土石坝防渗系统土工膜缺陷等效处理方法及严重缺陷致溃研究

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

摘要

【目的】土工膜缺陷是导致大坝溃决的一个潜在影响因素，然而在有限元计算中如何对土工膜缺陷进行准确地模拟以及土工膜缺陷对溃坝的影响至今尚未有定论。【方法】为精确模拟土工膜缺陷，利用有限元计算软件对土工膜缺陷的不同模拟方式以及因土工膜缺陷诱发的溃坝效应进行了探究，分别开展了土工膜完好、土工膜真实缺陷和土工膜等效缺陷三种工况的渗流、稳定性态以及不同溃口深度下的溃坝效应的模拟计算工作。【结果】研究表明：土工膜缺陷的产生会显著抬升坝体浸润线，降低下游坡安全系数，10 cm的土工膜缺陷需将其渗透系数扩大10⁸倍进行等效模拟。此外，较大面积的土工膜缺陷会诱发大坝溃口的形成，而不同的大坝溃口深度对下游的危害程度不同。溃口深度分别为9.0 m、15.0 m和21.5 m时，水流大概到达距离坝脚300 m、300 m和350 m处，此三种溃口深度下对应的溃坝水流压力最大值分别可达297.8 kPa、315.3 kPa和351.38 kPa,溃坝水流速度最大值分别可达21.3 m/s、20.7 m/s和20.3 m/s,溃口处流量分别为2.628×10³ m³/s, 6.240×10³ m³/s和12.040×10³ m³/s。【结论】修订后的土工膜缺陷模拟等效渗透系数能更加准确地反映土工膜真实缺陷情况；此外，土工膜缺陷存在情况下的溃口深度对溃坝动力特征的研究结果，可加强施工过程中对土工膜保护的重视。

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.

关键词

土工膜 / 缺陷模拟 / 渗流特性 / 溃坝 / 瞬时模拟 / 数值模拟

Key words

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

基金资助

国家重点研发计划(2022YFC3005505)

2021 年江苏省水利科技项目(2021068)

2022 年江苏省水利科技项目(2022011)