Formation mechanism and height calculation of the caved zone and water-conducting fracture zone in solid backfill mining

To study the heights of the caved zone and water-conducting fracture zone in backfill mining,the failure mechanism of strata during backfill mining was analyzed,and a method for determining the heights of the two zones was proposed based on key strata theory.The movement and failure regularity of the strata above the backfilling panel were revealed through numerical simulation.Considering the geologic conditions of the CT101 backfilling panel,the height of the fracture zone was determined using the proposed method along with empirical calculation,numerical simulation,and borehole detection.The results of the new calculation method were similar to in situ measurements.The traditional empirical formula,which is based on the equivalent mining height model,resulted in large errors during calculation.The findings indicate the reliability of the new method and demonstrate its significance for creating reference data for related studies.

Progress and prospects of mining with backfill in metal mines in China

Mining is the foundation of modern industrial development.In the context of the“carbon peaking and carbon neutrality”era,countries have put forward the development strategy of“adhering to the harmonious coexistence of humans and nature.”The ongoing progress and improvement of filling mining technology have provided significant advantages,such as“green mining,safe,efficient,and low-carbon emission,”which is crucial to the comprehensive utilization of mining solid waste,environmental protection,and safety of re-mining.This review paper describes the development history of metal mine filling mining in China and the characteristics of each stage.The excitation mechanism and current research status of producing cementitious materials from blast furnace slag and other industrial wastes are then presented,and the concept of developing cementitious materials for backfill based on the whole solid waste is proposed.The advances in the mechanical characteristics of cemented backfill are elaborated on four typical levels:static mechanics,dynamic mechanics,mechanical influencing factors,and multi-scale mechanics.The working/rheological characteristics of the filling slurry are presented,given the importance of the filling materials conveying process.Finally,the future perspectives of mining with backfill are discussed based on the features of modern filling concepts to provide the necessary theoretical research value for filling mining.

Mining pressure monitoring and analysis in fully mechanized backfilling coal mining face-A case study in Zhai Zhen Coal Mine

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.

A roof model and its application in solid backfilling mining

Through changing the axial load on backfilling material compaction test to reflect different overlying strata pressure on backfilling material, the stress-strain relations in the compaction process of backfilling material under the geological condition can be obtained. Based on the characteristic of overlying strata movement in backfill mining, a model of roof thin plate is established. By introducing the stress-strain relation in compaction process into the model and using RIZT method to analyze the bending deformation of roof, the bending deflection and stress distribution can be obtained. The results show that the maximum roof subsidence and maximum tensile stress occurring at the center are 255 mm and5 MPa, respectively. Tensile fracture of roof under the geological condition of Dongping Mine did not occur. The dynamic measurement results of roof in Dongping Mine verify the theoretical result from the aforementioned model, thereby suggesting the roof mechanical model is reliable. The roof thin plate model based on the compaction characteristic of backfilling material in this study is of importance to research on backfill mining theories and application of backfilling material characteristics.

Enhancing fly ash utilization in backfill materials treated with CO_(2)carbonation under ambient conditions

The environmental concerns resulting from coal-fired power generation that produces large amounts of CO_(2)and fly ash are of great interest.To mitigate,this study aims to develop a novel carbonated CO_(2)-fly ash-based backfill(CFBF)material under ambient conditions.The performance of CFBF was investigated for different fly ash-cement ratios and compared with non-CO_(2)reacted samples.The fresh CFBF slurry conformed to the Herschel-Bulkley model with shear thinning characteristics.After carbonation,the yield stress of the fresh slurry increased significantly by lowering fly ash ratio due to gel formation.The setting times were accelerated,resulting in approximately 40.6%of increased early strength.The final strength decreased when incorporating a lower fly ash ratio(50%and 60%),which was related to the existing heterogeneous pores caused by rapid fluid loss.The strength increased with fly ash content above 70%because additional C-S(A)-H and silica gels were characterized to precipitate on the grain surface,so the binding between particles increased.The C-S(A)-H gel was developed through the pozzolanic reaction,where CaCO_(3)was the prerequisite calcium source obtained in the CO_(2)-fly ash reaction.Furthermore,the maximum CO_(2)uptake efficiency was 1.39 mg-CO_(2)/g-CFBF.The CFBF material is feasible to co-dispose CO_(2)and fly ash in the mine goaf as negative carbon backfill materials,and simultaneously mitigates the strata movement and water lost in post-subsurface mining.

Joint Bearing Mechanism of Coal Pillar and Backfilling Body in Roadway Backfilling Mining Technology

In the traditional mining technology,the coal resources trapped beneath surface buildings,railways,and water bodies cannot be mined massively,thereby causing the lower coal recovery and dynamic disasters.In order to solve the aforementioned problems,the roadway backfilling mining technology is developed and the joint bearing mechanism of coal pillar and backfilling body is presented in this paper.The mechanical model of bearing system of coal pillar and backfilling body is established,by analyzing the basic characteristics of overlying strata deformation in roadway backfilling mining technology.According to the Ritz method in energy variation principle,the elastic solution expression of coal pillar deformation is deduced in roadway backfilling mining technology.Based on elastic-viscoelastic correspondence principle,combining with the burgers rheological constitutive model and Laplace transform theory,the viscoelastic solution expression of coal pillar deformation is obtained in roadway backfilling mining technology.By analyzing the compressive mechanical property of backfilling body,the time formula required for coal pillar and backfilling body to play the joint bearing function in roadway backfilling mining technology is obtained.The example analysis indicates that the time is 140 days.The results can be treated as an important basis for theoretical research and process design in roadway backfilling mining technology.

Control Mechanism of Surface Subsidence and Overburden Movement in Backfilling Mining based on Laminated Plate Theory

The backfilling mining technology is a type of high-efficiency coal mining technology that is used to address the environmental issues caused by the caving mining technology.In this paper,the mechanical model of symmetrical laminated plate representing the overburden movement caused by the backfilling mining technology is established,and the governing differential equation of the motion of the overburden is derived.The boundary conditions of the mechanical model are put forward,and the analytical solution of the overburden movement and surface subsidence is obtained.The numerical model of the overburden movement and surface subsidence,under mining with backfilling,is established by means of the FLAC3D numerical software,which aims to systematically study the influence of backfilling compactness,mining thickness,and mining depth on the overburden movement and surface subsidence in backfilling mining.When the compactnessηis less than 70%,the overburden movement and surface subsidence is greater,while whenηis greater than 70%,the overburden movement and surface subsidence is reduced significantly.On this basis,the control mechanism of surface subsidence and overburden movement in backfilling mining is obtained.The suitable backfilling compactness is the key to controlling surface subsidence and overburden movement in backfilling mining.

Mechanical analysis of roof stability under nonlinear compaction of solid backfill body

Based on the compaction characteristic test and the nonlinear compaction deformation characteristics of backfill material, this paper applies the theory of nonlinear elastic foundation of thin plate to establish a mechanical model of backfill body and roof in solid dense backfill coal mining. This study critically analyses the deflection equation of the roof by the energy method, derives the conditions of roof breakage and combined with concrete engineering practice analyses, determines roof movement regularity and stability in solid dense backfill mining. Analysis of the engineering practice of the 13,120 backfill panel of Pingmei 12# mine shows the theoretical maximum of roof convergence in backfill mining to be415 mm which is in significant agreement with the measured value. During the advancing process of solid backfill mining at the panel, the maximum tensile stress on the roof is less than its tensile strength which does not satisfy the conditions for roof breakage. Drilling results on the roof and ground pressure monitoring show that the integrity of roof is strong, which is consistent with the theoretical calculations described in this study. The results presented in the study provide a basis for further investigation into strata movement theory in solid dense backfill mining.

Experimental study on the mechanical properties and consolidation mechanism of microbial grouted backfill

Backfill mining technology is the practice of returning waste materials underground for both disposal and geotechnical stability,however,a challenge with current technologies is that they commonly require cement-based binders which have a relatively high environmental impact.Finding alternatives to cement-based binders can improve environmental performance and this paper proposes microbial grouted backfill(MGB)as a potential solution.In this paper,the effects of the cementation solution concentration(CSC),volume ratio of bacterial solution to cementation solution(VRBC),particle sizes of the aggregates,and the number of grouting batches on the mechanical properties of MGB are studied.The experimental results show that MGB strength increased,up to a peak value,as CSC was increased,before decreasing as CSC was increased further.The results also show that MGB strength increased,up to a peak value,as VRBC decreased,before decreasing as the VRBC was decreased further.The peak strength was achieved at a CSC of 2 mol/L and a VRBC of 1:9.The strength of the MGB also increased as the number of grouting batches increased.Graded MGB samples showed the highest UCS,25.12 MPa,at particle sizes of 0.2 to 0.8 mm,while full(non-graded)MGB samples displayed mean UCS values ranging from1.56 MPa when the maximum particle size was 0.2 mm,up to 13 MPa when the maximum particle size was 1.2 mm.MGB samples are consolidated by the calcium carbonate that is precipitated during microbial metabolism,and the strength of MGB increases linearly as calcium carbonate content increases.The calcium carbonate minerals produced in MGB materials are primarily calcite,with secondary amounts of vaterite.

Mass ratio design based on compaction properties of backfill materials

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.

Innovative backfilling longwall panel layout for better subsidence control effect-separating adjacent subcritical panels with pillars

In recent years,field trials of non-pillar longwall mining using complete backfill have been implemented successively in the Chinese coal mining industry.The objective of this paper is to get a scientific understanding of surface subsidence control effect using such techniques.It begins with a brief overview on complete backfill methods primarily used in China,followed by an analysis of collected subsidence factors under mining with complete backfill.It is concluded that non-pillar longwall panel layout cannot protect surface structures against damages at a relatively large mining height,even though complete backfill is conducted.In such cases,separated longwall panel layout should be applied,i.e.,panel width should be subcritical and stable coal pillars should be left between the adjacent panels.The proposed method takes the principles of subcritical extraction and partial extraction;in conjunction with gob backfilling,surface subsidence can be effectively mitigated,thus protecting surface buildings against mining-induced damage.A general design principle and method of separated panel layout have also been proposed.

Influence of backfilling rate on the stability of the"backfilling bodyimmediate roof"cooperative bearing structure

To reduce the cost of backfilling coal mining and utilize the underground space of coal mines,a new backfilling mining method with low backfilling rate called constructional backfilling coal mining(CBCM)is proposed.The "backfilling body-immediate roof" cooperative bearing structure of CBCM is analyzed by establishing the model of the medium thick plate on an elastic foundation.The influence of the backfilling rate on the stability of overlying strata is analyzed by the numerical simulation experiment.The control effect of CBCM is verified by a physic similar simulation test.The economic benefit of CBCM is analyzed.The conclusions are:the deformation characteristics of the immediate roof and critical backfilling spacing in CBCM can be analyzed based on the Hu Haichang’s theory.Exerting the bearing capacity of the immediate roof is beneficial to the stability of the overlying strata.The CBCM has a good control effect on the overburden in Xinyang Mine when the backfilling rate is lower than 25%.The backfilling cost of per ton coal is 37.39 yuan/t when the backfilling rate is 13.7%,with a decrease rate of 56.63%than the full-filling.The research results can provide theoretical support for the application of CBCM in coal mining.

Ground subsidence mechanism of a filling mine with a steeply inclined ore body

Long-term field monitoring finds that serious surface subsidence can still occur even if the high strength cemented fill method is adopted.Combining the results of numerical simulations with global position system(GPS)monitoring,we took a typical filling mining mine with a steeply inclined ore body as an example,and explored its ground subsidence mechanism.The results show that the ground subsidence caused by the mining of steep ore body is characterized by two settlement centers and a significantly uneven spatial distribution,which is visibly different from ground subsidence characteristic of the coal mine.The subsidence on the hanging wall is much larger than that on the footwall,and the settlement center tends to move to the hanging wall with the increase of mining depth.The backfill improves the strength and surrounding rock bearing capacity,which leads to a lag of about 3 years of the subsidence.However,under the actions of continuous and repeated mining disturbances,the supporting effect of the backfill can only reduce the amplitude of the deformation,but it cannot prevent the occurrence of settlement.