连续分布的粗粒土级配方程与压实性能

以Morgan等人提出的生长曲线为基础,提出了可反映粗粒土"S型"以及"上凸型"颗粒分布的2参数级配方程及参数取值范围;当形状参数a趋向无穷大时,则级配方程转化为分形分布公式。在此基础上,提出了采用相对密度试验手段确定最优压实性能级配的方法。建议级配方程对于长河坝、大石峡、两河口等高坝的填筑级配,具有很好的适用性。利用所得研究成果,对大石峡砂砾料进行室内相对密度试验,结果表明:①对于最大粒径60 mm的不同分布规律的粗粒土而言,随着级配参数的变化,其最大、最小干密度均存在极值点或拐点,且对应的临界P5值都在35%附近。②临界P5值对应粗粒土的极优压实性能级配;颗粒级配越接近分形分布,压实性能越好,临界P5值对应的分形分布级配,即为最优压实性能级配。接近分形分布的长河坝堆石料,较低的现场压实参数却获得了较高的填筑干密度,也佐证了这一结论的合理性。③利用临界分形维数的尺度无关性,可以方便地将室内最优压实性能级配的研究成果推广至现场不同最大粒径的工程级配。结论可用于粗粒土的级配设计以及压实性能评价。

Gradation equation and compaction characteristics of continuously distributed coarse-grained soil

Based on the growth curve proposed by Morgan et al., a two-parameter gradation equation that can reflect the "upward convex" and "S-shaped" particle distributions of coarse-grained soil is proposed. When the shape parameter a goes to infinity, the gradation formula is transformed into a fractal distribution equation. On this basis, a method for determining the optimal compaction performance gradation by using the relative density test method is proposed. The suggested gradation equation has good applicability to the filling gradation of high-rockfill dams in Changheba, Dashixia and Lianghekou. Using these research results, the indoor relative density tests on Dashixia gravel material are conducted. The results show that: (1) For the coarse aggregates with gradation of d_max=60 mm and different distribution laws, with change of gradation parameters, the maximum and minimum dry densities both have extreme points or inflection points, and the corresponding critical P5 values are approximately 35% and remain basically unchanged. (2) The critical P5 value corresponds to the excellent compaction performance gradation. The test value of dry density obtained by the fractal distribution gradation is the largest. When the particle gradation is close to the fractal distribution, the compaction performance is satisfactory, and the critical P5 value corresponding to the fractal distribution gradation is the optimal compaction performance gradation. The rockfill of Changehe dam with fractal distribution has a higher filling density under the lower field compaction parameters, which proves the rationality of this conclusion. (3) According to the scale independence of the critical fractal dimension, the research results of the indoor optimal compaction performance can be conveniently extended to different maximum particle size gradations on site. The conclusion can be used for the gradation design and compaction performance evaluation of coarse-grained soil.