Monitoring contact seepage between earth-fill dam and trans-dam culvert based on temperature variation regularity of optical fiber

The concrete-soil interface between earth-fill dam and trans-dam culvert has always been susceptible to seepage. The dam will break once the failure conditions are reached. To avoid dam disasters, it is important to carry out targeted monitoring according to the precursory information of contact seepage. Distributed optical fiber has been widely used to detect reservoir leakage, by virtue of its wide monitoring range and sensitive induction. However, very few scholars have systematically examined the layout mode and design parameters of distributed optical fiber for monitoring the contact seepage of earth-fill dams. Therefore, this paper conducts a contact seepage model test between the earth-fill dam and the trans-dam culvert, and then summarizes the temperature variation regularity of optical fiber in different stages of contact seepage monitoring. On this basis, a thermal-fluid coupling numerical calculation model is established for optical fiber, and used to analyze the temperature variation regularity of distributed optical fiber under different seepage flow velocities, heating powers, and fiber thermal parameters. The main conclusions are as follows: (1) the occurrence of the contact seepage between the earth-fill dam and the trans-dam culvert can be determined by the taken away of the heat generated by the heated distributed optical fiber. (2) The temperature variation of optical fiber decreases nonlinearly with the increase of thermal conductivity of optical fiber heater sheath and fluid velocity. The temperature variation of optical fiber increases linearly with the heating power of optical fiber. (3) When the thermal conductivity of optical fiber heater sheath is greater than 0.5 W/(m celcius), heating power and seepage flow velocity exert little impact on the temperature variation of optical fiber. (4) Based on the test data and numerical calculation results, the authors optimized the parameters of distributed optical fiber for monitoring the contact seepage between earth-fill dam and trans-dam culverts. Finally, a distributed optical fiber layout scheme suitable for contact seepage monitoring was proposed based on the structural form of earth-fill dam and the influence range of contact seepage failure.