Bridge foundation scouring monitoring sensor and monitoring data analysis method thereof

A monitoring data analysis method of a bridge foundation scouring monitoring sensor, comprising the following steps:

• step 1, disposing the scouring monitoring sensor at a bridge foundation scouring monitoring position via pile driving;
• connecting the scouring monitoring sensor with a fiber Bragg grating demodulator, disposed on a bridge pier or a bridge, through an armored cable;
• and obtaining strain responses, measured by fiber Bragg gratings in the scouring monitoring sensor, of optical fiber vibration strings by the fiber Bragg grating demodulator through analyzing a spectrum;
• step 2, assuming that sludge has a constraint on the optical fiber vibration strings buried by the sludge, according to a corresponding position where a scouring depth reaches on each polyhedral mass block in each scouring depth monitoring standard unit, establishing an optical fiber vibration string kinetic model which considers the constraint of the sludge at different scouring depths;
• step 3, calculating natural vibration frequencies of the optical fiber vibration strings at different scouring depths for the optical fiber vibration string kinetic model established in step 2;
• step 4, drawing a curve of a relationship between fixing depths of the sludge and the natural vibration frequencies of the optical fiber vibration strings according to a result of step 3 to establish a corresponding model between the different scouring depths of the bridge foundation and the natural vibration frequencies of the optical fiber vibration strings;
• step 5, measuring strain time-history responses of the optical fiber vibration strings by the fiber Bragg gratings on the optical fiber vibration strings;
• piecewise analyzing the continuously monitored strain time-history responses by a sliding window;
• if a dynamic strain response in the strain measured by the gratings is small, determining that scouring of the bridge foundation does not develop to a burial depth of the corresponding scouring depth monitoring standard unit;
• step 6, when there is an obvious dynamic strain response measured by the fiber Bragg gratings, performing Fourier transformation on the dynamic strain response;
• extracting a Fourier response peak;
• and identifying the natural vibration frequency of the corresponding optical fiber vibration string;
• and
• step 7, in combination with the natural vibration frequencies of the optical fiber vibration strings identified in step 6 and a model of a correspondence between the different scouring depths and the natural vibration frequencies of the optical fiber vibration strings established in step 3, determining a scouring depth of the bridge foundation.