Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • 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.

Students Click Here

Settlement with a Soil Vapor Extraction System

Settlement with a Soil Vapor Extraction System

Settlement with a Soil Vapor Extraction System

I am currently working on a building that is remediating a PERC spill using a Soil Vapor Extraction System. While remediating, severe building settlement started happening around the column closest to the remediation. We know the column is pulling everything down with it but aren't sure exactly what is happening beneath the slab. We plan to excavate the column footing as there are other site problems that are coming into play but I was wondering if anyone else has experienced settlement when dealing with a Soil Vapor Extraction System? I have been researching the systems and find no data involving foundation settlement but find it hard to believe the installation of the system and the column movement are not linked somehow.

RE: Settlement with a Soil Vapor Extraction System

If you are changing the relative humidity of the pore space, then using Kelvin's law (see Fredlund & Rahardjo,1993) you are altering the suction. So if the relative humidity is decreasing, then suction is increasing resulting in the compression you are observing.

RE: Settlement with a Soil Vapor Extraction System

. . . or you are somehow influencing the position of the ground water table and changing effective stress below the footing.

(I really like ausiegeoeng's explanation though. . .)


¡papá gordo ain’t no madre flaca!

RE: Settlement with a Soil Vapor Extraction System

I agree with both of you regarding the change in ground water and/or moisture content of the soil. In my opinion the use of this system would definitely affect the soils under our foundations. Of course the company that installed the system denies that this could be the case so I'm looking if anyone else has come across a situtaion like this. We will be excavating the area to observe what is happening, I guess we will find out when we see it.

RE: Settlement with a Soil Vapor Extraction System

They don't call it Oz for nothing.

Independent events are seldomly independent.

RE: Settlement with a Soil Vapor Extraction System

In my view there are two things happening, possibly three. Settlements of column footings can be: by compressing the subsoil, as would be done by lowering the ground water table; shrinkage of clay type soils by drying action; and actual movement of soil out from under, as with uniform sand, sometimes accompanied by vibration.

I understand most cleaning solvents are heavier than water, so, before that stuff comes up, chances are a bunch of water has to come along first. Did this system remove water? If so, look at possible action such as either increasing of soil unit density by taking away the buoyancy of that soil or by the drying of clays.

The solution might well be the coming in and injecting grout as with compaction grouting. Other treatments might be underpinning or mini piles with jacks, but the question is how deep are you affecting the supporting soil? Grout injection can go on until you have brought the column up and no further settling takes place.

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.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Low-Volume Rapid Injection Molding With 3D Printed Molds
Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Discover how this hybrid manufacturing process enables on-demand mold fabrication to quickly produce small batches of thermoplastic parts. Download Now
Design for Additive Manufacturing (DfAM)
Examine how the principles of DfAM upend many of the long-standing rules around manufacturability - allowing engineers and designers to place a part’s function at the center of their design considerations. Download Now
Taking Control of Engineering Documents
This ebook covers tips for creating and managing workflows, security best practices and protection of intellectual property, Cloud vs. on-premise software solutions, CAD file management, compliance, and more. 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:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close