防洪堤的可靠性设计方法探讨

Study on reliability design method of flood defenses

基于可靠性理论,提出了防洪堤的概率设计方法。按照堤防设计规范,建立典型斜墙式防洪堤漫顶、渗透稳定、边坡滑动稳定的极限状态方程,采用MonteCarlo法计算相应的可靠性指标。进而通过变动堤防几何参数(堤顶高程、顶宽和坡比)和土工参数,探讨了堤高与漫顶可靠性、堤防几何参数的变化对堤基渗透稳定的可靠性、坡率对边坡失稳可靠性的影响。结果表明:随着堤高的增加,堤防漫顶的可靠性指标逐渐增大;堤防坡率、堤顶宽度、堤基粘土层厚度、前滩地宽度、堤后压盖厚度和宽度等变量的增大,将使堤基渗透稳定的可靠性指标增大;堤基粘土层和砂土层渗透系数的增加,将使堤基渗透稳定可靠性指标减小;堤防上、下游坡率的增加,堤坡稳定可靠性指标增加。

The authors proposed a probabilistic design method based on theoretical analysis of reliability.According to the empirical expression in the code of dyke design,the limit state equations of overtopping,seepage stability and slope slide stability for a typical dyke with inclining facing and twophase fluvial base were formulated.The Monte Carlo method was employed to assess the stability.Discussion was made in detail about the influences of several geometric and geotechnical parameters on the reliability index.The reliability index for wave overtopping increases with the dyke height.The reliability index for seepage stability would increase with increasing of slope ratio,crest width,thickness of clay stratum,width of foreland,thickness and width of counter weight blankets,and it would decreases with increasing of the permeability coefficient of sand and clay stratum.The reliability index for slope stability would increase with increasing of the slope ratio.A design process for this type of dyke was suggested.