| The support technology of mining influenced roadway under close range goaf is studied in this dissertation. Mining pressure monitoring is carried out in a roadway under goaf belongs to Xinyu Mine. Deformation law and failure characteristics of surrounding rock influenced by mining are analysed in this work. Also informations of periodic weighting and deficiencies of roadway support are collected during the test. Based on results of mining pressure monitoring and theoretical calculation of support parameters, the optimization schemes of roadway support are put forward. In order to select out the best support scheme, FLAC3 D software is used to modeling and numerical simulation analysis. The best scheme is determined by comparing displacement, stress distribution and plastic area of surrounding rock. Centering on mining pressure, related research results are summarized. Static pressure effect and dynamic pressure effect are generalized by studying related research results, which become the design idea for manufacturing the new similar simulation equipment to study the support technology of dynamic pressure roadway. With the new equipment, similar simulation tests about support technology of mining influenced roadway are finished. Deformation and failure characters of surrounding rock caused by mining pressure are studied in the test, also include damage characteristics due to dynamic pressure effect. The feasibility of optimization scheme is verified by comparing deformation characteristics and stress distribution of surrounding rock between common support scheme and optimization scheme.(1) Mining pressure monitoring of both roadway and the working face under close range goaf in Xinyu Mine.For studying support technology of mining influenced roadway, the situation of roadway influenced by mining pressure must be investigated first to judge the rationality of common support scheme.Deformation characteristics of surrounding rock in No.6118 material roadway are investigated first. Through arranging displacement monitoring points, changes of roof sag, convergence between roof and floor, convergence between two side walls are monitored. In general, the change trend is that vertical convergence is more obvious than horizontal convergence, roof sag is approximately equal to convergence between two side walls. The convergence between roof and floor can be 2.02~3.09 times that between two side walls, so the floor heave is obvious. The roof is relatively complete, but sinking caused by the damage of support in two side walls due to lack of support strength. The intense influence area is 10 m front of working face, where deformation velocity will become fast. The two side walls are influenced more significant in this area.The characteristic parameters of periodic weighting are calculated by collecting and analyzing working resistance of hydraulic supports using pressure gauges with automatic memory function. The periodic weighting length is 12.9~19.4m, the average is 16.9m, two ends of working face is relatively large. The periodic weighting length will be used to design the related test.Finally, deformation mechanisms of surrounding rock are analyzed. The formation of side abutment pressure in upper coal pillars make a roadway under goaf has larger deformation, side walls supports are easy to damage because of compressive expansion in surrounding rock, layered floors are tend to heave. Roof sinking caused by the damage of support in side walls, and the seepage from goaf will aggravate the heave of al mudstones floor. So the advice for optimizing is strengthen the support in side walls, pump and drain the seepage from goaf.(2) Numerical simulation study of optimization scheme for roadway support under close range goaf in Xinyu Mine.On the basis of mine pressure monitoring, the deficiencies of roadway support under close range goaf in Xinyu Mine are optimized. The results of theoretical calculation show that support parameters of side walls are not meet the requirement. Diameter of bolt should not less than 16.9mm, and length of bolt should not less than 1860 mm. But in the common support, the diameter of bolt is only 16 mm, and the length is 1800 mm. The support strength must be increased firstly. There are not hard and complete strata in the roof of roadway under a goaf, so the anchor cable can not play suspension function. So the position of anchor cables are adjusted, anchor cables replace parts of bolts in the roof and lay in a same row with other bolts. The anchor cables and bolts in the roof form a whole support system combined with a W-type steel band.With the thought above, 4 optimization schemes are given to the roadway support under goaf in Xinyu Mine. Scheme 1 to scheme 3 belong to one group, which compare support effects with the increasing length of bolt. The effect of anchor cables in the side walls can be evaluated by comparing scheme 4 to others.With the help of FLAC3 D, the process of excavation and mining are reconstructed. The roadway is excavated 50 m long, and the distance of mining is 30 m. Several monitoring points are set in the numerical simulation to collecting informations about deformation and stress distribution of surrounding rock. The results show that increase the length and diameter of bolts in the side walls can decrease the deformation of surrounding rock. But with the length increasing, the cost grows fast and effect improvement become not significant. In scheme 4, with the help of anchor cables in the side walls, although the distance between two rows become larger, the support effect is best. Compared to the common support, roof sag decreases 2.63% and convergence between two side walls reduces 13.14%. In the process of mining, compare three former of all schemes, it can be found that with the length of bolt increasing, support effect become non-ideal inversely. So the length of bolt must be reasonably. Compare scheme 4 to common support, deformation of surrounding rock decrease significantly, roof sag decreases 21.54% and convergence between two side walls reduces 25.48%. Also scheme 4 can relieve stress concentration in upper coal pillar, and reduce plastic area of surrounding rock. Scheme 4 has the best support effect during mining process, and the lowest support cost. So scheme 4 is the best optimization scheme, set anchor cables in the side walls is more effective than improve the size of bolts in the side walls.(3) Study of dynamic pressure effect and static pressure effect related to mining.Centering on mining pressure, related research results are summarized. Distribution formulas of lead abutment pressure in front of working face are derived.Variations of vertical stress in surrounding rock during mining are obtained by numerical simulation. Variations of vertical stress in surrounding rock closed to working face accords with the distribution of lead abutment pressure. Concentration factors increase with the distance increasing in horizontal direction, and with the distance decreasing in vertical direction.Vertical stress in surrounding rock closed to another side has been growing when adjacent to the working face. Multiples of vertical stress increase with the distance increasing in vertical direction due to locating under the coal pillar. Through fitting the variation curves of stress, it can be found that curves obey exponential function to the base e mostly, denoted as .Working face under goaf has incomplete roof. So effects of abutment pressure decrease. The influence scope of abutment pressure is only 5~10m, which reduces obviously compared to common roadway.Static pressure effects of mining are summarized as, roadway only affected by primary stress at the beginning, the stress keep stable. With the distance between roadway and working face decreasing, the side abutment pressure start to affect together with lead abutment pressure. When working face close to the roadway, lead abutment pressure attenuates. So roadway will influenced by side abutment pressure till to the end.Finally, dynamic pressure effects are analyzed. Vibration effects produced by dynamic pressure can be divided into two kinds. One kind, seismic source locates the top of roadway, vibration is in the same direction with propagation like a longitudinal wave; another kind, seismic source locates somewhere horizontal direction, vibration perpendicular to propagation direction like a shear wave. Selection method of vibration load parameters is introduced on the bases of earthquake mechanics.(4) Development of similar simulation equipment for roadway support mining influenced.The best optimization scheme is given after numerical simulation. In order to verify the feasibility of scheme furthermore, similar simulation tests are carried out.So mining pressure can be divided into two parts, dynamic load and static load. During the similar simulation tests, two parts of mining pressure can be applied to the model directly. With this thought, the new similar simulation equipment for roadway support mining influenced is designed, manufactured, assembled and debugged.The new equipment is consist of inner-frame, outer-frame, top static-load cylinder, top vibrating cylinder and bottom vibrating cylinder. Inner-frame and outer-frame are designed nested structure, which make inner-frame can move along the guideway in the outer-frame with the effect of bottom vibrating cylinder. Inner-frame is an independent force system, so static load and dynamic load can be applied synchronously without interference. Top static-load cylinder applies static load to the model, simulating variation of lead abutment pressure and side abutment pressure. Both top vibrating cylinder and bottom vibrating cylinder apply vibration load to the model, but they have differences that seismic source of top vibrating cylinder locates the top of roadway model, vibration is in the same direction with propagation like a longitudinal wave; seismic source of bottom vibrating cylinder locates somewhere horizontal direction, vibration perpendicular to propagation direction like a shear wave.According to the design idea of equipment, the test processes are given composed of two parts. One is the process simulating change of lead abutment pressure and side abutment pressure applied by top static-load cylinder, the other is simulating vibration caused by mining such as roof breaking and roof caving, applied by top vibrating cylinder and bottom vibrating cylinder.(5) Similar simulation test on roadway support mining influenced.Research object is introduced at first, include common roadway support and geological conditions. Similar constants are calculated according to similarity theory. Then parameter requirements of model materials and support are determined. Finally, sieved river sand, 32.5# Portland cement and gypsum are chosen to make the model after proportioning test, tin wire is chosen to simulate bolt and anchor cable after tensile strength test. Also other simulative materials are chosen by experience. It is introduced that monitoring contents and monitoring points, such as displacement, stress and ultrasonic test. Then the process of laying model support is described in detail.Using the new equipment, similar simulation tests are carried out. Test schemes are determined according to the designed test process. The tests are divided into three groups, non-support, common support and optimization support. Distortion and failure characters of surrounding rock are observed during the test. Two kinds of support schemes are compared through deformation of surrounding rock, displacements of monitoring points and change of stress. It is found that support strength in the side walls of common scheme is insufficient, parts of them are broken in the test, deformation of surrounding rock is large. The effect of optimization support is perfect, it has less deformation, more proper stress distribution with the help of anchor cables in the side walls.Special tests are conducted around the vibration load. The results show that vibration load has not macro influences on roadway, no matter once vibration load or twice. Waveform and acoustic velocity can be gotten through ultrasonic test. By analyzing the results, acoustic velocities in surrounding rock have different degrees decrease, the roof is affected more obvious than the side walls. It also can be conjectured by comparing the change of waveform. Finally, mechanism of vibration load act is analyzed. |
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