Equivalent treatment methods for geomembrane defects in earth-rockfill dam seepage control systems and dam breach mechanisms induced by severe defects

Abstract

[Objective] Geomembrane defects represent a potential influencing factor causing dam breaches. However, there is no consensus yet on how to accurately simulate geomembrane defects in finite element calculations and on the influence of geomembrane defects on dam breach. [Methods] To refine simulation method for geomembrane defects, the finite element software was used to investigate different defect simulation approaches and the breach effects caused by them. Simulation calculations were carried out for three conditions: intact geomembrane, geomembrane with actual defects, and geomembrane with equivalent defects. The simulations analyzed seepage, stability states, and dam breach effects under different breach depths. [Results] The result showed that geomembrane defects significantly elevated the seepage line within dam bodies while reducing the safety factors of the downstream slope. A 10 cm geomembrane defect required the permeability coefficient to be increased by 10⁸ times for equivalent simulation. In addition, large-area geomembrane defects could induce the formation of dam breaches, and different breach depths result ed in different degrees of downstream hazard. When the breach depth reached 9.0 m, 15.0 m, and 21.5 m, respectively, the flow reached about 300 m, 300 m, and 350 m from the dam toe, respectively. The maximum water pressure corresponding to these three breach depths reached 297.8 kPa, 315.3 kPa, and 351.38 kPa, respectively, while the maximum breach flow velocities reached 21.3 m/s, 20.7 m/s, and 20.3 m/s, respectively. The discharge rates at breach locations were 2.628×10³ m³/s, 6.240×10³ m³/s, and 12.040×10³ m³/s, respectively. [Conclusion] The refined equivalent permeability coefficient for geomembrane defect simulations demonstrates enhanced accuracy in characterizing the actual condition of geomembrane defects. Furthermore, the findings on the influence of breach depth under conditions of geomembrane defects on dam breach dynamics can underscore the necessity of geomembrane protection during construction.

Keywords

geomembrane / defect simulation / seepage characteristics / dam breach / instantaneous simulation / numerical simulation