INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

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.

Jobs

Large Site Mechanical Pad - Rural Grassland - 3/4" crushed or Roadway Type Subbase

Large Site Mechanical Pad - Rural Grassland - 3/4" crushed or Roadway Type Subbase

(OP)
Having an issue with a client who 'has always used 3/4 crushed aggregate below his mechanical pads without a problem'. Current site within flood plain, has high water table and little to no drainage plan on site. I am recommending a mixed aggregate and clayey graded 'roadway' type (Class 2 AB) subbase material that in hopes it will act less like a reservoir below the mechanical pad during wet weather than a pourous 3/4" . Am I being 'too conservative',....again! Thinking about this one too much? Any thoughts? Thanks in advance, Bill

RE: Large Site Mechanical Pad - Rural Grassland - 3/4" crushed or Roadway Type Subbase

I don't have any problem with crushed aggregate. Think about your statement concerning aggregate being a reservoir below the pad during wet weather. With a high water table and minimal drainage, "wet weather" does not make any difference... it's always wet under the pad. Not a problem. Problems start when wet and dry conditions alternate.

www.SlideRuleEra.net idea
www.VacuumTubeEra.net r2d2

RE: Large Site Mechanical Pad - Rural Grassland - 3/4" crushed or Roadway Type Subbase

If you are in cold climate, that hi P=200 material is likely to frost heave and loosen it, voiding the strength you need. Sick with the crushed rock.

RE: Large Site Mechanical Pad - Rural Grassland - 3/4" crushed or Roadway Type Subbase

Structuralsteelhead:
I tend to agree with you. I would like the immediate area to drain away from the pad. Thus, a bit of attention to pad elevation and finished grading is needed. And, I have never liked the idea that the pad base excavation might act like a sump or bath tub under the pad, particularly so in cold climates. If you don’t have to worry about freezing, and the water table is near grade anyway, the whole area is a sump, so what have you gained? One advantage of the crushed rock, maybe with some geo-textile surrounding it, and with a high ground water table is, that your base material with a fair amount of fines, could be subject to some pumping at the edge of the pad. Make a list of your pros and cons of the two base material system, and let the contractor pick and respond to any issues you might have. Then record his selection in a letter, one for him and one for the file.

RE: Large Site Mechanical Pad - Rural Grassland - 3/4" crushed or Roadway Type Subbase

generally, roadway aggregate base is not "clayey". It is a well graded mixture of crushed aggregate, usually with very few fines and very low plasticity. In other words, no clay or silt is allowed. If you are in a floodplain, than suggest the pad be elevated above the flood level

RE: Large Site Mechanical Pad - Rural Grassland - 3/4" crushed or Roadway Type Subbase

(OP)
Thank you all for your comments. If left to the contractor, he would choose 3/4" crushed as it takes little to no compaction considerations provided placed over native adequate subgrade or prepared subgrade, and frankly cheaper. In Napa, CA. Heavy rains in Winter, moderately high temperatures in the Summer. Typically either dry or wet, not much cycling. Will stick with the 3/4" crushed for now. Thanks again, all. Bill

RE: Large Site Mechanical Pad - Rural Grassland - 3/4" crushed or Roadway Type Subbase

The base material you propose will retain a lot of moisture. Using crushed gravel provides a capillary break for rising groundwater. As SRE notes, crushed stone works fine and getting it wet is not an issue.

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!


Resources


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