Application of fiber optic sensing technology in anchor monitoring

Prestressed steel anchors are widely adopted in the stabilization of rock slope engineering. To ensure the safety of the stabilization system, reliable monitoring techniques should be used to evaluate the operating state of the anchorage system. Fiber optical sensors can achieve the distribution detection of strain along the whole length of the optical fiber. Therefore it will be very suitable to embed optical fiber in motar, esp. concrete to perform strain measurement as well as crack detection. This paper reports the development of a simple intensity modulated fiber optic sensor for detecting internal cracks of concrete structures. This sensor is embedded in a 1-meter-long concrete beam and its reliability and feasibility tests were conducted by loading this beam to failure. Experiments for the embedded sensor show that incipience and propagation of concrete cracks can be well displayed by light intensity meter and the sensor can endure large deformation before it cracks and the maximum concrete crack width endured by the sensor can reach 5 mm.