Relationship between Fractal Dimension of Fragmentation Degree and Energy Dissipation of Rock-Like Materials under Initial Stress

Ying Xu,Hailong Li,Rongzhou Yang,Jinjin Ge,Kun Wang,Shi Hu,Pengfei Wang

doi:10.1155/2020/8861971

Abstract

In order to obtain the relationship between fractal dimension and energy dissipation of rock-like materials under initial stress state, a variable cross-section split Hopkinson pressure bar (SHPB) test system with active confining pressure loading device was used to carry out impact compression and splitting tests on cemented sand specimens. The impact test results show that (1) the prediction value on the fragmentation degree of cemented sand specimens by using the fractal model is basically consistent with the screening results of actual test, which verifies the applicability of the fractal calculation model given in this study; (2) the more the fracture energy dissipated in the crushing process of cemented sand specimens, the more serious the fragmentation degree is, and accordingly the larger the fractal dimension is, that is, the fracture energy is positively correlated with the fractal dimension; (3) there is an exponential relationship between the fractal dimension and energy dissipation of cemented sand specimens under initial stress, which is so different from that under no initial stress. The experimental results in this study can be used to modify the fractal damage model for rock blasting considering the initial stress.

Highlights

In order to effectively control and obtain ideal blasting effect, it is necessary to describe the mechanical process of rock blasting mathematically and carry out theoretical research on rock blasting
The current blasting engineering gradually advances to the deep rock mass in high in-situ stress environment, which inevitably leads to the difference in the blasting fracture theory and surrounding rock stability mechanism compared with that in shallow rock mass [15,16,17,18,19], and the corresponding relationship between energy dissipation rate generated by damage and fractal dimension will be changed. erefore, it is of great significance to establish the relationship between fractal dimension and energy dissipation of rock under initial stress, so as to develop a numerical calculation model of rock blasting crack propagation considering initial in-situ stress
Analysis. e fragments after split Hopkinson pressure bar (SHPB) dynamic compression test on cemented sand specimens were collected, which were screened into 13 grades with 0∼0.15, 0.15∼0.3, 0.3∼0.6, 0.6∼1.18, 1.18∼2.36, 2.36∼4.75, 4.75∼9.5, 9.5∼13.2, 13.2∼16, 16∼26.5, 26.5∼31.5, 31.5∼37.5, and 37.5∼50 mm based on its fragment size

Summary

Introduction

In order to effectively control and obtain ideal blasting effect, it is necessary to describe the mechanical process of rock blasting mathematically and carry out theoretical research on rock blasting. The current blasting engineering gradually advances to the deep rock mass in high in-situ stress environment, which inevitably leads to the difference in the blasting fracture theory and surrounding rock stability mechanism compared with that in shallow rock mass [15,16,17,18,19], and the corresponding relationship between energy dissipation rate generated by damage and fractal dimension will be changed. Erefore, it is of great significance to establish the relationship between fractal dimension and energy dissipation of rock under initial stress, so as to develop a numerical calculation model of rock blasting crack propagation considering initial in-situ stress. The fractal dimension of fragmentation degree (Df) can be calculated [24]

SHPB Test

Transmitted wave

Test Results and Discussion

Intercept

Conclusions