Roof Subsidence Research Articles

Surrounding rock control mechanism of deep coal roadways and its application

Aiming at the surrounding rock control problem of mining and preparation entries in Xingdong mine with large mining depth, and the comprehensive control countermeasures including high pre-stress cable truss system, this study put forward powerful anchor support system and anchor cable adaption technology to surrounding rock deformation. Furthermore, the control measures possess the supporting performance with “primary rigid-following flexible-new rigid, and primary resistance-following yield-new resistance”, which suits deep roadway surrounding rock control. The mechanical model of truss anchor supporting roof beams was established, and the inverted arch deflection produced by the cable pre-stress with stress increment effect and roof beam deflection were obtained. And then the system working mechanism was illustrated. Finally, the surrounding rock support parameters were determined by means of comprehensive methods, and put into practice. The results show that surrounding rock deformation realized secondary stability after three months. The roadway sides convergence value was less than 245mm, and roof subsidence was less than 124mm. In addition, there was no expansion and renovation during service period.

Study on Safe Thickness of Stope Roof and Ground Subsidence Based on Numerical Simulation

It is mainly discussed that the minimum safe thickness of the stope roof and the ground subsidence deformation during mine excavation. The concrete method is deducing the theoretical calculation formula of minimum thickness of the stope roof according to the bending and shearing structural mechanics model respectively so as to gain the minimum safe thickness; A detailed engineering geological 3d model for mining concessions is built by using Auto CAD,and next a numerical calculation model is established by using ANSYS finite element software,following by importing it to numerical simulation software FLAC3D for calculation. By this method,the whole process of mine excavation can be simulated. Finally,the ground subsidence deformation obtained by simulation satisfies the specification requirements.

Roadway Anchor Support Design Method Based on the “Three Zones” of Roadway Roof

Aiming at the problem of serious deformation and failure of the surrounding rock of the main roadways in diabase zone in west wing on-500m leve in Dongbaowei Coal Mine and roof caving occurring several times, the rupture characteristics of roadway roof rock was observed in this paper. And the observation result shows that the rupture of the roof rock of the roadways in diabase zone has obvious zoning characteristics, and the roadway roof rock is divided into three zones: fragmentation zone, fissure zone and intact rock zone. According to this, this paper introduced a new concept of controlling roadway roof subsidence and redesigned the support parameters of the roof of the roadway in diabase zone. The deformation monitoring of the testing roadway roof rock was carried out, and the monitoring result shows that the anchor supporting scheme which was based on the “three zones” of roadway roof could control the roof rock deformation better. This indicates that roadway anchor support design method which is based on the “three zones” of roadway roof is correct and feasible.

Supporting Technics of Easily Mudding and Ultrahigh Roadway in Soft Coal Rock

According to the situation of the great height wall, soft and weak surrounding rocks and sliming characteristics of the 15# coal west-third panel sump in the Gushuyuan mine, the deformation characteristics and mechanism of the sump were analyzed by field survey, laboratory tests and the numerical simulation method. The results show that the sump deformation and failure were determined by its low strength, weakness structural, sliming characteristics and excavation disturbance. The roadway deformation occurs mainly in the middle, upper and lower of the sides and the floor. A comprehensive solution is proposed, including sealing surrounding rocks, strengthening soft and weak surrounding rocks, strengthening the structure stability, improving the surrounding rocks stress environment. This method was applied in the coal mine. Field application results show that this method was suitable for control sump deformation, the maximum roadway roof subsidence is 15 mm, the two sides convergence is 30mm, and the maximum amount of floor heave is 21mm.

Spontaneous caving and gob-side entry retaining of thin seam with large inclined angle

Based on the research method of combining simulation analysis with field testing by distinct element process UDEC, we have analyzed the roof deformation and failure laws and roadway support technology of gob-side entry retaining in a thin seam with a large inclined angle. The results show that during exploitation in seams with large inclined angle, rotational subsidence of the main roof under the gob area is small and can maintain balance, so there is no need to provide artificial permanent support resistance for the main roof near the upper side to control rotational subsidence. Obstructed by the dense scrap rail, waste rock from the immediate roof caving slides from the upper gob area to the lower area and fills it, which strikes a balance between the immediate roof under the goaf after it fractures into large pieces and filling waste rocks.

Investigation and analysis of the rock burst mechanism induced within fault–pillars

An investigation is made of the characteristic strata movement and mechanism underlying fault–pillar induced rock bursts (FPIRBs) in order to mitigate rock burst damage in fault areas. A mechanical analysis of the fault–pillar model is established and roof rotation criteria is obtained. A formula is derived for the average static stress in the pillar through theoretical analysis, physical simulations, and engineering practice. The results show that when a coalface approaches a fault area, two or more roof strata simultaneously fracture in the fault area, leading to an increase in the dynamic and static stresses in the pillar. The most important factors affecting FPIRB are the static stress in the pillar and the dynamic stress induced by fault slides. The roof block rotates more easily when the pillar width is smaller, the roof thickness larger, and the roof subsidence smaller. The average static stress in the pillar increases with decreasing pillar width and/or increasing roof fracture length. The stress is greater if there is a voussoir beam structure, in which case the stress is directly proportional to the squared length of the fractured roof, and inversely proportional to the squared width of the pillar just before rotation occurs. After rotation, it is directly proportional to the roof fracture length and inversely proportional to the pillar width. Based on the FPIRB mechanism and analysis of the mechanical model, six methods of FPIRB prevention are proposed. Also, we find that FPIRB occurrence can be effectively reduced by the use of de-stress blasting and large diameter drilling.

Determination Method of the Supporting Intensity of Fully-Mechanized Face in Deeply Inclined Medium-Thickness Seam

According to the occurrence conditions of deeply inclined coal seam of 81206 working face in Yanya coal mine, methods including transmission rock theory calculation and numerical calculation based on the relationship between supports and surrounding rock are used to calculate and analyze. The proper working resistance of support is 5979.2kN and the supporting intensity is 0.8~0.95MPa. The regression equation associated with roof subsidence displacement , thickness of the coal seam, working face length and supporting intensity is accomplished, which provides theoretical basis for the support selection.

INDUSTRIAL TESTS OF WASTE ROCK DIRECT BACKFILLING UNDERGROUND IN FULLY MECHANIZED COAL MINING FACE

For efficient, economical and environmentally disposing the waste rock underground, based on principles of waste direct backfilling in fully mechanized coal mining, this paper carries out a field test in 6304-1 working face of Jining No.3 Coal Mine. We first design a waste rock direct underground processing system, including screening-crushing system, transportation system, transfer system, stope backfilling system and coal mining system. Then optimize the waste backfilling and coal mining technology, update the waste backfilling process with start backfilling from backfill scraper conveyor s head to tail, gradually uplift tamping arm, gradually compact backfill materials, move backfill scraper conveyor forward when the tamping arm can t extend out and last fill roof gap by up material pushed by down material . At last, imply this system and check strata movement controlling effect by actual measuring the roof dynamic change law, which supported by the dense backfill body. The results show that the test working face can cut 0.6 million tons of raw coal one year, and direct backfill 0.74 million tons of waste rocks at the same time, and the maximum subsidence of immediate roof observed in situ is 340mm, the maximum caving speed is

Strata-pressure behavior of double-unit mining method combining fully-mechanized and mechanized coal face

Based on the engineering background of double-unit face mining under complicated geological conditions and the lagging fully-mechanized face surpassing the fore mechanized face of double-unit face in Zhou Yuanshan coal mine, strata-pressure behavior in the process was analyzed based on FLAC3D and on-site measurement. The results show that the stress concentration factor of superposition abutment pressure and the alternate distance of double-unit face are meeting gauss function, the relationship between the depth of stress concentration point and alternate distance also meets gaussian function. When the alternate distance is larger than 24 m, the superimposition of pilot support pressure in the double-unit face is weak. When the alternate distance is more than 12–15 m, the changes of the roof subsidence coefficient and the depth of stress concentration point are stabilized; when the alternate distance is 3–6 m, the fore working face end is in the greatest impact area of superposition abutment pressure, this area should be avoided in determining the reasonable alternate distance.

Deep-hole pre-split blasting mechanism and its application for controlled roof caving in shallow depth seams

The shallow depth coal seams mined in the Shendong Mining Area has led to large area roof weighting frequently due to large thickness, high tensile strength and small overlying load of the main roof. As a result, many accidents have happened including hydraulic support being iron-bound, water inrush through the penetrating cracks along coal wall, and potentially induce large area residual pillars instability and even wind blast damage particularly in the conditions beneath a room mining goaf. To prevent the large area roof weighting accidents, deep-hole pre-split blasting technology for controlled roof caving is a suitable method and has been widely applied in the mines, and many in situ trials have already achieved a sound performance. According to the field conditions of the shallow depth coal seams, this paper employs cylindrical cavity expansion theory to calculate the three blasting-induced divisions including break zone, fracture zone and elastic vibration zone. The software of LS-DYNA3D was applied to establish a deep-hole pre-split blasting model, which presented the rock stress field and the break scope affected by the high energy explosion stress wave. The simulation results revealed the blasting for controlled roof caving mechanism and also optimized the blasting parameters. The field observations showed that, with the application of deep-hole pre-split blasting technology in Shigetai Mine, Shendong Mining Area, the first main roof weighting length was about 17.4m, and neither a hydraulic support being iron-bound nor a serious roof subsidence in the form of step convergence in the mining face happened during the first weighting period. The field application of deep-hole pre-split blasting for controlled roof caving has achieved the expected effects.

Monitoring and Results Analysis of Tunnel Engineering

Through to the Henan tunnel engineering and observation hole, peripheral displacement measurement, measurement of subsidence of arch roof and surface subsidence measurement on-site real-time dynamic testing, obtained their changes over time curve, and the tunnel monitoring results were analyzed, thus improving the tunnel design and correctly guide the construction, ensure the safety and economy of the tunnel engineering.

Experimental Study on Double Truss Cable Supporting System of Coal Roadways in the Isolated Coal Pillar and Fold Region

The gangue in parts of underground coal mines in China is not to be hoisted to ground for direct accumulation but replace the coal resource in larger residual coal pillars. In order to solve the supporting problem of roadways in the isolated coal pillar and tectonic region, we firstly research the relationship between the supporting effect and fold or isolated coal pillar factor. Based on the analyzing results, the double truss cable support system (DTCSS) is proposed, and then the corresponding support structure and superiority are studied. Finally, a typical complex coal roadway affected by factors of synclinal axes, isolated coal pillar and intersection with another roadway was experimented using DTCSS, and the monitoring results of the roadway displacement showed that both of the largest roof subsidence and the convergence of both sides were no more than 170mm, which ensured the roadway safety and proved the efficiency of the DTCSS.

Mechanics model and numerical analysis of floor heave in soft rock roadway

The mechanism of floor heave was analyzed by establishing mechanics models and solving differential equations. The amount of floor heave is proportional to the abutment pressure of surrounding rock, roadway width, and the distance of support pressure peak to the roadway and is inversely proportional to the elastic modulus of floor rock. Using FLAC2D to simulate floor rock grouting in soft rock roadway verifies the active role of floor rock grouting in the floor controlling of soft rock roadway; floor rock grouting and grouting range directly impact on the stability scope of surrounding rock, namely, with the increase of grouting range, the subsidence of roof, the approach of both sides, and the amount of floor heave decreased gradually, the stability of surrounding rock is enhanced.

Stress Evolution and Deformation Control Technology for Deep Mining Influenced Roadway

In order to effectively control deep roadway under mining influence, based on the typical engineering geological conditions of Dingji coalmine in Huainan mining area, we researched on the laws of stress evolution and failure mechanism of roadway influenced by working face advancing by using numerical simulation and applying field test. The results showed that the surrounding rock stress of roadway ribs increased gradually with face advancing, vertical stress peak transfer to in-depth of roadway surrounding rock, the trend of roadway surface displacement variation consistent with corresponding stress variation. An appropriate coal pillar size (105 m) was proposed. We put forward the basic ideas for surrounding rock controlling and surrounding rock reinforce technology, namely U-steel support back grouting and bolt-cable cooperative supporting. By roadway deformation, roof layer separation and borehole detecting, we found out that displacement of roadway ribs was less than 250 mm, subsidence of roof was less than 110 mm, and the roadway deformation has been effectively controlled.

Mechanical and geometric controls on the structural evolution of pit crater and caldera subsidence

[1] Pit craters and calderas are volcanic depressions produced by subsidence of a magma reservoir roof. To identify how geometric and mechanical factors may influence the structural evolution of this subsidence, we used two-dimensional distinct element method numerical models. The reservoir host rock was represented as an assemblage of bonded circular particles that interact according to elastic-frictional laws. Varying particle and bond properties produced a range of bulk material properties characteristic of natural rock masses. Fracturing results when bonds break, once their shear or tensile strength is exceeded. The magma reservoir was represented as a region of nonbonded low-friction particles. Withdrawal of magma was simulated by incrementally reducing the area of the reservoir particles. Resultant gravity-driven failure and subsidence of the reservoir roof were explicitly replicated. Interaction of the roof's strength, Young's modulus, thickness/diameter ratio (T/D), and the reservoir's shape yields a variety of model structures and subsidence styles. In conceptual terms, four end-member subsidence styles developed: (1) “central sagging” favored by low strength and low T/D; (2) “central snapping” favored by high strength, low T/D, and a sill-like reservoir shape; (3) “single central block” favored by low to intermediate strength, high Young's modulus, and intermediate T/D; and (4) “multiple central blocks” favored by high strength, low Young's modulus, and high T/D. Most model realizations incorporated some combination of each style, however. The models provide a geomechanical framework for understanding natural pit crater or caldera structures, as at Nindiri (Nicaragua), Fernandina (Galapagos), Dolomieu (La Reunion), and Miyakejima (Japan).

Key Technology of Predicting Dynamic Surface Subsidence Based on Knothe Time Function

A method for calculating the parameter of Knothe time function was presented. The principle of predicting dynamic mining subsidence was discussed based to the relationship between the periodic fractures of main roof and surface subsidence. Pointed out there might be a section whose width was shorter than a mining unit when divided a workface into equal mining elements, the section should be calculated specially in the algorithm. A model of predicting dynamic mining subsidence was made according to the Knothe time function and probability integral method. A model how to divide a workface and two coordinate transformation models among three coordinates also were made. An algorithm step of the dynamic prediction model for multi-face mining was designed and implemented. And the algorithm was tested by nine measured subsidence data in different times of some mine 1176 east face, the result showed that the prediction results agreed well with the observation data, and the feasibility and effectiveness of the algorithm were demonstrated. Finally, the process of surface subsidence and deformation of 1176 east face was back analyzed.

Study On Numerical Simulation of the Arrangement about Mining Roadway with Short Distance

Based on numerical simulation test and test results, the stability of bare roadway with different staggered distance was studied. Conclusions can be drew as follows: Of these ulter-closed mining roadway arrangement modes, global stability of the inboard type roadway is better based on the aspects of degree of damage; Roof subsidence in the inboard-type roadway is smaller, offset at two sides of roadway is larger, its offset direction approaches toward the centre of roadway, and offset increases with staggered distance decreases, the supporting of two sides is the central difficulty for in-board type roadway; The degree of damage in overlapping-type roadway is larger, and roof subsidence of overlapping-type is similar with the inboard-type roadway, while the deformation is large at left side, there are few changes at right side. The destructive deformation is maximum when the staggered distance of outward-type roadway is 2m, and degree of damage is decreases with the increase of staggered distance in outward-type roadway. Overall, roof subsidence in the outward-type roadway is larger, and two sides of it are basically stable.

Research on integration of roadway excavation, bolting, support, and detection

According to the situation that temporary support equipment is backward, new type temporary support equipment is developed. This temporary support equipment can support roof and front wall of roadway quickly, can reduce roof subsidence, roof fall accidents, front wall collapse, and labor intensity, and has high economic and wide application value. Integration ideas of roadway excavation, bolting, support, and detection is put forward, i.e. to make roadheader as a platform and combine new type temporary support equipment, new type bolter, and detection devices with roadheader to achieve reasonable dynamic roof support design and safe rapid roadway excavation.

Study on Artificial Neural Network Method for Ground Subsidence Prediction of Metal Mine

Metal mine with fractured blocky rock mass is much different from coal mine, which shows discontinuity and irregularity, meanwhile large differences also exist in stratum structure, geological condition, ore body shape and mining methods, so the influential factors in metal mines is more complex and volatile. The research on theory and application of ground subsidence has not reached a mature stage at present. So this paper focused on the study of this issue based on neural network with its characteristic that it has fast learning speed and could approach to any non-liner mapping, which are adapted to the complex environment in metal mine. The time series prediction model was established, which is based on the measured data of the roof subsidence in the goaf of metal mine, and the tested sample data were trained and tested by many times. Finally the predicted value of the neural network was compared with the measured value by automatic optical level, which showed that the prediction model achieved good accuracy, and could be accepted in the engineering application. This method could fill the gap of incomplete monitoring data in mine ground subsidence, and provide a reference for production in the metal mine.

On the effect of crustal layering on ring-fault initiation and the formation of collapse calderas

Collapse calderas can be attributed to subsidence of the magma chamber roof along bounding sub-vertical normal faults (ring-faults) after a decompression of the magma chamber. It has previously been shown that for ring-faults to initiate, and thus facilitate collapse, the stress field both at the surface and around the magma chamber must satisfy specific critical conditions. Here, we present new numerical models that use a Finite Element Method to investigate the effects of crustal layering on local stress field distribution. Results are compared with existing criteria for ring-fault initiation. Different subsurface scenarios were simulated by varying the stiffness (Young's modulus) of layers placed above the magma chamber, and the host rock in which the chamber is seated. We consider depressurisation of a magma chamber, so as to simulate magma withdrawal. Results indicate that mechanical layering is a further first-order variable in the rare achievement of stress conditions required for ring-fault formation, and may be influential in facilitating or inhibiting caldera collapse. We show that for a given geometrical set-up, the magnitude and position of maximum tensional stress at the Earth's surface are influenced by the occurrence and relative distribution of mechanically stiff or soft lithologies above the magma chamber. For example, tensional stress at surface may be reduced by the presence of stiff layers (e.g. lavas), or increased by soft layers (e.g. pyroclastic units) compared to generic simulations using a homogeneous background medium. Overall we find that the presence of mechanically soft material promotes surface fracture initiation. In addition we suggest that the position of peak tensional stress at surface derived by the numerical models does not represent that related to the position of the bounding ring-fault, but is instead related to the position of initial tensional fractures appearing prior to the collapse faults.