AbstractThe present paper describes the failure of an under-reamed pile foundation supporting a transmission line tower. Assessment of in-service pile conditions, i.e., in-built length, depth of bulb, uniformity of cross-sectional area, and length of the pile, are estimated through low strain integrity test. Integrity test results reveal that improper bulb formation and shorter as-built length than the designed are the leading causes of failure. Different performance criteria (uplift, compressive, and lateral capacities) of the in-service pile foundation are estimated through extensive finite element analysis and conventional approaches. Different geometric characteristics, i.e., straight shaft, different diameter of the bulb, and pile length, are simulated to represent the in-service pile conditions in the field. The estimated performance criteria are compared with the initial design values to evaluate the required degree of strengthening measures. The paper presents the initial design criteria of pile, soil condition, low strain integrity test, finite element modeling, and strengthening measures of the pile foundation to ensure the long-term stability of the transmission tower.