Floor Deformation Research Articles

Research on Theory and Technology of Floor Heave Control in Semicoal Rock Roadway: Taking Longhu Coal Mine in Qitaihe Mining Area as an Example

Abstract As one of the most common disasters in deep mine roadway, floor heave has caused serious obstacles to mine transportation and normal production activities. The third section winch roadway in the third mining area of Qitaihe Longhu coal mine has a serious floor heave due to the large buried depths of the roadway and the semicoal rock roadway, and the maximum floor heave is 750 mm. For the problem of floor stability, this paper establishes a mechanical model to analyze the stability of roadway floor heave by analogy with the basement heave of deep foundation pit. It provides a model reference for analyzing the problem of roadway floor heave. Aiming at the problem of roadway floor heave in Longhu coal mine, the roadway model is established by using FLAC3D, and the roadway model after support is established according to the on-site support measures. Through the analysis of the distribution of roadway plastic area, stress nephogram, and displacement field simulation results, the results show that the maximum displacement of roadway roof and floor after support is reduced by 15% and 23%, but the maximum floor heave is still 770 mm, which is close to the measured floor heave of roadway. In order to solve the problem of roadway floor heave and integrate economic factors, this paper puts forward three support optimization schemes, simulates the support effect of each scheme, and finally determines that scheme 3 is the best support optimization scheme. Compared with that under the original support, the amount of floor heave is reduced by 81%, and the final amount of floor heave is 150 mm, which can meet the requirements of roadway floor deformation. The results provide a scheme and guidance for roadway support optimization.

Modeling of Floor Heave in Underground Roadways in Dry and Waterlogged Conditions

Floor heaving is a phenomenon that occurs in almost all mining roadways and tunnels. It can restrain the advance of the heading face or cause serious problems during roadway use. The highest levels of floor uplifting are observed in coal mines, which can reduce the output or even stop it altogether. The floor heaving intensity depends on the rock type, the stress in the rock mass, and rocks’ mechanical properties. Floor deformation develops when the secondary state of stress is formed around the working, and it is much higher and more dynamic in the case of waterlogged rocks. The presence of water increases the floor’s propensity to heave, especially clay rocks, such as claystones or mudstones, if they include water-absorbed minerals. In this paper, we present a new modeling methodology for roadway floor heave. The modeling covers a dry floor condition in which the parameters of the Hoek-Brown failure criterion are gradually lowered over time, and a waterlogged floor condition, in which the strength and strain parameters of the rocks are gradually reduced in line with their progressive saturation. In the second case, the claystone floor’s geomechanical parameters were investigated, and the rocks were subjected to water for up to 24 h. The results of the numerical simulation were compared with the in situ measurements of convergence and floor heave in the same coal mines from which the rock samples were collected. The consistency between the numerical simulations and the underground measurements reached 90–99%.

Analytical stress analysis method of interbedded coal and rock floor over confined water: a study on mining failure depth

Deep mining commonly causes redistribution of the stress-strain field for coal seam floor strata. The study of this distribution law was of great significance to analyzing the characteristics of floor deformation and failure and predicting the risk of floor water inrush. In this paper, the damage of a coal seam floor with strong water pressure in the Junggar Basin in western China was examined, and the stress analytical formula for every point of floor confined aquifer was constructed using a stress model in the direction of coal seam strike. Combined with Mohr-Coulomb failure criterion, the maximum depth of floor failure was 17.5 m. According to geological and stratigraphic data of the stope floor, a 3D numerical model of fluid-structure coupling was built. Simulation results showed that under a 1.5 MPa water pressure, the maximum floor failure depth was 18 m. The internal stress of the coal-rock interface and soft rock increases significantly, and the weak coal seam intensifies the transfer of stress and strain at depth to some extent. Water pressure had a certain influence on floor deformation and failure. The joint simulation results of stress-seepage-fracture were closer to the real stope measurements. In the boreholes, two types of sensors, distributed fiber and electrodes were arranged. When the coal floor broke, the compressive strain increased with a peak of 4152 με. Meanwhile, the apparent resistivity of the rock seam reached 500–700 Ω•m. The comprehensive analysis showed that: the floor failure depth in the monitoring area of the 61,303 working face was −18 m, and the floor failure disturbance depth was −35 m. The results presented in this contribution can provide reference for future examinations of coal and rock interbedded floor failure over deep confined water.

Numerical Simulation of Deformation and Failure Mechanism of Main Inclined Shaft in Yuxi Coal Mine, China

Disturbance stresses can cause deformation and damage to a tunnel’s rock, potentially threatening the mine’s safety. This paper investigates the effects of disturbance damage on the main inclined shaft due to the excavation of an electromechanical chamber in a deep inclined shaft at Yuxi Mine. Specifically, a numerical model was constructed using Midas GTX NX and Fast Lagrangian Analysis of Continua in Three Dimensions (FLAC3D) to match the actual engineering conditions, and to reveal the stresses and deformations in the surrounding rock of the main inclined shaft before and after the excavation of the main inclined shaft, the electromechanical chamber and the head chamber. The results revealed that the surrounding rock stress around the main inclined shaft is significantly influenced by excavation disturbance. The bottom bulge occurred due to the unstable vertical and shear stresses in the bottom coal bed moving into free space. After the excavation of the electromechanical chamber, the maximum displacement of the floor can be increased from 0.35468 m to 0.64301 m, nearly doubled, and a large area of surrounding rock deformation occurs in the inclined shaft falling roadway. Affected by excavation disturbance, the maximum deformation of floor can reach 1.06 m, with a wide fluctuation range. The main area of damage to the surrounding rock was identified, except for the main inclined shaft, which occurred near the intersection of the inclined shaft and the drop level location. This area is mainly affected by superimposed tensile stress damage, prone to large area floor heave and spalling. The research content is expected to provide certain theoretical support in taking measures to deal with the deformation and failure of the surrounding rock in a main inclined shaft.

Applied Research of Water Jet Technology in Preventing Rock Burst Occurred in Roadways

Taking mining area 2502 in the Huayan mine field which was affected by strong geological tectonic stress as an engineering background, the water jet technology is studied through in-site survey, laboratory test, theoretical analysis, numerical simulation, and field industrial test. The research results are as follows: the burst tendency of No. 5 coal seam can be reduced to a certain extent after softening with water, and then the water jet technology is used to prevent rock burst of roadways; the typical characteristics of rock-burst accidents mainly cause heaving floor and serious deformation of two sides. The occurrence mechanism of rock burst in roadway ribs has two different forms, and they are static load dominant type and dynamic load dominant type. The abutment stress concentration value is higher than a certain concentration static load, it will affect the coal and rock medium in the floor, and the coal and rock medium in the floor will be transformed into a plastic state and then occur rock burst; the water jet technology for roadway ribs can effectively prevent rock burst of roadway ribs and floor based on the dynamic and static loads superposition theory and Terzaghi theory. Based on the results of numerical simulation, the specific parameters of water jet technology for roadway ribs in 250204 tailgate are as follows: the diameter and length of initial borehole are 110 mm and 20.0 m, the diameter and length of water jet section are 500 mm and 15.0 m, and the spacing between adjacent water jet boreholes is 3.0 m; the monitoring result of signal intensity by EMR indicates that the decreasing amplitude of signal intensity of EMR is about 60.2% on the side of coal-pillar rib, and the decreasing amplitude of signal intensity of EMR is about 68.6% on the side of solid-coal rib; the convergences monitoring result indicates that the convergence ratio of roadway height is about 3.2%, and the convergence ratio of roadway width is about 2.3% in the pressure relief roadway part; the water jet technology is not only helpful to the prevention of rock burst for the roadway ribs but also can play a good prevention of rock burst for roadway floor. The research results provide a theoretical foundation and a new guidance for preventing rock burst in roadway ribs and floor with similar engineering geological conditions.

Математическая модель формирования глубины колеи лесной гусеничной машины

The paper considers the effect of external forces acting on the tracked vehicle chassis and participating in the redistribution of normal reactions on the bearing surface of the continuous track. In the systematic operation of logging and forestry tracked vehicles, conditions may arise when only a part of the bearing surface of the continuous track transmits normal and tangential reactions. In combination with the focus transmission of normal loads, characterized by local maximum loads in the area of supporting rollers, the effect under consideration leads to an increase in overloads, as well as normal and tangential deformations of the soil. The fundamental works on the theory of motion of tracked vehicles practically do not consider this effect, but the results of observations on them and examples of its mathematical description in the related field, the theory of motion of transport vehicles, are known. The research purpose is to propose a mathematical model to estimate the track depth of a tracked vehicle, to predict the energy consumption in case of its motion on deformed forest soils, taking into account the effect of underutilization of the track support surface length in contact with the ground. The objects of research are the chassis of skidders, forwarders and harvesters based on tracked tractors, as well as the chassis of transporters-swamp buggies and other transport and transport technology machines used in logging and timber transportation industry. Conditions under which the epure of normal reactions under the track takes the form of a triangle and does not capture the bearing surface as a whole are formulated. Dependencies have been proposed to quantify the track depth to be formed, the value of work at the vertical deformation of the forest floor and the relative increase in the power of resistance to the motion of the chassis, depending on the relative effective length of the bearing surface. The results of calculations for cohesive and weakly cohesive soils are used as an illustration. The developed model is used independently; however, its integration into the method of the calculated estimation of the operating parameters of machine chassis is also possible.

Geothermal Accumulation Constrained by the Tectonic Transformation in the Gonghe Basin, Northeastern Tibetan Plateau

Abstract Advances in the exploration of the geothermal resources with remarkably high temperatures in the Gonghe Basin, northeastern Tibetan Plateau, provide an enhanced understanding of the origin and emplacement of hot dry rock (HDR). Based on the integrating analysis on the boundary faults distribution and their activity histories, springs and geothermal borehole data, and magnetotelluric data, we propose that the Gonghe Basin formed in a zone of slip dissipation between two major large-scale left-lateral strike-slip faults of the Kunlun fault to the south and the Haiyuan fault to the north during the Neogene time. During the evolution of these two major strike-slip faults, the basin has experienced two-phase developments: the transrotational Gonghe-Qinghai lacustrine basin system during the Miocene and the transpressional Gonghe-Tongde basin system during the Pliocene-Quaternary. In response to the crustal transtension components of the transrotational Gonghe Basin, the partial melting zone at depths of 10–25 km in the thickened crust (~54 km) has been uplifted by ~10 km compared with adjacent regions since the Pliocene. This uplifted partial melting zone may have provided prominent potential heat energy for the HDR in the Triassic granitoid batholith at shallower depths (~3–10 km) by effective enhancement of the geothermal conduction process via deep faulting. With obliquely south-verging thrusting of the Gonghe Nan Shan thrusts in the northern, the Gonghe Basin has transformed from transrotation to transpression-domination during the 6–3 Ma, as well as accompanying with the depocentre migrating to the northwest and in turn the basement elastically uplifting in the southeast. This differential deformation of the basin floor has resulted in a northeastward upward tilting of the Triassic batholith and an isothermal surface. It finally developed the high-temperature and shallow-burial HDR with anomalously temperatures of over 100°C at a depth of 1.5 km in the Qiabuqia and Zhacang geothermal areas in the Gonghe Basin, NE margin of the Tibetan Plateau.

A young age of formation of Rheasilvia basin on Vesta from floor deformation patterns and crater counts

AbstractDelivery of significant volumes of howardite–eucrite–diogenite (HED) meteorites from Vesta to Earth is linked to the largest impact events on that protoplanet, especially the giant Rheasilvia basin. Dawn mapping of Rheasilvia reveals a well‐preserved impact structure with extensive deformation patterns and moderate superposed cratering. Spiral and radial deformation features across the floor of Rheasilvia are also common to complex craters on Ceres and icy satellites, as well as larger bodies like the Moon, Mars, and Mercury, when floor units are not buried by impact melt and debris. These deformation features predate the solidification of such melt/debris mixtures and are important structural elements in complex craters related to failure in converging floor material during late stages of crater formation. The similarity and commonality of such features and lack of preserved ancient units within Rheasilvia indicate that these patterns formed during the latter stages of the impact event and that the original basin floor and subsequent cratering record are preserved. Updated counts and interpretation of this observed superposed cratering indicate an ~0.8–0.9 Ga age of basin formation, supporting a young impact and ejection age. This young age is consistent with recent Ar‐Ar ages of feldspar grains in HED (Lindsay et al., 2015), and it may also be consistent with ancient bulk Ar‐Ar ages (>~3.2 Ga) for some HEDs because resetting such ages requires prolonged heating from the residual impact heating of rocks left on Vesta during earlier impacts. The complex morphology and recent formation of Rheasilvia basin are also consistent with dynamical estimates for delivery of these meteorites to the Earth–Moon system.

Experimental Test on Nonuniform Deformation in the Tilted Strata of a Deep Coal Mine

Taking a deep-mine horizontal roadway in inclined strata as our research object, the true triaxial simulation technique was used to establish a model of the inclined strata and carry out high-stress triaxial loading experiments. The experimental results show that the deformation of surrounding rock in the roadway presents heterogeneous deformation characteristics in time and space: the deformation of the surrounding rock at different positions of the roadway occurs at different times. In the process of deformation of the surrounding rock, deformation and failure occur at the floor of the roadway first, followed by the lower shoulder-angle of the roadway, and finally the rest of the roadway. The deformation amount in the various areas is different. The floor heave deformation of the roadway floor is the greatest and shows obvious left-right asymmetry. The deformation of the higher side is greater than that of the lower side. The model disassembly shows that the development of cracks in the surrounding rock is characterized by more cracks on the higher side and fewer cracks on the lower side but shows larger cracks across the width. The experimental results of high-stress deformation of the surrounding rock are helpful in the design of supports, the reinforcement scheme, and the parameter optimization of roadways in high-stress-inclined rock, and to improve the stability control of deep high-stress roadways.

Evolution of a Fault-Controlled, Deep-Water Sub-Basin, Tabernas, SE Spain

The Neogene Tabernas Basin, SE Spain, provides important evidence at outcrop for the interplay between tectonic deformation of the sea floor, slope instability and turbidity current behaviour. Dextral-oblique strike-slip faults and associated folds propagated along the basin axis to deform the palaeo-sea floor, creating structurally-controlled depressions in which turbidity currents were trapped and ponded. EW-trending syn-depositional faults define a narrow sub-basin that subsided asymmetrically as a negative flower structure. The sub-basin contains an expanded succession (>300 m of ponded turbidite sheets, debrites and slumps) along its northern margin flanked by the principal fault strand defined by a wide zone of sheared and calcite-veined marl. A narrower fault zone with a smaller displacement marks the southern margin of the sub-basin and the fill close to it is thin with internal discordances, evidence of local failure and southward thinning of sandstone sheets. Both northern and southern faults ‘died’ at the same stratigraphic level and were overstepped by basin floor turbidites showing evidence of weaker and longer-range topographic confinement. As turbidites healed and aggraded out of the sub-basin to progressively onlap the southern margin of the basin, major gravity failures occurred emplacing thick (>100 m) mass-transport complexes. The first initially reworked the southern part of the sub-basin fill together with the early onlap wedge, the second remobilised the onlap wedge, and the third records failure of the upper part of the slope well above the wedge. The first two were toe-confined failures, the third and furthest travelled was confined by basin axis topography. All three failures are lateral to or directly overlain by ‘megabed’ sheets on the basin floor, implying either a common trigger (earthquakes) or slope instability following reflection of large volume flows. Tabernas turbidites highlight the role of basin tectonics (as opposed to up-dip supply and sea level fluctuations) in directly impacting on deep-water processes and stratigraphy. Small deep-water transtensional sub-basins opened up along long transfer faults accommodating regional extension.

Design of Longwall Coal Pillar for the Prevention of Water Inrush from the Seam Floor with Through Fault

Setting up a waterproof coal pillar is an important measure to prevent water inrush from the Weibei mining through fault floor. Based on the plastic slip line field theory, a mechanical model of floor water inrush induced by confined water in the through fault zone was established. The mechanical expressions of confined water pressure and the width of the waterproof coal pillar under the state of limit equilibrium were derived. Combining the laws of floor deformation, failure and fault activation under two kinds of coal pillar width, the safety width of the waterproof coal pillar was determined. Furthermore, the safety threshold is better than the empirical value mentioned in the “coal mine safety regulations.” Following this, grouting transformation was carried out on the K2 sand layer of the cut roadway floor. This provided a theoretical basis and engineering practice for water disaster prevention and the control of the structural floor under similar conditions in the Weibei mining area for future benefit.

NUMERICAL ANALYSIS OF FIRE BEHAVIOR OF CONCRETE SLABS IN FULL-SCALE STEEL-FRAME STRUCTURE

The influence of the position and quantity of fire span on the fire behavior of concrete floor in the structure is studied. Based on Vulcan software, using thick plate element and beam-column element, combined with EC2 material high temperature constitutive model, the temperature and deformation of fire top floor (corner and middle) and second floor (four) in a steel frame structure are simulated numerically. The influence of concrete expansion strain on the deformation of floor slab under fire is analyzed, and the membrane mechanism, crack distribution and internal force development of steel beam are investigated. The results show that: the predicted results of floor temperature and deformation are in a good agreement with the experimental results, and the concrete expansion strain has a decisive influence on the mid-span deformation of the fire zone in the structure, that is, when the expansion strain is larger, the predicted deformation is larger; the boundary conditions have a decisive influence on the membrane mechanism and crack distribution of the heated plate, and the heated plates have three kinds of membrane mechanisms: ring type, opposite-edge U type and diagonal U type. The bending moment and axial force of the steel beam near the heated grid gradually increase, and the increase of the axial force of the steel beam is relatively large.

Three-dimensional physical model experiment of mining-induced deformation and failure characteristics of roof and floor in deep underground coal seams

Underground mining engineering causes complex changes in the three-dimensional stress near the working face of a mine, resulting in deformation and failure of the roof and floor rocks, as well as ground subsidence. To study the stress, deformation, and fracture field characteristics of the roof and floor strata due to mining, an indoor large-scale three-dimensional physical similarity model was developed. A novel method was used to simulate the mining process of coal seams. The results show that coal seam mining disrupted the original stress balance; consequently, a bearing pressure was generated in front of the working face, and a significant pressure relief state appeared in a particular area. The collapsed rock blocks of the overburden strata filled the goaf and played a supporting role, causing the overburden stress to increases again to a value close to the original rock stress. After complete mining, the overburden strata subsided, and the floor strata bulged. With an increasing vertical distance from the working face, the deformation of the rock formation gradually decreased. Evident fractured fields were formed in the surrounding rock of the goaf. In the horizontal section of the overburden rock layer, the cracks were distributed in a “rounded rectangular” shape. As the distance from the coal seam increased, the “rounded rectangular” boundary became smoother; the coverage area decreased; and the degree of crack opening and development in the plane decreased. The fractal dimensions of fractures with different overburden heights and different strike positions are calculated using the fractal geometry theory. We found that as the distance from the excavation face increased, the fractal dimensions of the fractures gradually became stable. In addition, numerical simulation methods were used to verify the correctness of the physical similarity model experiments. The research results can provide important references for the stability of deep underground projects such as coal mining process, tunnel excavation process, nuclear waste storage and other engineering stability.

Numerical Investigation on Time-Dependent Deformation in Roadway

The roadway deformation normally relates to time especially for underground coal roadway. The strength of soft coal is low, and therefore the deformation increases gradually under constant stress with time, which is called rheology deformation. In this study, based on a field case, the rock mass properties and deformation data of the roadway were obtained according to the field test. A 3D numerical model was then established, and the rheological deformation including horizontal and vertical deformation of the coal roadway was systematically analyzed. The results showed that the rheological deformation of horizontal sidewall accounts for almost 30% of the whole deformation, and the stable time for such roadway is around 60 days after excavation. The tendency of the roof deformation is similar to the sidewalls, and however, the floor deformation is different. Then the related suggestions for maintaining the stability of such roadway were proposed, which is useful in-field application.

Testing Crack Resistance of Non-Load-Bearing Ceramic Walls with Door Openings.

Cracking in non-load-bearing internal partition walls is a serious problem that frequently occurs in new buildings within the short term after putting them into service or even before completion of construction. Sometimes, it is so considerable that it cannot be accepted by the occupiers. The article presents tests of cracking in ceramic walls with a door opening connected in a rigid and flexible way along vertical edges. The first analyzes were conducted using the finite element method (FEM), and afterward, the measurements of deformations and stresses in walls on deflecting floors were performed on a full scale in the actual building structure. The measurements enabled to determine floor deformations leading to cracking of walls and to establish a dependency between the values of tensile stresses within the area of the door opening corners and their location along the length of walls and type of vertical connection with the structure.

Mechanism of Roadway Floor Heave Controlled by Floor Corner Pile in Deep Roadway under High Horizontal Stress

In order to overcome the support difficulty of serious floor heave caused by rock burst, with the floor heave of ventilation roadway in Hegang Xing An Coal Mine as the engineering background, the treatment scheme of the concrete-filled steel tube corner pile and floor grouting is put forward. Based on the solution of the slip line field under plane strain condition, the mechanical model of the slip-type floor heave is established, and the formula for calculating the critical failure depth of the roadway floor and the minimum support depth of the corner pile is derived. Through numerical analysis and similar model tests, the deformation and stress distribution of surrounding rock under the support of the corner piles are studied, and the force law of the pile under high horizontal stress is analyzed. The results show that, compared with the floor corner anchor, the floor corner pile + floor grouting support scheme can significantly improve the mechanical properties of the floor rock mass, and the plastic slip line of the floor plate part can be cut by corner piles, which effectively controls the deformation of the floor plate under high horizontal stress; the length and inclination angle of the corner pile have a great influence on the support effect. In the on-site treatment scheme, 1.1 times the calculated length of pile should be selected. The results of a similar model and field test show that the corner pile is effective in controlling the deformation of roadway floor and two sides.

Compositional control on impact crater formation on mid-sized planetary bodies: Dawn at Ceres and Vesta, Cassini at Saturn

High-resolution mapping of Ceres, Vesta and the icy satellites of Saturn, Uranus and Pluto reveals a rich variety of well-preserved impact crater morphologies on these low gravity bodies. These objects provide a natural laboratory to study effects of composition on crater formation processes under similar surface gravity conditions (though mean impact velocities vary by several factors). Simple craters occur on all these bodies but subtle differences in morphology on Ceres and Vesta are recognized. Immature complex craters (with large floor mounds but not terraces or conical central peaks) occur on Vesta and while smaller than predicted are consistent with its silicate composition. Asymmetric simple craters (with incomplete scarp development) on all bodies are likely related to differential overburden stresses in the rim, and their occurrence is consistent with lower crustal strength on icy bodies including Ceres. Immature and mature complex craters exhibit increasing degrees of complexity, including spiral floor deformation patterns (related to failure in converging floor material), central peaks, and impact melt. Cerean crater morphologic types and simple-complex transition diameters are smaller than on Vesta but similar to those on icy satellites, indicating a much weaker rheology for Ceres' outer layers under impact conditions. These are consistent with geophysical indications of a low-density water ice and probably clathrate rich outer shell. Fluidized floor deposits (impact melt or melt-solid mixtures) are significant in craters >25 km across on Ceres but absent on Saturn satellites. Central pit craters are common on Ceres (at diameters of ~75 to 150 km consistent with gravity scaling from the larger Galilean satellites) but are absent on Saturnian satellites and Charon. The contrasting impact melt and central pit behaviors on Ceres and Saturn's moons is contrary to expectation given the higher impact velocities at Saturn but might be related to lower internal temperatures, or the higher fraction of non-ice material on Ceres. The correlation or scaling of transition diameters to surface gravity is near −0.65 rather than −1, perhaps due to increased porosity on lower gravity bodies. The fundamental similarity of crater morphologies on Ceres and icy satellites, however, indicates that the weaker rheology of water ice results in similar craters even if the non-(ice+clathrate) components are as high as ~30 vol%.

RETRACTED: Prefabricated construction process and unloading monitoring of space steel grid cassettle structure multi-storey large-span gymnasium

The gymnasium of Fule International School in Mianyang, Sichuan are multi-storey large-span buildings with a maximum span of 36 m and use a new system-steel grid cassettle structure. In this paper, the structure form, prefabricated construction method and support unloading process of the gymnasium are introduced in detail. To ensure smooth construction unloading, the deflection deformation of the large span floor and the field splicing node are monitored. Results show that the prefabricated construction method of the Mianyang Fule International School Gymnasium and the steel column-scaffold combination support system are affordable. After unloading, the floor has the traits of plates and relatively greater rigid reserve. Thus, it is applicable for large-span and high-load floor structure. The stress in the splicing node in the inflection point (L/2, L is the size of the grid) is relatively small, the bolt and the shearing-resistance plate have no slump, and the field splicing node is safe and reliable. The findings provide a certain reference value for the research and innovation in the process of assembly construction of multi-storey and large-span building.

Floor damage mechanism with cemented paste backfill mining method

This paper aims to address the coal seam floor behavior after mining with CPB method. Firstly, the numerical model by using Midas/GTS-Flac3d method is developed on the basis of 2353 working face, Daizhuang Coal Mine; then, the slip line field theory of plastic mechanics is applied to calculate the floor damage depth. Furthermore, field observation is carried out by using water injection method. The results show that the floor deformation is well controlled by using CPB; the tensile zone reduces greatly to one-sixth of the size with traditional caving mining method; the coal seam excavation with CPB mining method is equivalent to reducing the original mining thickness; and the depth of the fracture floor is around 2 ~ 4 m. The numerical simulation and analytical calculation in terms of floor damage depth coincide with the in situ measurement. The proposed analytic model provides insight into the floor behavior with backfilling mining method.

Comprehensive Measurement of the Deformation and Failure of Floor Rocks: A Case Study of the Xinglongzhuang Coal Mine

The isolated island panel 10304 of the Xinglongzhuang coal mine was used as the research subject to study the deformation and damage characteristics of the coal seam floor. The damage of the floor was studied using the borehole strain sensing method and borehole imaging technology, and FLAC3D was used to study the influence of abutment pressure on floor failure. The result shows that the floor under the superimposed area which is affected by lateral and advanced abutment pressure is damaged firstly, and the maximum depth reaches 26 m, other areas of the working face about 23 m. The degree of deformation and failure of floor rock at different depths is decreased. The deformation damage increases with the advancement of the working face until a certain distance at the same depth. The hole image can clearly show the influence range of the abutment pressure in front of the coal wall and influence the degree of the advancement and lag by means of the strain increment curve for each sensor probe and the images from different drilled positions. On the basis that the results of simulation and field measurement are consistent, the results can reflect the three-dimensional failure characteristics of the whole island working face floor in the process of coal mining more comprehensively and accurately; moreover, they also can provide important information for mine flood prevention and ecological environment protection.