Net Allowable Soil Bearing
Net Allowable Soil Bearing
(OP)
I'm reading the soil report for the area where my job is located and it refers to the net allowable soil bearing value of a footing foundation and a mat foundation.
I need to design a foundation for a small, skid mounted horizontal storage tank (approx 5'x15'). The foundation needs to be wider than the tank itself in order to house some pumps as well, so the foundation dimensions are 10'x20'. Would this foundation be considered a footing foundation or a mat foundation?
Also, the soil report gives values for net allowable soil bearing which it says includes a factor of safety of 3.0 against actual failure of the subsoils due to shear. So does this mean that this is my allowable bearing capacity and my ultimate bearing capacity would be the allowable divided by 3? I'm a young engineer and am having trouble understaing the relationships between allowable, ultimate, and factor of safety.
I need to design a foundation for a small, skid mounted horizontal storage tank (approx 5'x15'). The foundation needs to be wider than the tank itself in order to house some pumps as well, so the foundation dimensions are 10'x20'. Would this foundation be considered a footing foundation or a mat foundation?
Also, the soil report gives values for net allowable soil bearing which it says includes a factor of safety of 3.0 against actual failure of the subsoils due to shear. So does this mean that this is my allowable bearing capacity and my ultimate bearing capacity would be the allowable divided by 3? I'm a young engineer and am having trouble understaing the relationships between allowable, ultimate, and factor of safety.





RE: Net Allowable Soil Bearing
RE: Net Allowable Soil Bearing
Terzagis formula for determining ultimate bearing pressure based on earth parametars, foundations width and depth of foundation is given by:
qult=c*Nc+qo*Nq+0,5*gama*B*N(gama) - strip footing
After various reaserches gave formulas that incorporate square footings, rectangular and circular footings.
But what aboth raft foundation?
How to deal with them?
RE: Net Allowable Soil Bearing
RE: Net Allowable Soil Bearing
Question comes to mind. If your foundation solution is a raft, and your know frost-depth is around 0,80m below ground surface.
What to do?
Should this frost limit be considered as with other types of foundation or not?
Outer ground perimeter will be most exposed to this temperature differences, and vertical perimetar line load will be highest at this position.
Should one bulid raft beams at this point that have a depth of 0,80m...
RE: Net Allowable Soil Bearing
RE: Net Allowable Soil Bearing
Please correct you posting to make it more understandable.
www.PeirceEngineering.com
RE: Net Allowable Soil Bearing
I was trying to mention that I would read the geotechnical report closely. In my understanding, when they mention "net allowable" bearing pressure they are typically allowing you to neglect the weight of the foundation. As the weight of the foundation almost offsets the weight of the soil that was in place prior to the foundation, the weight of the foundation is often neglected.
RE: Net Allowable Soil Bearing
RE: Net Allowable Soil Bearing
I was merely saying that a lot of the geotech reports I have used for relatively shallow foundations do not require you to include the weight of the footing in the bearing capacity checks.
RE: Net Allowable Soil Bearing
When I use net allowable bearing pressure, I mean that pressure that can be used to meet serviceability requirements.
RE: Net Allowable Soil Bearing
I curently reading "Foundation Analysis and design"-Bowels book.
I came across Hansen formula for calculating ultimate bearing capacity. Im having a hrad time inderstanding the B`,L` dimesnions that author uses.
If the footing is loaded with inclined force you calculate inclination factors. Later on when inserting values for B`,L` real values are multiplyed with inclination factors. in every term for shape factor formulas.
Is this correct?
If scenario is that I have a vertical force and a moment acting on a footing, B´=B-2*ex, L´=B-2*ey and no inclination foctors. Basicly they are all equal to =1
RE: Net Allowable Soil Bearing
In my reports I proved a net allowable soil bearing pressure which means the "new added" pressure over and above the "pre-existing pressures" that is added on by the new loads.