Recommendations on Two Acceleration Measurements with Low Strain Integrity Test

As more existing structures need to be reevaluated, repaired or expanded, the demand of use of a low strain integrity testing (LST) to determine/corroborate the existing pile/shaft length and integrity under existing structures has also increased. When applying LST to the piles under existing structures, multiple downward travelling waves will superpose with the upward traveling waves (reflection from defects and the toe). This makes the data interpretation very difficult when only one acceleration measurement is obtained. Two acceleration measurements were introduced about 20 years ago as an extension to LST and significantly improve the reliability of application of LST to piles under existing structures. However, due to the complexity of testing conditions, lack of clear guidelines, and experience, this technique has not been frequently applied. After discussing the background of this method, this paper presents case studies and recommendations on the application of this technique.