Plate Load Test 1

[pnmkapoor]

For one of the project we have planned to conduct plate load test. The bearing capacity has been checked for both shear failure criteria (of soil) and settlement criteria as well. Settlement of footing governs the design. The allowable bearing pressure has been estimated as 500kPa for settlement less than 1-inch, at 0.5m below ground (consist of very dense gravelly sand). We have planned to conduct confirmatory plate load test upto 500kPa just to confirm that our settlement is less than 1-inch at 500kPa. I have been questioned that usually plate load test shall be conducted upto 2.5 to 3 times the allowable bearing pressure. I feel conducting full scale load test upto 2.5 to 3 times the allowable bearing pressure may not be necessary here since our allowable bearing pressure is governed by limiting settlement of 1-inch. Am I correct? Thanks & regards

 

[BigH]

Can you provide us some information as to anticipated size of structure's footings; what is type of structure? 500kPa is quite a high allowable bearing pressure and for normal foundations, the size is likely to be quite small. Thanks and

 

[pnmkapoor]

Thanks BigH, The structure is an industrial unit with inbuilt operating Crane. The size of foundation is 2.5mx1.5m. I have been told that size of footing being governed by overturning stability requirements. However,maximum foundation contact pressure at the edge during worst case of loading (with moments) is 450kPa. Regards

 

[BigH]

I know this will sound "non-engineering" - but if you have the room, why not just make the footing a bit bigger? If you make the footing 3m x 2m, then the footprint would be just about double; hence your acting bearing pressure would be halved (in a rough sense). A little more concrete, but if only a couple of footings, it is not that much and then you wouldn't have to even consider worries about bearing pressures. Look at it this way - what is the cost of the PLT? How much more concrete can I get out of the equivalent cost? I haven't dwelled on the aspects of the problems associated with the PLT that Focht3 and I (and several others) have put forth in other threads). Just a suggestion.

I remember, when I first started out - I was doing a "bearing capacity" analysis and told the senior geotech that we could increase the bearing pressure from 1500psf to 1600psf. He looked me in the eye and said "Why? Keep it at 1500psf and sleep at night." Whilst this is against the "grain" there is some wisdom in his comment. He was a damn fine geotech.