Abutment Pressure Distribution Research Articles

Research on abutment stress distribution of roof-cutting coalface: numerical simulation and field measurement

During the processing of deep mining, revealing the distribution of abutment pressure is significant for controlling stability of the entry. In this study, the abutment pressure distribution of roof-cutting coalface was investigated by FLAC3D and self-developed flexible detection unit (FDU). In the numerical simulation, the double-yield model was built to analyze the goaf abutment pressure under the fracturing roofs to maintain entry (FRME). Compared with the non-fracturing side, the peak value of the advanced abutment pressure on the fracturing side is reduced by 19.29% on average, the influence range (span) increases by 30.78% and the distance between the peak value and the working face increases by 66.7%. The goaf abutment pressure within 23m near the cutting side is significantly higher than other areas along the dip. The FDU was employed in the coalface to record the change of advanced abutment stress. And the field measured results are in well agreement with the numerical results.

Research on the Change Law of Side Abutment Pressure Distribution in Stope with Coal Thickness Variation

Research on the Change Law of Side Abutment Pressure Distribution in Stope with Coal Thickness Variation

Analysis of overburden movement and side abutment pressure distribution in deep stope with varying coal seam thickness

To investigate the overburden movement and the side abutment pressure distribution concerning the variation in deep mines with varying coal seam thickness, this study focused on the No. 72 mining area of Tianchen Coal Mine and obtained the following results: Variations in coal seam thickness within a stope lead to increased immediate roof thickness. When the coal seam thickness is 8 m, the maximum immediate roof thickness reaches 18 m. The roof is composed of a “Combined short cantilever-Voussoir beam” structure. Displacement curves of overburden in coal seam thickness-varying stopes exhibit asymmetry, with the overburden closer to the coal seam being more asymmetric. After post-goaf stabilization, the peak side abutment pressure decreases with increasing coal seam thickness and shifts deeper into the coal wall. Concurrently, the ultimate equilibrium area width expands. With an increase in coal seam thickness from 4 m to 8 m, the peak side abutment pressures decreased from 44.98 MPa to 41.04 MPa. The peak position shifted from a distance of 9 m from the coal wall to 14 m, while the stress-relaxation area expanded from 3 m to 5 m. This research provides essential insights for safe and efficient mining in similar conditions.

Lateral abutment pressure distribution and evolution in wide pillars under the first mining effect

The wide pillars are generally popular due to the high productivity and efficiency in Northwest China. The distribution of lateral abutment pressure in coal pillars is important for mining safety. To reveal the effect of the first mining on the lateral abutment pressure distribution and evolution in wide pillars, an in-situ experiment, theoretical analysis and numerical simulation were performed. First, the field monitoring of lateral abutment pressure was conducted from the perspective of time and space in the Chahasu Coal Mine, Huangling No. 2 Coal Mine and Lingdong Coal Mine during the first mining. Based on the field monitoring stress, a theoretical model was proposed to reveal the lateral abutment pressure distribution. The methodology was demonstrated through a case study. Aiming at the distribution mechanism, a numerical experiment was conducted through the finite-discrete element method (FDEM). Last, field observations of borehole fractures were performed to further study the damage distribution. In addition, two types of lateral abutment pressure evolution with mining advance were discussed. Suggestions on the stress monitoring layout were proposed as well. The results could provide foundations for strata control and disaster prevention in wide pillars in underground coal mines.

Abutment Pressure Distribution Law and Support Analysis of Super Large Mining Height Face.

Under the condition of the shallow coal seam, the laws of roof activity after large mining height longwall face mining and prevention measures for large-area roof weighting are problems that need to be solved urgently. In the background of the super large mining height working face in the upper 108 working face of Jinjitan Coal Mine 12-2, the spatial distribution characteristics of the development and change of the mining-induced abutment pressure and the related support design in the 8.2 m super large mining height and fully mechanized mining face were conducted. It reveals the distribution characteristics of the dynamic stress field and internal and external stress fields. The influence range of the abutment pressure of the super high mining height working face was measured on site. The numerical simulation is carried out, the roadway support structure is analyzed, and the improvement measures are proposed. The research results demonstrate that: The influence range of abutment pressure is 234 m, the obvious influence range of the leading pressure is 47-60 m, and the peak position of the influence of the leading pressure is 15-20 m. The 5 m range is the lateral inward stress field of the coal pillar, the 10-15 m range is the outward stress field of the coal pillar, and the 20 m range is the original rock stress field of the coal pillar. Therefore, it is proposed that the reasonable size of the coal pillar for roadway protection is 20-22 m. Adjusting the distance between screw steel and FRP bolts from 1000 mm to 1200 mm, the length of the roof prestressed anchor cable should be appropriately reduced to 5.5-6 m according to the lithology of the roof.

A Study on the Calculation Method of Support Pressure in the Structure of Typical Upper Cladding Rock Formations

Aiming at the calculation problem of bearing pressure of typical overlying strata structure, in this paper, mechanical calculation, field monitoring and other methods are used to study the influence range of abutment pressure. Recently, many major rock burst accidents in working surface show that with the increase of mining depth and the change of overlying strata structure, the abutment pressure distribution has become one of the problems of safe mining. The influence range, distribution of high stress area and peak position of working surface support pressure need to be solved urgently; and through theoretical analysis, this paper reveals (whole rock single-layer structure, whole rock layered structure, whole rock single-layer structure—without arch in soil layer, whole rock layered structure—without arch in soil layer, whole rock single-layer structure—with soil arching, whole rock layered structure—with soil arching) the stress transfer mode, transfer size, and arching conditions of overlying strata in different areas. The mechanical system of abutment pressure calculation for typical overburden structure is established, which provides theoretical basis for mine optimization design scheme, mining sequence, and limited personnel distance.

Study on the Key Factors of Terminal Mining Line Layout in Repeated Mining of Close-Distance Thick Coal Seams

In order to mater the reasonable layout basis of the terminal mining line position in the repeated mining of close-distance thick coal seams, taking Yan mine as the engineering background, we conducted theoretical analyses, numerical simulations, and field measurements to study the action mechanism of the stress arch. The results show that (1) with repeated mining, the shape of the left and right half arches of the stress arch changes in the order of time and space until it is stable; (2) the shape of the stress arch is highly related to the distribution of abutment pressure in the working face. If the shape is unchanged, the distribution of abutment pressure is unchanged; (3) in the final mining stage of repeated mining, when the shape of the right half arch is stable, the difference stagger distance of the terminal mining line has little effect on the distribution of abutment pressure of the working face where the front arch foot is located; (4) when the internal stagger distance between 3216 working face and terminal mining line of 4216 working face is greater than 22 m or the external stagger distance is greater than 30 m, 3216 working face is located in a relatively safe position. This study clarifies the key factors for the layout of terminal mining lines in close-distance thick coal seams, which can provide a scientific basis for similar projects.

Roadway Protection by Roof-Cutting in the Support Removing Channel of the Long-Wall Mining Face

Aiming at strong mining pressure and large deformation of surrounding rock in the main roadway, a mechanical model of the advanced abutment pressure distribution in the long-wall mining face was established. The main reason for the large deformation of the surrounding rock in the main roadway was found to be unreasonable position of the stop line, which brings the main roadway under the influence of mining operations. Therefore, on the premise of an unaltered stop line, the technique of cutting the roof and use of pressure relief to protect the main roadway were proposed. The technique will form a weak surface along the stop line, blocking the rock layer from transmitting the abutment pressure. Engineering practice shows that by using the advanced roof cutting and pressure-relief technique, the abutment pressure on the long-wall mining face is reduced and the main roadway is protected.

The Effect of Joint Damage on a Coal Wall and the Influence of Joints on the Abutment Pressure on a Fully Mechanised Working Face with Large Mining Height

Coal wall spalling is regarded as a key technical problem influencing safe and efficient mining of large-mining-height working faces while the distribution of abutment pressure within the limit equilibrium zone (LEZ) influences coal wall spalling within a large-mining-height working face. This research attempted to explore the distribution characteristics of abutment pressure within the LEZ in a large-mining-height working face. For this purpose, the influences of the orientation of joints on mechanical characteristics of coal with joints and on the distribution of abutment pressure within the LEZ in the large-mining-height working face were analysed by theoretical analysis and numerical simulation. Research results show that the damage variable of coal with joints first rises, then decreases, and finally increases with increasing dip angle of the joints; as the azimuth of the joints increases, the damage variable first declines, then increases; the damage variable gradually declines with increasing joint spacing; an increase in the dip angle of joints corresponds to first reduction, then growth, and a final decrease of the abutment pressure at the same position in front of the coal walls; on certain conditions, the abutment pressure at the same position within the LEZ first rises, then declines as the azimuth of joints increases; with the growth of the joint spacing, the abutment pressure at the same position within the LEZ rises. The dip angle and azimuth of joints marginally affect the abutment pressure within the LEZ.

Research on Pressure Relief Hole Parameters Based on Abutment Pressure Distribution Pattern

Borehole pressure relief technology is an effective way to reduce the elastic energy in the surrounding rock of deep roadways, thereby reducing the risk of regional rock bursts. To avoid large deformation of the roadway caused by pressure relief holes with large diameters and insufficient pressure relief with small pore diameters, this study proposes precise pressure relief holes with nonequal diameters in order to achieve strong pressure relief with minimal disturbance based on the abutment pressure distribution pattern. To verify the pressure relief effect of the nonequal diameter holes, numerical simulations were performed in FLAC3D. This study investigated stress field, deformation laws, and plastic failure zone of roadway surrounding rock with 100 mm pressure relief holes, nonequal diameter precision pressure relief hole (100 mm + 300 mm), and 300 mm pressure relief holes. The simulation results show that, as the diameter of the pressure relief hole increases, the coupling effect of evenly spaced adjacent pressure relief holes is strengthened, thus improving the pressure relief efficiency. When pressure relief holes of nonequal diameter are adopted, the stress environment of the surrounding rock is clearly improved compared to100 mm pressure relief holes, and the plastic failure range increased by 2-3 times. The roof-to-floor convergence with nonequal diameter is 30.8% that of 300 mm pressure relief holes and 41% that of 100 mm pressure relief holes. Furthermore, the rib displacement is 30.4% and 46.9% that of 300 mm and 100 mm pressure relief holes, respectively. Thus, precise pressure relief holes with nonequal diameter provide both strong pressure relief associated with large diameter holes and small disturbance of small diameter of small holes. This study provides a reference for precise pressure relief application with pressure relief holes.

Influence of Upper Seam Extraction on Abutment Pressure Distribution during Lower Seam Extraction in Deep Mining

Pressure-relief coal mining provides an effective way to decrease stress concentration in deep mining and ensures mining safety. However, there is currently a lack of research and field verification on the pressure-relief efficiency and influencing factors during upper seam extraction on the lower seam. In order to make up for this deficiency, in this study, field measurements were conducted in panel Y485, which has a maximum depth of 1030 m and is partially under the goaf of the upper 5# seam in the Tangshan coal mine, China, and evolution of advanced abutment pressure was analyzed. Numerical simulations were conducted to study of influence of key strata on advanced abutment pressure. Influence mechanisms of the upper seam extraction on the advanced abutment pressure distribution during lower seam extraction were revealed. The results indicate that the distribution of advanced abutment stress is influenced by the key strata in the overlying strata. The key strata above the upper coal seam were fractured due to the upper coal seam mining, and the advanced abutment stress was only influenced by the key strata between the two seams during lower coal seam mining. When key strata were present between two seams, the extraction of the lower seam still faces potential dynamic disasters after the extraction of the upper seam. In this case, it would be necessary to fracture the key strata between the two seams in advance for the purpose of mining safety. Key strata in the overlying strata of the 5# seam were fractured during extraction, and advanced abutment pressure was only influenced by the key strata located between the two mined seams. The influence distance of advanced abutment pressure in panel Y485 decreased from 73 m to 38 m, and the distance between the peak advanced abutment pressure and the panel decreased from 29 m to 20.5 m, achieving a pronounced pressure-relief effect.

Test research on advance abutment pressure caused by coal mining based on optical fiber monitoring

The strata movement and deformation caused by underground mining activities is a typical “black box” problem, it is difficult to grasp the structural characteristics of complete overburden and the law of ground pressure. Abutment pressure is the vertical supporting force acting on coal and rock mass due to the redistribution of surrounding rock stress caused by underground engineering excavation. The distributed optical fiber and fiber Bragg grating are implanted into the physical similar model to monitor the distribution characteristics of abutment pressure in front of the working face during the whole excavation process. The results show that FBG monitoring to reach the peak strain needs to meet two conditions: the working face passes under it, and the cantilever beam structure above the working face is unstable and collapses, and the grating is located at the end of the suspended fixed beam. When FBG is located in front of the working face, the whole process is divided into four stages: 150-81 m from the grating is the weak influence area; 81-49.5 m is the significant influence area; 49.5-21 m from the grating is the severe influence area; 21-0 m from the grating is the influence recovery area. Based on this, the abutment pressure distribution model of FBG sensing detection is given. The influence range is within 81 m, the peak value is 21 m in front of the working face, and the pressure relief area is directly above the working face. The distributed optical fiber monitoring results show that the upward compressive stress value of the abutment pressure affected area decreases rapidly, and enters into the high roof tensile stress affected area. The tensile stress distribution presents a single peak shape, and gradually decreases after reaching the peak until it returns to the elastic area. The research results provide a new research idea for abutment pressure monitoring caused by mining.

A Control Approach of the Roof in No-Pillar Roadway Formed by Roof Cutting and Pressure Releasing

Roof control is one of the eternal themes of mine pressure theory, and it is also a key step of roadway formed by roof cutting. Based on the analysis of abutment pressure distribution, the viewpoint of controlling roadway roof by roof cutting distance is put forward according to the failure limit of roadway roof, and the calculation method of roof cutting distance is given. Based on the Qiuji coal mine’s background, the numerical and field test study is conducted to verify the theoretical analysis, and the allowable variation range of roof cutting distance is obtained. The research shows that the roof cutting distance, abutment pressure, and roadway deformation are closely related. By controlling the roof cutting distance, the roadway roof can be placed in the low-stress area, the roadway deformation can be reduced, and the support cost can be saved. This study provides a theoretical basis for explaining the roadway’s abnormal mine pressure and controlling the roadway roof by roof cutting.

Study on rib spalling control of shortwall drilling mining technology with a large mining height

The drilling shearer and drilling mining technology has been developed in order to effectively control the rib spalling of a shortwall with a large mining height face in a soft thick coal seam. Working face no. 1305 of the Zhaozhuang Coal Mine was taken as the research subject. The rationality and superiority of shortwall drilling mining technology with a large mining height (SDMTLMH) were explained by combining the theoretical analysis with a numerical simulation. First, based on the occurrence characteristics of the immediate roof, the mechanical model of a simple supported beam was established to calculate the maximum unsupported roof distance. The advance of the working cycle was determined. Then, based on the spatial mobilization plane (SMP) theory, the abutment pressure distribution in the reserved coal was deduced by establishing the unit mechanical model. The appropriate range of the width of the reserved coal (WRC) was determined according to the principle of conservation of energy. Finally, six drilling mining schemes were proposed according to the range of the WRC. In addition, we redeveloped the constitutive model of supports and compacted rock mass in the gob using FLAC3D software. The distribution of the abutment pressure in the drilling mining face and the control effect of the rib spalling were obtained. It was proved that the SDMTLMH can effectively suppress rib spalling and roof fall. The distribution of the strain energy and the external potential energy in reserved coal in six schemes was plotted by Surfer software. The rationality of the theoretical analysis was verified. Considering the caving effect of the reserved coal, the control effect of rib spalling, and the appropriate advancing speed of the working face, the appropriate WRC was determined to be 0.4 m. A field investigation showed that the control effect of rib spalling for working face No. 1305 was much better than that of other large mining height faces in this coal mine.

A new monitoring-while-drilling method of large diameter drilling in underground coal mine and their application

Large Diameter Drilling (LDD) is a widely-used pressure relief method in underground coal mine, but LDD is now only used as a measure to reduce the occurrence probability of rock burst, the drilling difficulties and dynamic phenomena are not used efficiently. Innovative Monitoring-While-Drilling (MWD) technology is put forward by using microseismic (MS) system to monitor the vibration signals and excellent results have been achieved. MS monitoring results can display the actual depth of LDD holes and express the drilling difficulty of different depths to reflect stress state. Besides, measurement coal vibration events can reveal the degree of pressure relief. The experimental results are of great value to drilling depth supervision, abutment pressure distribution, and pressure relief effect evaluation.

Abutment pressure distribution pattern and size optimization of coal pillar under repeated mining: a case study

Abutment pressure distribution is the decisive factor affecting the stability of coal pillars, which has an important significance in realizing safe and efficient mining. In recent years, many working faces adopting double-roadway arrangement have appeared in the western mining areas in China, which makes coal pillar abutment pressure complex under repeated mining. In order to reveal the distribution pattern of coal pillar abutment pressure under repeated mining, the evolution of a stress field of surrounding rock was analyzed by a numerical method based on the actual situation of a double-roadway arranged mining roadway in Longde Coal Mine, and the distribution characteristics of coal pillar abutment pressure were revealed. The reasonable width of the section coal pillar was given further. The research results showed that (1) the surrounding rock stress is transferred to the working face coal body and section coal pillar between roadways under the influence of mining advance the working face, while the stress is transferred to the section coal pillar between roadways under the mining influence behind the working face. The presence of goaf in the upper segment makes the stress distribution of surrounding rock more complicated. (2) The distribution of coal pillar abutment pressure shows a staged change. The influence of mining advance the working face on the peak abutment pressure is notable, which highlights the significance of temporary reinforcement support in the advanced section of the working face. (3) After the mining of the upper working face is finished, the yield damage width of the coal pillar on the side of the goaf was about 4.0 m. During the second mining period, the yield damage width of the coal pillar was totally about 7.0 m. (4) Taking into account factors such as safe production and economic rationality, it was finally determined that the reasonable section coal pillar width is 12.5 m for this mine.

Stress Analysis of Negative Coal Pillar Gob-Side Entry and Its Principle of Preventing Rock Burst

Gob-side entry is an area where it is difficult to prevent and control the frequent occurrence of rock burst. Based on “Longwall Mining with Split-level Gateways” (LMSG), this paper puts forward the technology of preventing rock burst by a new gob-side entry (NCPG). The abutment pressure distribution of LMSG shows that the stress peak of solid coal is lower than the conventional panel, and the width of the limit equilibrium zone is also reduced by a small percentage. After the narrow coal pillar gob-side entry has been excavated, the peak stress in solid coal increases, and the width of the limit equilibrium zone decreases, so the practical stress concentration increases. However, the NCPG located in areas of lower stress. The peak stress in solid coal of the NCPG does not increase, but the width of the limit equilibrium zone increases, so the practical stress concentration decreases. NCPC makes the concentrated stress transfer into the deep coal body and plays the role of pressure avoidance. Compared with the narrow coal pillar gob-side entry, the NCPG reduces the energy stored in coal and rock masses and increases the energy consumption. It has significantly improved the regionality, initiative, safety, and timeliness of rock burst prevention in deep high-stress coal seam mining.

Coal Mine Abutment Pressure Distribution Based on a Strain-Softening Model

The coal in front of mining face presents strain softening deformation characteristics. An analytical model is proposed to simulate the abutment pressure distribution over the coal in front of mining face under elastic and inelastic conditions. A new theoretical formula is derived to calculate the abutment pressure distribution and its width in elastic and inelastic regions of the coal under limit equilibrium condition. The influences of UCS, residual strength, mining height, softening modulus and deformation angle on abutment pressure distribution are discussed. The study results show that, (1) stress gradient in plastic area is larger than crushed zone; (2) the width of plastic region is independent of the peak abutment pressure, but it is dependent of UCS, residual strength, mining height, softening modulus and deformation angle; (3) the width of crushed zone in inelastic area is closely related to peak abutment pressure, coal-floor interface cohesion and friction coefficient; (4) the width of elastic zone is dependent of mining height, coefficient of horizontal pressure, coal-floor interface friction coefficient and peak abutment pressure where the coefficient of horizontal pressure has the highest impact that the width of elastic zone has logarithmic decrease with the increase of the coefficient of horizontal pressure. A case study is carried out at longwall panel 07 of No. 5 coal seam in Dongjiahe Coal Mine to verify the analytical model. The abutment pressure distribution and the widths of elastic and inelastic zones under limit equilibrium condition are calculated based on the relevant parameters. The theoretical results are compared with the field monitoring data which shows very good fit. It is proved that the proposed analytical model has high accuracy and the feasibility of the model is verified. The study results can provide guidance for similar engineering applications.

Case study on the mining‐induced stress evolution of an extra‐thick coal seam under hard roof conditions

AbstractA strong mining disturbance may cause the superposition of local stresses and serious disasters such as crushed supports and severely destroyed roadways. To study the distribution law of mining‐induced stress under hard roof conditions, an advance abutment pressure distribution model was developed. By monitoring the support pressure, a novel method of reckoning intensive factors was proposed, and then, the pressure distribution characteristics were obtained. An innovative in situ test of the mining‐induced stress increment was performed. At the Tongxin coal mine, the field monitoring of no. 8309 working face revealed the following. (a) The peak position of the fully mechanized working face with a hard roof was 5.9 m away from the mining face in which the average intensive factor K was 1.48. The pressure of the single props developed could be roughly divided into the fluctuation, slow increase, and stable stages. (b) A theoretical model of the stress evolution of the working face was proposed. Using an in situ uniaxial compression test, a law governing the variation of the advance abutment pressure was developed. The peak strength was reported to be 36 MPa, which is consistent with the advance prop pressure. (c) Mining‐induced stress violently fluctuated during the process of top coal caving; the K values in the supports in the middle of the working face and their rates of growth were apparently higher than those in the end supports. A Gaussian distribution of K was established for this phenomenon. The results obtained provide first‐hand data for safe and efficient mining under similar geological conditions.

Study on the abutment pressure distribution in top coal caving

The investigation on the deformation and failure of top coal and its roof strata is the key topic of fundamental research of the fully mechanized top coal caving method. In this paper, the mechanical model of continuous damage and failure of top coal is established based on damage mechanics and statistical strength theory. Owing to the declining of horizontal pressure in top coal during caving, the distribution of the abutment pressure is also studied. The theoretical results are in agreement with the experimental data.