Beam me up, Scotty!

Despite everything else you see on this website, LTC is not in the business of testing piles or shafts.  We test the geotechnical load-bearing capacity of these deep foundation elements.  Which is another way of saying, we are testing the shear capacity (plus bearing capacity at the tip) of the soil into which the element has been installed.

This may seem self-evident, but it needs to be emphasized to make the following point:  the concrete and steel which make up a test shaft are themselves not being tested.  Which is to say, the steel reinforcement and concrete mix design do not have to be the same as for production shafts.  The only requirement is that the test foundation has the correct shape (depth and diameter) and that the concrete transmits the compressive test load to the sidewalls and base, to mobilize the soil resistance.

This is where a carrying beam (or in some cases, frame) comes in.  Concrete in compression requires no reinforcement.  A rebar cage is relatively expensive (lots of steel, plus labor to tie/assemble onsite), and can be tricky to pick without deformation.  In a dedicated test shaft, its only function is to suspend the bi-directional jack and instruments at the correct elevation until the concrete cures.  A rolled W-section can serve the same purpose and is cheaper, easier to work with (to square up the jack assembly, add on instrumentation and conduits, etc.), and also easier to pick and install (lighter and pound-for-pound, stiffer than a rebar cage).

At LTC we have been advocating the use of beams or frames for dedicated test piles wherever possible.  We’ve done them for both augercast piles and drilled shafts, with great success.  The next time you’re looking at a deep foundation test program, skip the cage and go with a beam.