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