洪水条件下粉煤灰坝非饱和入渗特性及稳定性分析

Unsaturated infiltration characteristics and stability of fly ash dams under flood conditions

燃煤发电厂干式贮灰场内的粉煤灰坝多处于非饱和状态,在遭遇洪水时表层灰体经历了由非饱和到饱和的变化过程,不考虑该过程将极大地影响边坡稳定分析结果,国内外对该过程中粉煤灰的非饱和渗流特性试验研究鲜见报道。以某燃煤电厂的粉煤灰作为研究对象,研发了一套非饱和入渗试验装置,开展了灰坝在遭遇1.0,2.5,3.3,5.2 m等不同洪水水头条件下入渗特性试验研究,结果表明非饱和粉煤灰在洪水入渗下前锋面的平均入渗系数为1.2×10-3cm/s,饱和面的入渗系数在A×10-4 cm/s量级,且随着试验水头提高而越来越接近前锋面入渗系数,基于此提出一种洪水条件下灰坝内饱和区域的估算方法,即低洪水水头时饱和区入渗系数可取试验结果,大于10.0 m洪水水头时可取前锋面入渗系数来估算饱和区范围,并对比数值模拟结果验证了其准确性。最后,通过对比考虑洪水入渗与否下典型灰坝上游侧边坡稳定性分析结果,验证了基于估算饱和区下的边坡稳定分析方法更能反映上游边坡的实际稳定性,研究成果可以为粉煤灰坝的非饱和渗流与稳定分析提供借鉴。

The fly ash dams in the storage field of coal-fired power plants are mostly in unsaturated state.The surface ash body experiences the change from unsaturated state to saturated one during floods,which will greatly affect the slope stability.However,the experimental researches on the unsaturated characteristics of fly ash in this process are rarely reported.A coal fly ash is chosen as the research object,and the related unsaturated infiltration test device is developed.The systematical tests are then carried out on the infiltration characteristics of a fly ash dam under different flood water-head conditions such as 1.0,2.5,3.3 and 5.2 m.The test results show that the average infiltration coefficient of forward edge surface for unsaturated fly ash is 1.2×10-3 cm/s,while the infiltration coefficient of saturated surface is A×10-4 cm/s level,and it is closer and closer to that of弹the forward edge surface with the increasing flood water-head.Based on this,a method for estimating the saturated area in the fly ash dam is proposed,that is,the infiltration coefficient of saturated surface under low flood water-head can be obtained from the test results,while the coefficient of forward edge surface can be used to estimate the saturated area when the flood water-head is larger than 10.0 m.The accuracy of the proposed method is verified by comparing with the numerical results.As a result,based on the stability analysis results of upstream slope of a typical fly ash dam considering flood infiltration,the analysis method based on the estimation of saturated zone can be better reflect the actual stability of the upstream slope,and the research results may provide reference for the unsaturated seepage and stability analysis of fly ash dams.