Numerical Study on Mechanical Properties and Energy Conversion Characteristics of Soft Rock Anchored by CRLD Anchor Cables Containing Random Cracks

Abstract

This paper is based on the discrete-element software Particle Flow Code (PFC), establishing a hybrid contact model to simulate the mechanical behavior of deep soft rock. The constant resistance constraint effect of the constant resistance large deformation (CRLD) anchor cable on the rock mass is achieved through the pallet servo control principle. Subsequently, a numerical model of anchoring soft rock with varying numbers of random fractures in CRLD anchor cables is constructed, and the mechanical property and energy conversion characteristics are studied. The results indicate that with an increase in the number and total length of cracks, the elastic modulus and peak strength of the CRLD anchored rock exhibit an approximate linear decreasing trend. Few newly generated cracks occur in the vicinity of the pallet and the opposing area far from the pallet. A smaller quantity of random cracks leads to better final integrity of the CRLD anchored rock. The distribution of acoustic emission event numbers is relatively uniform, with its variation trend corresponding to the fluctuation pattern of pallet stress values. The stages of uniform and nonuniform energy absorption by the constant resistance pallet, respectively, correspond to the prepeak elastic deformation and postpeak plastic softening stages of the anchored rock, with the nonuniform stage showing significantly higher total energy absorption values and rates than the uniform stage. Moreover, when the number of cracks is at its maximum, both stages exhibit the lowest total energy absorption values and rates. Based on the theory of energy dissipation and release, a calculation method for the energy conversion of CRLD anchored rock containing the crack characteristic parameters is proposed. As the number of cracks increases, the total input energy U and dissipative energy Ud of each anchored rock decrease gradually at the same strain value, while the elastic strain energy Ue increases gradually. The pallet absorption energy Ucable shows a decreasing trend initially and then increases. This indicates that the constant resistance pallet demonstrates efficient energy absorption characteristics when the number of cracks is relatively large.