Crosshole Sonic Logging Interpretation

[massagung]

hi all,

i have problem with CSL test on test-pile with instrumented pile. but CSL test in this test pile indicated that pile has defect from depth 0-7 m (debonding)at all pair tube, and for tube pair 1-2 and 2-3 at depth 8-13.6 m (with remark 70% velocity reduction).
can anyone give technical comment regarding this CSL test, is it possible to conduct static loading test until load 250%?

thanks in advanced.

M.A.

 

[BigHarvey]

It might be more a "technological" problem than a defect in the pile. Did you use steel tubes ? Plastic tubes do not provide the necessary bonding for this kind of test. In order to check you can perform an impedance test (hammer blow on the head of the pile and measurement of travel time both ways), if there is a discontinuity, which should be according to your test results, it will show it. You can also dig around the pile up to 2 m depth and chack for any visible defect. Otherwise just proceed with your loading test and whether it fails or not !

 

[massagung]

BigHarvey,

thanks for comment, i have been discuss with owner to conduct PIT test to makesure the pile integrity have defect or not, since as second opinion from our geotechnical professional this test pile can't to conduct static loading test with load until 250%, because possible the pile will have large settlement (25 mm until 40 mm) due to defect at depth 8-13.6 m. he is very sure that at depth 8-13.6 m is the defect since CSL test indicate velocity reduction its not because debonding.

fyi : this tube using PVC tube, with 3 tube. this pile also instrumented pile with vibrating wire strain gauge. if we can not do SLT, our cost for instrumented pile will useless. and as writen at drilling record also reported that while pooring concrete have been waiting for 4 hours, from 4th Truck Mixer to 5th Truck Mixer.

please advice, if there any treatment so this test pile instrumented not useless.

thanks,

M.A.

 

[BigHarvey]

You can core through the pile down where you suspect to have a defect but make sure your hole is vertical. Obviously you can experience problems if you wait so long between concrete trucks without looking at the rheology of you concrete. For a successfull concreting session you must maintain a slump of 16 to 20 cm all over the session, otherwise you will have inclusions of mud within the concrete.
Repairing such defects is not an easy task and success is not guaranteed. You must drill holes to reach the defects, wash the cavities and grout them. I would advise you to construct another test pile but before doing it check and improve your concrete procédures.

 

[aeoliantexan]

There is a thermal test that measures the temperature at depth intervals in each tube, but it usually needs to be done within 2 or 3 days after placement while the heat of hydration is still high.

 

[massagung]

thanks all for your helpful input,

for Thermal Test is it worth than CSL? what is the limitation of both of the test?

M.A.

 

[aeoliantexan]

I don't know if the debonding will affect the thermal profiling test, but I doubt it. There is a thermal gradient from center to perimeter of the pier as the concrete hardens. If the shaft is uniform, the temperatures in all three tubes at any given depth should be the same. Cold spots may indicate diluted concrete. Hot spots may indicate an external bulge, etc. Call GRL in Cleveland for information. But hurry; the temperature drops fast after two days.

 

[massagung]

Hi all,

we have been conduct axial compression static loading test on this pile without treatment, and the maximum settlement at 250% Design Load only about 18 mm (thats mean this pile actualy safe).

but now we still have the question :
1. what is the really problem of CSL and PIT Test result that both of NDT Test on this pile that indicating have defect, but actualy we conducted SLT 250% of Design Load, Max. Settlement still acceptable in local code (for Diameter 100 cm, max. settlement < 4% x D)? is the NDT Test not acceptable or maybe there is anomaly?

M.A.

 

[BigHarvey]

It can come from the testing company itself. When I have such problem, which alway happens when the client has selected the testing company, I generally hire the best one (Rincent BTP who have invented the test) to perform a second test which generally proves that the pile is good.

 

[aeoliantexan]

Often the capacity of a pile is controlled by the soil, and the diameter is based on constructibility or some other parameter, so the stress in the pile itself is fairly low. Your pile could have a flaw that affects part of the cross sectional area, but the remainder can carry the test load, even at 250% of design load. The fact that it passed the load test confirms its geotechnical design, but doesn't mean it is structurally acceptable. For example, it may have exposed reinforcing that will corrode in time.

Congratulations on a successful test.