Fig. 1. Simulation diagram. (a) Simulation model of water content in rock mass; (b) simulation result of wave velocity variation with water content; (c) propagation process of longitudinal wave with 0 water content; (d) propagation process of longitudinal wave with 50% water content

Fig. 2. Optical fiber sensor. (a) Schematic diagram of optical fiber sensor structure; (b) reflective spectrum of optical fiber sensor (inset is reflective spectrum of word point 1)

Fig. 3. Optical fiber ultrasonic detection of water content in rock mass. (a) Experimental system; (b) time-domain signals

Fig. 4. Sensitivity characterization of optical fiber sensor and PZT

Fig. 5. Relationship between water content and wave velocity measured by different sensors. (a) PZT; (b) optical fiber sensor

Fig. 6. Change of main frequency and normalized main frequency amplitude with water content. (a) Change of main frequency with water content measured by PZT; (b) change of normalized main frequency amplitude with water content measured by PZT; (c) change of main frequency with water content measured by optical fiber sensor; (d) change of normalized main frequency amplitude with water content measured by optical fiber sensor

Fig. 7. Water content reconstruction. (a) Relationship between optical fiber sensor measurement values and actual water content; (b) relationship between PZT measurement values and actual water content