools. Read this White Paper to learn about how digital tools such as analysis and simulation help in aircraft structure certification. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

• Talk To Other Members
• Notification Of Responses To Questions
• Favorite Forums One Click Access
• Keyword Search Of All Posts, And More...

Register now while it's still free!