Abstract
The effect of rockbolt density on fractured specimens and the distribution law of fragments were studied using the fractal method. The results show that with the increase of rockbolt density, the strength of specimens is improved. Its degree of fragmentation is increased, but the average size of fragments is decreased. The fragmentation and surface fractal dimensions are increased, their difference value is 1 in theory, but the value is slightly less than 1 in practical application due to the uncertain factors such as anisotropy of specimen. There is a positive correlation between the deformation of surrounding rock and its fractal dimension. The surface fractal dimension of surrounding rock can give a quantitative description of its degree of fragmentation and can give a comprehensive reflection to the roof stability. The support mechanism of rockblots can be understood as improving the probability of refragmentation of fragments, making its distribution gradation close to the optimal one with minimum porosity, thus reducing the deformation of surrounding rock.
Highlights
Cement mortar, which can simulate the surrounding rock more realistically, is a kind of heterogeneous material with similar mechanical properties and stable characteristics to rock mass [20]. e similar materials used in this paper are composed of quartz sand, cement, and gypsum by mixing with water according to a certain mass ratio. e mass ratio of quartz sand, cement, and gypsum is 75% : 10% : 15%, while the weight of water accounts for 10% of solid mass
Unit volume of the rock mass is fractured into fragments of different sizes, whose volume accumulated is related to its gradation. e fragments refractured several times will form an optimal gradation among themselves, while, at the same time, the accumulated volume is the smallest
E surrounding rock in the plastic zone without rockbolts is in a loose state
Summary
A set of triaxial loading testing device, which can simulate the actual stress conditions in the field, was developed in order to study the support effect of rockbolts on rock mass. Erefore, the specimens need to be prefractured to simulate the fractured surrounding rock. In order to reduce the friction between the specimen and the test bench, the plastic film was used to wrap the specimen. Four different test conditions, including no rockbolt, one rockbolt, two rockbolts, and three rockbolts, were carried out to study the effect of rockbolts on postpeak fractured specimens
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