Strain monitoring of distributed optical fiber in concrete raft

To realize strain monitoring of concrete raft foundation structures, a strain monitoring system based on distributed optical fiber sensing technology was designed and constructed with the concrete raft foundation of a residential project in Kunshan as the engineering background. Laboratory tests and on site monitoring investigations were carried out. Laboratory test results show that the strain transfer efficiency of 5 mm steel strand cased optical fiber reaches 0.9968, which verifies the reliability of this type of optical fiber in practical engineering. Based on the laboratory test results, 5 mm steel strand cased optical fibers were embedded in the concrete raft foundation, which can accurately record the internal strain evolution law of the raft foundation. After concrete pouring, the strain changes drastically during the temperature rising stage with a maximum value of 75 μɛ. The strain further increases during the cooling stage due to temperature gradient, with a peak value of approximately 125 μɛ. As the temperature tends to stabilize, strain growth gradually slows down and begins to decrease in most regions. The research achievements provide engineering application techniques for monitoring the health condition of concrete raft foundations using distributed optical fiber sensing technology.