Application of Optical Fiber Sensing Technology in Permeability Test of Three-Dimensional Physical Model of Medium and Long-Distance Diversion Tunnel

Abstract

In order to accurately simulate the dynamic change law of seepage field during construction, this paper proposes the application of optical fiber sensing technology in the permeability test of three-dimensional physical model of medium and long-distance headrace tunnel. This paper introduces the principle of optical fiber sensing, analyzes and compares the application advantages of optical fiber and general electrical signal sensing in the safety monitoring of long-distance diversion tunnel. Taking the safety monitoring of a 16# long tunnel of a diversion project as an example, the selection of monitoring sections, monitoring items, and the layout and networking of monitoring instruments are studied. In addition, combined with the tunnel project, the physical simulation of the construction process of the deep buried headrace tunnel under high seepage pressure is carried out, and the water pressure automatic control water supply system and the discrete flower tube seepage generation system are designed and manufactured to realize the high simulation of the seepage field. The seepage and evolution law in the surrounding rock of headrace tunnel during dynamic construction are calculated and analyzed. The test results show that the maximum external water pressure of the headrace tunnel is 15 MPa, which is equivalent to 1500 m head pressure, and the similar scale of head pressure is 100. Therefore, taking 15 m constant head water supply pressure for simulation calculation, the excavation of the tunnel is 120 cm, and the two-dimensional seepage of the vertical section of $Z=91\text{cm}$ . The seepage flow of the two sides of the tunnel is large, and the contour of the hydraulic gradient is dense. The coordinates are 0.7 m, 2.090 m, and 0.9 m. This point in the original rock mass is located at the same elevation point of the four headrace tunnels and directly below the model exploratory tunnel. The head pressure is 1.40 m, and the corresponding prototype point pressure head is 140 M. During construction, such a high external water pressure is a great safety hazard. Conclusion. The test conclusion provides a theoretical basis for the seepage prevention construction technology design of the headrace tunnel and is of great significance to the long-term stability, safety evaluation, and prediction of the headrace tunnel.