Study On Space-Time Relationship Between Strata Behaviors And Surface Deformation Of Fully Mechanized Top Coal Caving In Extra Thickness Seam

At present,the researches on the movement rule of overlying strata in stope are mainly focused on two aspects.On the one hand,it's about the research of breaking and motion law of the near-field roof strata that influence stope strata behaviors;On the other hand,it's about the research of movement and deformation law of the surface loose layer which is mainly studied in geoengineering.In the past,the two phenomena have been studied separately,and the combination of two phenomena is less.However,fully mechanized top coal caving in extra thickness seam is larger scale and higher intensity.The height of overburden fracture zone increases greatly,which will cause the movement of wider range rock structure to affect the stope pressure.So we should combine strata behaviors with surface deformation and try to realize that the organic unity of "stope ore pressure-rock strata movement-surface subsidence".This paper is based on the working face of luzigou 3108 extra thickness seam under the condition of hard roof in Datong mining area.The thesis carry out the study on space-time relationship between strata behaviors and surface deformation of fully mechanized top coal caving in extra thickness seam.Firstly,based on the KJ21 coal roof disaster warning system,the work resistance of hydraulic support in 3108 working surface is monitored and analyzed online,and obtain strata behaviors regulation of fully mechanized top coal caving stope;Based on the CORS network system,the surface deformation was observed,and obtaining surface deformation regulation of fully mechanized top coal caving stope;According to the field measured data,we obtain space-time relationship between strata behaviors and surface deformation of fully mechanized top coal caving in extra thickness seam.Secondly,using similar simulation experiment and 3DEC numerical simulation method to study large space structure dynamic evolution law of overburden rock of the special thick seam fully mechanized,further reveals the evolution process of relationship between strata behaviors and surface deformation.Thirdly,proposing stratum movement theory of “substation control layer of fissure zone”,to analyse the fracture characteristics and movement rules of substation control layer of fissure zone,and reveal the formation mechanism of the relationship between strata behaviors and surface deformation.Finally this paper put forward far field on hard roof and surface dynamic subsidence prediction method based on far-field periodic weighting and synergetic weakening control technology of combination of near,this achievement not only may effectively slow down strong strata behaviors,but also can be more accurately used to predict the dynamic process of surface subsidence.The thesis mainly obtains the following achievements:(1)Acquiring space-time relationship between strata behaviors and surface fissure of fully mechanized top coal caving in extra thickness seam.The result shows that the working face occur periodic weighting of which dynamic load is obvious and duration is long with an average of 88.7m steps.And at the same time,the surface periodically shows obvious permanent and dense fracture with an average of 90.2 m.Periodic strong mining pressure of working face and periodic obvious fracture of surface has a one-to-one relationship.The position that surface periodic fracture lag working face periodic weighting is 65 m,lag angle fissure is 79.5°.After working face occur periodic strong mining pressure 3.5d(during working face advancing 5m),fracture began to develop rapidly and its width and drop increased quickly.(2)Acquiring space-time relationship between strata behaviors and surface subsidence velocity of fully mechanized top coal caving in extra thickness seam.The result shows that after working face occur the first strong mining pressure 9d(during working face advancing 15.2m),or after working face occur periodic strong mining pressure 4.1d(during working face advancing 6.5m),deflection and subsidence velocity of surface began to increase rapidly.Maximum subsidence velocity of surface occur peridoc fluctuation change with an average of 90.33 m following working face periodic strong mining pressure.At the same time,surface single-point subsidence velocity which is affected by working face periodic strong mining pressure appear multiple-peaked change features.Working face periodic strong mining pressure have a significant influence on surface that lag periodic mining pressure range 0~151.3m,and delay distance of strongest influence position is 87.8m.(3)Based on similar simulation test,this paper acquire dynamic evolution rule of large space stope overburden structure for extra thick seam mining.The near-field roof rock layer breaks with small structure and small period in the form of "cantilever beam + masonry beam".The main key stratum,as the main carrier of overburden load,which controls the dynamic deformation process of overlying strata up to surface,will occur large structure or large period instability breakage.Meanwhile a large period fracture contains several small periods breakage of near field roof strata.Under the condition of large space stope and high intensity mining,the range of overburden affected by mining increases.The overlying strata of stope move violently,the height of fracture zone increases,and fracture zone can develop to the surface gradually.Failure mode of overburden transform from the traditional "three belt" gradually to "two belt".(4)Based on discrete element numerical calculation,this paper acquire evolution process of the relationship between strata behaviors and surface deformation in fully mechanized top coal caving in extra thickness seam.The instability breakage of large structure on upper main key stratum upward causes synchronous increase of surface subsidence value and subsidence velocity and downward causes strong mining pressure of working face,which closely combine with strata behaviors of working face and surface deformation.Meanwhile further revealing relational degree affected by mining thickness between strata behaviors of working face and surface deformation.When primary mining thickness increases,overburden range affected by mining disturbance increases.Surface deformation becomes more serious and strata behaviors of working face is more intensely,which causes higher relevancy between strata behaviors of working face and surface deformation.(5)Based on "black box model",this paper proposes stratum movement theory of “substation control layer of fissure zone” under the condition of large space stope and high intensity mining,which is a method and approach to determine whether or not stope strata behaviors related to surface deformation.Based on elastic thin plate theory,this paper analysed fracture characteristics and movement rules of substation control layer of fissure zone.According on Galerkin method,the primary limit fracture step of substation control layer of fissure zone is calculated.It's pointed out that the primary instability fracture of substation control layer of fissure zone occurs transverse "O-X" type.At the same time,the structure on substation control layer of fissure zone is divided into sector block and trapezoidal block.Deriving its "S-R" stability theory and acquiring theoretical criteria of sliding instability and turning deformation instability.(6)By establishing structural mechanics model of overburden strata on large space of fully mechanized top coal caving in extra thickness seam,this paper point out that cantilever beam + masonry beam structure formed by vertical "O-X" type small period fracture occurs in the near field basic roof strata and substation control layer of fissure zone happens lateral "O-X" type large period fracture,which together constitute overburden structural characteristics of large space of fully mechanized top coal caving in extra thickness seam.(7)This paper reveal influence mechanism of substation control layer of fissure zone on stope strong mining pressure.It's pointed out that sector block structure is very easy to be unstable,which has a significant impact on strata behaviors of working face.When higher sector block structure becomes unstable,it will oppress middle masonry beam structure and lower cantilever beam structure,causing them to break in advance.The linkage instability effect in the near and far field rock strata makes support working resistance of working face rise instantaneously,and then causes working face occur strong mining pressure with high dynamic load coefficient and long duration.(8)This paper describe the mechanism of substation control layer of fissure zone on the surface deformation.It's pointed out that the movement of trapezoidal block structure plays a leading role in the deformation of overlying strata to surface,and trapezoidal block along working face is inclined to be fracture beam structure.Whether block structure is stable determines failure degree of surface deformation.The large step periodic fracture of substation control layer of fissure zone can cause uneven drop of overlying strata,and it's easy to form dense step-type and graben-type permanent fractures when it develops to the surface.In addition,single structural fracture can cause synchronous deformation of overburden within its control range,resulting in a significant increase in surface subsidence and subsidence velocity.At the same time,the strata movement and deformation caused by upward structural fracture is a process that develops with time.The speed of transmission to surface depends on the distance between substation control layer of fissure zone and surface and overburden activity intensity.(9)According on theory of mine pressure,studying in depth surface dynamic deformation law under condition of fully mechanized top coal caving in extra thickness seam,and putting forward a modified forecasting methods of surface subsidence based on stope periodic weighting.This model can't only be more accurately used to predict surface dynamic subsidence process,but also has a very important significance in engineering applications,such as the process of prevention and reinforcement on surface gas extraction.(10)This paper put forward the combination control technology of near and far field on hard roof together weakening,which can realize to attenuation of hard roof strata,weaken overall rock strength and mechanical properties,reduce limit breakage step,prevent substation control layer of fissure zone occurring failure mode of "O-X" type,reduce energy release of rock breakage,achieve the goal slowing down stope strong mining pressure.