| High-concentration cement backfilling(HCCB)is prepared by mixing coal gangue,fly ash,cement,admixture and water,which is used to fill the coal mine goaf,to limit the movement and deformation of overlying strata,to control surface subsidence while the coal resource was mined.In order to analyze the deformation mechanism of single-working face(SWF)roof and the displacement and deformation law of overlying strata in cross-working faces(CWF)(The "cross-working faces area" is defined as the region composed of several adjacent parallel working faces.)in coal mine with HCCB,the mechanical model of roof beam of SWF and the mechanical model of roof strata of CWF were established,by the means of theoretical analysis,experiment test,similar material simulation and numerical simulation.Based on the mechanical model of "coal wall-support-roof rock beam-filling body" structure,the stress and bending moment of roof rock beam are analyzed in the area of SWF with HCCB,and based on the model of the elastic foundation beam,the law of moving deformation was analyzed.The mechanical model of "coal pillar-roof rock mass-filling body" structure was constructed in the area of SWF with HCCB,and based on this structure,the continuous "W" elastic plate(CWEP)theory is proposed to study the deformation and deformation characteristics of overlying strata in coal mine with HCCB.The main research works are as follows:(1)The physical and chemical properties of HCCB materials were analyzed.The reasonable ratio of HCCB was obtained by designing orthogonal experiment.The variation law of uniaxial compressive strength of the filled HCCB with time was analyzed and fitted.The whole process curve of the stress and strain of the filled HCCB was obtained by experiments.The results show that: The uniaxial compressive strength of HCCB body increases with the increase of the coagulation time,and reaches the maximum at about 28 days.The data fitting results show that the uniaxial compressive strength of the filling body is the quadratic function of the coagulation time,and the linear relationship can also characterize the relationship between the two.In the operation,to simplify the calculation,the uniaxial compressive strength of the filling body can be regarded as a linear function of the coagulation time.The whole process curve of the stress and strain of the filled HCCB is similar to that of siltstone,which is divided into four phases: compaction phase,linear elastic phase,yield deformation phase and failure phase.(2)The structure of the surrounding rock stress in the goaf was changed with HCCB,reforming a small structure of "coal wall-support-roof-filling body" in in the area of SWF and a large structure of "coal pillar-roof rock-filling body" in the area of CWF.Based on the characteristics of the strength of the filling body with time,the mechanical structure model of "coal wall-support-roof-filling body" was established.Analyzed the shear forces and bending moments of the roof rock beam,the relationship between the working face advancing velocity and the filling body strength formation rate was obtained.Regarded the filling body as the elastic foundation,the deformation analysis of the roof rock beam was carried out,and the theoretical analysis results were verified by similar material simulation test.(1)Based on the combined action of coal wall,stope support,filling body and roof,the mechanics model of roof rock beam with cemented filling was established.The model is an indeterminate mechanical structure with two fixed supports and supported by "coal wall-support-filling body".According to the relationship between the strength of cemented filling materials and the time,the area of the filling body is divided into two regions: the intensity growth region and the intensity constant region in the direction face advance,and the strength boundary of the two regions was analyzed.By analyzing the stress of the roof rock beam,the shear forces and bending moments of the roof rock beam were found out,as well as the two fixed ends’ bearing reaction forces 1R and 2R,the bending moments 1M and 2M were figured out.The working resistance of the working face support and the supporting ability of the filling body have a great effect on the distribution of the shear forces and bending moments of the roof rock beam.Compared with the caving method,the bearing reaction forces and bending moments of the rock beam are smaller.The relationship between the strength formation rate of the filling body and the advancing velocity of the working face was discussed.According to the concept of the filling mining limit span and the time relation with HCCB strength formation,the quantity relationship between the advancing velocity of the working face and the strength formation rate of the filling body was calculated.(2)The cemented filling body is regarded as elastic foundation on which the movement and deformation of roof rock beam are analyzed.The sinking curves of the roof rock beam on the sides of the coal wall and the goaf,and the vertical stress equations of the coal wall and the filling of the goaf were worked out by the initial parameter method.Analyzed that the depth of coal seam H,the foundation coefficient of coal mk,the foundation coefficient ck of filling body,the elastic modulus of rock beam E,the thickness of rock beam h and the amount of sinking 0z of roof beam and the filling body effected on the sinking volume of roof rock beam and the vertical stress of coal wall and filling body,the results show that the amount of subsidence 0z is the main influencing factor when the roof contacted with the filling body,and 0z is the key factor to control the roof rock beam sinking and reduce the vertical stress of the coal wall.(3)Similar simulations and numerical simulations show that the roof rock beam only undergo subsidence and no collapse occurs during the filling mining.The pressurized area appears in front of the working face and the decompression area appears on the filling side.With the increase of the filling rate,the deformation of the overlying strata decreases,and the bearing pressure of the filling body and the coal in front of the working face becomes smaller.The amount of sinking of roof in contact with the filling body is the key factor that affects the movement and deformation of the roof rock in filling mining.It can reduce the amount of sinking of roof in contact with the filling body by increasing the filling rate,so that the filling mining can control overlying strata movement and deformation,and control the effect of surface subsidence.(3)Taking the mining area ten of Xinyang Mine as the background,the paper researched the movement and deformation characteristics of the overlying strata in the form of "pillar-roof rock-filling body" in CWF,and analyzed the mechanism of coal pillar and filling body.The CWEP theory was proposed in CWF with HCCB,the mechanical model of CWEP was established,and the law of surface subsidence was analyzed under the condition of movement and deformation of this structure.The CWEP theory was verified by similar material simulation experiment.(1)In CWF,the stress of the roof rock strata with high concentration cementation was carried out,and the cooperative support system of "coal body-roof-filling body" is constructed.The working mechanism of coal pillar and filling body is analyzed,the pillar plays the role of supporting roof and overlying strata load.And the filling body has two aspects to support: the vertical support function against roof rock,the lateral support force to the coal pillar which makes its force from the two-dimensional into three-dimensional and improves its compressive strength.The conditions of stability of coal pillar and “coal body-roof-filling body” system were deduced under the cementation filling mining.And on this basis,the theory of CWEP relied on elastic plate theory was proposed.(2)The CWEP mechanical model was established in CWF,and the formed foundation of the CWEP the condition of the continuous slab structure and the maximum deflection were analyzed.The relationships between the maximum sinking amount max? of the roof and the filling rate η,the filling body compression rate ?,the displacement amount 0z before the roof contacted the filling body were analyzed.The filling rate was increased,the compression rate of the filling body was reduced and the amount of displacement before the contact between the roof and the filling body was reduced,which was beneficial to the stability of the "pillar-roof-filling body" cooperative support system,and also helped to reduce the roof sinking and control the surface subsidence.(3)Similar simulation and numerical simulation results show that in CWF with HCCB,the basic top in the tendency of the coal seam occurred "W"-shaped continuous bending subsidence,no break,and the maximum subsidence occurred at the midpoint of each working face.In the CWF,the peak value of the vertical stress of the basic top is located at the boundary of the coal pillar.The peak value of the basic roof stress is related to the filling rate,and increases with the decrease of the filling rate.(4)Taking 10203 working face in Xinyang mine and 14259 working face in Xiaotun mine as the engineering background,the industry test of mining with HCCB was carried out.Based on the analysis of mine pressure and surface subsidence monitoring results of 10203 working face in Xinyang Coal Mine and14259 working face in Xiaotun Coal Mine,the results show that the supporting pressure in the cemented filling mining working face is much lower than that of the collapse method,the working face cycle to pressure is not obvious,the movement and deformation of overlying strata movement as a whole,and the maximum deformation of the surface movement is about 218.8mm in Xiaotun Coal Mine. |
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