Slope Length Effect Of Roof Fracture Mechanism And Stress Distribution Characteristics Of Irregular Stope

With the increase in the strength of coal mining and the deterioration of geological conditions,the phenomenon of the coal seam mining of irregular stope increases.The universal existence of irregular stope leads to the complexity and variability of the coal seam mining, causes the enhancement in the severe degree of nonlinear fracture of Coal rock containing gas mining and increases the difficulty of exploitation of high gas coal seam group of Low permeability and strong adsorption. At the same time the overlying strata spatial structure of irregular stope is more diversified,the damage morphology of surrounding rock is more irregular,and the evolutionary process of stress is more complicated and variable.It shows the unique development rule and aging characteristic compared with the normal stope.Through the comprehensive study method of the theoretical analysis,the rock mechanics test,the numerical simulation,the Similarity model testand the field monitoring,the research topic focuses on the security mining problem of irregular stope and studies on the Structure characteristics and fracture mechanism of overlying strata spatial and the time and space evolution law of mining stress field,overlying strata displacement field and roof fracture field.Research results obtained are as follows:Combined with the irregular stope mining phase of different strata stacking characteristics and movement rules,rock structure model was established for irregular face "three zone three three structure by using theoretical analysis."Roof breaking has spatial and temporal characteristics of transient,piecewise extension and partition mobility. Taking the slope length turned from big to small working face as example,which experienced a facet of stope, surface mining field and large surface stope three stages of development in the coalface advance, overburden each stage of mining area, different pressure slow pressure static variable mining area and the pressurizing moving mining area three change process, overlying strata spatial structure into the corresponding stage for the slow pressure type structure, process variant structure and boosting type structure of three types.With the help of indoor rock mechanics experiment, obtained the full seam roof of single axis and three axis test under the conditions of the stress-strain curve and the rock strength, elastic modulus, deformation modulus,poisson’s ratio and other mechanical parameters,completed a comprehensive assessment and evaluation of state of surrounding rock mechanics environment in mining process of working face.Taking the slope length turned from small to big and the slope length turned from big to small working face as the research background, the mechanical model of stope roof under five different boundary conditions was established by using elastic plate theory, the large and small stope roof deflection before and after initial fracturing, bending moment and stress distribution were obtained through theoretical calculation, and the fracture mechanism of stope roof was analyzed theoretically, the evolutionary law of roof fracture was revealed.Small stope roof firstly formed "O" shape fracture in the plate boundary, then the "X" type fracture was formed in the middle of the plate, both of them combine together formed "0-X" shape fracture; While large stope roof firstly formed "X" type fracture in the middle of the plate, then combined with "0" shape fracture which was formed in the plate boundary constitute "X-0" shape fracture.The law between mechanical evolutionary behavior and rock movement under three conditions of different slope length working face about normal working face,the slope length turned from small to big and the slope length turned from big to small working face was studied by using numerical simulation method. The roof of plastic zone and the expansion of space derived trend, mining stress field and displacement field evolutionary characteristics of overburden rock deformation law in irregular stope were obtained.The synchronized characteristics of stress distribution and special mechanism of strata movement about working face with variable length and the regular work face were revealed.The breaking characteristics of overlying rock, fracture development state, movement rule of overlying strata and stress evolution process in different exploitation stages of working face with variable length were studied by using the 3D similarity model test. Roof breaking has spatial and temporal characteristics of transient, piecewise extension and partition mobility, strata fracture field has experienced spatial and temporal evolution process of pressure relief and instability losing, extensional cracking, fracture shrinking and turning small, fitting and closing.The time-space effect of subsidence strata movement non-linearity and overburden stress about the tendency towards the distribution rule of stress evolution were also obtained.Through the site observation obtained 1622(3) irregular working face in Pansan coal mine the operation status of hydraulic support, during the operation status of working resistance of load distribution, the roof pressure characteristics and surrounding rock displacement.The irregular mining field of large, small mining face and the working face of general laws and internal relations connected with the interval of underground pressure were revealed.Which provides reliable engineering verification for the main contents and related conclusions of the thesis. In view of specific zoning features and stage specific field effect of irregular stope, according to different mining periods of the working surface, the feasible roof control measures are worked out, and a long-term mechanism for roof control of irregular stope is established. The roof control system of the multi integrated space-time cooperative mode of prevention-control-maintenance-monitoring is builded up.