堆石体的填筑标准与级配优化研究

基于分形理论,进行了大量堆石料室内相对密度试验、压缩试验以及三轴试验,对堆石料级配与干密度、压缩模量、破坏强度、颗粒破碎等工程特性之间的关系进行了深入研究。结果表明:(1)级配对堆石料的物理力学性质影响明显,且随着试验应力的增加,其差异性越来越大。如粒度分形维数D在2.22~2.63的良好级配范围内,制样相对密度取1.0时,堆石料干密度在2.026~2.311 g/cm~3之间,相差14%;在3.2~6.4 MPa压力范围内的压缩模量相差2.47倍;制样相对密度取0.8时,在1.6 MPa围压时的三轴试验破坏剪应力相差23%。(2)相同相对密度条件下,随着粒度分形维数的增加,堆石料的极值干密度或孔隙率、压缩模量、破坏应力均表现为先增大、后减小的规律,在D=2.56~2.62附近均存在极值点,对应P5含量在35%左右,细粒含量过多时的"砂化"现象,导致颗粒骨架效应减弱,堆石的工程性质劣化,极值点对应的临界分形维数控制堆石料的工程性质。(3)堆石料的粒度分形维数与颗粒破碎之间存在良好的规律,即粒度分形维数越高,颗粒破碎越小,可通过级配优化设计控制堆石料的颗粒破碎。(4)基于堆石体的孔隙率可描述为粒度分形维数和相对密度的函数,首次提出了基于变形控制的孔隙率和相对密度双控指标,作为高坝堆石体的填筑标准,并结合如美300 m级堆石坝,提出了堆石料级配优化确定的方法。

Filling standards and gradation optimization of rockfill materials

Based on the fractal theory, a large number of relative density tests, compression tests and triaxial tests on rockfill are carried out. The relationships among gradation, dry density, compressive modulus, failure strength and particle breakage of rockfill are thoroughly investigated. The results show that: (1) The particle gradation has obvious effect on the physical and mechanical properties of rockfill, such as when the particle fractal dimension D is in a good gradation ranging from 2.22 to 2.63, the relative density of samples is 1.0, and the dry density of rockfill is 2.026 ~ 2.311 g/cm³, the differences increase by 14%. The compressive modulus in the range of 3.2 ~ 6.4 MPa increases by 2.47 times. The test breaking strength of triaxial tests under confining pressure of 1.6 MPa increases by 23%. (2) Under the same relative density, with the increase of the particle fractal dimension D, the values of extreme dry density or porosity, compressive modulus and shear failure strength of rockfill materials increase firstly and then decrease, the extreme points occur at D = 2.56 ~ 2.62, and the corresponding P5 content is about 35%. The differences of the above values are more and more obvious with the increasing stress. When the content of fine particles is too high, the "sanding" phenomenon decreases the particle matrix effect and the engineering properties of rockfill are deteriorated, and the critical fractal dimension corresponding to the extreme points is adopted to control the engineering properties of rockfill materials. (3) There is a good rule between the fractal dimension of rockfill and the particle crushing, that is, the higher the fractal dimension of the particle gradation is, the smaller the particle crushing is, and it is effective to control the particle crushing of rockfill through the optimal design of the gradation. (4) Because the porosity of rockfill can be described as a function of fractal dimension and relative density of particles, the double control standards of porosity and relative density based on the deformation control of high