Please answer the following questions: 1- While conducting a pile integrity test
ID: 1714471 • Letter: P
Question
Please answer the following questions:
1- While conducting a pile integrity test on a 20 meter long drilled shaft, the accelerometer records a reflected wave at a time of 6.66 milliseconds after the hammer blow. Assume the wave speed of a stress wave is 3000 m/sec in concrete. Is this pile defected or not?
2- For a drilled shaft, the displacement required to mobilize the ultimate capacity of the shaft in a compression test could be as much as 5 times larger than the displacement required in a tension test. TRUE or FALSE ???
Explanation / Answer
Answer 1
For a 20 meter long pile which is free of any defect the reflection of wave would occur when the wave meets the interface of pile bottom and the surrounding soil at the bottom bearing end of pile and thus the distance travelled by wave would be twice the length of pile
Thus time after which wave reflection would be detected in an undetected pile = 2*20/3000 s = 1/75 seconds or 13.34 milli seconds however time of reflected wave recoded after hammer blow =6.66 milli seconds which is less than 13.34 milli seconds and thus indicate that the pile is defective .
Answer 2
True . In compression test the displacement required is more because for a pile in normal c- phi soils have higher ultimate capacity in compression as compared to tension or pull out.