Fractal characteristics of particle size distribution of broken coal samples with different immersion time

Deformation and compaction of fractured rock mass under water conditions is one of factors that causes subsidence in gob areas．In order to explore the influence of water immersion time，the gradation and axial compression displacement on fractal characteristics of particle size distribution and compaction characteristics．Using small displacements，the compaction test of five groups of different proportions of broken coal samples is carried out through the method of axial compression displacement control．The results show that：1) In the condition of small axial displacement，the fractal dimension of size distribution with same grade of broken coal decreases with increasing the immersion time；2) The fractal dimension curve of water immersion time and particle size distribution can be fitted by an exponential function；3) With increasing the ratio index n，the fractal dimension of particle size distribution decreases gradually；4) With increasing axial compression displacement，the fractal dimension and the axial stress with same type of broken coal are increasing，which can be divided into the slow increasing stage of 0`15 mm and the rapid increase stage is after 15 mm．Based on the change rule of bearing ca- pacity and grain size distribution under different immersion time，the bearing capacity decreases with the increase of immersion time，while the fractal dimension of particle size distribution decreases．Such findings could provide a basis for further study of the strength，deformation and particle size distribution of broken rock mass under loadings． © 2018, Editorial Board of Journal of Mining and Safety Engineering. All right reserved.