Research on the hydrofracturing mechanism of termitarium occurrence in earth-rock dam under changing water levels based on numerical models

Abstract

[Objective] Termites nests within earth and rock dams severely damages the integrity of the dam structure. Their complex nest structure under variable water levels can significantly change the seepage characteristics and stress distribution inside the dam body. However, there is a lack of clear understanding of the extent to which different parts of the dam body are affected by the nests. [Methods] Taking the auxiliary dam of Baiguishan Reservoir as an example, six monitoring points were selected upstream and downstream of the dam. Numerical simulations on the damage of termitarium to earth and rock dams were conducted, and the influence on the hydraulic characteristics and stability of the dam were analyzed. [Results] The findings show that:(1) Under design flood level conditions, the termitarium system has a significant impact on the dam's seepage and stability characteristics. This phenomenon is primarily related to the water level on the upstream slope and the location of the termite tunnel ventilation openings, rather than the position and size of the termitarium itself.(2) The presence of termite tunnels creates seepage channels within the dam body, allowing water to flow through the dam more rapidly, which result in an elevated phreatic line. This, in turn, reduces the matric suction of the dam. Additionally, an increase in the diameter of the termite tunnels will slow down the rate at which the phreatic line drops, thereby increasing the risk of seepage failure.(3) When the water level is high, the rate of increase and the peak value of pore water pressure in the dam body are higher under the influence of the termitarium compared to a dam without termitarium. The pore water pressure also shows higher sensitivity to changes in water level.(4) In the displacement field, the termitarium system mainly affects the area above the termitarium within the dam. The displacement amplitude in this area increases during the water level rise and decreases during the water level drop. Moreover, the larger the scale of the termitarium, the greater the displacement amplitude.(5) The termitarium system weakens the overall stability of the dam and leads to a decrease in the safety factor. The impact of the rate of water level rise and fall on the safety factor is more significant than the position and size of the termitarium. [Conclusion] Numerical simulation can effectively diagnose the damage level of earth and rock dams under termite damage and quickly assess the safety condition of termite-hazardous earth and rock dams. This study combines termite damage with earth and rock dam safety evaluation by observing the structural and performance changes of the dam and quantifying the damage caused by termites to the dam, revealing the hydraulic destruction mechanism of the dam termitarium, and providing support for the safety evaluation of earth and rock dams affected by termites.

Keywords

termitarium / hydrofracturing mechanism / numerical simulation / pore pressure distribution / stability coefficient / earth-rock dam