| Water-inrush from working face floor after being grouted is a typical problem in the abundant water mining area with high ground stress and high water pressure. It is influenced by several factors, including high water pressure, high ground stress, grouting, mining, rock mass properties and so on. Based on the project of Zhaogu mining area, working face floor water-inrush mechanism after grouting and the grouting reinforcement mechanism were studied with methods of theoretical analysis, TAW-2000 triaxial apparatus, two dimensional similarity simulation experiment, numerical simulation and situ engineering tests.Now the achievements of this paper are as follows:(1) Summarize and analyze the complex and variable characters of water control in Zhaogu mining area: ① the buried depth of coal seam is large, with high ground stress;② water pressure of limestone aquifer is up to lOMpa while the next level being developed in the future;③ the floor of coal seam exists fault fracture zone;④ water-inrush from floor occurs in separated grouted working face.(2) Mechanical properties are different between primary rock and grouted rock in three-dimensional stress. Particularly, the water-inrush mechanism of reinforced rock after grouting in high water pressure area affects the safe production directly when the coal seam released. The water-inrush from floor after grouting has close relations with relieved confining pressure mechanical performance of floor rock in high water ground stress area. The mechanical properties before and after grouting were first studied, and then water burst characteristics and mechanical properties were analyzed when the stress state was changed by mining in high water pressure area. The following conclusions are obtained.①Get the full stress-strain curve of original complete sandstone and limestone under the condition of confining pressure 25 MPa, water pressure 6 MPa, the implementation of load, in the process of loading, axial stress increasing, sandstone strength 168 MPa, limestone peak strength 313 Mpa. After peak the strength is reduced, achieve the residual strength, and have no water inrush. Analysis found that the sample occurs shear damage, the failure surface clear, and the sample at the bottom of the top is complete without damage. Under the 20 mpa confining pressure, while the sample inside produce cracks, water pressure also cannot penetrate the top bottom intact specimens, and the experiment of prefabricated crack sample, prone to water inrush. Under 25 Mpa confining pressure conditions, the fracture is the important condition of water inrush.②The rock’s whole stress-strain curve before and after grouting reinforcement of ascending segment were different. The rock specimen is relatively compact, the fracture development is not obvious, the whole stress-strain curve is smooth,and there is no big fluctuation.The whole stress-strain curve of the cracked rock mass after being grouted has a fluctuation, which shows that there are still some cracks and pores after the grouting reinforcement of broken rock mass.③The condition of confining pressure 25MPa and water pressure 6MPa were designed, and the characteristics of strength variation of two kinds of limestone and sandstone after reinforcement were compared and analyzed.When Limestone with I fragmentation degree was being grouting, the peak effective stress reached 105MPa, and the total stress reaches 111MPa. The effective stress is restored to 33.5% of the strength of the original intact rock mass. When Limestone with Ⅱ fragmentation degree was being grouting, the peak effective stress reached 93MPa, and the total stress reaches 99MPa. The effective stress is restored to 29.7% of the strength of the original intact rock mass. When Sandstone with Ⅰ fragmentation degree was being grouting, the peak effective stress reached 76 MPa. The effective stress is restored to 45.2% of the strength of the original intact rock mass. When Sandstone with Ⅱ fragmentation degree was being grouting, the peak effective stress reached 68MPa. The effective stress is restored to 40.5% of the strength of the original intact rock mass.④The strength of fractured rock mass can be improved, under the condition of 25Mpa confining pressure. But the larger the degree of fragmentation, the lower the strength of the rock mass is relatively small. Compare the strength of crushed limestone and sandstone after grouting,the fact was found that the strength of limestone is higher than that of sandstone after grouting reinforcement. But although the integrity of the original limestone rock strength is high but increasing of the proportion of sandstone strength is smaller than sandstone.⑤Grouting reinforcement of rock mass unloading confining pressure water test was done under the conditions of confining pressure 6MPa and water pressure 25MPa. Under the conditions of keeping the axial load 18MPa, keep the axial strain invariable, and then the water flow in the confining pressure decreases rapidly, the axial strain changes little, and the radial strain changes obviously.When the confining pressure decrease from 15MPa down to 8MPa, the radial strain has obvious increasing trend,and then it will decrease to a certain value.When the confining pressure is reduced to zero repeatedly, the radial strainalways changes.To a certain extent,the radial strain represents the extent of the expansion of the vertical crack. Test shows the fracture water flow rate is not constant in coal seam floor,which is influenced by lithology, fracture surface stress and pore pressure. When the confining pressure is less than the water pressure, the radial strain increases, and the seepage water volume increases. When the confining pressure is relatively large, the permeability coefficient of soft rock fracture surface is greatly influenced by the stress, which makes the rock mass have strong water resistance ability. The confining pressure is an important influence factor of water inrush, especially in the presence of cracks, the higher confining pressure can prevent the expansion of the vertical crack, and the relieving of confining pressure makes the water inrush risk increased.⑥The relationship between the fracture degree, the wave velocity and the limit strength of the three axes is analyzed, and the damage coefficient is calculated by comparing the elastic modulus and the wave velocity. According to elastic modulus, the damage coefficient of limestone with I fragment degree after reinforcement is 0.74, and the value of limestone with II fragment degree is 0.71. The damage coefficient of sandstone with I fragment degree after reinforcement is 0.33, and the value of sandstone with II fragment degree is 0.24. According to elastic modulus, the damage coefficient of limestone with I fragment degree after reinforcement is 0.78, and the value of limestone with II fragment degree is 0.71. The damage coefficient of sandstone with I fragment degree after reinforcement is 0.33, and the value of sandstone with II fragment degree is 0.29. The results of the two calculation methods are similar, and the bigger the damage coefficient is, the smaller the intensity is. The fact that the greater the damage coefficient is, the smaller the intensity of the strength is verified.(3) On the basis of the theory of pore fissure and biot theory, combined with damage mechanics, fracture mechanics and the theory of mining pressure, combined dynamic analysis and the measured data, study the rock mass before and after grouting reinforcement of fluid-structure coupling control equation, build water inrush mechanics model considering the effects of injury, grouting and mining at the same time.㏑eference pore fissure elastic theory, according to the base plate breakage degree of rock mass and fracture connectivity, divided rock mass into four types, respectively is:water invasion from complete watertight rockmass (I type), non connected fractured rock mass (II type), connected fissure rock (Ⅲtype) and broken rock mass (IVtype), and give solid-liquid coupling equations respectively.②Floor grouting reinforcement have the effect that reduce the type of rock mass. Grouting reinforcement is difficult to change the mechanical properties of the rock, mainly makes the broken rock fracture and karst filling, become dense, rock mass fracture connectivity drops, so reduce the rock type. If the grouting effect is ideal, whether it is type IV, III type of rock mass, or type II, rock mass will become type I rock mass.Jiaozuo mining area zhao gu coal mine 11011 face tape gateway electrical method detection of grouting plate before and after the disappearance of the watershed rich illustrates the mechanism of action.③Similar experimental studies show that when the mining height is 6 m,the fracture is the largest, the number of cracks is the most, the bottom of the floor is the biggest, and the fracture is developed to L8 limestone.,comparing with the height of 4.5m. At the bottom of the spring group, there was a crack at the bottom of the spring, where is the most dangerous place. The experiment clarifies. Mining action is an important reason for the failure of the working face, the development of vertical fracture and the type of fracture.④The development test of water injection fracture in underground floor is carried out, and finds that the abutment pressure causes the rock mass to be destroyed, pressurized water injection makes the fracture further through,and The expansion of the crack is consistent with the direction of the flow. Water inrush occurred with floor heave, floor heave failure characteristics of floor rock stress,and floor control has a great effect on the control of water inrush. The amount of floor heave moment increases at a time, floor failure is abrupt, and support can inhibit the floor heave deformation can be reduced and the inflow of water.⑤The similar experiments and the field water injection tests have proved that the effect of mining on the crack growth of the floor rock mass is well proved.Mining influence ascension magmatic rock type of. After grouting reinforcement working face floor rock fracture penetration condition is:oz>oi. Influenced by mining, when the vertical stress of surrounding rock stress reaches through strength of rock bridge (oz>gi), the crack extending through began in rock mass; Originally to reinforce for type I, II do not guide water rock mass due to crack again, to a higher type development; Face plate may take the lead to develop individual site for type III, IV, rock mass formation water channel, cause working face water inrush accidents. Increases local weakness because it is first to shear type, which guide the water channel of "vertical, small range of water channel" characteristics.⑥tilizing fissure elastomer theory, combining the theory of damage mechanics, fracture mechanics and mining pressure, build the "pore-fracture lifting type " mechanical model for floor water inrush of the grouting reinforcement working face. Research results has a guiding significance of north China type coal working face floor water inrush accident prevention and control work.(4) According to the high density and length characteristics of the grouting engineering casing, the mechanical model of the interaction between the floor grouting reinforcement casing and surrounding rock is established.The maximum vertical displacement formula of coal seam floor is derived.The influence degree and the control mechanism of the casing pipe to the floor were determined.Finally, in a typical mine as an example, the numerical calculation of casing for the influence of floor deformation.①Establish the mechanical model of the interaction between the floor grouting reinforcement casing and surrounding rock.The part of casing in the floor damage zone, part in the surrounding rock stability region, which is a boundary surface casing can be divided into two segments, the free segment (floor damage area) and a fixed period of casing pipe (region) of surrounding rock. A fixed period of casing are in bondage to the fixed end free period of the casing pipe resistance of rock mass under distributed force and casing over effect. When the above resistance is less than the casing pipe below distribution force, casing upward bending deformation. Because of the casing itself has higher flexural performance can prevent deformation of base plate. Casing mechanical parameters is palpable, easy to get the deformation characteristics in the casing, and then is derived according to the relationship of action and reaction plate deformation characteristics, the stress of the casing deformation and failure characteristics was measured bottom grouting and solid deformation and failure of the important parameters.② Analyze the single casing flexural performance.Grouting pipe as the distributed force at one end of the fixed beam is bounded (S), stability of surrounding rock in casing by the fixed end constraints. And according to the above analysis, the elastoplastic limit equilibrium condition, the casing of the floor damage length above and below the distribution of power and casing pipe resistance of rock mass can be obtained.(a) Point S of tube bending moment Mp (x, y)Critical state, the elastoplastic limit equilibrium in casing section on [0, rp], dip Angle of beta casing on the distribution of normal stress at point S bending moment is:(?) Bending normal stress under the condition of σ and the relationship between the bending moment is:σ= My/Iz. The bending strength condition of casing is:(?) (b) According to the situation of cantilever beam under the action of force distribution calculation of casing at the top point A, maximum deflection obtained by grouting the top casing maximum deflection ωA is: Get the top of the casing section angle θA as follow: So the casing under the maximum deformation of the slab vertical:ωt=ωA·cosβ.③The failure of the front and rear floor of the casing is calculated by numerical simulation, and the following conclusions are obtained.(a) Without casing, motherboard failure pattern conforms to the conventional numerical results; After applying casing, floor damage becomes discontinuous. Due to applying casing, grouting and solid strength, reduced floor area of damage; But junction between casing and the surrounding rock weak plane, prone to local damage under shearing action. After applying the casing, the floor vertical displacement decreases, which shows the Resistance to bending capacity of casing can restrain the deformation of floor rock. Compared with the non-casing, the displacement of A decreased by 14%; the displacement of B decreased by 19.5%; the displacement of C decreased by 16.2%; the displacement of D decreased by 32.4%; the displacement of E decreased by 21.4%. It can be seen that the casing has main effect on D displacement, D point is located at damage critical that the depth is relatively large. The change of absolute displacement is large because casing limits the deformation. E is located at the passive area that is the damage intuitively show area. It is also affected by the deep rock mass, and the change of deformation is obvious when the reinforcement effect of transition zone is good.(b) By the comparative analysis, casing has the main effect on the transition zone Ⅱ. The region is the key area to control broken floor, and the ability to resist deformation of floor can be enhanced when the casing applies to this region. Although the failure of floor is inevitable, but due to the role of the casing which can strengthen the transition zone Ⅱ, casing can control the destruction of the floor. According to this conclusion, the grouting borehole can be better arranged. |
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