堆石坝离散元模拟中缩尺碾轮等效荷载确定

Determination of equivalent loads on downsized rollers in DEM simulation of rock-fill dams

在采用离散元模拟堆石坝料碾压施工过程时,考虑到计算效率,需要对施工仓面进行缩减,并需缩小碾轮尺寸。与实际碾轮荷载等效是保证离散元碾压模拟与实际碾压具有相同压实效果的前提,作用于碾轮上的荷载与碾轮尺寸有关,故需准确确定作用于缩尺碾轮上的等效荷载。文章提出了以坝料孔隙率相等为依据的缩尺碾轮等效荷载确定方法。首先,采用PFC(particle flow code)软件,建立能反映堆石坝料级配、颗粒形状、接触特性的坝料二维和三维模型,并考虑到PFC二维模型孔隙率与工程实际孔隙率的差异,建立了二维模型孔隙率与工程实际孔隙率间的定量关系。然后,根据压实能力系数相同,导出缩尺碾轮等效荷载的确定公式,进而依据实际孔隙率相等的原则,对该公式进行修正,从而建立了不同碾轮尺寸与作用荷载的定量关系。实例验算表明,该方法所计算得到的等效荷载作用在缩尺碾轮上的坝料碾压效果能够与真实尺寸碾轮的碾压效果一致,从而可为缩尺情况下离散元碾压模拟提供依据。

In discrete element method（DEM） simulation of rock-fill dam compaction, the sizes of the work area and the roller are usually reduced for lower computational cost, and applying a load on the roller equivalent to its real value is the premise of numerical simulation. This equivalent load depends on the roller size, and hence an accurate calculation of it is crucial to simulation accuracy. This paper develops a method of determining the equivalent load on downsized rollers considering the same porosity of dam material to be compacted. First, we use the particle flow code（PFC） to construct a 2 D model and a 3 D model that describe the features of rock-fill materials： aggregate gradation, particle shape, contact characteristics, etc., and establish a quantitative relationship between the modeled porosity and the real one. Then, we derive a formula for determining the equivalent load on downsized rollers based on the same compaction ability coefficients, and modify it by matching the modeled porosity with the real one, therefore establishing a relationship of the equivalent roller load versus the roller size. A case study shows that the equivalent load calculated by our method leads to the same compaction effect compared to that of the real roller, thus laying a basis for numerical simulation of downsized roller compaction.