Load Test Performance of Bored Pile with Distributed Fibre Optic Strain Sensing

A novel technique of instrumenting the performance of a bored pile during a maintained load test was performed using optical fibre sensing technology. The technology, namely Brillouin Optical Time Domain Analysis (BOTDA), allows strains to be measured continuously along the whole length of the pile, producing a complete load-transfer regime (t-z curve) and shaft friction profile along the pile. This paper describes a pile load test on a 1.2m diameter bored pile at Putrajaya founded on weathered granitic residual soils. Methods to convert the distributed strain measurements to the load transfer response, shaft resistances, and compression profile are described in the paper. Comparable results were obtained between the distributed fibre optic strain sensor and the conventional system (vibrating wire strain gauges) and theoretical calculation. However, the distributed fibre optic strain sensor has the added advantage of detecting localized defects such as pile necking, bending, and overall behaviour of bored piles effectively.