Fibre optic is well known in the communication field, providing fast internet worldwide that penetrates even further into the construction industry. Instrumented pile load tests are frequently required during the design and construction of cast in-situ concrete piles (also known as bored piles) to validate the load-bearing capacity and allowable deformation against structural loadings. To check for structural flaws, non-conformance, and unusual stresses and strains in a pile, various sensors and non-destructive test (NDT) methods are typically used. The Malaysian construction industry has recently adopted Distributed Optical Fibre Strain Sensing (DOFSS) through Brillouin Optical Time-Domain Analysis (BOTDA), particularly due to improvements in pile load testing. In comparison to discrete electrical-based sensors like vibrating wire, the benefits of DOFSS in piles include measuring a full (continuous) strain profile and load transfer along the pile shaft. This study aims to methodically examine the connections between anomalies of the distributed strain profile in concrete piles and various pile defects that typically exist in the field, such as necking, bulging, honeycombing, and concrete contamination. A series of axial load tests on reinforced concrete (RC) columns are carried out under various defect scenarios to simulate the pile defect in a controlled environment. The RC columns are fully instrumented with strain gauges and DOFSS (necking, bulging, etc.). Back-analysis of some field case studies of instrumented pile load tests with suspected defects and complex strain profiles from DOFSS, which required careful interpretation, was done using 3D Finite Element pile models based on Rocscience 3.