Junwei Yang

The installation of a rigid wall is a main approach to mitigate a granular flow. The methods of the impact load against a rigid wall still remains a challenge. In this study, the progresses in the estimation of the impact load of granular flow against a rigid wall are introduced in detail. The influences of the slope angle, the installed angle of rigid wall, the volume of granular flow are not fully considered into the present models. The discrete element method is employed to reveal the effects of these factors on the impact load. The numerical results show that the volume of granular flow is a key factor to determine the evolution of the impact load on a rigid wall. The dynamic impact load of granular flow at the initial stage is decided by the angle between the rigid wall and slope surface. If the installation angle is same, the slope angle mainly determines the static load of granular flow. Based on these findings, we propose simplified model that the relationship between the impact load and the multiple physical parameters, such as slope angle, installation angle, repose angle, flow height and flow velocity, basal friction angle, and the volume of granular flow, is taken into account.

Shale heterogeneity directly determines the alteration ability and gas content of shale reservoirs, and its study is a core research topic in shale gas exploitation and development. In this study, the shale from the Longmaxi Formation from well Ld1 located in western Hunan and Hubei is investigated. The shale’s heterogeneity is analyzed based on shale mineral rocks, microslices, geochemistry, and low-temperature N₂ adsorption-desorption. It is found that the shales of the Longmaxi Formation from well Ld1 are mainly composed of siliceous shale, mixed shale, and clayey shale. The three types of shale facies exhibit strong heterogeneity in terms of the occurrence state of organic matter, organic content, mineral composition, microstructure and structure, brittleness, and micropore type. Sedimentation, late diagenesis, and terrigenous input are the main factors influencing the shale’s heterogeneity. With a total organic carbon (TOC) of 0.41%-4.18% and an organic matter maturity () of 3.09%-3.42%, the shales of the Longmaxi Formation from well Ld1 are in an overmature stage, and their mineral composition is mainly quartz (5%-66%) and clay minerals (17.8%-73.8%). The main pore types are intergranular pores, intragranular pores, microfractures, and organic pores. The results of the low-temperature N₂ adsorption-desorption experiment show that the shale pores are mainly composed of micropores and mesopores with narrow throats and complex structures, and their main morphology is of a thin-necked and wide-body ink-bottle pore. Based on the Frenkel-Halsey-Hill (FHH) model, the pore fractal dimension is studied to obtain the fractal dimension (2.73-2.76, mean 2.74) under low relative pressure ( ) and (2.80-2.89, mean 2.85) under high relative pressure ( ). The shales of the Longmaxi Formation in the study area have a strong adsorption and gas storage capacity; however, the pore structure is complex and the connectivity is poor, which, in turn, imposes high requirements on reservoir reformation measures during exploitation. Moreover, the fractal dimension has a positive correlation with organic matter abundance, TOC, clay mineral content, and pyrite content and a negative correlation with quartz content. Since the organic matter contained in the shales of the Longmaxi Formation in the study area is in the overmature stage, the adsorption capacity of the shales is reduced, and the controlling effect of organic matter abundance on the same is not apparent.

Owing to the high mineralization and high treatment cost, Ordovician limestone water is often regarded as a mine wastewater. In order to make rational use of mine water with high mineralization and turn waste into treasure. In this work, the natural water quality of Ordovician mine water in the Weibei coalfield had been tested, and the suspended matter and trace elements of Ordovician mine water in the selected deep detained area had been further tested. As a contrast, the water quality of Ordovician mine water after heating and concentration had been tested. The mechanical and hydraulic parameters of concentrated mine water-loess and concentrated mine water-cement slurry had been tested and compared with conventional slurry. The results showed characteristics of deep detained Ordovician limestone mine water is high salinity, certain suspended matters, limited special material and high permanent hardness. However, compressive strength of loess samples increased, while the permeability reduced. The initial setting-time of the modified material was short, while it showed an increased compressive strength. In practical terms, the quantity of grouting produced in engineering applications can be reduced by 16%, whereas the discharge of high-mineralized mine water can be decreased by about 40,000 m3/a.

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.