Overburden Strata Movement Research Articles

Study on action mechanism between rated working re-sistance of support and overburden strata movement

Based on the pressure regulating test curve describing support–surrounding rock relationship, the relationship between rated working resistance (RWR) and overburden movement is investigated. It is discov-ered that between RWR and movement of direct roof strata, the relationship is “must control and must be controlled”, which is qualitatively expressed as Pze=hzγz; between movement of main roof strata and RWR, the relationship is “degree-controlling and degree controlled”, which is hyperbolic and qualitatively expressed as Pre=QSm/2Sx; between RWR and movement of bend zone strata, the relationship is that of “unable to control and unable to be controlled”, which is qualitatively expressed as Pb=0. Finally, the author examines the characteristics of the “hyperbola”, the prerequisite for its existence, and the influence of main roof fault block movement parameters on the position of the hyperbola in the coordinate system, the degree of support control, and the degree of roof movement. This research outcome represents an innovation and a breakthrough on the basic mine pressure theory. It has great academic significance to the discipline of mine pressure and stratum control and provides theoretical basis for the application of strata control.

Effect of particle size on re-crushing characteristics of crushed coal during axial loading

The deformation and re-crushing characteristics of crushed coal and rock directly affect the porosity and permeability distribution of the mining gob and overburden strata movement, which significantly affects the methane enrichment zone and surface subsidence of mining gobs. The effect of particle size on re-crushing characteristics is investigated in this study based on an innovative compression–acoustic emission (AE) positioning method. The main results are as follows: 1) The AE counts and energy are associated closely with three deformation stages, i.e., initial compression, linear compression, and plastic compression. A larger particle deforms more easily and results in more AE counts and energy under the same compression; 2) crushed coal exhibits layered re-crushing characteristics, i.e., particle re-crushing first occurs in the middle layer, and as stress increases, re-crushing shifts gradually to the upper and lower layers; 3) larger particles re-crush more easily, and the re-crushing occurs more severely in the middle layer under the same compression stress; 4) screened results after final compression show and verify the characteristics of layered re-crushing. The lower layer exhibits the least reduction in porosity for each particle size. A larger particle exhibits a greater re-crushing rate under the same compression stress.

Study on the Mine Pressure Law and the Pressure Frame Mechanism of an Overlying Goaf in a Shallow Coal Seam

To study the problems of dynamic load pressure and frame pressure caused by the concentration of stress by coal extraction pillars during the mechanized short-distance mining of goaves in shallow coal seams, a frame pressure accident, in the Shendong Shigetai Coal Mine, during the overlying of a fully mechanized mining goaf is taken as a research example. By applying the field measurement, theoretical analysis, and numerical simulation methods, we throughly analysed the working face coal pillar, got the regular pattern of fully mechanized overburden pressure, summarized a pillar of fully mechanized working face in the overburden strata movement regularity and development characteristics, analyzed the reason and mechanism of broken coal pillar, and put forward the corresponding prevention measures and management method. The results show that when the fully mechanized mining face enters the goaf by about 3 m, the pressure arches of the lower coal face and the upper goaf arising from the extracted coal overlap. When the vertical stress is greater than the supporting force of the hydraulic support and the coal wall, a roof ejection accident may occur.

Function relational expression of backfilled body’s density and its influencing factors

ABSTRACT Filled body is the main carrier for restraining overburden strata movement in solid backfill mining, and degree of restraint is strictly controlled by density of backfill body. Through 3D model of backfill body compacted by backfill support, main factors influencing density of backfilled body during backfilling and compacting process are analyzed, the function relational expression of backfill body’s density is established, the mechanism of dense backfill body changed from loose materials through compaction is revealed, namely, density is determined by factors of backfill technology, including pileup height, tamping angle, tamping times, backfill equipment, backfill materials, geological conditions, and other influence factors. When backfill equipment, an especial geological condition given and backfill material selected, higher pileup height, more tamping times and larger variation range of tamping angle result in larger density. The engineering practice of Chengjiazhuang Coal Mine shows: the function relational expression of backfill body’s density is ρ = ρ 0(4.94 + 1.85h d − 0.15β + 0.16n)/(h·d·k), so when coal mining height (β) is 2.8 m, width of support (k) is 1.5 m, backfill web width (d) is 0.6 m, initial density of backfill body (ρ 0) is 1.35t·m−3, pileup height (h d) is 1.822 m, natural repose angle (β) is 42°, tamping times (n) is 5 (variation range of tamping angle is 3.0–29.6°), the density of compaction forming of gangue (ρ) is 1.71t·m−3, and backfill body’s compression ratio is controlled over 91%.

Effects of solid backfilling on overburden strata movement in shallow depth longwall coal mines in West China

Effects of solid backfilling on overburden strata movement in shallow depth longwall coal mines in West China

Experimental Study and Engineering Practice of Pressured Water Coupling Blasting

Overburden strata movement in large space stope is the major reason that induces the appearance of strong mining pressure. Presplitting blasting for hard coal rocks is crucial for the prevention and control of strong pressure in stope. In this study, pressured water coupling blasting technique was proposed. The process and effect of blasting were analyzed by orthogonal test and field practice. Results showed that the presence of pressure-bearing water and explosive cartridges in the drill are the main influence factors of the blasting effect of cement test block. The high load-transmitting performance of pore water and energy accumulation in explosive cartridges were analyzed. Noxious substances produced during the blasting process were properly controlled because of the moistening, cooling, and diluting effect of pore water. Not only the goal of safe and static rock fragmentation by high-explosive detonation but also a combination of superdynamic blast loading and static loading effect of the pressured water was achieved. Then the practice of blasting control of hard coal rocks in Datong coal mine was analyzed to determine reasonable parameters of pressured water coupling blasting. A good presplitting blasting control effect was achieved for the hard coal rocks.

Comparative Analysis of Overburden Strata Movement in Fully Mechanized Top Coal Caving Mining in Entire (Sub) Layer of Ultra Thick Seam

Reasonable determination of entire layer or sublayer mining method is the key factor of safe and efficient mechanized caving mining of 14.0～28.0m ultra thick seam , numerical simulation on the entire (sub) layer coal caving mining by the FLAC3D , studying the stress and displacement variation of overburden strata , combining the underground pressure theory , comparative analysis on the calculation results . The results show that entire (sub) layer mining roof stress , movement contours are presented in a semi-elliptical arch morphology , indicating the existence of a high arch structure overburden formations , mining process appears roof tensile destruction , but the entire layer caving tensile stress intensity is lower than sublayer caving . When advancing the same distance , entire layer caving puts a greater impact on the overburden strata than the sublayer caving , has some features such as big range of influence and extent , small roof pressure , lead abutment pressure forward from grand , short time of achieving full extraction , etc.

Overlying strata movement law in fully mechanized coal mining and backfilling longwall face by similar physical simulation

Fully mechanized coal mining and backfilling technology with gangue, fly ash and losses etc. changes the overlying strata movement characteristics and strata behavior law in the fully mechanized coal mining and backfilling longwall face (FMCMBLF). Based on the similar theory, a model of the overlying strata movement in FMCMBLF is established with sponge and plastic foam whose thickness ratio is 1:2 as the similar backfilling body. From the similar physical simulation, the following conclusions have been drawn: (i). The overlying strata movement develops from bottom to top as the mining progresses in the FMCMBLF and consequently, the subsidence curve of the strata assumes symmetrical bowl. (ii) No caving zone but only fissured and bended zones are found in the overlying strata herein. (iii) The subsidence velocity undergoes a changing process of “minimum, successive accretion, reduction, and stabilization,” and the overburden strata movement lasts for a long time. The test results would provide reference for further research of strata control as well as fully mechanized coal mining and solid backfilling technology.