Stability of Deep Underground Mine Drift through Complex Geology Conditions in Quang Ninh Coal Area

The stability of deep underground mine drifts is pivotal to sustainable, safe mining in underground coal mines. The main objective of this research is to determine the stability and drifting safety issues in 500-m-deep deep underground mine drift through complex geology in the Quang Ninh coal area. The laboratory experimentation and field measurements were used to analyze the large deformations and failure characteristics of the surrounding rock, the influence factors of safe excavation and stability of deep underground mine drift, and to study the stability control countermeasures. This study also shows the main factors influencing the stability and drifting safety include complex geology zones, high in situ stress, poor mechanical properties and engineering performance of the argillaceous rock mass. According to the field study, the groutability of cement-matrix materials in the argillaceous rock in the complex geology zones were extremely poor, and deformations and failure of the surrounding rock were characterized by dramatic initial deformation, high long-term creep rate, obviously asymmetric deformations and failure, the rebound of roof displacements, overall loosened deformations of deep surrounding rock on a large scale, and high sensitivity to engineering disturbance and water immersion. Various geo-hazards occurred during the underground mine drift excavation, including roof collapse, groundwater inrush. Control techniques are proposed and should be adopted to ensure drifting safety and to control the stability of deep underground mine drift through complex geology zones, including choice of reasonable drift shape, reasonable support type, steel sets, regional strata reinforcement technique such as ground surface pre-grouting, primary enhanced control measures, grouting reinforcement technique, and secondary enclosed support measures for long-term stability, which are critical for ensuring the sustainable development of the underground coal mine.

A Multi-Phasic Perspective of the Intact Permeability of the Heterogeneous Argillaceous Cobourg Limestone

The Cobourg limestone is a heterogeneous argillaceous rock consisting of lighter nodular regions of calcite and dolomite, interspersed with darker regions composed of calcite, dolomite, quartz and a clay fraction. The intact permeability of the Cobourg limestone is estimated to be in the range of K ∈ (10−23, 10−19) m2. This paper discusses the factors influencing the measurement of the intact permeability of the Cobourg limestone and presents an upscaling approach for estimating this parameter. The procedure first involves the dissection of a cuboidal sample of the rock measuring, 80 mm × 120 mm × 300 mm, into ten 8 mm-thick slabs. Digital imaging and mapping of the larger surfaces of these sections are used to create, from both surface image extrusion and surface image interpolation techniques, the fabric within the dissected regions. The estimated permeabilities of the lighter and darker regions are used in the computational models of the computer-generated fabric to estimate the effective permeability of the rock. These results are complemented by estimates derived from mathematical theories for estimating permeabilities of multiphasic composites.

Modeling of Creep Behavior of an Argillaceous Rock by Numerical Homogenization Method

This paper is devoted to modeling the creep behavior of argillaceous rock and a comparison with experimental and numerical results from literature. The proposed time dependent modeling is based on a numerical homogenization method, matrix-inclusion material microstructure and a creep micromechanical model. The nonlinear viscosity of the argillaceous matrix is described by the creep model “Modified Time Hardening”, while classical linear elasticity is applied for the calcite and quartz inclusions. The simulation accuracy was analyzed under single and multistage creep test. A satisfactory agreement between the simulation and the experimental results are obtained by assuming the main mineral phases of the Callovo-Oxfordian argillite. It was found that better agreements could be obtained when the multi-scale modeling is performed on sample with a given mineralogical composition and much more precisely volume fraction. The results show how numerical homogenization method is capable of effectively modelling macroscopic creep deformation.