×
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!
  • Students Click Here

*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

Jobs

Max Ground Pressure / Bearing Capacity

Max Ground Pressure / Bearing Capacity

Max Ground Pressure / Bearing Capacity

(OP)
I'm jacking up a large electric mining shovel (1.5m lbs) and am wondering what a safe bearing capacity would be?

The pad is built out of 3-4" rock with a layer of compacted 3/4" crush on top.


 

RE: Max Ground Pressure / Bearing Capacity

How thick is your pad?  What type of soil is underlying the pad?

RE: Max Ground Pressure / Bearing Capacity

what is the bearing area of the tracks / feet on the existing shovel? Back calculate the bearing pressure exerted by the tracks on the ground. Provide enough jacks and cribbing to maintain a bearing pressure equal or less than the pressure on the tracks.

RE: Max Ground Pressure / Bearing Capacity

Those tracks are sitting on a concrete strip footing from what I see.  

Look to the footing dimensions and reinforcing, if known, to get a bearing approximation, which may be lower for an isolated as opposed to strip condition.

Mike McCann
MMC Engineering
Motto:  KISS
Motivation:  Don't ask

RE: Max Ground Pressure / Bearing Capacity

1.5 kgf/cm2 is safe in most not bad grounds. Your base seems not a bad ground, being crushed rock; maybe you can get 5 kgf/cm2 without problems.

However the coarse quality of the rock base may mean some tilt may happen. To forestall this I would try to (jack?) brace the machine against sidewise displacement.

RE: Max Ground Pressure / Bearing Capacity

(OP)
Pad thickness
3-4" is 3 feet
3/4" is 1 foot

Under the pad is rock (see picture)

Yah i know the ground pressure exerted by the tracks (48.9 psi)  but i dont want to have to put that much cribbing under my jacks b/c we need to be able to work in there.

In the first picture the shovel is on the pad (no concrete)

 

RE: Max Ground Pressure / Bearing Capacity

At 0.9m of 75 to 100mm rock with 0.3m of 20mm crush topping; you should have 200kPa brg easy. The photos are a good attribute.  

RE: Max Ground Pressure / Bearing Capacity

I'd do some trial and error jacking.

If, as you jack, you see displacement, just increase the bearing area and try again.  Displacement of your granular mat is likely to be instantaneous or near that. I'd keep the mat as thin as possible, since you have rock below.

Then, once you find the situation does not move, at each support, you supplement it with say 50 percent added area support nearby each main support.

Consider what is safe when working under a car.  You don't depend on any hydraulic other mechanical lift, but supplement with jack stands.  Do the same here.

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