During upward horizontal stratified backfill mining,stable backfill is essential for cap and sill pillar recovery.Currently,the primary method for calculating the required strength of backfill is the generalized three...During upward horizontal stratified backfill mining,stable backfill is essential for cap and sill pillar recovery.Currently,the primary method for calculating the required strength of backfill is the generalized three-dimensional(3 D)vertical stress model,which ignores the effect of mine depth,failing to obtain the vertical stress at different positions along stope length.Therefore,this paper develops and validates an improved 3 D model solution through numerical simulation in Rhino-FLAC^(3D),and examines the stress state and stability of backfill under different conditions.The results show that the improved model can accurately calculate the vertical stress at different mine depths and positions along stope length.The error rates between the results of the improved model and numerical simulation are below 4%,indicating high reliability and applicability.The maximum vertical stress(σ_(zz,max))in backfill is positively correlated with the degree of rock-backfill closure,which is enhanced by mine depth and elastic modulus of backfill,while weakened by stope width and inclination,backfill friction angle,and elastic modulus of rock mass.Theσ_(zz,max)reaches its peak when the stope length is 150 m,whileσ_(zz,max)is insensitive to changes in rock-backfill interface parameters.In all cases,the backfill stability can be improved by reducingσ_(zz,max).The results provide theoretical guidance for the backfill strength design and the safe and efficient recovery of ore pillars in deep mining.展开更多
The stability of the“surrounding rock-backfill”com posite system is crucial for the safety of mining stopes.This study systematically investigates the effects of steel slag(SS)content and interface angle on the stre...The stability of the“surrounding rock-backfill”com posite system is crucial for the safety of mining stopes.This study systematically investigates the effects of steel slag(SS)content and interface angle on the strength and failure characteristics of rock and SS-cemented paste backfill composite specimens(RBCS)through uniaxial compression strength tests(UCS),acoustic emission systems(AE),and 3 D digital image correlation monitoring technology(3 D-DIC).The intrinsic mechanism by which SS content influences the strength of SS-CPB was revealed through an analysis of its hydration reaction degree and microstructural characteristics under varying SS content.Moreover,a theoretical strength model incorporating different interface angles was developed to explore the impact of interface inclination on failure modes and mechanical strength.The main conclusions are as follows:The incorporation of SS enhances the plastic characteristics of RBCS and reduces its brittleness,with the increase of SS content,the stress-strain curve of RBCS in the“staircase-like”stag e becomes smoother;When the interface angle is 45°,the RBCS stress-strain curve exhibits a bimodal feature,and the failure mode changes from Y-shaped fractures to interface and axial splitting;The addition of SS results in a reduction of hydration products such as Ca(OH)_(2) in the backfill cementing system and an increase in harmful pores,which weakens the bonding performance and strength of RBCS,and the SS content should not exceed 45%;As the interface angle increases,the strength of RBCS decreases,and the critical interface slip angle decreases first and then increases with the increase in the E S/E R ratio.This study provides technical references for the large-scale application of SS in mine backfill.展开更多
Narrow backfill earth pressure estimation is applied to study the stability of supporting structures in the vicinity of existing buildings.Previous narrow backfill earth pressure studies have neglected seismic-unsatur...Narrow backfill earth pressure estimation is applied to study the stability of supporting structures in the vicinity of existing buildings.Previous narrow backfill earth pressure studies have neglected seismic-unsaturated seepage multi-field coupling,resulting in inaccurate estimates.To address these deficiencies,this paper proposed a calculation method for seismic passive earth pressure in unsaturated narrow backfill,based on inclined thin-layer units.It considers the interlayer shear stress,arching effect,and the multi-field coupling of seismic-unsaturated seepage.Additionally,this paper includes a parametric sensitivity analysis.The outcomes indicate that the earthquake passive ground pressure of unsaturated narrow backfill can be reduced by increasing the aspect ratio,seismic acceleration coefficient,and unsaturation parameterα.It can also be reduced by decreasing the effective interior friction angle,soil cohesion,wallearth friction angle,and vertical discharge.Furthermore,for any width soil,lowering the elevation of the action point of passive thrust can be attained by raising the effective interior friction angle,wall-earth friction angle,and unsaturation parameterα.Reducing soil cohesion,seismic acceleration coefficient,and vertical discharge can also lower the height of the application point of passive thrust.展开更多
The cemented-gangue-fly-ash backfill(CGFB)prepared from coal-based solid waste materials commonly exhibits high brittleness,leading to an increased susceptibility to cracking.Uniaxial compressive strength(UCS),acousti...The cemented-gangue-fly-ash backfill(CGFB)prepared from coal-based solid waste materials commonly exhibits high brittleness,leading to an increased susceptibility to cracking.Uniaxial compressive strength(UCS),acoustic emission(AE),and scanning electron microscopy tests were conducted on CGFB samples with recycled steel fiber(RSF)contents of 0,0.5%,1.0%and 1.5%to assess the mechanical properties and damage evolution law of the CGFB.The research findings indicate that:1)When RSF contents were 0.5%,1%,and 1.5%,respectively,compared to samples without RSF,the UCS decreased by 3.86%,6.76%,and 15.59%,while toughness increased by 69%,98%,and 123%;2)The addition of RSFs reduced the post-peak stress energy activity and increased the fluctuations in the b-value;3)As the RSF dosage increased from 0 to 1.5%,the per unit dissipated strain energy increased from 5.84 to 21.51,and the post-peak released energy increased from 15.07 to 33.76,indicating that the external energy required for the CGFB sample to fail increased;4)The hydration products,such as C-S-H gel,ettringite,and micro-particle materials,were embedded in the damaged areas of the RSFs,increasing the frictional force at the interface between the RSF and CGFB matrix.The shape variability of the RSFs caused interlocking between the RSFs and the matrix.Both mechanisms strengthened the bridging effect of the RSFs in the CGFB,thereby improving the damage resistance capability of CGFB.The excellent damage resistance occurred at an RSF content of 0.5%;thus,this content is recommended for engineering applications.展开更多
Utilizing mine solid waste as a partial cement substitute(CS)to develop new cementitious materials is a significant technological innovation that will decrease the expenses associated with filling mining.To realize th...Utilizing mine solid waste as a partial cement substitute(CS)to develop new cementitious materials is a significant technological innovation that will decrease the expenses associated with filling mining.To realize the resource utilization of magnesium slag(MS)and blast furnace slag(BFS),the effects of different contents of MS and BFS as partial CSs on the deformation and energy characteristics of cemented tailings backfill on different curing ages(3,7,and 28 d)were discussed.Meanwhile,the destabilization failure energy criterion of the backfill was established from the direction of energy change.The results show that the strength of all backfills increased with increasing curing age,and the strengths of the backfills exceeded 1.342 MPa on day 28.The backfill with 50%BFS+50%cement has the best performance in mechanical properties(the maximum strength can reach 6.129 MPa)and is the best choice among these CS combinations.The trend in peak strain and elastic modulus of the backfill with increasing curing age may vary depending on the CS combination.The energy index at peak stress of the backfill with BFS as a partial CS was significantly higher than that of the backfill under other CS combinations.In contrast,the enhancement of the energy index when MS was used as a partial CS was not as significant as BFS.Sharp changes in the energy consumption ratio after continuous smooth changes can be used as a criterion for destabilization and failure of the backfill.The research results can provide guidance for the application of MS and BFS as partial CSs in mine filling.展开更多
The backfill-mining mass ratio is the ratio of the mass of the backfill materials in the goaf to the mass of the produced raw coal during solid backfill mining and it is regarded as a direct control index of the backf...The backfill-mining mass ratio is the ratio of the mass of the backfill materials in the goaf to the mass of the produced raw coal during solid backfill mining and it is regarded as a direct control index of the backfill effect in solid backfill mining. To design the backfill-mining mass ratio in a solid backfill mining panel, the backfill-mining mass ratio was defined on the basis of the basic principle of solid backfill mining. In addition, the density-stress relationship of backfill materials under compaction was obtained for five types of materials to derive a design formula for backfill-mining mass ratio. Moreover, the 6304-1 backfill panel under the large-scale dam of Ji′ning No. 3 coal mine was taken as an engineering case to design the backfill-mining mass ratio. In this way, it is found that the designed backfill-mining mass ratio is 1.22, while the mean value of the measured backfill-mining mass ratio is 1.245. Besides, the maximum roof subsidence is only 340 mm which effectively guarantees the backfill effect in the panel and control of strata movement and surface subsidence.展开更多
Taking cemented coal gangue pipeline transportation system in Suncun Coal Mine, Xinwen Mining Group, Shandong Province, China, as an example, the hydraulic calculation approaches and process about gravity pipeline tra...Taking cemented coal gangue pipeline transportation system in Suncun Coal Mine, Xinwen Mining Group, Shandong Province, China, as an example, the hydraulic calculation approaches and process about gravity pipeline transportation of backfill slurry were investigated. The results show that the backfill capability of the backfill system should be higher than 74.4 m3/h according to the mining production and backfill times in the mine; the minimum velocity (critical velocity) and practical working velocity of the backfill slurry are 1.44 and 3.82 m/s, respectively. Various formulae give the maximum ratio of total length to vertical height of pipeline (L/H ratio) of the backfill system of 5.4, and then the reliability and capability of the system can be evaluated.展开更多
Physical-chemical properties of phosphorous gypsum, proportion and cemented mechanism of slurry with gypsum as aggregate were studied to remove the harms of gypsum pile, combining with difficult problems of excessive ...Physical-chemical properties of phosphorous gypsum, proportion and cemented mechanism of slurry with gypsum as aggregate were studied to remove the harms of gypsum pile, combining with difficult problems of excessive mined-out gobs, enormous ore body under roadway and low recovery ratio of Yongshaba Mine, Kaiyang Phosphor Mine Group, Guizhou Province, China. An appropriate backfill system and craflwork were designed, using shattering milling method to crush gypsum, double-axles mixing and strong activation mixing way to mix slurry, cemented slurry and mullock backfill alternately process. The results show that gypsum is fit for backfilling afterwards by adding fly ash, though it is not an ideal aggregate for fine granule and coagulate retardation. The suggested dosage （the mass ratio of cement to fly ash to gypsum） is 1：1：6-1：1：8 with mass fraction of solid materials 60%-63%. Slurry is transported in suspend state with non-plastic strength, and then in concretion state after backfilling. The application to mine shows the technology is feasible, and gypsum utilization ratio is up to 100%. Transportation and backfill effect is very good for paste-like slurry and drenching cemented slurry into mullock, and the compressive strength and recovery ratio are 2.0 MPa and 82.6%, respectively, with the maximum subsidence of surface only 1.307 mm. Furthermore, the investment of system is about 7 × 10^6 yuan （RMB）, only 1/10 of that of traditional paste backfill system.展开更多
To ensure compacted backfilling, it is essential to ensure the reliability of the performance of a solid backfill support, key equipment for integrating backfilling and mining. To evaluate the backfilling performance ...To ensure compacted backfilling, it is essential to ensure the reliability of the performance of a solid backfill support, key equipment for integrating backfilling and mining. To evaluate the backfilling performance of a backfill support, the concept of backfill and operation properties is proposed in this study. Moreover, it is elaborated in terms of five aspects, namely, structural property, supporting property, tamping property, mechanical response property, and geological adaptation property, which are specifically reflected by 14 indexes including the supporting intensity and vertical roof gap. Seven separate evaluation indexes are selected to build a backfill and operation properties based system for evaluating the design schemes of the backfill support via a multi-index comprehensive evaluation method; then, the evaluation method and process together with measures to control the backfill and operation properties are proposed. By using this system, 11 schemes for optimizing the ZC5200/14.5/3 backfill support at Zhaizhen Coal Mine are evaluated, and scheme #10 is found to show superior vertical roof gap and other backfill and operation properties, thus demonstrating the reasonability of the evaluation system. On this basis, the backfill support research framework of designing initial scheme, optimizing design scheme, selecting the best evaluation indexes, evaluating optimizing scheme, and evaluating operation properties is built; this should serve as an important reference for further studies on the roof controlling performance of a backfill support.展开更多
Understanding the temperature effect on shear behavior of the ore-backfill coupling structure is critical for the safety and stability of backfill stope under the condition of high horizontal stress in deep mining.Dir...Understanding the temperature effect on shear behavior of the ore-backfill coupling structure is critical for the safety and stability of backfill stope under the condition of high horizontal stress in deep mining.Direct shear tests were carried out on the cemented rod-mill sand backfill(CRB)and ore-CRB(OCRB)coupling specimens at various temperatures(20,40 and 60°C).The shear behavior and AE characteristic parameters of OCRB at different shear directions were compared and analyzed.The results show that the temperature effect on the shear performance of CRB mainly depends on the characteristics of microstructures and main mineral phases;the performance of CRB at 40°C is relatively good;the shear deformation of OCRB has one more“peak fluctuation stage”than CRB and has a good correlation with AE characteristic parameters.The temperature can positively or negatively impact the shear strength of OCRB,depending on the temperature and shear direction;the shear performance of OCRB along the axis direction(D1)is significantly better than that perpendicular to the axis direction(D2).The co-bearing capacity of the ore-backfill coupling structure(i.e.,stopes)is closely related to the ambient temperature and principal stress orientation.展开更多
The stability of room mining coal pillars during their secondary mining for recovering coal was analyzed. An analysis was performed for the damage and instability mechanism of coal pillars recovered by the caving mini...The stability of room mining coal pillars during their secondary mining for recovering coal was analyzed. An analysis was performed for the damage and instability mechanism of coal pillars recovered by the caving mining method. During the damage progression of a single room coal pillar, the shape of the stress distribution in the pillar transformed from the initial stable saddle shape to the final arch-shaped distribution of critical instability. By combining the shapes of stress distribution in the coal pillars with the ultimate strength theory, the safe-stress value of coal pillar was obtained as 11.8 MPa. The mechanism of instability of coal pillar groups recovered by the caving mining method was explained by the domino effect. Since the room coal pillars mined and recovered by the traditional caving mining method were significantly influenced by the secondary mining during recovery, the coal pillars would go through a chain-type instability failure. Because of this limitation, the method of solid backfilling was proposed for mining and recovering room coal pillars, thus changing the transfer mechanism of stress caused by the secondary mining(recovery) of coal pillars. The mechanical model of the stope in the case of backfilling and recovering room coal pillars was built. The peak stress values inside coal pillars varied with the variance of backfilling ratio when the working face was advanced by 150 m. Furthermore, when the critical backfilling ratio was 80.6%, the instability failure of coal pillars would not occur during the solid backfill mining process. By taking Bandingliang Coal Mine as an example, the coal pillars' stability of stope under this backfilling ratio was studied, and a project scheme was designed.展开更多
Backfill hydraulic support is the key equipment in achieving coal mining and solid backfilling simultaneously in solid backfill mining technology.Based on the summary and analysis of main types,basic structural proper...Backfill hydraulic support is the key equipment in achieving coal mining and solid backfilling simultaneously in solid backfill mining technology.Based on the summary and analysis of main types,basic structural properties and filed application of backfill hydraulic support,this work has firstly proposed the basic principle of backfill hydraulic support optimization design and provided the method of optimal design of key structural components,like four-bar linkage,rear canopy and tamping structure;the method is further elaborated as changing hinging position of upper bar to optimize four-bar linkage,by lengthening or shortening the rear canopy to optimize length ratio of canopy;and by changing length and hinging position of tamping structure as well as suspension height of backfill scrape conveyor to realize optimization of tamping structure.On this basis,the process of optimal design of backfill hydraulic support is built.The optimal design case of ZC5200/14.5/30 six columns-four bar linkage used in 7203 W workface of Zhaizhen Coal Mine shows that the backfill properties like horizontal roof gap,vertical horizontal gap,tamping angle and tamping head gap are improved obviously through optimizing four-bar linkage,canopy length and tamping structure according to the optimal design method proposed in this work.展开更多
Adding polypropylene(PP)fibers and coarse aggregates has become a popular way to enhance the strength and stability of the cemented tailings backfilling(CTB)body.It is essential to explore the influence of tailings-ag...Adding polypropylene(PP)fibers and coarse aggregates has become a popular way to enhance the strength and stability of the cemented tailings backfilling(CTB)body.It is essential to explore the influence of tailings-aggregate ratio and fiber content on the mechanical properties of CTB samples.The comprehensive tests of the unconfined compressive strength(UCS),slump and microstructure were designed,and the regression models were established to characterize the effect of the strength,ductility and fluidity.The results indicate that the tailings-aggregate ratio of 5:5 and PP fiber content of 0.5 kg/m^(3) are the optimum point considering the UCS,cracking strain,peak strain and post-peak ductility.The tailings-aggregate ratio is consistent with the unary quadratic to the UCS and a linear model with a negative slope to the slump.Microstructural analysis indicates that PP fiber tends to bridge the cracks and rod-mill sand to serve as the skeleton of the paste matrix,which can enhance the compactness and improve the ductility of the CTB.The results presented here are of great significance to the understanding and application of coarse aggregates and fibers to improve the mechanical properties of CTB.展开更多
Cemented tailings backfill(CTB) is made by mixing cement, tailings and water together, thus cement hydration and water seepage flow are the two crucial factors affecting the quality of CTB. Cement hydration process ca...Cemented tailings backfill(CTB) is made by mixing cement, tailings and water together, thus cement hydration and water seepage flow are the two crucial factors affecting the quality of CTB. Cement hydration process can release significant amount of heat to raise the temperature of CTB and in turn increase the rate of cement hydration. Meanwhile, the progress of cement hydration consumes water and produces hydration products to change the pore structures within CTB, which further influences the hydraulic behavior of CTB. In order to understand the hydraulic behavior of CTB, a numerical model was developed by coupling the hydraulic,thermal and hydration equations. This model was then implemented into COMSOL Multiphysics to simulate the evolutions of temperature and water seepage flow within CTB versus curing time. The predicted outcomes were compared with correspondent experimental results, proving the validity and availability of this model. By taking advantage of the validated model, effects of various initial CTB and curing temperatures, cement content, and CTB's geometric shapes on the hydraulic behavior of CTB were demonstrated numerically. The presented conclusions can contribute to preparing more environmentally friendly CTB structures.展开更多
It is of great significance for safety reason to obtain the triaxial compressive properties of cemented tailings backfill(CTB).The influence of cement content,curing age and confining pressure on strength and deformat...It is of great significance for safety reason to obtain the triaxial compressive properties of cemented tailings backfill(CTB).The influence of cement content,curing age and confining pressure on strength and deformation properties of CTB was examined and discussed.Results indicate that the triaxial compressive and deformation behavior of CTB is strongly affected by the cement content,curing age and confining pressure.The increase in cement content,curing age and confining pressure leads to a change in stress−strain behavior and an increase in the axial strain at failure and post-peak strength loss.The cohesion of CTB rises as the curing age and cement content increase.However,the enhancement in internal friction angle is trivial and negligible.It should be noted that the failure pattern of CTB samples in triaxial compression is mainly along a shear plane,the confining pressure restrains the lateral expansion and the bulging failure pattern is dominantly detected in CTB samples as curing age length and cement content increase.The results will help to better understand the triaxial mechanical and deformation behavior of CTB.展开更多
Fully mechanized solid backfill mining(FMSBM) technology adopts dense backfill body to support the roof. Based on the distinguishing characteristics and mine pressure control principle in this technology, the basic pr...Fully mechanized solid backfill mining(FMSBM) technology adopts dense backfill body to support the roof. Based on the distinguishing characteristics and mine pressure control principle in this technology, the basic principles and methods for mining pressure monitoring were analyzed and established. And the characteristics of overburden strata movement were analyzed by monitoring the support resistance of hydraulic support, the dynamic subsidence of immediate roof, the stress of backfill body, the front abutment pressure, and the mass ratio of cut coal to backfilled materials. On-site strata behavior measurements of 7403 W solid backfilling working face in Zhai Zhen Coal Mine show that the backfill body can effectively support the overburden load, obviously control the overburden strata movement, and weaken the strata behaviors distinctly. Specific performances are as follows. The support resistance decreases obviously; the dynamic subsidence of immediate roof keeps consistent to the variation of backfill body stress, and tends to be stable after the face retreating to 120-150 m away from the cut. The peak value of front abutment pressure arises at 5-12 m before the operating face, and mass ratio is greater than the designed value of 1.15, which effectively ensures the control of strata movement. The research results are bases for intensively studying basic theories of solid backfill mining strata behaviors and its control, and provide theoretical guidance for engineering design in FMSBM.展开更多
Cemented backfill used in deep mines would inevitably be exposed to the ambient temperature of 20−60℃in the next few decades.In this paper,two types of cemented gravel sand backfills,cemented rod-mill sand backfill(C...Cemented backfill used in deep mines would inevitably be exposed to the ambient temperature of 20−60℃in the next few decades.In this paper,two types of cemented gravel sand backfills,cemented rod-mill sand backfill(CRB)and cemented gobi sand backfill(CGB),were prepared and cured at various temperatures(20,40,60℃)and ages(3,7,28 d),and the effects of temperature and age on the physico-mechanical properties of CRB and CGB were investigated based on laboratory tests.Results show that:1)the effects of temperature and age on the physico-mechanical properties of backfills mainly depend on the amount of hydration products and the refinement of cementation structures.The temperature has a more significant effect on thermal expansibility and ultrasonic performance at early ages.2)The facilitating effect of temperature and age on the compressive strength of CGB is higher than that on CRB.With the increase of temperature,the compressive failure modes changed from X-conjugate shear failure to tensile failure,and the integrity of specimens was significantly improved.3)Similarly,the shear performance of CGB is generally better than that of CRB.The temperature has a weaker effect on shear strength than age,but the shear deformation and shear plane morphology are closely related to temperature.展开更多
基金Project(2024ZD1003704)supported by the Deep Earth Probe and Mineral Resources Exploration-National Science and Technology Major Project,ChinaProjects(51834001,52130404)supported by the National Natural Science Foundation of China。
文摘During upward horizontal stratified backfill mining,stable backfill is essential for cap and sill pillar recovery.Currently,the primary method for calculating the required strength of backfill is the generalized three-dimensional(3 D)vertical stress model,which ignores the effect of mine depth,failing to obtain the vertical stress at different positions along stope length.Therefore,this paper develops and validates an improved 3 D model solution through numerical simulation in Rhino-FLAC^(3D),and examines the stress state and stability of backfill under different conditions.The results show that the improved model can accurately calculate the vertical stress at different mine depths and positions along stope length.The error rates between the results of the improved model and numerical simulation are below 4%,indicating high reliability and applicability.The maximum vertical stress(σ_(zz,max))in backfill is positively correlated with the degree of rock-backfill closure,which is enhanced by mine depth and elastic modulus of backfill,while weakened by stope width and inclination,backfill friction angle,and elastic modulus of rock mass.Theσ_(zz,max)reaches its peak when the stope length is 150 m,whileσ_(zz,max)is insensitive to changes in rock-backfill interface parameters.In all cases,the backfill stability can be improved by reducingσ_(zz,max).The results provide theoretical guidance for the backfill strength design and the safe and efficient recovery of ore pillars in deep mining.
基金Project(52308316)supported by the National Natural Science Foundation of China,Project(BBJ2024088)supported by the Fundamental Research Funds for the Central Universities(PhD.Top Innovative Talents Fund of CUMTB),China。
文摘The stability of the“surrounding rock-backfill”com posite system is crucial for the safety of mining stopes.This study systematically investigates the effects of steel slag(SS)content and interface angle on the strength and failure characteristics of rock and SS-cemented paste backfill composite specimens(RBCS)through uniaxial compression strength tests(UCS),acoustic emission systems(AE),and 3 D digital image correlation monitoring technology(3 D-DIC).The intrinsic mechanism by which SS content influences the strength of SS-CPB was revealed through an analysis of its hydration reaction degree and microstructural characteristics under varying SS content.Moreover,a theoretical strength model incorporating different interface angles was developed to explore the impact of interface inclination on failure modes and mechanical strength.The main conclusions are as follows:The incorporation of SS enhances the plastic characteristics of RBCS and reduces its brittleness,with the increase of SS content,the stress-strain curve of RBCS in the“staircase-like”stag e becomes smoother;When the interface angle is 45°,the RBCS stress-strain curve exhibits a bimodal feature,and the failure mode changes from Y-shaped fractures to interface and axial splitting;The addition of SS results in a reduction of hydration products such as Ca(OH)_(2) in the backfill cementing system and an increase in harmful pores,which weakens the bonding performance and strength of RBCS,and the SS content should not exceed 45%;As the interface angle increases,the strength of RBCS decreases,and the critical interface slip angle decreases first and then increases with the increase in the E S/E R ratio.This study provides technical references for the large-scale application of SS in mine backfill.
基金Project(42277175)supported by the National Natural Science Foundation of ChinaProject(NRMSSHR-2022-Z08)supported by the Key Laboratory of Natural Resources Monitoring and Supervision in Southern Hilly Region,Ministry of Natural Resources,China。
文摘Narrow backfill earth pressure estimation is applied to study the stability of supporting structures in the vicinity of existing buildings.Previous narrow backfill earth pressure studies have neglected seismic-unsaturated seepage multi-field coupling,resulting in inaccurate estimates.To address these deficiencies,this paper proposed a calculation method for seismic passive earth pressure in unsaturated narrow backfill,based on inclined thin-layer units.It considers the interlayer shear stress,arching effect,and the multi-field coupling of seismic-unsaturated seepage.Additionally,this paper includes a parametric sensitivity analysis.The outcomes indicate that the earthquake passive ground pressure of unsaturated narrow backfill can be reduced by increasing the aspect ratio,seismic acceleration coefficient,and unsaturation parameterα.It can also be reduced by decreasing the effective interior friction angle,soil cohesion,wallearth friction angle,and vertical discharge.Furthermore,for any width soil,lowering the elevation of the action point of passive thrust can be attained by raising the effective interior friction angle,wall-earth friction angle,and unsaturation parameterα.Reducing soil cohesion,seismic acceleration coefficient,and vertical discharge can also lower the height of the application point of passive thrust.
基金Projects(52274143,51874284)supported by the National Natural Science Foundation of China。
文摘The cemented-gangue-fly-ash backfill(CGFB)prepared from coal-based solid waste materials commonly exhibits high brittleness,leading to an increased susceptibility to cracking.Uniaxial compressive strength(UCS),acoustic emission(AE),and scanning electron microscopy tests were conducted on CGFB samples with recycled steel fiber(RSF)contents of 0,0.5%,1.0%and 1.5%to assess the mechanical properties and damage evolution law of the CGFB.The research findings indicate that:1)When RSF contents were 0.5%,1%,and 1.5%,respectively,compared to samples without RSF,the UCS decreased by 3.86%,6.76%,and 15.59%,while toughness increased by 69%,98%,and 123%;2)The addition of RSFs reduced the post-peak stress energy activity and increased the fluctuations in the b-value;3)As the RSF dosage increased from 0 to 1.5%,the per unit dissipated strain energy increased from 5.84 to 21.51,and the post-peak released energy increased from 15.07 to 33.76,indicating that the external energy required for the CGFB sample to fail increased;4)The hydration products,such as C-S-H gel,ettringite,and micro-particle materials,were embedded in the damaged areas of the RSFs,increasing the frictional force at the interface between the RSF and CGFB matrix.The shape variability of the RSFs caused interlocking between the RSFs and the matrix.Both mechanisms strengthened the bridging effect of the RSFs in the CGFB,thereby improving the damage resistance capability of CGFB.The excellent damage resistance occurred at an RSF content of 0.5%;thus,this content is recommended for engineering applications.
基金Projects(52274108,U2341265)supported by the National Natural Science Foundation of ChinaProject(2022YFC2904103)supported by the National Key Research and Development Program of China。
文摘Utilizing mine solid waste as a partial cement substitute(CS)to develop new cementitious materials is a significant technological innovation that will decrease the expenses associated with filling mining.To realize the resource utilization of magnesium slag(MS)and blast furnace slag(BFS),the effects of different contents of MS and BFS as partial CSs on the deformation and energy characteristics of cemented tailings backfill on different curing ages(3,7,and 28 d)were discussed.Meanwhile,the destabilization failure energy criterion of the backfill was established from the direction of energy change.The results show that the strength of all backfills increased with increasing curing age,and the strengths of the backfills exceeded 1.342 MPa on day 28.The backfill with 50%BFS+50%cement has the best performance in mechanical properties(the maximum strength can reach 6.129 MPa)and is the best choice among these CS combinations.The trend in peak strain and elastic modulus of the backfill with increasing curing age may vary depending on the CS combination.The energy index at peak stress of the backfill with BFS as a partial CS was significantly higher than that of the backfill under other CS combinations.In contrast,the enhancement of the energy index when MS was used as a partial CS was not as significant as BFS.Sharp changes in the energy consumption ratio after continuous smooth changes can be used as a criterion for destabilization and failure of the backfill.The research results can provide guidance for the application of MS and BFS as partial CSs in mine filling.
基金Project(51421003)supported by the Foundation for Innovative Research Groups of the National Natural Science Foundation of ChinaProject(2014ZDPY02)supported by the Fundamental Research Funds for the Central Universities,China
文摘The backfill-mining mass ratio is the ratio of the mass of the backfill materials in the goaf to the mass of the produced raw coal during solid backfill mining and it is regarded as a direct control index of the backfill effect in solid backfill mining. To design the backfill-mining mass ratio in a solid backfill mining panel, the backfill-mining mass ratio was defined on the basis of the basic principle of solid backfill mining. In addition, the density-stress relationship of backfill materials under compaction was obtained for five types of materials to derive a design formula for backfill-mining mass ratio. Moreover, the 6304-1 backfill panel under the large-scale dam of Ji′ning No. 3 coal mine was taken as an engineering case to design the backfill-mining mass ratio. In this way, it is found that the designed backfill-mining mass ratio is 1.22, while the mean value of the measured backfill-mining mass ratio is 1.245. Besides, the maximum roof subsidence is only 340 mm which effectively guarantees the backfill effect in the panel and control of strata movement and surface subsidence.
基金Project(50490270) supported by the National Natural Science Foundation of China
文摘Taking cemented coal gangue pipeline transportation system in Suncun Coal Mine, Xinwen Mining Group, Shandong Province, China, as an example, the hydraulic calculation approaches and process about gravity pipeline transportation of backfill slurry were investigated. The results show that the backfill capability of the backfill system should be higher than 74.4 m3/h according to the mining production and backfill times in the mine; the minimum velocity (critical velocity) and practical working velocity of the backfill slurry are 1.44 and 3.82 m/s, respectively. Various formulae give the maximum ratio of total length to vertical height of pipeline (L/H ratio) of the backfill system of 5.4, and then the reliability and capability of the system can be evaluated.
基金Project(2006BAB02A03)supported by the National Key Technology Research and Development ProgramProject(08MX16)supported by Mittal Scientific and Technological Innovation Projects of Central South University during 2008
文摘Physical-chemical properties of phosphorous gypsum, proportion and cemented mechanism of slurry with gypsum as aggregate were studied to remove the harms of gypsum pile, combining with difficult problems of excessive mined-out gobs, enormous ore body under roadway and low recovery ratio of Yongshaba Mine, Kaiyang Phosphor Mine Group, Guizhou Province, China. An appropriate backfill system and craflwork were designed, using shattering milling method to crush gypsum, double-axles mixing and strong activation mixing way to mix slurry, cemented slurry and mullock backfill alternately process. The results show that gypsum is fit for backfilling afterwards by adding fly ash, though it is not an ideal aggregate for fine granule and coagulate retardation. The suggested dosage （the mass ratio of cement to fly ash to gypsum） is 1：1：6-1：1：8 with mass fraction of solid materials 60%-63%. Slurry is transported in suspend state with non-plastic strength, and then in concretion state after backfilling. The application to mine shows the technology is feasible, and gypsum utilization ratio is up to 100%. Transportation and backfill effect is very good for paste-like slurry and drenching cemented slurry into mullock, and the compressive strength and recovery ratio are 2.0 MPa and 82.6%, respectively, with the maximum subsidence of surface only 1.307 mm. Furthermore, the investment of system is about 7 × 10^6 yuan （RMB）, only 1/10 of that of traditional paste backfill system.
基金Project(2017QNA21)supported by Fundamental Research Funds for the Central Universities,ChinaProject supported by the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD),China
文摘To ensure compacted backfilling, it is essential to ensure the reliability of the performance of a solid backfill support, key equipment for integrating backfilling and mining. To evaluate the backfilling performance of a backfill support, the concept of backfill and operation properties is proposed in this study. Moreover, it is elaborated in terms of five aspects, namely, structural property, supporting property, tamping property, mechanical response property, and geological adaptation property, which are specifically reflected by 14 indexes including the supporting intensity and vertical roof gap. Seven separate evaluation indexes are selected to build a backfill and operation properties based system for evaluating the design schemes of the backfill support via a multi-index comprehensive evaluation method; then, the evaluation method and process together with measures to control the backfill and operation properties are proposed. By using this system, 11 schemes for optimizing the ZC5200/14.5/3 backfill support at Zhaizhen Coal Mine are evaluated, and scheme #10 is found to show superior vertical roof gap and other backfill and operation properties, thus demonstrating the reasonability of the evaluation system. On this basis, the backfill support research framework of designing initial scheme, optimizing design scheme, selecting the best evaluation indexes, evaluating optimizing scheme, and evaluating operation properties is built; this should serve as an important reference for further studies on the roof controlling performance of a backfill support.
基金Project(KFJ-STS-QYZD-174)supported by the Science and Technology Service Network Initiative of the Chinese Academy of SciencesProjects(41941018,42077251)supported by the National Natural Science Foundation of China+1 种基金Project(P2018G045)supported by the Science&Technology Research and Development Program of China RailwayProject(2018CFA013)supported by the Hubei Provincial Natural Science Foundation Innovation Group,China。
文摘Understanding the temperature effect on shear behavior of the ore-backfill coupling structure is critical for the safety and stability of backfill stope under the condition of high horizontal stress in deep mining.Direct shear tests were carried out on the cemented rod-mill sand backfill(CRB)and ore-CRB(OCRB)coupling specimens at various temperatures(20,40 and 60°C).The shear behavior and AE characteristic parameters of OCRB at different shear directions were compared and analyzed.The results show that the temperature effect on the shear performance of CRB mainly depends on the characteristics of microstructures and main mineral phases;the performance of CRB at 40°C is relatively good;the shear deformation of OCRB has one more“peak fluctuation stage”than CRB and has a good correlation with AE characteristic parameters.The temperature can positively or negatively impact the shear strength of OCRB,depending on the temperature and shear direction;the shear performance of OCRB along the axis direction(D1)is significantly better than that perpendicular to the axis direction(D2).The co-bearing capacity of the ore-backfill coupling structure(i.e.,stopes)is closely related to the ambient temperature and principal stress orientation.
基金Project(2014ZDPY02)supported by the Fundamental Research Funds for the Central Universities
文摘The stability of room mining coal pillars during their secondary mining for recovering coal was analyzed. An analysis was performed for the damage and instability mechanism of coal pillars recovered by the caving mining method. During the damage progression of a single room coal pillar, the shape of the stress distribution in the pillar transformed from the initial stable saddle shape to the final arch-shaped distribution of critical instability. By combining the shapes of stress distribution in the coal pillars with the ultimate strength theory, the safe-stress value of coal pillar was obtained as 11.8 MPa. The mechanism of instability of coal pillar groups recovered by the caving mining method was explained by the domino effect. Since the room coal pillars mined and recovered by the traditional caving mining method were significantly influenced by the secondary mining during recovery, the coal pillars would go through a chain-type instability failure. Because of this limitation, the method of solid backfilling was proposed for mining and recovering room coal pillars, thus changing the transfer mechanism of stress caused by the secondary mining(recovery) of coal pillars. The mechanical model of the stope in the case of backfilling and recovering room coal pillars was built. The peak stress values inside coal pillars varied with the variance of backfilling ratio when the working face was advanced by 150 m. Furthermore, when the critical backfilling ratio was 80.6%, the instability failure of coal pillars would not occur during the solid backfill mining process. By taking Bandingliang Coal Mine as an example, the coal pillars' stability of stope under this backfilling ratio was studied, and a project scheme was designed.
基金Project(2017QNA21)supported by the Fundamental Research Funds for the Central Universities of ChinaProject supported by the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD),China
文摘Backfill hydraulic support is the key equipment in achieving coal mining and solid backfilling simultaneously in solid backfill mining technology.Based on the summary and analysis of main types,basic structural properties and filed application of backfill hydraulic support,this work has firstly proposed the basic principle of backfill hydraulic support optimization design and provided the method of optimal design of key structural components,like four-bar linkage,rear canopy and tamping structure;the method is further elaborated as changing hinging position of upper bar to optimize four-bar linkage,by lengthening or shortening the rear canopy to optimize length ratio of canopy;and by changing length and hinging position of tamping structure as well as suspension height of backfill scrape conveyor to realize optimization of tamping structure.On this basis,the process of optimal design of backfill hydraulic support is built.The optimal design case of ZC5200/14.5/30 six columns-four bar linkage used in 7203 W workface of Zhaizhen Coal Mine shows that the backfill properties like horizontal roof gap,vertical horizontal gap,tamping angle and tamping head gap are improved obviously through optimizing four-bar linkage,canopy length and tamping structure according to the optimal design method proposed in this work.
基金Project(51722401)supported by the National Science Foundation for Excellent Young Scholars of ChinaProject(51334001)supported by the Key Program of National Natural Science Foundation of ChinaProject(FRF-TP-18-003C1)supported by the Fundamental Research Funds for the Central Universities,China。
文摘Adding polypropylene(PP)fibers and coarse aggregates has become a popular way to enhance the strength and stability of the cemented tailings backfilling(CTB)body.It is essential to explore the influence of tailings-aggregate ratio and fiber content on the mechanical properties of CTB samples.The comprehensive tests of the unconfined compressive strength(UCS),slump and microstructure were designed,and the regression models were established to characterize the effect of the strength,ductility and fluidity.The results indicate that the tailings-aggregate ratio of 5:5 and PP fiber content of 0.5 kg/m^(3) are the optimum point considering the UCS,cracking strain,peak strain and post-peak ductility.The tailings-aggregate ratio is consistent with the unary quadratic to the UCS and a linear model with a negative slope to the slump.Microstructural analysis indicates that PP fiber tends to bridge the cracks and rod-mill sand to serve as the skeleton of the paste matrix,which can enhance the compactness and improve the ductility of the CTB.The results presented here are of great significance to the understanding and application of coarse aggregates and fibers to improve the mechanical properties of CTB.
基金Project(SKLCRSM13KFB05)supported by State Key Laboratory for Coal Resources and Safe Mining(China University of Mining&Technology)
文摘Cemented tailings backfill(CTB) is made by mixing cement, tailings and water together, thus cement hydration and water seepage flow are the two crucial factors affecting the quality of CTB. Cement hydration process can release significant amount of heat to raise the temperature of CTB and in turn increase the rate of cement hydration. Meanwhile, the progress of cement hydration consumes water and produces hydration products to change the pore structures within CTB, which further influences the hydraulic behavior of CTB. In order to understand the hydraulic behavior of CTB, a numerical model was developed by coupling the hydraulic,thermal and hydration equations. This model was then implemented into COMSOL Multiphysics to simulate the evolutions of temperature and water seepage flow within CTB versus curing time. The predicted outcomes were compared with correspondent experimental results, proving the validity and availability of this model. By taking advantage of the validated model, effects of various initial CTB and curing temperatures, cement content, and CTB's geometric shapes on the hydraulic behavior of CTB were demonstrated numerically. The presented conclusions can contribute to preparing more environmentally friendly CTB structures.
基金Projects(2018YFC0808403,2018YFE0123000)supported by the National Key Technologies Research&Development Program of ChinaProject(800015Z1185)supported by the Yueqi Young Scholar Project,ChinaProject(2020YJSNY04)supported by the Fundamental Research Funds for the Central Universities,China。
文摘It is of great significance for safety reason to obtain the triaxial compressive properties of cemented tailings backfill(CTB).The influence of cement content,curing age and confining pressure on strength and deformation properties of CTB was examined and discussed.Results indicate that the triaxial compressive and deformation behavior of CTB is strongly affected by the cement content,curing age and confining pressure.The increase in cement content,curing age and confining pressure leads to a change in stress−strain behavior and an increase in the axial strain at failure and post-peak strength loss.The cohesion of CTB rises as the curing age and cement content increase.However,the enhancement in internal friction angle is trivial and negligible.It should be noted that the failure pattern of CTB samples in triaxial compression is mainly along a shear plane,the confining pressure restrains the lateral expansion and the bulging failure pattern is dominantly detected in CTB samples as curing age length and cement content increase.The results will help to better understand the triaxial mechanical and deformation behavior of CTB.
基金Project(SKLCRSM12X01)supported by State Key Laboratory of Coal Resources and Safe Mining,China University of Mining&TechnologyProject(2014ZDPY02)supported by the Fundamental Research Funds for the Central Universities,ChinaProject(CXLX13_951)supported by the Research Innovation Program for College Graduates of Jiangsu Province,China
文摘Fully mechanized solid backfill mining(FMSBM) technology adopts dense backfill body to support the roof. Based on the distinguishing characteristics and mine pressure control principle in this technology, the basic principles and methods for mining pressure monitoring were analyzed and established. And the characteristics of overburden strata movement were analyzed by monitoring the support resistance of hydraulic support, the dynamic subsidence of immediate roof, the stress of backfill body, the front abutment pressure, and the mass ratio of cut coal to backfilled materials. On-site strata behavior measurements of 7403 W solid backfilling working face in Zhai Zhen Coal Mine show that the backfill body can effectively support the overburden load, obviously control the overburden strata movement, and weaken the strata behaviors distinctly. Specific performances are as follows. The support resistance decreases obviously; the dynamic subsidence of immediate roof keeps consistent to the variation of backfill body stress, and tends to be stable after the face retreating to 120-150 m away from the cut. The peak value of front abutment pressure arises at 5-12 m before the operating face, and mass ratio is greater than the designed value of 1.15, which effectively ensures the control of strata movement. The research results are bases for intensively studying basic theories of solid backfill mining strata behaviors and its control, and provide theoretical guidance for engineering design in FMSBM.
基金Project(P2018G045)supported by the Science&Technology Research and Development Program of China RailwayProject(2018CFA013)supported by the Hubei Provincial Natural Science Foundation Innovation Group,China+1 种基金Project(KFJ-STS-QYZD-174)supported by the Science and Technology Service Network Initiative of the Chinese Academy of SciencesProject(51709257)supported by the National Natural Science Foundation of China。
文摘Cemented backfill used in deep mines would inevitably be exposed to the ambient temperature of 20−60℃in the next few decades.In this paper,two types of cemented gravel sand backfills,cemented rod-mill sand backfill(CRB)and cemented gobi sand backfill(CGB),were prepared and cured at various temperatures(20,40,60℃)and ages(3,7,28 d),and the effects of temperature and age on the physico-mechanical properties of CRB and CGB were investigated based on laboratory tests.Results show that:1)the effects of temperature and age on the physico-mechanical properties of backfills mainly depend on the amount of hydration products and the refinement of cementation structures.The temperature has a more significant effect on thermal expansibility and ultrasonic performance at early ages.2)The facilitating effect of temperature and age on the compressive strength of CGB is higher than that on CRB.With the increase of temperature,the compressive failure modes changed from X-conjugate shear failure to tensile failure,and the integrity of specimens was significantly improved.3)Similarly,the shear performance of CGB is generally better than that of CRB.The temperature has a weaker effect on shear strength than age,but the shear deformation and shear plane morphology are closely related to temperature.
