Ultimate bearing capacity on Tarmac
Ultimate bearing capacity on Tarmac
(OP)
Dear all
I have a site which is 200mm of tarmac overlying 400mm of hardcore, overlying 1800mm of made ground:gravelly, silty fine to coarse sand.
How do i work out the Ultimate bearing capacity of the tarmac, if i wanted to place a crane on it (base 1.5x1.5m)?
What dry density and internal friction angle should i use?
Thank you
ash
I have a site which is 200mm of tarmac overlying 400mm of hardcore, overlying 1800mm of made ground:gravelly, silty fine to coarse sand.
How do i work out the Ultimate bearing capacity of the tarmac, if i wanted to place a crane on it (base 1.5x1.5m)?
What dry density and internal friction angle should i use?
Thank you
ash





RE: Ultimate bearing capacity on Tarmac
Finally you need to apply some method of relating eccentric footing loads into your bearing capacity formula. It may involve some approximations however.
Another method may be considered. That is an actual bearing test, called plate bearing test, which then has to be extrapolated upward to the size of your foundation pad. That extrapolation is an estimate, not precise, due to the larger pad affecting more zones below.
If it were me, I'd start with that plate bearing test to get an idea of just what I am up against for the larger size pad. This extrapolation probably means your full size pad has less bearing capacity than the plate bearing test result.
RE: Ultimate bearing capacity on Tarmac
RE: Ultimate bearing capacity on Tarmac
RE: Ultimate bearing capacity on Tarmac
RE: Ultimate bearing capacity on Tarmac
Now, your crane load + rigging load + crane weight + boom weight + counterweight will probably be divided between those 4x pads, right?
RE: Ultimate bearing capacity on Tarmac
I have logs, with no N values or triaxial data or density data.
I know the crane to be used will provide a load of 135kn/m2 and its base will be 1.5x1.5m in size. I just need to know how to calculate whether the tarmac(0.2m) over hardcore (0.4m) over Made ground: gravelly silty, fine sand (1.8m)will hold the weight of the crane or will a crane mat be needed?
how do i calculate this?
Ive been using the standard formula in tomlinson (7th edition) p.46 (2.8) - the parts im unsure about are the dry density values and phi values to use.
What do you all suggest?
thank you
Ash
RE: Ultimate bearing capacity on Tarmac
how do i work it out for both?
Thanks
RE: Ultimate bearing capacity on Tarmac
I don't know what kind of tarmac this is, but you can always compare the tire pressure of the vehicle it was designed to carry against the bearing pressure from your crane. Might be able to rule out local failure that way.
Also, the NAVFAC manuals have some generic allowable bearing capacities for different classifications of soil/pavements/rock. May be worth looking into if you don't have proper geotechnical information.
Finally, consider whether soil shearing is truly an acceptable failure condition, or if you'll be limited by settlement requirements of your crane. A lot of cranes get derated if they have a cross-slope of 1 or 2%.
RE: Ultimate bearing capacity on Tarmac
I mention this only as it hasn't been mentioned in your second post regarding loading. It is absolutely essential that you take into account the effects of wind which will result in a moment, and introducing an eccentricity into your foundation. The crane supplier should be able to give you this information. Is it anchored to the ground? Make sure you put a healthy FoS against overturning on the crane.
RE: Ultimate bearing capacity on Tarmac
RE: Ultimate bearing capacity on Tarmac
Unless the person who wrote the text book question/homework assignment didn't know what he was doing. (a 1.5 meter x 1.5 meter stack of "logs" ????? No way. Stack of square cut timbers maybe, but then you'd need a "nested" stack at least 3x timbers "high" to get the load back evenly spread between the cross-beams.)