Chengguo Zhang

Mechanism of mining-induced slope movement for gullies overlaying shallow coal seams

This paper provides an improved understanding of the movement mechanisms of both bed-rock gully and sandy soil gully when underground mining occurs underneath, followed by systematic analysis of the contributing factors such as mining advance direction, gully slope angle, gully erosion coefficient and mining height. This paper presents the results from monitoring, theoretical analyses and up to date modeling based on the geological features in the gully affected area, and the implications of these results to the success of roof support trial. It was observed that when mining occurred towards the gully, sliding of slope block along the fracture surface occurred, which resulted in unstable roof condition; when mining progressed away from the gully, polygon blocks developed in the gully slope and rotated in reversed direction forming hinged structure; within the bed-rock slope, the hinged structure was unstable due to shear failure of the polygon block; however, within the sandy soil slope, the structure was relatively stable due to the gradual rotating and subsiding of the polygon block. The increase of the value of slope angle and mining height lead to a faster and more intensive fracture development within the gully slope, which had a pronounced effect on gully slope stability and underground pressure. Various remediation approaches are hence proposed in this paper including introducing more powerful support and reasonable mining height, setting up working face along or away from gullies, using room and pillar, strip mining and backfill instead of longwall mining.

FRACTAL CHARACTERISTICS OF CRACK PROPAGATION IN COAL UNDER IMPACT LOADING

This paper studied the fractal characteristics of crack propagation in coal containing beddings under impact loading condition. Split Hopkinson pressure bar (SHPB) system was applied to determine t...

Analysis of Mining-induced Valley Closure Movements

Valley closure movements have been observed for decades in Australia and overseas when underground mining occurred beneath or in close proximity to valleys and other forms of irregular topographies. Valley closure is defined as the inward movements of the valley sides towards the valley centreline. Due to the complexity of the local geology and the interplay between several geological, topographical and mining factors, the underlying mechanisms that actually cause this behaviour are not completely understood. A comprehensive programme of numerical modelling investigations has been carried out to further evaluate and quantify the influence of a number of these mining and geological factors and their inter-relationships. The factors investigated in this paper include longwall positional factors, horizontal stress, panel width, depth of cover and geological structures around the valley. It is found that mining in a series passing beneath the valley dramatically increases valley closure, and mining parallel to valley induces much more closure than other mining orientations. The redistribution of horizontal stress and influence of mining activity have also been recognised as important factors promoting valley closure, and the effect of geological structure around the valley is found to be relatively small. This paper provides further insight into both the valley closure mechanisms and how these mechanisms should be considered in valley closure prediction models.

Evaluation of valley closure subsidence effects under irregular topographic conditions

Abstract When mining occurs beneath or in the vicinity of valleys and other forms of irregular surface topography, the observed vertical subsidence at the base of the valley is less than that would be expected in flat terrain, while the observed horizontal movement of valley sides is greater than that in flat terrain. The reduction in subsidence at the bottom of the valley is referred to as upsidence and the convergence of two sides of the valley is termed valley closure. Researchers have identified the phenomenon of valley closure and upsidence as being very significant parts of non-conventional subsidence effects over the past 15 years in Australia. This paper aims to review and evaluate the recent developments in studying mining induced valley closure subsidence effects. The main issues addressed in this paper are: empirical predictions of valley closure and upsidence; numerical modelling approaches; and mechanisms behind this behaviour based on field measurements.

Assessment and Prevention of Water and Sand Inrush Associated with Coal Mining Under a Water-filled Buried Gully: A Case Study

Mining under a water-filled buried gully risks a potentially serious water and sand inrush, especially if the bedrock is thin. A case study was conducted at a Chinese coal mine, where the thin overlying overburden was covered by widely distributed gullies. Several empirical formulas and numerical modelling indicated that the overlying strata was almost totally fractured and that all of the conditions for an inrush were met. Pre-mining dewatering and grout injection were initiated. The groundwater table was lowered by 13 surface pumping wells and 33 underground upholes that were drilled around the gully. Those located at the bottom of the gully were generally better in aquifer dewatering than those located at the banks. A barrier was constructed to avoid a water inrush by injecting a chemical grout into the bottom of the buried gully through 25 surface holes. Field observations of the water table, underground water yield, and overburden movement prove the validity of the assessment methods and treatments.抽象隐伏含水沟谷下采煤尤其是在薄基岩条件下具有潜在突水和溃沙危险。以中国某煤矿为例,研究区薄覆盖层上沟谷广布。经验计算和数值模拟结果表明,上覆地层裂隙发育且具有突水危险。采用采前疏水和注浆综合防治措施。在隐伏沟谷附近施工13个地面钻孔和33个井下上仰孔疏降地下水位。沟谷底疏水孔的疏降效果比沟谷边缘疏水孔更好。通过25个地面孔向沟谷底化学注浆建立隔水屏障。野外水位、水量和覆岩移动监测证明了该方法的合理性。ZusammenfassungBei Abbau unter mit wassergesättigten Sedimenten gefüllten Erosionsrinnen kann es zu schwerwiegenden Wasser- und Sandeinbrüchen kommen, insbesondere wenn das Felshangend geringmächtig ist. In einem chinesischen Kohlenbergbau bei dem das geringmächtige Felshangend von ausgedehnten Erosionsrinnen überlagert wird, wurde eine Fallstudie durchgeführt. Einige empirische Formeln und nummerische Modellierung zeigten, dass das Hangend nahezu vollständig zerklüftet und die Bedingungen für einen Einbruch gegeben waren. Vorentwässerung und Injektionsmaßnahmen wurden veranlasst. Der Grundwasserspiegel wurde mit 13 Entwässerungsbohrungen von der Oberfläche aus und mit 33, um die Erosionsrinne herum ausgeführten untertägigen Fächerbohrungen, abgesenkt. Die Bohrungen am Fuße der Erosionsrinnen waren für die Entwässerung wirksamer als die in den Flanken. Mit 25 Bohrungen von der Tagesoberfläche aus wurde am Fuß der sedimentgefüllten Erosionsrinne mit chemischen Injektionsmitteln eine Barriere errichtet. Feldbeobachtung des Grundwasserspiegels, des untertägigen Wasserzuflusses und die Hangendbewegung belegen die Wirksamkeit der Verfahrensweise und der getroffenen Maßnahmen.ResumenLa minería debajo de un sumidero enterrado relleno de agua implica un riesgo potencial de irrupción de agua y arena, especialmente si el lecho de rocas es delgado. El estudio de un caso se realizó en una mina de carbón china donde la capa superior estaba cubierta por sumideros ampliamente distribuidos. Varias formulas empíricas y modelos numéricos indicaron que el estrato de la cobertura estaba casi totalmente fractura y que estaban dadas todas las condiciones para una irrupción. Se iniciaron los desagotes pre-minería y la inyección de lechada. El nivel del agua subterránea se descendió a través de 13 pozos de bombeo de superficie y 33 agujeros subterráneos que se perforaron alrededor del barranco. Aquellos localizados en el fondo del sumidero fueron generalmente mejores en el desagote del acuífero que aquellos localizados en las orillas. Se construyó una barrera para impedir una irrupción de agua a través de la inyección de lechada en el fondo del sumidero enterrado a través de 25 agujeros desde la superficie. Las observaciones del nivel de agua, de la extensión del agua subterránea y del movimiento de la capa probaron la validez de los métodos de relevamiento y tratamiento.

Numerical analysis on mining-induced fracture development around river valleys

ABSTRACT This paper presents a detailed study of the mechanisms contributing to fracture development around river valleys associated with mining operations. Due to the geology and geomorphology of the Southern Coalfield of New South Wales, Australia, non-conventional subsidence effects usually occur. The influences associated with valley closure and upsidence are principally tensile and shear fracturing/cracking of the river and underlying strata, which act as underground flow paths for surface water. This paper explicitly simulates the mining-induced fracture development around the valley structure, utilising a distinct element method modelling technique with Voronoi tessellation. The fracture propagations within intact rock as well as along existing discontinuities are simulated in this study. It is demonstrated that the presence of natural geological discontinuities and the mining-induced stress field play an important role in determining the extent and pattern of fracture propagation. Analysis of the mining-induced explicit fracturing system in the vicinity of valley provides an improved understanding of the near-surface hydrological cycle and enables effective remediation of the mining-induced adverse impacts on river valleys.

RECOMENDACIONES BASADAS EN EL EFECTO DESCARGA SOBRE LOS PARÁMETROS DE DETERIORO DE LAS ROCAS CIRCUNDANTES DURANTE LA EXCAVACIÓN DE TÚNELES PROFUNDOS

How to ensure the construction safety is one of the key problems for the deep tunnel excavation. Since a tunnel excavation is an unloading process in essence, a novel method to accurately evaluate the damage evolution of the surrounding rock was conducted to study the deformation and failure mechanism of the tunnel by considering the unloading effect. A typical tunnel in Shimen Mine in China was regarded as the background, the three-dimension computational model was built by using FLAC3D technique. Then the different unloading zones of the surrounding rock were determined according to the unloading principle of tunnel excavation. The results show that the mechanical parameters for the different unloading zones, such as cohesion, internal friction angle, elastic modulus, and Poisson’s ratio, display the nonlinear degradation characteristics. And it can be found that the increasing range of the mechanical response index, such as displacement, stress and force, increase about 0.73-2.10 times comparing the conventional analysis with the unloading calculation. The unloading effect has a great influence on the stress field, the displacement field, and the forces of the supporting during the tunnel excavation. So it is more practical to consider the unloading effect during the deep tunnel excavation. The conclusions obtained in the study are of important theoretical value to direct the similar engineering practice. Keywords: Deep tunnel, Surrounding rock, Unloading effect, Deformation mechanism, Mechanical parameter

Design of Automatic End-Advanced Hydraulic Support in Coal Face with Deep Dip Angle and Large Mining Height

ZTZL60000/25/45 Automatic End-Advanced Hydraulic Support is developed to meet the needs of the fully mechanized coal face with deep dip angle and large mining height, mechanizing the advanced support of the end and drift, while greatly reducing the construction personnels labor intensity. Not only the end support strength is enhanced, which improves the safety and reliability of advanced support and generates methods to solve problems related to reserving triangle coal on the face that enhances the support efficiency and reduces support costs, but also more recovered coal resources become available since the height of roadway increases, spawning a certain amount of economic benefits.