高土石坝几个问题探讨

Discussion on some problems observed in high earth-rockfill dams

对影响高土石坝安全的几个关键问题进行了探讨,并介绍了近年来相关领域的研究进展。分析了筑坝粗粒料尺寸效应的影响因素,联合采用室内试验、数值试验及反演分析等多种手段,较为系统地研究了粗粒料变形特性参数的尺寸效应,提出了一种由室内试验参数预测粗粒料现场变形特性参数的方法;介绍了粗粒料长期变形特性的测试方法及其发展,深入研究了流变变形的时间发展规律,提出了可广泛适用于描述粗粒料坝长期变形发展模式的对数幂流变经验模型;分析了含砾心墙土渗透特性受密度等因素的影响规律,构建了含砾心墙土非线性渗透模型,在此基础上探讨了心墙高孔隙水压力的形成机制及其对大坝安全的影响;研究了高应力、高水头作用下砾石土心墙的水力破坏模式,首次揭示了水力击穿的破坏机理,提出的水力击穿破坏判据克服了传统水力破坏判据对应力方向的依赖性,为心墙渗透安全评估与控制提供了重要依据;探讨了心墙与坝壳相互作用的演变机制以及岸坡约束作用对大坝安全的影响,进一步深化了对高土石坝变形协调问题的认识。

A few key issues influencing the safety of high earth-rockfill dams are discussed, and the research progress in recent years is reviewed. The factors which influence the scale effects of coarse-grained materials are analyzed. Both the experimental tests and the numerical simulations on the custom-made granular materials, besides the back analysis of the actual deformation parameters of embankment dams are carried out to study the scale effect on deformation parameter of rockfills. Then a method is proposed to determine the on-site mechanical parameters of coarse-grained materials according to laboratory test parameters. The test methods to determine the long-term deformation characteristics of coarse-grained materials and the development of those methods are discussed. The evolution laws of rheological deformation with time are studied, and a logarithmic powerrheological model is proposed. Such a model can be more widely used in the analysis of the long-term deformation development in many kinds of high earth-rockfill dams. The influences of density and other factors on the actual permeability of gravelly soil in the earth core are analyzed. A nonlinear seepage model for gravelly soil is established. The formation mechanism of high water pressure in earth core and its influence on dam safety are also discussed. The hydraulic failure modes of gravelly soil in the earth core under high stress and high water head are studied. The criterion and mechanism of hydraulic fracturing are proposed for the first time. Such a criterion overcomes the stress direction dependency of the traditional criterion of hydraulic failure and provides an effective technique for the safety assessment and management of the seepage through the earth core. The interaction between the soil skeleton of the earth core and the pore fluid, i.e., water, the interaction between the earth core and the dam shell, and the long-term behavior evolution mechanism of high earth-core rockfill dams under complicated conditions such as the constrains of deformation from the bank slopes and dams are discussed. The cognition on the deformation coordination of high embankment dams is deepened.