Papers by Author: Yong Nian He

Abstract: Rock is a kind of complex and high-disordered geological material, its damage and fracture process usually shows obvious criticality. In this paper, percolation theory is applied to analyze and describe this critical property. First, we discuss the critical fracture probability of rock through percolation and renormalization analysis, and present the equivalence between fracture probability and damage variable. Based on scaling law and the relationship between critical exponents, a critical fractal dimension is obtained. Furthermore, according to the analysis of relationship between damage and fractal dimension, we suggest a damage-fractal formula, ω=ω0+ (D-D0)/Dc. This formula can not only be used to describe the damage evolution through the variation of fractal dimension, but also to define initial damage in rock. Finally, the theoretical conclusions are validated by a series of model experiments, and the experimental results agree with that of theoretical.

Abstract: A complete stress-strain experiment curve, gained through exerting low confining pressure on brittle rock, reflects the deformation and destruction process of rock under different confining pressure, and reveals that after the destruction of rock, not only slip deformation but also re-destruction process will take place, which would possibly lead to further reduction of the mechanical properties of the rock mass. Through the analysis of the relation between complex failure modes, load carrying capacity after rock destruction and the volumetric strain, the paper gives us a further explanation of the complex destructive process of rock. The basis for the rock’s load-carrying capacity after destruction is an effective restraint stress, which shows that effective supporting in underground engineering is the key factor for providing the cracked surrounding rock with load-carrying capacity and guaranteeing the stability of the structure.

Abstract: Rock masses usually contain intermittent joints. The existence of joints not only significantly affects the static properties of rock masses, but also their dynamic response and stability under blast waves. The present study focuses on investigating the fundamental fracture characteristics of intermittent jointed rock masses subjected to blast loading. A series of blasting tests were conducted on organic glass samples. The results are analyzed in order to obtain the characteristics of initiation, propagation and coalescence of wing cracks in rock bridges. The study indicates that the fracture behavior of intermittent jointed rock masses may be significantly affected by the preliminary static stress fields, the density and filling states of rock joints, the incident angles of blast waves relative to the joints, and the amplitudes of incident waves. From visual observation, three initiation modes and four coalescence modes of wing cracks are suggested. Finally, a comparison has been made between the fracture characteristics of intermittent jointed rock masses under single static stress field and that of under blast loading.

Abstract: Surrounding rocks of deep underground engineering are generally cracked, between which and support exists combined effect that can be reflected by the mechanical characteristics of cracked rock mass under lateral Constraints. In this paper, the strength and deformation characteristics of the cracked rock mass under lateral Constraints are investigated with methods of physical and numerical experiments. The results show that the rock mass behaves as equivalent continuum and tends to stable after deforming and re-fracturing, and has stress hardening behavior. These characteristics are obviously different from that of shearing slippage of rock samples at the residual stage of triaxial experiment.