Plate Load Test

[geomane]

I have a project that is requiring 3 plate load tests to be performed at depths of 2 feet below existing grades to determine the modulus of subgrade reaction per ASTM D 1196. The project is for a relatively small parking lot, maybe 100' x 100'.

What do you typically use for your reaction force to perform the test? The project is not currently under construction, so I will have to bring in whatever equipment I decide to use.

 

[oldestguy]

For plate load tests I've used two large size tracked dozers, back to back. Can't recall the details of what the jack worked up against however. Be aware that if a rubber tired vehicle is jacked against, you probably need to jack it up and support it, possibly on 4 other jacks, not needing the tires. Otherwise you have to have plenty of "throw" for the jack on the plate to make up for the springs and tires flexing. Sounds like Gilding the Lilly, which test cost may be a very significant part of the job cost. Most people make an engineering estimate of soil properties for small jobs, and especially one of not great value..

 

[geomane]

It's a government job. I tried to get away from the plate load test, but they want it done. This test doubled the cost of the geotechnical exploration. Seems a little overkill to me for a small parking lot for commercial vehicles (e.g. light duty pavement).

 

[Okiryu]

I put the jack underneath the excavator that I use to dig the hole for the test.

 

[Ron]

Agree this is overkill for a small parking lot. Probably wouldn't do one except for airfield pavement!

Have used equipment hauling trailers for reaction. Gives you plenty of room to maneuver everything for the test.

 

[Okiryu]

Agree with Ron and jmcc, for parking lots, I would just use CBR correlations for getting the modulus of subgrade reaction. Ron, yes, my experience with plate test is only for airfield pavements. I was thinking that in the US, the plate test is done for even small projects. Based on your comments, this is not true. Good to know this.

 

[Terratek]

Can you use a drill rig to press on the plates using the same action for pushing a Shelby tube?

 

[Ron]

I doubt you could get the load with drill rig hydraulics. If it's a large rig, you could use it as a reaction.

 

[oldestguy]

jmcc3265 It would be an unusual situation to justify what you are suggesting. Perhaps you can lighten us as to why.

 

[geomane]

Oldestguy, I don't follow what you are getting at. Are you asking why I think the test is overkill? Or, why they are requiring the test?

 

[Okiryu]

jmcc3265, I found some photos for plate bearing test using the back of the excavator as the reaction device. See attached. The photo shows a 12" plate, but I have done the same arrangement for 30" plates.

 

[geomane]

Okiryu, I like the set-up. My only question is are the tracks at least 8 feet away from the circumference of the plate? This is one of the requirements per the ASTM.

 

[oldestguy]

OG here again. Is this a parking lot that has to carry say the very large, heavy wheeled carriers for some very movement sensitive thing such as a large mirror celestial telescope? If it is just airplanes, cars, etc. who OK's spending money for this unnecessary test?

On a plate load test set-up with a large back-hoe, you use the bucket on the end of its boom, but rest the bucket on some sort of bracket "saw-horse" to keep it there and the jack doesn't have the ability to lift it off the supports, with operator applying full downward bucket direction during the test. Thus the bucket is carried by the support and what ever resistance is needed by the jack. That easily can be 10 feet from the tracks. If necessary, fill the bucket with rock.

 

[geomane]

Oldestguy, As far as I know it is for passenger cars. Maybe it will serve as a platform for an aircraft to land on during an emergency. The requirement/specification to run this test is coming from NAVFAC.

I like the idea of using the bucket of a large excavotor. I wonder what load you could apply that way?

 

[oldestguy]

Now it is clearer. Back in 1956 I designed and drew up plans for a new taxiway and a bridge for it at a USNavy air field, under the direction of an experienced former engineer with the US Corps of Engineers. There may have been some Navy standard for investigations, but I can't recall the details. All I do recall however is meeting with the civilian Navy engineers in charge of facilities in that area. After some test borings were done and lab tests run, in no way was there any requirement for a plate bearing test. There was discussion as to the pavement design and what was recommended was approved. Assuming the same, level headed Navy civilian engineers these days, I'd bet there would be no problem eliminating any plate load test and making a conservative judgement as to the soil properties for pavement design. Give it a try.

 

[Okiryu]

jmcc3265,I did not know about that ASTM requirement. I doubt there is an 8 ft of clearance from the tracks. However, as far as I know, Japanese standards allow for this configuration. Sometimes we dig a trench (~0.5 m below existing grade) to do the test. Now, I understand the reason why OG is suggesting to eliminate this test for your project.

Also, this is not related to your question, but just curious, do you also need to use PCASE software for pavement recommendations?

 

[geomane]

So, I have come up with a preliminary plan. The attached photo is the tractor trailer I plan on using. I plan on jacking up against 1 of the beams running along the base of the trailer. I am going to rent a 30k pound excavator, use it to dig my 3 trenches to perform the tests, then load it up on the trailer to add the weight.

Do you all think I should try to span the 2 beams along the base of the trailer to center my load? I'm not sure if the trailer tilting would cause issues or if a point load on the beam would be a problem? The trailer should not tilt much much because the jack cannot travel more than 6 inches.

 

[oldestguy]

See my comment above about rubber tires. I'd do some checking on the ability of the connection joint of trailer to truck to take uplift against the truck. No point in breaking that joint. That required clearance between test and nearby support might be too small also.

 

[geomane]

Here's another photo of the trailer. I have about 20 feet from the tires to the trailer connection. I think if I come 8 feet off of the tires, it won't put so much stress on the connection.

 

[Okiryu]

jmcc, how the testing set up is going?