| In order to study the surrounding rock control and support optimization of gob side entry retaining,Theoretical analysis,in-situ deformation monitoring,laboratory similar model test and numerical simulation analysis are taken to study the deformation law of surrounding rock,the deformation mechanism of surrounding rock and the control methods based on the engineering background of gob side entry of Zhongxing mine.Firstly,the deformation law and deformation mechanism of gob side entry retaining are studied by in-situ monitoring data,theoretical analysis and numerical simulation,Then two different optimization support schemes are put forward on the basis of the concept of "The strong sidewall and corner supporting theory of coal roadway",and use numerical simulation method to verify the feasibility of the optimization scheme.Finally,the dynamic pressure roadway support experiment system is upgraded to realize the vibration on the top of the model and the overall vibration of the model at the same time.The similar model test of gob side entry retaining with different support schemes under 3 conditions was carried out.On the one hand,the supporting effect of the optimization scheme is tested.On the other hand,the influence of the dynamic pressure effect on the gob side entry retaining is further explained.The main conclusions.are as follows:(1)Deformation law of typical roadway along gob side entry retaining in Zhongxing mine.According to the deformation characteristics of the roadway along the roadway in different periods,the service process of the roadway along the roadway is divided into the following stages:Excavation and excavation stabilization stage,a mining ahead of the stage,a post-mining stage,the second mining ahead of the stage.Excavation and excavation stabilization stage:Excavation of roadway is completed to a stage of 40m from the working face.The excavation of this stage is less affected by mining,and the deformation is mainly elastic and plastic deformation.A mining ahead of the stage:The deformation rate of the roadway is increased in the stage of the roadway recovery stage within 40m in the front of the working area,but the overall deformation is still small and the deformation accounts for 6%of the total deformation.A post-mining stage:Roadway Mining Face 60m behind the stage within this stage roadway deformation rate increased significantly,the amount of deformation of 35%of the total amount of deformation.The secondary mining advance stage:the roadway recovery stage within 100m before the secondary mining,in which the secondary mining time is 30m ~Om for the roadway deformation of the most intense period,roadway deformation accounted for 59%of the total deformation.The post-mining stage and the secondary mining advance stage are the main periods of the deformation of the roadway,and the resulting deformation accounts for more than 90%of the deformation in the use of the roadway.The deformation caused by the secondary mining in the secondary roadway is much greater than that in the first mining period.In the post-mining stage and the secondary mining ahead of the stage,Zhongxing mining along the roadway with the deformation of the top and bottom plate deformation and help the development of the Department,the deformation of the two bars is greater than that of the top and bottom plate.(2)Mechanism of surrounding rock deformation along gob-side entry under influence of miningRespectively,from the static pressure and dynamic pressure effect to consider the impact of mining.Static pressure effect,according to the monitoring and numerical simulation results obtained along the edge of the roadway loading and unloading law.During each unloading process,the increase of the principal stress caused the surrounding rock damage,and the deformation of the surrounding rock occurred with the strong expansion in the unloading direction.The repeated loading and unloading effect would cause the fatigue and damage of the roadway surrounding rock,Whether the unloading load is the same as the previous load and unloading load,the range of plastic damage of the surrounding rock is increased on the basis of the last cycle and unloading,and the loading and unloading of the surrounding rock will inevitably lead to the increase of the deformation of the surrounding rock.In the aspect of dynamic pressure,the mechanical properties of coal and rock under dynamic load and the dynamic characteristics of coal and rock under the action of stress wave are described.Then,from the point of view of damage mechanics,And the critical stress of the surrounding rock crack propagation under the action of dynamic load is put forward:When the stress value is greater than the critical stress,the crack occurs.And this extension is unstable,collinear cycle cracks will be through the joint,along the wall to form a separation layer,while generating a new free surface.This process is often repeated,so that the wall near the wall into a layered structure,and under the action of compressive stress to free space buckling.(3)Based on the numerical simulation of Zhongxing mine along the roadway retaining support optimization programAccording to the characteristics of the surrounding rock of the roadway along the roadway,two kinds of optimization support schemes are proposed for the typical roadway along the gob-side of the Zhongxing Mine,based on the "reinforce the support strength of the sidewall and corner" and "anchor cable coordination" support,and through FLAC3D to verify the effectiveness of support.The simulation results show that the optimization scheme of supporting the concept 2 of" reinforce the support strength of the sidewall and corner" and" anchor cable coordination" is adopted.Through the strengthening of the sidewall and the corner,using the anchor cable with the row layout,collaborative support way,in the roadway throughout the service period,the surrounding rock force is more reasonable.The sidewall,the top and bottom plate plastic area have different degrees of reduction,the amount of deformation in the recovery period and the second recovery period compared to the original program to reduce 68%and 61%,the top and bottom plate deformation in a mining period and the second mining period compared to the original program by 37%and 62%.It is proved that" The strong sidewall and corner supporting theory of coal roadway" and "anchor cable coordination" can effectively inhibit the deformation of roadway gangs,improve the supporting role of the roof,and to achieve the effect of strong support of roof.(4)Designing the similar model test of gob side entry retaining under combined dynamic and static loads.The dynamic pressure roadway support test system was upgraded,which makes the test system that can only finish static loading and dynamic loading at the top of the model has the function of whole dynamic loading.The top oil cylinder and the bottom cylinder cooperate with each other,and do not interfere in order to simulate the vibration load caused by the roof movement and the dynamic load generated by the stress wave propagation in the goaf and the distant stratum.The complex three-dimensional,dynamic and static loading problem of the gob side entry retaining is transformed into a two-dimensional plane strain problem.According to the law of surrounding rock stress variation,the static load is loaded by the following subsection function:the dynamic load is calculated by the expression formula of the vibration energy in seismic mechanics,the final test amplitude is 0.5mm,and the vibration frequency is 10Hz.The design method of the loading method provides a reference for the similar model test under static and dynamic loads.(5)Analyzing the results of the similar model test of gob side entry retaining under combined static and dynamic loads.Test results of 4 groups under 3 conditions showed,the damage of the common roadway was due to the stress concentration of the sides of surrounding rock,the sides of shallow surrounding rock broke first,bearing capacity reduced,at the same time,the whole roof sank(such as the roof support strength is not enough,the roof will fall);the damage of gob side entry was mainly due to the rapid increase of surrounding rock stress in the stage of second advanced mining,the sides of shallow surrounding rock broke first,which caused the whole roof sinking.Through the comparison of two support schemes,it proves that the optimized support scheme with the idea of "strong sides and strong angles" can effectively transfer the sides of surrounding rock stress to the deep surrounding rock,so as to reduce the stress concentration degree of the sides of surrounding rock,it plays a good supporting role to the roof at the same time of protecting the sides of rock surrounding from damage,reduce the roof subsidence,restrain the large deformation of roadway,achieve a good supporting effect.The contrast test of the two groups of optimized support scheme shows that the static pressure effect in the mining effect,that is,the abutment pressure,lateral abutment pressure and surrounding rock stress increase,is the main factor of the large deformation and failure of the roadway;the effect of dynamic pressure,that is,the role of vibration plays an auxiliary role,It will accelerate the development of cracks in the shallow surrounding rock of the roadway to reduce the strength of surrounding rock,it is the secondary factor of large deformation and failure of roadway.The paper is innovative in the following aspects:(1)The mining effect was divided into static effect and dynamic effect.According to static effect,every unloading process of surrounding rock of gob-side entry retaining increased the main stress difference caused by rock damage and multiple loading and unloading caused accumulative destruction.Moreover,the critical stress of the surrounding rock crack was considered under the action of dynamic loads,and the critical stress of the surrounding rock was considered from the perspective of damage mechanics.(2)According to the typical roadway of gob-side entry retaining in Zhongxing Mine,a simulation study of support optimization was carried out.It was found that the optimization scheme of "The strong sidewall and corner supporting theory of coal roadway" and "anchor cable coordination" was effective.Of the reinforcement,as well as the use of anchor cable with the row of layout,collaborative support way,in the roadway throughout the service period,the surrounding rock force was more reasonable,the gang and the top and bottom plate plastic area had different degrees of reduction.In addition,the amount of sidewall deformation decreased by 68%and 61%compared to the original plan during the first and second times,and concer deformation decreased by 37%and 62%during the first and second times.(3)On the basis of the existing test conditions,the experimental system of dynamic roadway support is upgraded so that the test system can simultaneously perform the function of static loading at the top,the dynamic loading at the top and the dynamic vibration of the whole.Meanwhile,the vibration of the top is independent from the whole vibration,without interfering with each other.(4)Based on the improved support experiment system of hydrodynamic roadway,a similar model test was carried out for the gob-side entry retaining under dynamic and static load.The deformation mechanism of the surrounding rock was analyzed,the effect of "The strong sidewall and corner supporting theory of coal roadway" and"anchor cable coordination" was tested.Moreover,from the perspective of damage,we analyzed the dynamic effect of gob-side entry retaining under the dynamic loads by using ultrasonic testing technology. |
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