Effects of sand compaction piles on ground improvement of a coal ash pond and lateral performance on two drilled shafts through improved coal ash layer at a power plant in southern Taiwan is studied in this paper. Effects of the sand compaction piles improvement is evaluated by comparing the SPT-N values before and after ground improvement. The load versus displacement relation at head and the lateral performance along shaft, which are the main concerns of shaft lateral load test results, are presented and discussed in the paper. The shaft performance is also evaluated via the available computer code, LPILE, by comparing to the test measured results.