Roof Deformation Research Articles

Instantaneous discharge characteristics and its methane ignition mechanism of coal mine rock damage.

The goaf is the main site of gas explosions in coal mines. A large number of accidents indicate that the occurrence of gas explosion in the goaf is related to the deformation and fracture of the goaf roof. An experimental system was constructed to study the instantaneous discharge characteristics and its ignition mechanism caused by rock damage. The research results reveal that different rocks produce avalanche-like dust clouds ejected outward during the fracture process, and the generation process takes an extremely short time. This dust cloud is not caused by rock fragments heated to incandescence because of friction. The electric sparks produced in the process of rock rupture and the appearance of instantaneous discharge are related not only to the quartz content of the rock, but also to the compressive strength of the rock. The piezoelectric effect of the rock becomes the key factor for the strength or the generation of an electric spark. The instantaneous discharge leaded to the collision of high-energy electrons released during the fracture process with air molecules, ionising, and breaking down the air. When the surrounding medium is gas air within the explosion limit, ionisation is formed and causes gas explosions.

Roof deformation characteristics and experimental verification of advanced coupling support system supporting roadway

AbstractThe advanced hydraulic support group combined with bolts (cables) constitutes the advanced coupling support system, which can ensure the stability of coal mine roadway safely and effectively. To explore the influence of the initial bearing capacity of the advanced hydraulic support on roadway roof deformation under anchor bar (cable) action. According to the actual geological conditions and roadway support of the 15106 working faces in Pingshuo Coal Mine, Yangquan, and Shanxi. Based on the change in the stress and displacement of the half‐space body under normal force in elastic theory and combined with the linear superposition principle, the contact mechanics model of the advanced hydraulic support group and roadway roof under anchorage is established. Selecting the measured anchor bar (cable) preload in the coal mine as the input load of the model, the stress and displacement distribution of the roadway roof under different initial bearing capacities are calculated. The calculation results show that the stress and displacement of the roadway roof along the axis exhibit a “symmetrical distribution” and the whole roadway exhibits a “saddle surface” gradient distribution during the active support of advanced hydraulic support under anchorage. The increase in the initial bearing capacity of the advanced hydraulic support has a great influence on the support effect in the middle area of the roadway and has a relatively small influence on the support effect in the surrounding area of the roof. With an increase in an initial support capacity, the stress gradient changes violently but substantially less than it would under the crushing strength of the surrounding rock. Using the similar simulation experiment theory, a similar simulation experiment roadway was established at 1:40, and the simulation experiment of an advanced hydraulic support coupling active support under anchor protection was carried out. The maximum error percentage of the theoretical calculation and experimental results of roof deformation under different initial bearing capacities is 19.51%, and the maximum error percentage of stress is 13.77%. The accuracy of the distribution law of roof stress and displacement under the initial bearing capacity in the process of active support obtained by theoretical calculation is verified. The research results provide a theoretical basis for advanced coupling adaptive support and the control of fully mechanized mining faces.

Investigation on the key techniques and application of the new-generation automatically formed roadway without coal pillars by roof cutting

The first-generation automatically formed roadway without coal pillars by roof cutting (AFRCPRC) technology has achieved significant technical and economic benefits in the period 2009–2019. However, it adopts shaped charge blasting for roof cutting, which is not only unsafe but also troublesome with respect to explosive approval. Besides, the installation procedure of macro-negative Poisson's ratio (NPR) anchor cable is rather complicated. To overcome these drawbacks, the second-generation AFRCPRC technology was developed in 2020. It employs a non-explosive blasting method, i.e., instantaneous expander, forming a single fracture (IESF), and thus its safety is greatly improved. In addition, micro-NPR anchor cables, which are easy to operate and have the characteristics of large elongation, high strength, strong impact resistance and no obvious necking phenomenon, are used for roadway support. In this paper, the basic principles, key techniques and main processes of the second-generation AFRCPRC technology are introduced, and experiments that were conducted in a coal mine are described. The experimental results show that IESF has excellent directional roof-cutting ability which can replace the explosive energy-focusing blasting, and the micro-NPR anchor cable boasts superior supporting performance which can effectively control roof deformation. The automatically formed roadway deforms insignificantly and satisfies the requirement of the next working face, illustrating the success of the second-generation AFRCPRC technology. Compared with the first-generation AFRCPRC technology, the remarkably improved second-generation one will have greater application potential in the mining field.

Numerical Investigation on Stratum and Surface Deformation in Underground Phosphorite Mining Under Different Mining Methods

With the ending of deep-concave open-pit phosphorite extractions and gradual exhausting of shallow mineral resources, stoping of phosphorite seams has entered or will enter into underground mining. Particularly for excavating slightly inclined thin and medium-thick phosphorite orebodies, roof and surface control under different mining methods is crucial for safe and efficient exploitations. In this study, the study area is located in Kunyang Phosphorite Mine characterized by slightly inclined thin and medium-thick deposits. Based on the occurrence conditions, orebody thickness, dip angle, and more factors, the mining methods of underground phosphorite are selected, including room and pillar mining, cement backfill mining, and caving mining. Numerical analysis on roof deformation and surface subsidence under the three methods is performed. The results show that the amount of roof and surface subsidence decreases successively by the caving method, room and pillar method, and cement backfill method. The maximum roof and surface subsidence by the caving method is 45.7 and 13.3 cm, respectively. Regarding shallow orebodies, the open-pit slope is obviously disturbed by the caving method and room and pillar mining method. Hence, slope displacement monitoring should be emphasized. Compared with the other two methods, the backfill mining method can use mined wastes as backfill materials and has less influence on the roof and surface during stoping and is better at controlling slope stability.

Complications Associated with Spreader Grafts and Spreader Flaps: A Systematic Review.

Spreader grafts and spreader flaps are one of the most common techniques utilized in rhinoplasty surgeries. The aim of this study was to determine the complications, satisfaction, and revision rates associated with spreader grafts and spreader flaps and to compare these two modalities. PRISMA guidelines were followed for conducting this systematic review. The authors searched the literature systematically for pertinent materials in PubMed/Medline and Google Scholar. Inclusion criteria of this search included: randomized and non-randomized clinical trials, cohorts, and case series with more than 5 participants on rhinoplasty using spreader grafts or spreader flaps with detailed report either on complications, revision, and satisfaction rates. Furthermore, exclusion criteria included: any cadaveric or non-human study, case reports, technical notes, and review articles. The initial literature search yielded a total of 193 studies. Following screening each paper and implementing the inclusion and exclusion criteria, 40 articles were chosen. In the spreader graft group, from 21 studies reporting complications, 6 of them reported no complication. The most common complications were nasal obstruction, inverted V deformity and open roof deformity, deviation, and infection. In the spreader flap group, from 6 studies reporting any existing complications, 1 reported no complications. Five other studies reported some degree of complications. In terms of revision rate, 10 patients (0.62%) underwent revision surgery after spreader graft placement, while only 2 patients (0.35%) revised surgically in the spreader flap group. These two methods seem to have no significant difference in terms of complication rates, and both are recommended as a choice in middle vault reconstruction when each of their clinical use is indicated. This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266.

An Analytical Elastic Solution for Right-Angle Trapezoidal Opening in Steeply Inclined Coal Seam

In the process of underground mining, steeply inclined rocks or coal seams are often encountered, forming the openings of right-angle trapezoid. According to the geological conditions of a mining project in China, an analytical elastic solution of stress and displacement around right-angle trapezoidal opening in a homogeneous, isotropic, and linear elastic geomaterial is presented, which is based on the evaluation of the conformal mapping representation by an appropriate numerical calculation and the complex potential functions. The different results from other shaped openings are shown as follows. In a right-angle trapezoidal opening, the maximum displacements of roof falling occur on the low side, while the most horizontal displacements on the low side are around the roof and the most horizontal displacements on the high side are around the middle of the high side in this opening. These results are also compared with the numerical calculations in FLAC software, illustrating that the solution may be easily applied to rock mechanics or rock engineering for understanding the deformation of floor heave and roof falling down. The solution is also suitable for optimum design of bolt supporting in a right-angle trapezoidal opening, which is different from the traditional concept of symmetrical bolt supporting. Finally, a methodology is proposed for the estimation of conformal mapping coefficients for a given cross-sectional shape of an opening without symmetrical axis.

Analysis and Design of the Accessory Structure under the Large Deformation of a Flexible Roof

An increasing number of large‐span space structures use flexible roofs to achieve a light and splendid architectural effect. When a flexible structural system such as a cable net is applied in a large‐span stadium, the roof will deform significantly under the self‐weight and wind load. Accessory structures of the roof such as catwalks, radial drainage pipes, circular drainage channels, and radial cable trenches need to cooperate with the large deformation of the roof to prevent damage caused by the large deformation of the roof. To thoroughly unveil the analysis and design method of an accessory structure, this paper first carried out the wind tunnel test to determine the wind load of the structure. Then, the gust response factors of each roof area and the dynamic amplification coefficient of the accessory structure considering the roof vibration were determined. Next, circular and radial catwalks were designed based on static analysis. A sliding joint was set in the accessory structure to adapt to the large deformation of the roof. Finally, a time history analysis of the catwalk was carried out to obtain the maximum deformation value of the sliding joint for the safety of the structure. The results demonstrate that the maximum deformation is less than the value given by the design and meets the specification.

Research on Surrounding Rock Stability Affected by Surrounding Rock Pressure and Rock Fracture under Blasting Vibration Load Action

The influence mechanisms of factors, such as high confining pressure and in situ stress caused by deep mining on the stability of surrounding rock of roadways, are complex. Particularly, the motion and energy release of the rock mass medium can be caused by vibration transmission induced by blasting excavation in the underground mining. Based on this, by taking a metal mine with the buried depth of 498 m as a research object, influences of different excavation distances on roof deformation and stress of roadway surrounding rock during the excavation were studied by using a three‐dimensional numerical model. Moreover, the weak position of the roof of surrounding rock was determined. Finally, influences of fractured rock mass on propagation of blasting vibration waves in surrounding rock and energy distribution characteristics were analyzed. The research shows that rock mass around the excavated roadway moves towards the excavated space in different advance stages of a working face. The displacement fields on the top of a lateral tunnel present a heart‐shaped distribution along the working face and the maximum displacement appears to the roof at the junction of the lateral tunnel and a horizontal roadway along veins. As the advance distance of the working face increases, compression‐shear failure mostly occurs in the roadway surrounding rock, and tensile failure and combined tensile and shear failure occur at the unsupported roof and floor of the roadway. With the rise of the confining pressure, the total energy in frequency bands increases and its increase amplitude also rises. Furthermore, energy in a frequency domain of response signals to blasting vibration is transmitted from a secondary frequency band to a primary frequency band and is increasingly concentrated. With the increase of the damage degree of the roadway, signal energy in the frequency domain is transmitted from the primary to the secondary frequency band and signal energy is distributed more dispersedly. The test results are basically consistent with numerical simulation results. This study could provide technical guidance for the stability evaluation of surrounding rock of underground engineering structures.

Roof Deformation and Collapse of Stamps With Isolated Grooves: A Contact Mechanics Approach

Abstract This paper has revisited the roof deformation and collapse of stamps with isolated grooves based on a contact mechanics approach, with emphasis on establishing the nonadhesive and adhesive contact solutions for surfaces containing a shallow rectangular groove with the effects of applied load and interfacial adhesion taken into account. By solving singular integral equations and using the energy release rate approach, closed-form solutions are derived analytically for the deformed groove shapes, interfacial stress distributions, and equilibrium relations between load and contact size, which reduce to the previously proposed solutions without adhesion or without applied load. Finite element (FE) analysis is performed to validate the nonadhesion solutions, while experiment results of stamp collapse reported in the literature are adopted to examine the adhesion solutions. By introducing the Johnson parameter α to represent a competition between surface energy and elastic strain energy of the groove, four kinds of contact behaviors of the groove roof can be characterized appropriately: nonadhesion, weak adhesion, intermediate adhesion, and strong adhesion. Hysteresis loop and energy loss due to distinct load/unloading paths are revealed in the cases of intermediate and strong adhesion. We have also provided the critical applied pressure to achieve roof collapse and the corresponding equilibrium contact size for full range of α.

Mechanism of Rock Bursts Induced by the Synthetic Action of “Roof Bending and Rock Pillar Prying” in Subvertical Extra-Thick Coal Seams

When studying the rock burst mechanism in subvertical extra-thick coal seams in the Wudong coal mine in Xinjiang, China, most studies focus on rock pillars, while the effect of the roof on rock bursts is usually ignored. In this paper, a rock burst mechanism in subvertical extra-thick coal seams under the control of a “roof-rock pillar” is proposed. A theoretical analysis is first performed to explain the effect of roof-rock pillar combinations on rock bursts in coal seams. Numerical modeling and microseismic analysis are implemented to further study the mechanism of rock burst. The main conclusions are as follows: 1) During the mining of the B3+6 coal seam, an obvious microseismic concentration phenomenon is found in both the roof and rock pillar of B3+6. The rock bursts exhibited obvious directionality, and its main failure characteristics are floor heave and sidewall heave, but there will also be some failures such as shoulder socket subsidence in some parts. 2) The stress transfer caused by rock pillar prying is the main reason for the large difference in rock burst occurrence near the vertical and extra thick adjacent coal seams under the same mining depth. 3) Under the same cantilever length, the elastic deformation energy of the roof is much greater than that of the rock pillar, which makes it easier to produce high-energy microseismic events. With an increasing mining depth, the roof will become the dominant factor controlling the occurrence of rock bursts. 4) The high-energy event produced by the rock mass fracture near the coal rock interface easily induces rock bursts, while the high-energy event produced by the fracture at the far end of the rock mass is less likely to induce rock burst. 5) Roof deformation extrusion and rock pillar prying provide high static stress conditions for the occurrence of rock bursts in the B3+6 coal seam. The superposition of the dynamic disturbance caused by roof and rock pillar failure and the high static stress of the coal seam is the main cause of rock burst in the B3+6 coal seam.

Physical Simulation Test on Surrounding Rock Deformation of Roof Rockburst in Continuous Tunneling Roadway

To study the occurrence process, as well as the temporal and spatial evolution laws, of rockburst disasters, the roof deformation of continuous heading roadways during rockburst was studied through a physical similarity simulation test with a high similarity ratio and low strength. The deformation and failure evolution law of the roadway roof in the process of rockburst were analyzed by using detection systems, including a strain acquisition system and a high-power digital micro-imaging system. The results show that the rockburst of the roadway roof can be divided into four stages: equilibrium, debris ejection, stable failure, and complete failure stage. According to the stress state of a I–II composite crack, the theoretical buckling failure strength of the surrounding rock is determined as 1.43 times the tensile strength. The flexural failure strength of a vanadium-bearing shale is 1.29–1.76 times its compressive strength. With continuous advancement in the mining time, the internal expansion energy of the roadway roof-surrounding rock in the equilibrium stage continuously accumulates. The fracture network continuously increases, developing to the stable failure stage, with bending deformation, accompanied by continuous particle ejection until the cumulative stress in the failure stage increases, and the tensile state of the rock surrounding the roof expands radially into deep rock. A microscopic damage study in similar material demonstrated that the deformation of the roadway roof is non-uniform and uncoordinated. In the four stages, the storage deformation of the rock surrounding the roadway roof changes from small accumulation to continuous deformation, to the left (or deep rock). Finally, the roadway roof-surrounding rock becomes completely tensioned. The research results presented in this study provide a reference for the prediction and control of rockburst in practical engineering.

Failure characteristics and stability control technology of dynamic pressure roadway affected by the mining activity: A case study

Dynamic pressure roadway affected by the mining activity (DPRAMA), which is aimed at promoting the efficiency of panel replacement, is a new mode of roadway arrangement in neighboring panels. However, the failure characteristics and stability control of DPRAMA surrounding rock are rarely reported. In this study, the fragment grade of two-side coal mass of DPRAMA in Gaojiapu Coal Mine was evaluated using the basic measurement scale-fragment grade evaluation method. Then, the evolution of rock mass failure was analyzed through Flac3D software. The results show that (1) under static loading, DPRAMA is highly stable. (2) Under the second dynamic loading, the stress concentration coefficient and deformation value of surrounding rock both surges. (3) Under dynamic-static loadings, the roof falling value is far larger than the floor heave value, and the deformation of pillar-side coal mass is more serious than that of panel-side coal mass. Surrounding rock deformation is divided into three phases, and the specific support strategy is selected in accordance with the characteristics of each stage. (4) The plastic region shows a tendency of butterfly-shaped failure. Based on these findings, the surrounding rock control strategy of “slow yield and long-short control” was proposed to alleviate roof and pillar-side coal mass deformation. Furthermore, the coupling support scheme of “high-strength yield bolt (cable) & steel band” was designed for DPRAMA.

Quantitative investigation on the stability of salt cavity gas storage with multiple interlayers above the cavity roof

For the sake of safety and stability, a salt roof with certain thickness is usually designed above the cavity. While some rock salt often contains multi-interlayers above the cavity roof in China, which brings new challenges to designing salt roof thickness and evaluating cavity stability. On this basis, the factors affecting the stability of cavity with multiple interlayers above cavity roof is investigated. Combining single factor sensitivity analysis and analytic hierarchy process, the influence of each factor on cavity stability and roof deformation is quantitatively analyzed. Numerical simulation results show that when there are multiple interlayers above cavity roof, the stress and deformation of the cavity are increased compared with general conditions. The rock salt roof thickness has little effect on the stability of the cavity, but the cavity tightness is at risk when it is small. When the operating pressure is setting reasonably, the rock salt roof thickness should be greater than 11 m at around 1000 m deep and 17 m at about 2000 m deep. When the depth of the cavity is less than 1700 m and greater than 2000 m, the minimum operating pressure should be 0.3 and 0.4 times of the gravity stress at the depth of cavity roof. The change of the interlayers stiffness has a little impact on the stability of the cavity. The quantitative analysis indicates that the minimum operating pressure and buried depth are two critical factors that need special attention to ensure the stable operation of the salt cavity gas storage.

Rebound Mechanism and Control of the Hard Main Roof in the Deep Mining Roadway in Huainan Mining Area

Taking the occurrence conditions of the hard main roof in the deep 13-1 coal mining roadway in Huainan mining area as the research object, based on the mechanical parameters of the surrounding rock and the stress state of the main roof obtained by numerical simulation, a simply supported beam calculation model was established based on the damage factor D, main roof support reaction RA, RB, and critical range C (9 m) and B (7 m) at the elastoplastic junction of the solid coal side and mining face side (hereinafter referred to as “junction”). Considering that the damage area still has a large bearing capacity, the vertical stress of the main roof at the junction is K1γH (0.05γh, 0.15γh, and 0.25γh) and K2γH (0.01γh, 0.10γh, and 0.2γh). The maximum deflection is 21 mm, 324 mm, and 627.6 mm, respectively. According to the criterion of tensile failure, the maximum bending moment of the top beam is 209 mN·m at the side of the working face 3.1 m away from the roadway side when K1 = 0.15 and K2 = 0.10, and the whole hard main roof is in tensile failure except the junction. To control the stability of the top beam and simplify the supporting reaction to limit the deformation of the slope angle, RC and RD are used to construct the statically indeterminate beam. By adding an anchor cable and advance self-moving support to the roadway side angle, the problem of difficult control of the surrounding rock with a large deformation of the side angle roof is solved, which provides a reference for roof control under similar conditions.

Study on the dynamic evolution characteristics of deformation and collapse of the extra-thick hard roof

Study on the dynamic evolution characteristics of deformation and collapse of the extra-thick hard roof

Analysis on accumulated deformation and stress of the steel roof of Beijing Opera House during construction

This paper aims to study the stress and deformation of large steel structure buildings in the actual construction process. Midas Gen finite element software is used to simulate and analyze the whole construction process of the curved reticulated shell roof, the peripheral steel columns and the permanent support. The stress and deformation results of the structure in the final construction state are compared with those in the design state under one-time loading. The results show that, in the final construction state, the maximum tensile stress and the maximum compressive stress are 1.9 times and 2.0 times of that in the design state under one-time loading respectively, which is very significant. When the design model is loaded with weight at one time, the maximum tensile stress and the maximum compressive stress of the structure both appear near the opening of the steel roof, while in the final construction state, the maximum tensile stress of the structure appears near the boundary frame beam, and the maximum compressive stress appears on the main ridge beam. The maximum vertical displacement of the structure in the final construction state is 2.0 times of that when the design model is loaded at one time. The maximum vertical displacement of the design state appears near the opening of the steel roof, while the maximum vertical displacement of the structure in the final construction state appears on the main ridge beam. In view of the above, the effective guidance for the construction of steel roof structure is provided in this paper to ensure the safety of the structure.

Research and Practice on Filling Technology of Fully Mechanized Coal Mining Face through Trend Abandoned Roadway

Taking the fully mechanized mining face (FMMF) through the abandoned roadway (AR) in a coal mine in Shanxi Province, China as the engineering background, the field investigation, theoretical analysis, numerical simulation and field test were comprehensively used to study the instability mechanism of the trend AR. The deformation and failure evolution of the trend AR roof were deduced into four stages: initial deformation, bending and separation deformation, fracture failure, and collapse destruction. The high span ratio proved to be the key factor affecting the stability of the trend AR, and the control principle of timely support and reduction of roof span should be followed for controlling the roof of trend AR. Comparing the traditional method through the trend AR with the perspectives of technological and economic benefits, the technology of filling and controlling the trend AR with the high water material over in the FMMF was proposed, and the effect of the filling body on the roof of the trend AR was revealed. The key parameters of the filling body were identified: the strength of the filling body is 1.0 MPa, and the water-cement ratio corresponding to the high-water material is 8:1. Based on this information, the process of the trend AR filling was designed systematically. Industrial tests show that during the FMMF through the trend AR, the roof was effectively supported by the filling body and the normal coal mining was not significantly affected, so the safe mining of coal resources was guaranteed.

Investigation on the Movement and Fracture Characteristics of an Extra-Thick Hard Roof during Longwall Panel Extraction in the Yima Mining Area, China

As an extra-thick hard roof is a significant contributing factor to frequently induced sudden roof collapse accidents and coal bursts, this study investigates the relationship between extra-thick hard roof movement and mining-induced stress using physical experiments and numerical simulation methods based on mining activities in a longwall panel in the Yima mining area, Henan province, China. The results suggested that the movement and failure processes of the extra-thick roof could be divided into three main periods: the undisturbed, movement stabilization, and sudden collapse periods. The roof displacement remained essentially unchanged during the undisturbed period. During the movement stabilization period, the displacement gradually increased into the upper roof. However, the extra-thick main roof remained undisturbed until the immediate roof experienced its fourth periodic caving in the physical model. Consequently, the displacement expanded rapidly into the extra-thick main roof during the sudden collapse period and the strain energy was violently released when it accumulated in the extra-thick main roof. Additionally, the mining-induced stress was characterized by a sudden decrease in the gradual increase trend when the extra-thick roof instantly collapsed. The deformation and fracture of the extra-thick roof could cause a sudden decrease in the mining-induced stress and lead to continuous and unstable subsidence pressure exerted on the mining panel and roadway. This significantly contributes to the occurrence of coal bursts.

Evolution Mechanism and Stability Analysis of Roof Deflection of Composite Structure Roadway Under Dynamic Load Disturbance

The lithology of the roof of the mining roadway is compound and the thickness of each layer varies considerably, and it is disturbed by dynamic load all the year round. The above factors has caused a huge difference in the stability of the roadway surrounding rock. Taking the 11,020 lower tunnel of a mine in Henan Province as the engineering geological background, using on-site investigation, formula derivation, numerical simulation and other methods, the composite roof roadway model group was established to study the deflection evolution characteristics of the surrounding rock under dynamic load disturbance, and summarize the plastic zone of the surrounding rock of the roadway Deformation and evolution of roof surrounding rock to evaluate the stability of surrounding rock with different roof structures. The research results show that the change of the roof surrounding rock structure will also lead to the change of the center deflection of the roadway roof. Therefore, the center deflection of the surrounding rock of various roof composite structures is different, and the deflection is the most direct indicator of the stability of the surrounding rock. The center deflection (\(\omega_{0}\)) of the soft rock type is the largest, the center deflection (\(\omega_{0}\))of the upper soft and the lower hard type, and the soft and hard type is larger, and the soft and hard progressive type, thin, hard and thick soft type (\(\omega_{0}\)) is the smallest, and the dynamic load The relationship between the magnitude of deflection before and after the disturbance is consistent. By constructing a composite roof roadway numerical model group, using the plastic failure zone of the roadway as the evaluation standard, the surrounding rock stability is evaluated and divided, and then the cross-point field measurement method is used to verify the stability of the surrounding rock on the roof of different composite structures. And the development of composite roof roadway surrounding rock deformation and failure mechanism and numerical simulation method has important theoretical significance and practical value for the analysis and control of composite roof roadway surrounding rock stability.

Effect of Compressive Behaviours of Tail Salt Filling Materials on Roof Deformation in Potash Mine

To resolve the problem of top mine instability and the consequent ecological damage caused by different grades of ore deposits in the layered mining process, layered filling-pillar-mining-displacement method (LFPMD) is proposed using a potash mine as an example. Based on the operation principles of the tail salt filling system, the mechanical behaviours of the tail salt under initial tamping and overburden loading were obtained through compaction tests in the laboratory. In addition, the mining-filling mass ratio of tail salt was derived. Based on the mining geological conditions of a potash mine in Laos and the compaction characteristics of tail salt, a mechanical model of top control by tail salt and a numerical model of top control by the pillars were established to discuss the stability of the upper-layer top mine and the lower-layer top mine. It was found that when the elastic foundation coefficient of the tail salt is greater than 550 MN·m−3, and the width of the retained pillars is 10 m, stability of the upper layer and the lower layer can be guaranteed. The results revealed that the LFPMD method can ensure stability of the overburden in the stope and reduce environmental damage while treating tail salt underground.