蚁巢赋存及库水位升降下土石坝水力破坏机理研究

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

摘要

【目的】白蚁在土石坝内筑巢严重损害了坝体的结构完整性，其复杂的巢穴结构能够显著改变坝体内部的渗流特性和应力分布。然而，目前库水位升降下坝体不同部位受到蚁巢影响的具体程度，尚缺乏明确的认识。【方法】以白龟山水库顺河坝为研究对象，建立有限元模型，选取坝体上下游布置六个监测点，分析不同蚁巢赋存及库水位升降下土石坝内部结构渗流特征、应力变形及稳定性变化规律。【结果】结果表明：(1)在设计洪水位下，蚁巢系统对坝体的渗流和稳定性具有显著影响，这种影响与迎水坡水位和蚁道通风口的位置密切相关，而与蚁巢本身的位置和尺寸关系相对较小。(2)蚁道的存在造成坝体内部形成渗流通道，使水流能够迅速通过坝体，导致坝体浸润线升高，从而使坝体基质吸力降低，同时蚁道直径的增加会导致浸润线下降速度变缓，增加了渗透破坏的风险。(3)蚁巢赋存下坝体孔隙水压力在高水位时增速与峰值均高于无蚁巢情景，并对水位变化呈现出高敏感性。(4)在位移场方面，蚁巢系统主要影响坝体蚁巢系统以上的区域，并随着库水位的升降变形幅度增大或减少。此外蚁巢规模越大，位移幅度也越大。(5)蚁巢系统的存在削弱了坝体整体稳定性，导致坝体安全系数降低。相较于蚁巢的位置和尺寸，水位升降速率对坝体安全系数的影响更为显著。【结论】有限元分析可以有效了解蚁巢系统对土石坝不同部位的水力破坏程度，揭示库水位升降速率和蚁巢规模对土石坝的水力破坏机理，快速评估土石坝的安全状况，为土石坝白蚁危害安全评价提供支撑。

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.

关键词

蚁巢分布 / 水力破坏 / 数值模拟 / 孔压分布 / 稳定性系数 / 土石坝

Key words

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

基金资助

河南省水利工程安全技术重点试验室开放基金项目(HNAZ202407)

2024 年自然灾害防治技术装备工程化攻关专项项目-监测预警和灾害信息获取(TC240HE75-3)