Burst-prone Ground Research Articles

ISRM Suggested Method for Determining the Properties of Rock Bolt Assemblies by Mass Freefall Impact Testing in the Laboratory

AbstractThis Suggested Method proposes impact tests to determine selected properties of full-scale rock bolt assemblies subject to an axis-aligned impact force. These properties include the stiffness of the bolt assembly, the rise time, the tensile strength, the ultimate displacement, and the energy absorption of the rock bolt assembly. These properties may be used to design or select ground support for burst-prone ground conditions. This Suggested Method is limited to the mass freefall impact test method. It is performed using a test frame in the laboratory. The Method specifies the requirements for the testing apparatus and measurement sensors, the test procedures, the data processing methods and the reporting items.

Analysis of the damage mechanism of strainbursts by a global-local modeling approach

Strainburst is the most common type of rockbursts. The research of strainburst damage mechanisms is helpful to improve and optimize the rock support design in the burst-prone ground. In this study, an improved global-local modeling approach was first adopted to study strainburst damage mechanisms. The extracted stresses induced by multiple excavations from a three-dimensional (3D) global model established by fast Lagrangian analysis of continua in 3 dimensions (FLAC3D) are used as boundary conditions for a two-dimensional (2D) local model of a deep roadway built by universal distinct element code (UDEC) to simulate realistic stress loading paths and conduct a detailed analysis of rockburst damage from both micro and macro perspectives. The results suggest that the deformation and damage level of the roadway gradually increase with the growth of surrounding rock stress caused by the superposition of mining- or excavation-induced stresses of the panel and nearby roadways. The significant increase of surrounding rock stresses will result in more accumulated strain energy in two sidewalls, providing a necessary condition for the strainburst occurrence in the dynamic stage. The strainburst damage mechanism for the study site combines three types of damage: rock ejection, rock bulking, and rockfall. During the strainburst, initiation, propagation, and development of tensile cracks play a crucial role in controlling macroscopic failure of surrounding rock masses, although the shear crack always accounts for the main proportion of damage levels. The deformation and damage level of the roadway during a strainburst positively correlate with the increasing peak particle velocities (PPVs). The yielding steel arch might not dissipate kinetic energy and mitigate strainburst damage effectively due to the limited energy absorption capacity. The principles to control and mitigate strainburst damage are proposed in this paper. This study presents a systematic framework to investigate strainburst damage mechanisms using the global-local modeling approach.

Development of two new rockbolts for safe and rapid tunneling in burst-prone ground

Strainbursts are the most frequently encountered rockburst in underground mines. Conventional approach to support strainburst-prone ground is to install rock reinforcement system using rebar and wire mesh first and then install yielding support system using dynamic rockbolts at a later stage. This two-stage rock support installation process is not safe and effective because it can adversely impact worker’s safety and mine production schedule.Two new patented dynamic rockbolts for reinforcing and holding rock masses, which are called Superbolts, were developed for safe and rapid tunneling in burst-prone grounds. Laboratory testing was conducted to confirm the design. The new rockbolts are characterized by high reinforcement load capacity, high shear resistance capacity, high dynamic energy absorption capacity, and the ability to withstand repeated dynamic loadings. The new rockbolts can be used in cost-effective support systems in burst-prone grounds. Most importantly, they are quick to install and can be used in a one-pass rock support system to facilitate safe and rapid tunnel development in underground mines and increase mine safety and productivity.

Characterisation of burst-prone grounds at Vale’s Creighton Mine

Rockbursting is one of the important challenges faced in deep and high stress mines. Ground support systems designed for supporting static loads are often not able to manage the imposed dynamic loads. Consequently, in anticipation of dynamic-loading conditions, stiff support systems are typically enhanced using reinforcement or surface support elements that are perceived to improve the yielding capacity. In order to develop cost-effective ground support strategies, it is important to quantify the conditions that lead to an increased likelihood of rockburst. This paper provides an objective and practical guideline for the identification of burst-prone ground conditions based on the anticipated magnitude events and the associated probability of rockburst, the proximity of large-scale geological structures, and mining-induced stress conditions. The guideline was developed using passive monitoring of ground support performance under dynamic-loading conditions at Creighton Mine, operated by Vale in Sudbury, Ontario, Canada. A comprehensive database was constructed of 123 seismic events and the resulting 184 damage locations. The reported rockbursts occurred between January 2000 and September 2013. The majority of pertinent information was obtained through on-site field assessments, seismic monitoring records, and numerical stress analyses. The proposed guideline is validated for Creighton Mine and the employed methodology is transferable to other deep underground mines.

Theoretical Calculation and Analysis on the Composite Rock-Bolt Bearing Structure in Burst-Prone Ground

Given the increase in mining depth and intensity, tunnel failure as a result of rock burst has become an important issue in the field of mining engineering in China. Based on the Composite Rock-Bolt Bearing Structure, which is formed due to the interaction of the bolts driven into the surrounding rock, this paper analyzes a rock burst prevention mechanism, establishes a mechanical model in burst-prone ground, deduces the strength calculation formula of the Composite Rock-Bolt Bearing Structure in burst-prone ground, and confirms the rock burst prevention criterion of the Composite Rock-Bolt Bearing Structure. According to the rock burst prevention criterion, the amount of the influence on rock burst prevention ability from the surrounding rock parameters and bolt support parameters is discussed.

Estimation of rockburst wall-rock velocity invoked by slab flexure sources in deep tunnels

For rock support in burst-prone ground, the wall-rock velocity adjacent to the surface of underground openings is a vital support design parameter, and depends on the seismic source mechanism inducing rockburst damage. In this study, to estimate the wall-rock velocity evoked only by rock slab buckling (an important rockburst source mechanism), a comprehensive velocity assessment method is proposed, using an excellent slab column buckling model with a small eccentricity, which relies on a novel compressive or tensile buckling failure criterion of rock slab. The true-triaxial loading–unloading tests and rockburst case analyses reveal that rock mass slabbing induced by high rock stress has major impacts on the evolution and formation of buckling rockburst in deep tunnels. Using a method based on the energy balance principle, the slabbing thickness of intact rock mass is also calculated by an analytical method, which indicates that the slabbing thickness parameter has a nonlinear relation to the following six parameters: uniaxial tensile strength (UTS), uniaxial compressive strength (UCS), normal stress (σn), length of joint (L), friction angle ([Formula: see text]), and joint roughness coefficient (JRC). These proposed models and methods have been quite successfully applied to rockburst and slabbing cases occurring in deep tunnels. These applications show that slab flexure is an important source mechanism invoking high wall-rock velocities and leading to severe rockburst damages in the area surrounding deep tunnels.

Principles of rock support in burst-prone ground

Rock support in burst-prone ground requires a good understanding of rock mass behavior under high stress conditions and the behavior and functionality of each rock support element as well as the behavior of the rock support system. Seven principles which can lead to making the right judgment and decision with regards to rock support design in burst-prone ground are presented in this paper. A good understanding of these principles helps ground control engineers to master the art of rock support in burst-probe grounds so as to develop useful methodology for design.

Design of rock support system under rockburst condition

As mining and civil tunneling progresses to depth, excavation-induced seismicity and rockburst problems increase and cannot be prevented. As an important line of defense, ground control measures and burst-resistant rock support are used to prevent or minimize damage to excavations and thus to enhance workplace safety. Rock support in burst-prone ground differs from conventional rock support where controlling gravity-induced rockfalls and managing shallow zones of loose rock are the main target. Rock support in burst-prone ground needs to resist dynamic loads and large rock dilation due to violent rock failure. After reviewing the rockburst phenomenon, types of rockbursts, damage mechanisms, and rockburst support design principles and acceptability criteria, this paper describes that the support selection process in burst-prone ground is iterative, requiring design verification and modification based on field observations. An interactive design tool for conducting rockburst support design in underground tunnels is introduced to facilitate cost-effective design.

Friction bolt anchored wire rope for rock support in burst-prone ground

Friction bolt anchored wire rope for rock support in burst-prone ground

Evaluation of current support practices in burst-prone ground and preliminary guidelines for Canadian hard rock mines : McCreath, D R; Kaiser, P K Proc International Symposium on Rock Support, Sudbury, 16–19 June, 1992P611–619. Publ Rotterdam: A A Balkema, 1992

Evaluation of current support practices in burst-prone ground and preliminary guidelines for Canadian hard rock mines : McCreath, D R; Kaiser, P K Proc International Symposium on Rock Support, Sudbury, 16–19 June, 1992P611–619. Publ Rotterdam: A A Balkema, 1992