Floor Heave Research Articles

Evolution Mechanism and Control of Floor Heave in the Deep Roadway with Retained Bottom Coal

Roadways with retained bottom coal are common in thick coal seam mining, and floor heaving is a prominent problem. In this study, based on the interaction between the floor and two sides of the roadway-surrounding rock, a Winkler elastic foundation beam model is established to analyze the floor heave problem. A 3DEC model was used to analyze the failure range, failure mode, and migration law of the floor-surrounding rock with different bottom coal thicknesses and coal body strengths. The results show that (1) an increase in the thickness of the bottom coal results in a decrease in the stiffness of the roadway side coal body (the foundation of the supporting rock layer) and an increase in the bending deformation range, the amount of floor rock beam deformation, and the extrusion force. This leads to an expansion in the range of the sides of the coal body that are squeezed by the floor rock layer, resulting in additional failure and deformation of the coal body sides. Therefore, the damage to the floor rock layer is extended and increased. (2) The expansion of the floor pressure-bearing arch and surrounding rock in the arch are the causes of floor heave in the deep coal roadway with retained bottom coal. (3) Because of an increase in the thickness of the bottom coal and a decrease in the coal body strength, the floor pressure-bearing arch expands to the deeper part; thus, the range of surrounding rock in the arch with deformation and failure increases, resulting in an increase in floor heave. The field practice indicates that the support strategy of the “high prestressed strong rock bolt (cable) supporting two sides and bottom corners in time” can effectively control the floor heave of a roadway with retained bottom coal.

Research on main influencing factors and complete support technology for dynamic pressure and large deformation roadway

To determine the main factors influencing dynamic pressure and large deformation roadways, a targeted set of support technologies was designed. The 2603 air inlet roadway of the Zhangcun coal mine in Lu'an, Shanxi Province, was taken as an example. The influence of the Wenwangshan South normal fault and in situ stress field on the dynamic pressure roadway was analyzed theoretically, and the main factors influencing this dynamic pressure and large deformation roadway under natural geological conditions were determined. The effect of the existing roadway support scheme was evaluated by field test methods such as nondestructive bolt testing. The influence of mining two working faces on the dynamic pressure and large deformation roadway was studied by the FLAC3D numerical simulation method. On this basis, a new grouting material was developed, a complete set of technical schemes of full-section integrated cooperative support of dynamic pressure and large deformation roadways was proposed, and the field application effect was verified. The results showed that under natural geological conditions, the 2603 air inlet roadway was located within the influence range of the Wenwangshan South normal fault, which was significantly affected and controlled by the fault. The included angle between the roadway extension direction and the maximum principal stress was 74°, which was not conducive to the stability of the roadway. The range of the roadway loose zone was large. Under the existing support conditions, the surrounding rock could not form a relatively stable structure, which was one of the main reasons for the large deformation of the surrounding rock in the dynamic pressure roadway. The 2603 air inlet roadway was affected by the mining of both the adjacent working face and the 2603 working face. The stresses were superimposed, and the roadway was greatly deformed and damaged. A new grouting material was developed. A crosslinking agent prepared by toluene diisocyanate and polyether polyol was added to the existing polyurethane material to form a new grouting material, and a complete supporting technical scheme was proposed. The field application results showed that the displacement and floor heave of both sides of the roadway were reduced by approximately 87%, the deformation and failure of the coal and rock mass of the roadway were effectively controlled, and the deformation of the dynamic pressure roadway was greatly reduced.

A new floor heave mechanism considering the influences of the in-situ stress lateral coefficient and rock tensile strength

Floor heave is a disaster that is frequently encountered in tunnel engineering. Existing explanations of floor heave mechanisms have many limitations, and the most important of which is that the stress concentration, release and transfer phenomena and the influences of the in-situ stress lateral coefficient and tensile strength are ignored. Therefore, the combined finite-discrete element method (FDEM) is used to study the failure process of floor rock masses and propose a new mechanical mechanism of floor heave that can consider the influences of the in-situ stress lateral coefficient and tensile strength. The type I fracture energy corresponding to different tensile strengths is calibrated using a direct tensile simulation test. Then, the floor heave mechanism is investigated under different lateral coefficients and tensile strengths, and five different floor heave modes are proposed under different in-situ stress lateral coefficients and tensile strengths. The floor heave modes controlled by the various in-situ stress lateral coefficients and tensile strengths are different, but they can all be explained by the maximum concentrated tangential stress.

Experimental Study on the Size of Rock Fragments Ejected from Boreholes Drilled in Coal Mine Roadway Floors

Borehole drilling is required if floor heave in underground mines is to be controlled using bolts through the floor. How well the bolt is anchored depends, in part, on the borehole’s quality. A major factor that can reduce borehole quality is the difficulty of discharging rock fragments from a small-diameter borehole drilled at a downward angle. Therefore, a fuller understanding of the sizes of the rock fragments will aid attempts to achieve smooth fragment discharge. In this study, drilling experiments in the laboratory and SEM imaging were carried out to determine the size and shape of the fragments generated when drilling boreholes in three sedimentary rocks typically found in roadway floors. The results show that the size distribution of the rock fragments conformed to the three-parameter generalized extreme value distribution. The mean fragment size increased with rock density and the mean size of the fragments larger than 1.5 mm increased with the rock’s uniaxial compressive strength. The fractal dimension of the cracks in the fragments was lower for high-density rocks and the mean fragment size was larger for rocks whose cracks had a lower fractal dimension. When a drill rod drills through very dense or high-strength rock, the mean size of the fragments will increase and the discharge power should be increased to prevent fragment discharge blockages. This paper may provide a theoretical basis and a data reference for discharge power settings and discharge channel optimization.

Study on Floor Heave Characteristics and the Control Method of Gob-Side Entry Driving in Weakly Cemented Soft Rock

Aiming at the problems of large deformation, long duration, and difficult control of floor heave in gob-side entry driving in weakly cemented soft rock, this paper takes the weakly cemented soft rock mining area in Western China as the engineering background, and studies the characteristics and mechanism of floor heave in gob-side entry driving in weakly cemented soft rock by means of a field investigation, physical component analysis, mechanical property tests of the surrounding rock, and the stress monitoring of the surrounding rock. The classification control method of floor heave is put forward, and field tests are conducted. The results show that: (1) The floor heave characteristics of the dynamic change in the floor heave peak position of gob-side entry driving from the coal pillar side to the mining side are obtained through field observation. (2) Based on the analysis of field data and laboratory test data, it is concluded that the stability time of the overlying strata in gob-side entry driving is about 8 to 12 months. The main internal cause of roadway floor heave is the low load resistance of weakly cemented soft rock. High stress and strong disturbances are the main power sources of strong floor heave. The mechanism of floor heave affected by dynamic lateral abutment pressure is summarized, and the classification control method of floor heave is proposed. (3) The gob-side entry driving support technologies of “adjusting excavation deployment” and “surrounding rock pressure relief and improving support” are proposed. Through field tests, the floor heave can be effectively controlled.

A case study on the deformation and failure mechanism of a soft rock mining roadway in the Xin'Shang'Hai No. 1 coal mine, China

Mining roadways in soft rock are seriously deformed and damaged, which affects the normal production of the mine. Based on the Xin'Shang'Hai No. 1 Coal Mine project, a true 3D physical model test was carried out to obtain the deformation evolution and failure features of the mining roadway. The results show that the strata movement of the panel drives the surrounding rock of the mining roadway to deform toward the center; the net size of the roadway near the longwall face decreases by 48.3%. The convergence of soft rock mining roadways can be divided into four phases, and the average convergence rate of a fast phase is 3.1 times that of a slow phase. The evolution of roadway failure is deformation accumulation → sidewall cracking → lining spalling → coal sidewall breaking → floor heave → bolt (cable) failure → full section deformation. Coal sidewall failure is an important turning point of mining stress-induced roadway failure. The extension of the broken area into the rock leads to the failure of the coal seam between the roof and floor and then induces the overall instability of the roadway. The radial deformation and stress evolution of the mining roadway are analyzed by numerical simulation, and the model test results are verified. The mining roadway in soft rock shows full section convergence characteristics under the stress of mining. Finally, countermeasures are proposed according to the failure mechanism to provide a reference for similar roadways.

Study on the Dynamic Characteristics of Bit Anchor Cable Drilling in the Gravel Sediments of a Soft Rock Bottom Hole

During the pore-forming stage of floor heave treatment, the phenomenon of gravel sediment accumulation in the bottom hole often occurs, which causes great difficulties in the normal installation of the anchor cable. Based on this observation, a new anchor cable installation method was proposed, which involves installing a drill bit at the front end of the anchor cable to assist its drilling. With the help of an anchor cable drilling test bench, the influence of the bit, motion parameters, and hole environment on the performance of anchor cable drilling was studied. Through the co-simulation of the discrete element method (i.e., multibody dynamics (DEM-MBD)), the drilling process of the bit anchor cable was simulated, and the dynamic characteristics of the bit anchor cable drilling in the bottom hole gravel sediment were analysed. The results show that installing a drill bit in front of the anchor cable can greatly reduce the drilling resistance and hamper torque during anchor cable drilling. When the rotational direction of the bit anchor cable is consistent with the spiral direction of the anchor cable, the bit anchor cable can exhibit better drilling performance. The drilling resistance and hindering torque of the bit anchor cable are the largest when drilling in soaked particles, followed by drilling in dry particles, and the smallest occurs when drilling in moist particles. The research results can provide reference for the parameter setting of anchor cable auxiliary installation equipment.

Research on Floor Heave Mechanisms and Control Technology for Deep Dynamic Pressure Roadways

In order to study the influencing factors of floor deformation and floor heave mechanisms of deep mining roadways, this paper takes the deep dynamic pressure mining roadway of a mine as the engineering background and adopts a research method combining theoretical analyses, numerical simulations and field observations to study the influence of various factors on floor deformation and floor heave mechanisms. It is determined that the influencing factors on floor heave are a large buried depth, a long duration of dynamic pressure, unique characteristics of the surrounding rock and an insufficient support strength. A bearing mechanics model of the roadway floor beam is established, and it is determined that the displacement of the roadway floor is negatively correlated with the elastic modulus and floor thickness and positively correlated with the buried depth of roadway, the roadway width and the width of fracture zone. A numerical simulation method is used to study the influence of the original geological conditions, strengthening the elastic modulus of floor, strengthening the strength of the side wall rock and increasing the thickness of the floor rock on the displacement of the roadway floor. It is determined that increasing the thickness of floor rock controls the floor heave the most, followed by strengthening the elastic modulus of the floor rock and then strengthening the strength of the side walls. The results of the numerical simulation agree well with those of the theoretical analysis. After the control method of “bottom lifting + bottom angle bolt + floor bolt ” is adopted on site to treat the floor heave, the floor heave volume of the roadway is small during the service period of the 303 working face return air roadway, which meets the application requirements of the roadway. Meanwhile, the theoretical analysis and numerical simulation results are indirectly verified.

Research on Deformation and Failure Law of the Gob-Side Roadway in Close Extra-Thick Coal Seams

To reveal the deformation and failure law of the gob-side roadway (GSR) and the main influencing factors in close extra-thick coal seams, the research methods of field monitoring, theoretical analysis, and numerical simulation are adopted in this paper. Field monitoring data shows that microseismic events occur and accumulate frequently in the surrounding rock and some overlying key layers of the GSR. Large deformation is experienced in the middle part of roadway near the solid coal side, the middle and upper parts of the roadway near the coal pillar side, and the roadway floor. The overlying strata of the GSR are fractured to form a composite structure as “low-level cantilever beam and high-level masonry beam”. The coal pillar is squeezed and effected by the composite beam structure and the rotation moment M, causing serious bulge in middle and upper part of the coal pillar side. The stability of the solid coal side of the roadway is affected by the stress transferred from gangue contact point. Numerical simulation shows that the immediate roof and key layer breakage are induced by the mining of the 30,501 working face. Shear and tension failures happen in the GSR due to overburden subsidence and rotary extrusion. The stress and displacement at the middle and upper of the roadway on the coal pillar side are larger than the other area. Compared with the solid coal side, the coal on the coal pillar side is obviously more fractured, with a lower bearing capacity. The peak stress in the coal pillar shows up 2 m away from the roadway, which is close to the length of bolt support. The mining-induced stress and the stress transferred from gangue contact point are the direct reasons for solid coal bulge beside the roadway. The peak stress on the solid coal side is located 7 m away from the roadway, at the gangue contact point where overburden fractures. The overburden strata loads and the transferred stress near the gangue contact point are transferred from the sides to the roadway floor. Their coupling effect with the in situ horizontal stress acts as the force source for the plastic floor heave.

<b>Performance Verification of Design Method for Plain Concrete Linings and Inverts Assuming Ground Displacement after Completion</b>

There are various structures in railway systems. These structures including tunnels need to have the same level of performance and their performance should be verified quantitatively. Therefore, we proposed a method for verifying the performance of plain concrete linings and inverts, and developed a trial design assuming a mountain tunnel receiving ground deformation after completion. In the trial design, we imposed the displacement to the lining and invert using a ground deterioration model. As a result, it was found that the performance can be verified using the proposed method, and that the required performance can be satisfied by adopting strong invert structures against floor heave.

Numerical Studies of Floor Heave Control in Deep Mining Roadways with Soft Rocks by the Rock Bolts Reinforcement Technology

The floor heave is one of the key factors that can restrict high-efficiency and safety mining, especially in the deep roadways with soft rock. Considering the influences of rock fracturing over time on rock mass properties, a case study of the floor heave evolution and rock bolts reinforcement technology was performed in this paper. A numerical simulation was used to study the stress-strain state and displacement of surrounding rocks. It was found that significant floor heave caused by nonlinear deformation of laminated immediate floor under an increase in rock fracturing. The post-peak strain regions appear in the bottom corners of the roadway, after which strata in the immediate floor are destroyed one by one. The joint spacing of 0.45 m on the immediate floor is critical. At this step, post-peak strain regions merge in the central part of the roadway floor, which is the cause of uncontrolled floor heave. Rock bolts reinforcement was proposed to control the floor heave. Three floor support schemes with two types of support elements, different bolt orientations, and lengths of reinforcement were studied. The numerical simulation demonstrated that after reinforcement, post-peak plastic strain in the floor strata was reduced effectively. The optimal floor support scheme and depth of reinforcement were determined by the allowable floor heave. Ideally, the floor heaves could be reduced by rock bolts with a steel belt installed according to the support scheme III and reinforcement length of 2.0 m for outer bolts and 3.0 m for central bolts.

Research on Stability Control Technology of Mining Roadway Based on Energy Transformation

The process of roadway surrounding rock deformation and instability is always accompanied by energy changes, and the energy transformation of surrounding rock directly drives its deformation and failure. In order to realize the stability control of mining roadway, the distribution of elastic strain energy and plastic strain energy of surrounding rock was analyzed by using FLAC3D numerical simulation software on the basis of the energy transformation law of sandstone under different confining pressures revealed by indoor triaxial compression test. Based on this, combined with the energy transformation, the principle of roadway surrounding rock stability control technology is proposed. One is to reduce the elastic strain energy of surrounding rock, that is, by increasing the extension of support body, part of the roadway energy is transferred to the support body, so as to improve the energy release of surrounding rock, or by optimizing the layout of roadway to reduce the energy accumulation of surrounding rock. The second is to increase the plastic strain energy of surrounding rock, that is, to increase the energy dissipation of surrounding rock by setting weak structure. The above research results are applied to the surrounding rock control of the right second transport roadway in the 91st coal of Xinjian coal mine. After the optimization of support measures, the roadway surface displacement and its increase rate decreased significantly, roof subsidence decreased from 247 mm to 62 mm, floor heave decreased from 120 mm to 26 mm, and the right rib shrinkage decreased from 292 mm to 94 mm, that is, the floor heave control effect was particularly obvious. The deformation of surrounding rock gradually stabilized after 45 days.

Law of strata pressure behavior of surrounding rock in nearby goaf roadway for extra-thick coal seams of Datong mine area

The nearby goaf road in the extra-thick coal seam of the Datong mining area exhibits intense strata pressure behavior, which affects the working face mining. Herein, we study the laws of the strata pressure behavior of this road in detail using various methods, including laboratory tests, theoretical analyses, numerical simulation, and field monitoring. Considering the mine pressure characteristics of the nearby goaf road, namely, roof cracking, two-side deformation, and floor heaving, the mechanical tests and theoretical failure analyses of the surrounding rock in the mining-induced non-uniform stress field were carried out. The circular-oval-butterfly failure trend of the surrounding rock in the nearby goaf road under the influence of mining was obtained. The steady failure evolution lateral pressure coefficient (λ=0.5∼1.8) and butterfly mutation lateral pressure coefficient (λ<0.35 or λ>2.1) of the surrounding rock in the nearby goaf road were analyzed. We performed numerical simulation to study the stress field and the plastic zone shape-size characteristics of the surrounding rock during excavation and mining (with or without the top extraction road), and the theoretical law of the mine pressure was obtained for the Tong Xin coal mine. Finally, field monitoring indicates that the mine pressure behavior of the nearby goaf road exhibits spatial differences, namely, the difference between the stresses of the two sides and roof, and the stress characteristics of the deep and shallow surrounding rock. The findings of this study on the mine pressure behavior in the nearby goaf road have great practical significance for targeted measures to control the surrounding rock stability.

Layout timing of mining roadways considering goaf and roof stability

Reasonable roadway layout timing can effectively reduce the deformation of the rock surrounding the roadway and relieve mining and excavation tension. To analyze the mine pressure behavior of the gob-side entry at the edge of a goaf and the roof stability along the strike direction in the middle of a goaf, field observations and particle flow discrete element numerical simulation (PFC) method were performed. The results showed that deformation of the surrounding rock mainly occurred because of roof-to-floor convergence, caused mainly by floor heave. The mechanical behaviors of the rock mass, such as elasticity, fracture, and post-peak softening, could be simulated using the model of a jointed rock mass generated by rigid block elements in the PFC method. Considering the length of the violent and reduced roof activity zones and the activity duration as the indices to determine the basic stability of the goaf, the basic stability distance of the tested goaf edge was 135 m after coal seam mining, and the basic stability time was 27 days. The basic stable distance in the middle of the goaf was 183.4 m after coal seam mining, and the basic stability time was 37 days.

Study on the Influence of Roadway Structural Morphology on the Mechanical Properties of Weakly Cemented Soft Rock Roadways

We used the 11,303 return air roadway of the Hongqingliang coal mine as the engineering background for a study exploring the impact of the structural morphology of the roadway on the stress distribution characteristics and the stability of a weakly cemented soft-rock mine roadway. This work studies the evolution law of stress and deformation, and the plastic zone of weakly cemented soft-rock roadways with retaining the top or bottom coal seams. The results show that when retaining the top coal is replaced by the bottom coal, the high-stress zone of the vertical stress is reduced, the peak stress is decreased, and the stress concentration coefficient is slightly reduced from 1.67 to 1.64. The peak value of the vertical displacement of the roof of the shaft which was 78.4% of that of the top coal also decreases significantly, while the peak value of the vertical displacement of the floor, which was 1.37 times that of the top coal, increases. The equal area method was used to change the aspect ratio of the roadway. When the aspect ratio decreased from 1.38 to 0.88, the high-stress zone of the vertical stress was reduced, the stress peak decreased, and the stress concentration coefficient decreased from 1.8 to 1.75. The vertical displacement of the roof increased by 27.7% from 10.91 mm to 13.93 mm, and the vertical displacement of the floor increased by 15.2% from 6.60 mm to 7.60 mm. The plastic failure range was significantly reduced, particularly at the bottom corners. These findings show that structural morphology has a great influence on the floor heave of weakly cemented soft rock. Reasonable retention of the top or bottom coal and the aspect ratio of the roadway can prevent the deformation and failure of the roadway in weakly cemented soft rock.

Asymmetric Damage Mechanisms and Prevention Technology in Large-Section Gob-Side Entry Retaining

Based on the deformation and damage characteristics of the surrounding rock in a large-section gob-side entry retaining and combined with field observations and an analysis of the dominant factors, an overall deformation control plan is formulated. The plan mainly includes a structure of high strength, high stiffness and high ductility for roadside support; the reinforcement of the roadway-in support; and the setup entry hydraulic fracturing pressure release mechanism and advanced long, horizontal borehole “fracturing-jet” pressure relief technology. Industrial field tests were completed taking Tangan coal mine as the engineering background. The research shows that the large-section gob-side entry retaining has the typical “asymmetric” overall deformation and damage characteristics, including top coal sinking along the inner side of the roadside support, the whole roadside support structure skewing, and even splitting damage; floor heaving; and the coal-side bolt support structure basically losing support ability and bulging out from the coal side. The dominant factors of deformation damage are disintegration of the floor mudstone by water and deflection deformation under horizontal stress, splitting damage in the concrete roadside support under asymmetric load, damage and expansion due to the insufficient strength of the coal side support, strong dynamic pressure on the roof, and the mutual influence of support and pressure relief. The industrial test shows that the deformation control scheme optimizes the stress environment of the gob-side entry retaining space, the deformation control effect is remarkable, and the roadside fully meets the reuse requirements.

Method for controlling the floor heave in mine roadways of underground coal mines

Method for controlling the floor heave in mine roadways of underground coal mines

Numerical Modeling of Controlling a Floor Heave of Coal Mine Roadways with a Method of Reinforcing in Wet Soft Rock

A floor heave is usually a serious failure phenomenon in mine roadways, especially in the conditions of a wet soft rock. There are bright prospects for using a method of reinforcing for controlling a floor heave in mine roadways under a dramatic heave. In the current research, a floor heave mechanism in the wet soft rock of mine roadways was investigated while the moisture content of the rocks was increasing. That was done by performing numerical simulations in a finite element analysis software system Ansys and by reinforcing the floor in the shape of inverted arch. It was found that a decrease in the modulus of elasticity of rocks caused by saturation leads to a nonlinear increase in a floor heave. This can be explained by the fact that rocks of the floor become plastic strains. A stable correlation was established between water content and a floor heave of a wet rock. It was found that when the floor is reinforced, the proportion of plastic strains in the soil is significantly reduced. The growth of the modulus of elasticity of rocks in the reinforced zone, caused by reinforcing of the floor in the form of inverted arch, leads to a nonlinear decrease of a floor heave. The effective range of floor reinforcing was established. A reliable relation was established between the ratio of the modulus of elasticity of rocks of the reinforced zone to the modulus of elasticity of the surrounding rock and heaving of reinforced rocks. The obtained results can be used to predict the magnitude of heaving of rocks at their saturation, as well as after they are reinforced.

Control technology for floor heave of Jurassic soft rock in the Erdos Basin of China: A case study

Control technology for floor heave of Jurassic soft rock in the Erdos Basin of China: A case study

Study on large deformation and failure mechanism of deep buried stratified slate tunnel and control strategy of high constant resistance anchor cable

Aiming at the significant deformation problem of deep buried stratified soft rock tunnel, taking the No.3 inclined shaft of Muzhailing tunnel as background, the deformation and failure mechanism of the tunnel and the control strategy of high constant resistance anchor cable are studied. The deformation and failure mechanism of stratified tunnel surrounding rock is studied by physical model test, including the tunnel's temperature field, strain field, and displacement field from excavation to failure. Lateral stress significantly influences the deformation of the surrounding rock of the horizontal stratified tunnel. The surrounding rock of the tunnel forms a dumbbell-shaped tensile stress zone under the action of stress. The high tensile stress of the roof and floor leads to dislocation and layer separation, which causes floor heave failure and temperature change. The indoor tensile test verified the super strength characteristics and large deformation of the high constant resistance anchor cable. Based on the excavation compensation method and the coupling control mechanism of high constant resistance long and short anchor cables, a new high prestress constant resistance coupling control strategy is proposed. The numerical simulation and field test studies according to the new design are presented, which show that the high constant resistance anchor cable coupling support significantly reduces the tensile stress zone, effectively controls the deformation of tunnel surrounding rock, and avoids the damage of supporting structure and the cracking and deformation of the lining. The research results can provide a reference for constructing and supporting deep-buried, stratified soft rock tunnels.