Abstract
When an impact source is applied to the top of a pile, the waves near the top exhibit strong three-dimensional characteristics. When an anomaly is locally distributed near the top of the pile (shallow anomaly), there are some blind areas on the top, where the waves scattered from the anomaly are very weak or absent. The scattered waves cannot be analyzed by the widely adopted theory of one-dimensional stress waves. When the ratio of the characteristic wavelength of the pulse to the radius of piles is large, the tip reflections approximately behave as the plane waves. The upward tip reflections are reflected at the top. These newly formed second incident waves will be reflected at the shallow anomaly. These reflections from the locally distributed anomaly can be approximately regarded as the plane waves, detected by the receiver at any position of the top and analyzed based on the one-dimensional theory. It can be concluded that with the help of the reflections following the tip reflections, it could be possible to detect shallow anomalies more reliably.