Whether lateral load test can be allowed prior to vertical load test

[1967pradyot]

Load test (vertical & lateral) is to be carried out on same pile. Contractor wants to do the lateral load test first and then after a month will carry out vertical load test on the same pile.
Please suggest me whether this will provide a correct picture on vertical compression capacity since due to lateral load test around 4-5D of the surrounding soil will be disturbed and side friction may not generate.
How much time it will take for soil (clayey silt) to come back to its original position and regain its strength (thixotropic action).
Or do we suggest to perform the vertical load test first and then go for lateral load test.

 

[Ron]

If you must test the same pile, do the vertical test first, for exactly the reasons you mentioned. The contractor isn't thinking! He should want you to do the vertical test first!

 

[Focht3]

Ron is right - vertical first. Lateral test can screw up the axial load test; but the axial should not affect the lateral load test. Er, unless you push it too far!

 

[1967pradyot]

If we wait for a month or more before conducting the vertical load test, the soil may come back to its original position and regain strength. Why in that case, we cannot allow to do lateral load test prior to vertical load test?

Actually, whether any references are there where this time requirement of regaining soil strength is established? Probably, for overconsolidated soil, the gap between pile and soil continues to persist if lateral load test done first and thus shaft friction will not be generated for that part when vertical load test will be performed.Is it true?

 

[jheidt2543]

One question, if you are so worried about the time element between tests, why not test two piles, one for vertical and one for lateral? That way you get both tests done in a shorter time period and can get on with the job. The setup cost can't be much different for two piles vs one, because the setup for each test is so different.

 

[Focht3]

The 30 day delay after installation has to do with the loss of soil strength immediately adjacent to driven piles. Clay soils are thixotropic (pronounced "thicks-o-TRO-pick" for you 'non-dirt' guys), which means they regain much of their undisturbed strength over time. Thirty days has been found to be a good time delay before testing in order to achieve the maximum soil resistance. (This delay should not be applied to drilled piers in most cases...)

When you run a lateral load test, you run the risk of separating a significant portion of the pier/pile from the adjacent soils. Loss of contact means loss of axial capacity. That's why you need to run the axial test first.