Numerical Simulation of Water Flow from the Coal Seam Floor in a Deep Longwall Mine in China

Cao

et al. 2020

Geofluids

Widely distributed in North China, Ordovician karst is characterized by having high thickness, nonuniform aquosity, and significant water pressure-bearing properties. Deep mining in North China is threatened by associated water hazards; hence, research on the hydrogeological characteristics of deep Ordovician karst is needed. In this study, the Weibei coalfield in Shaanxi Province, China, was selected as the study area, especially mines in the Hancheng and Chenghe mining areas. In situ experiments, including water pumping, water drainage, water injecting and water pressure, and laboratory experiments, were conducted to study the hydrogeological characteristics of the Ordovician karst top in the study area. A comprehensive analysis was conducted on controlling factors for the development of the Ordovician karst top in the study area, and a method for evaluating the water inrush risk in coal mining areas based on karst hydrogeological characteristics was proposed. The research results indicated that the Ordovician karst top in the study area was characterized by heterogeneity, vertical zonation, and partially filled properties, which were mainly controlled by two factors: sedimentation and tectonism. The hydrogeological conditions of the Ordovician karst could be divided into three types: nonfilled and nonsignificant tectonism, filled and nonsignificant tectonism, and significant tectonism. Among them, the filled and nonsignificant tectonism type Ordovician karst top type had a filling thickness of 20 m. Based on karst hydrogeological characteristics, the methods were proposed to evaluate the water inrush risk in the coal mining floor. The practical tests verified the methods.

Section: Introductionmentioning

confidence: 99%

Hydrological Characteristics of Ordovician Karst Top in a Deep Region and Evaluation of Its Threat to Coal Mining: A Case Study for the Weibei Coalfield in Shaanxi Province, China

Cao

et al. 2020

Geofluids

“…Modeling flow and its coupled processes in fractured porous rocks are important for subsurface environmental and energy problems [1,2], such as solute transport in groundwater or at radioactive waste disposal sites [3][4][5], geothermal energy exploitation [6,7], gas hydrate stability [8], and coal mine water inflows [9]. The numerical models can be roughly divided into two categories: equivalent fracture models and discrete fracture models [10][11][12].…”

Section: Introductionmentioning

confidence: 99%

Equivalent Permeability Distribution for Fractured Porous Rocks: The Influence of Fracture Network Properties

Chen

2020

Geofluids

Equivalent fracture models are widely used for simulations of groundwater exploitation, geothermal reservoir production, and solute transport in groundwater systems. Equivalent permeability has a great impact on such processes. In this study, equivalent permeability distributions are investigated based on a state-of-the-art numerical upscaling method (i.e., the multiple boundary method) for fractured porous rocks. An ensemble of discrete fracture models is created based on power law length distributions. The equivalent permeability is upscaled from discrete fracture models based on the multiple boundary method. The results show that the statistical distributions of equivalent permeability tensor components are highly related to fracture geometry and differ from each other. For the histograms of the equivalent permeability, the shapes of k x x and k y y change from a power law-like distribution to a lognormal-like distribution when the fracture length and the number of fractures increase. For the off-diagonal component k x y , it is a normal-like distribution and its range expands when the fracture length and the number of fractures increase. The mean of diagonal equivalent permeability tensor components increases linearly with the fracture density. The analysis helps in generating stochastic equivalent permeability models in fractured porous rocks and reduces uncertainties when applying equivalent fracture models.

“…Many water-burst hazards have occurred in coal mines in China during the past few decades, causing casualties and significant property losses [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]. To prevent water ingress, the grouting technique has been extensively and effectively applied to water-bearing strata in underground constructions for more than two hundred years [18][19][20][21].…”

Section: Introductionmentioning

confidence: 99%

“…Due to the maturity of back wall grouting technology, its convenient operation, and its high adaptability, the method of back wall grouting is employed widely in the treatment of frozen boreholes. e following design for back wall grouting was introduced as follows: (1) gathering in situ data; (2) determining the appropriate stratum for a grouting field trial based on the analysis of accessible geological exploration data; (3) calculating the spatial position of the freezing holes according to the inclinometer data of the boreholes; (4) defining the grouting parameters such as the slurry recipe, injection pressure and injection borehole position; (5) implementing the grouting process under the guidance of the grouting design; and (6) stopping grouting and utilizing the geophysical exploration and/or hydrogeological analysis to evaluate the grouting effect.…”

Section: Introductionmentioning

confidence: 99%

Grouting Mechanism of Cement-Based Slurry in a Concentric Annulus under High Groundwater Pressure

Han

Advances in Civil Engineering

et al. 2019

Self Cite

The flow of cement-based slurry within concentric annular geometry is a major problem of study in the field of engineering, especially regarding the prevention of water ingress in an annulus formed during shaft construction utilizing the artificial freezing technique in China. In this study, an analytical governing equation of motion for the axial flow of an incompressible Newtonian fluid in a long concentric annulus is derived under the condition of high groundwater pressure. A stepwise calculation method is proposed to describe the grouting process based on two injection modes, namely, flow rate control and pressure control. The injection time is divided into a series of time segments; correspondingly, the grouted zone is subdivided into infinitesimal elements. Some key parameters, such as the location, dimension, slurry viscosity, and pressure gradient of each element, can be obtained using the developed MATLAB program. On this basis, the distribution of pressure and slurry viscosity in the grouted zone and the variations in injection pressure at the grouting point and grouting flow rate are determined. Two injection mode cases are investigated to reveal the grout propagation in the concentric annulus. Finally, numerical simulations are conducted and employed to validate and calibrate the calculated results. The results obtained by the present stepwise calculation method show good agreement with the numerical results.