Research Of Rock Bolt's Anchorage Effect On Fractured Rock Mass's Mechanical Properties Based On Laboratory Experiment And Numerical Simulation

Rock bolting represents one of the most effective and economical geo-structural reinforcing technologies widely used in practical civil engineerings. It has great prospects as more civil constructions are to be built during the socio-economic development. In the field of rock mass engineering, the reinforcing effect of the rock bolt(s) on rock mass is much more obvious due to the large number of natural fractures in rock masses. However, the mechanism of anchorage is still not being studied clearly now. The effective use of the rock bolt(s) for constructing safety and long-term stability of the rock mass engineering requires further the research into rock bolts' anchorage effect upon rock mass.The research program studies the rock bolts' anchorage effects on fractured specimens' mechanical properties from the two perspectives: laboratory experiment and numerical simulation. With a comprehensive analysis of the research results, some useful directions are deduced for the design and installation of the practical rock bolt(s).In the laboratory experiment stage, the research objects are three kinds of specimens, namely intact specimens, fractured specimens and anchored-fractured specimens. Their relationship is as follows:Compared with intact specimen, fractured specimen is a specimen with an opening mode fracture, and anchored-fractured specimen is a specimen with fracture and rock bolt(s). Anchored-fractured specimen has 4 anchorage angles, which are 30 degrees, 45 degrees, 70 degrees and 85 degrees, and the numbers of rock bolts are single, binary and ternary. These 4 kinds of anchorage angles and 3 kinds of rock-bolt numbers constitute different anchored-fractured specimens.The main contents of the laboratory experiment are as follows:Firstly, design 5 groups of the mortar's mixing proportion; test these 5 different mixing-proportion specimens' uniaxial compressive strengths and splitting tensile strengths; define a mixing proportion that make the mortar specimen's physical and mechanical parameters accord with a fixed similar ratio compared to the real rock mass; choose aluminium alloy bar as the similar rock bolt based on the similar ratio.Secondly, test fractured and anchored-fractured specimens' uniaxial compressive strengths and splitting tensile strengths; combined with the testing results of the intact specimens' uniaxial compression and splitting test, analyze the fracture's weakening effects and rock bolts' strengthening effects on the specimens' mechanical properties; summarize the disciplines of anchorage angle and rock- bolt number influencing the anchorage effects of the rock bolt(s) to the fractured specimens.Lastly, launch biaxial compressive test to intact specimens, fractured specimens, and anchored-fractured specimens; analyze fracture's weakening effects and rock bolts' strengthening effects on the specimens' mechanical properties under different lateral pressures; summarize the disciplines of anchorage angle and rock- bolt number influencing the anchorage effects of the rock bolt(s) to the fractured specimens under different lateral pressures and study the influence of lateral pressure on different specimens' biaxial compressive strengths.In addition, the specimens' mechanical properties influenced by the rock-bolt number and anchorage angle are studied; the rock bolts' failure patterns and its influences on the specimens' destruction process are also observed.In the numerical simulation stage, the axial compressive experiment of the three kinds of specimens including intact specimens, fractured specimens and anchored-fractured specimens is simulated by FLAC-3D; obtain the different specimens' numerical stress vs. strain curves, mortar's contour of the minimum and maximum principle stress, and the stress or force state of the rock bolt(s). Use the included pile element of FLAC-3D to simulate the rock bolt(s) while simulating the anchored-fractured specimens' axial compressive experiment. Adopt the two methods of solid-entity method and solid-entity and equivalence compounding method to simulate rock-bolt anchorage effect on the fractured specimens' mechanical properties. The solid-entity and equivalence compounding method's simulation result is much better than the solid-entity method in terms of multi-rock-bolt's reinforcing effect comparing to the results of laboratory experiment. Besides, by taking the single-anchored fractured specimen's axial compressive experiment as an example, one discipline of the anchorage angle influencing the anchorage effect is got by the simulation of FLAC-3D.The discipline about the rock bolt's number and anchorage angle on rock-bolt anchorage effect to fractured specimens is obtained by summarizing the results of the laboratory experiment and numerical simulation. The results of this research will be significant for the practical engineering, since the materials' mechanical and physical parameters used in laboratory experiment and numerical simulation are strictly accordant to a fixed similar ratio comparing the real materials.