Overburden Strata Behavior Of Close Distance Coal Seams And Its Control

There are four theoretical problems when exploiting the close distance coal seams,the first is the calculation method of the damage depth and damage value of the strata between the coal seams;the second is the stability analysis of the overburden strata of the lower coal seams;the third is the support resistance and supporting measures in the lower coal seams’ working faces;the fourth is the calculation principle and calculation method of overburden load in the lower coal seams.Aiming at the problems of coal mining in close distance coal seams,this thesis have researched the overburden strata behavior of close distance coal seams and its control by using the mathematical statistics,theory analysis and similar simulation methods.The main research contents are as following: the limit damage depth and damage value of upper coal seam’s floor are calculated by using damage mechanics and the main influence factors of the floor damage value is also researched,and then the extension strength and the limit breaking length of the strata between the close distance coal seams based on the above results.The critical conditions of the damage main roof’s sliding and rotary instability are acquired based on the theoretical calculation results of the strata between the coal seams and the voussoir beam theory,meanwhile the influence of the damage to the two types instability is also researched.According to the criterion of the damage main roof,the calculation methods of the support working resistance which is suitable for the close distance coal seams both with and without main roof between the coal seams is acquired,meanwhile the space bearing characteristics and the range of application of the four-pillar and two-pillar support are contrast which can provide the basis to the support type choice.Field validity is made using the 8707 working face in Jinhuagong coal mine,the verification results match the theoretical calculation results.The main conclusions are as follows:(1)According to the interlayer structure characteristics of the close coal seam,and considering the damage effect on coal seam floor by the mining of upper coal seam,can divide close coal seam into extremely short-range coal seam,having no structure of close distance coal seam,thick immediate roof of close distance coal seam,basic roof completely injury of close distance coal seam,a part of injury of basic roof of close distance coal seam,having no injury of close distance coal seam six types.(2)Ground pressure behavior regularity of the close distance coal seam working face can matter not only the caving of overburden movement form but also with the upper working face floor damage depth and injury of rock fault structure characteristics,appeared close distance coal seam mining under pressure regulation and control to solve the main problems are:(1)layer between the calculation method of rock injury depth and injury degree;(2)the analysis about stability of the overlying rock for working face of lower coal seam;(3)the support working resistance and the supporting measures of lower coal seam working face;(4)calculation principle and method of the overlying strata of lower coal seam.(3)After close distance coal seam mining floor caused different degree damage.Damage quantitative results show that the floor damage region of "spoon" distribution.The damage quantity diminish from the "nuclear damage" area to the marginal area.The depth of coal seam and floor strata cohesion and internal friction Angle are the three main factors influencing the floor damage quantity distribution(4)After coal mining goaf on the amount of floor rock damage produced by the process of mining is the measure of the damage of the decision,goaf floor damage amount decreases gradually with the increase of depth,and interlayer basic roof strata can be divided into the "no damage","damage","full damage" three categories according to layer rock formations in the mined-out area damage area.(5)The reduce of interlayer rock tensile strength caused by damage,frost breakage length of layer between the basic roof is significantly reduced than complete strata.The damage of basic roof mechanics of elasticity analysis shows that the fracture length increases with the amount of damage to a linear smooth decreasing and then exponential attenuation and there is limit damage mount.The limit damage quantity decreases with increasing overburden load on the top of the basic roof and the basic roof slide with the increasing mining collapse.(6)The common point of stability analysis of six types of overlying strata in the contiguous seams is related to the stability analysis of basic roof,the difference is that the analysis of contiguous seams which is no structure between layers is the stability of basic roof in the upper coal seam,which is stable or not mainly make a difference on the rock pressure between the layers,and the contiguous seams with voussoir beam structure between the layers need to analysis the effect of damage on the s(7)The larger damage of rock is,the voussoir beam structure is more easily to happen sliding instability rather than rotating instability.In order to ensure the safety of the working surface with damaged voussoir beam structure,it must have the enough support strength to resist the initial weighting.(8)The concept of support bearing body is proposed,it is pointed out that the bearing characteristics can not be reflected totally by the support bearing body.There are some limiting prerequisites to use the support bearing body.(9)For the layer spacing is close,close distance coal seam mining under without basic,between the open mining pressure appeared to rule for the basic roof of coal seam,the master of strata basic roof rock in case of rotary,can form a masonry beam structure bear the overburden pressure;If encounter clip of waste rock,the cantilever beam structure has been formed.The rule of mine pressure show of lower coal seam working having big layer spacing and having a thick layer of rock strata is controlled by Layer thickness between layers forming masonry beam structure after fracture.The higher level of basic roof can form the structure after turning and prevents the overlying rock pressure passed down.(10)Coal mining of 7-4# coal seam can damage basic roof of 11# coal seam,when 11# coal seam is mined,interlayer basic roof is in a state of partial damage,belong to the fifth kind of close distance coal seams.Calculated by theory of 11# basic roof of coal seam is the measure of the damage of the 0.3,fracture interval period is 22 m,basic roof sliding instability occurs easily,so we should choose four-pillar type support.(11)Field mineral pressure observation shows that 8707 working face in the process of advancing distance of 240 m,for 10 times of basic roof periodic weighting,periodic weighting distance average of 21.93 m,was coincident with the theoretical calculation results...