Experimental Study On Detection And Representation Of Mining-induced Overburden Deformation With Distributed Optical Fiber Sensing

Deformation monitoring of overlying strata caused by underground coat mining is an important component of coal mine safety and green mining.The establishment of mine rock mass detection network has become a new direction for coal mine rock formation control.However,under the conditions of large space in the stope,large deformation of overburden and large range of rock migration,the deformation monitoring of the overlying strata is facing the problem of increasing the range of the strata to be measured,the multi-scale development of the strata and the alienation of the rock strata,These problems become the mai n factors that restrict the safe and efficient development of coal.Distributed fiber sensing technology has the characteristics of distributed,multi-scale and high precision in geotechnical deformation test,wich can help to realize large-scale and multi-scale rock deformation test.It is an effective way to promote the informatization of coal mine production and to construct intelligent mine by carrying out distributed fiber detection research of overlying strata deformation and its structure evolution.Based on the distributed fiber detection of mining overburden deformation,based on physical model test,combined with theoretical analysis and numerical simulation,distributed optical fiber detection theory,distributed optical fiber testing technology system,and distributed optical fiber characterization of rock formation deformation model and special structural overburden deformation characteristics of fiber detection and other issues to study.The main work is as follows:The theoretical model of stress distribution of optical fiber is established.The stress distribution of the optical fiber caused by the deformalion of the rock formation is analyzed,and the distribution of the fiber stress caused by the fracture of the rock formation,the development of the fractured layer and the bending subsidence are revealed.The results show that the fiber force in the rock with different deformation degree has the stage characteristics.The concept of deformation of rock formation based on optical fiber frequency shift is proposed.It is shown that the contact coefficient between rock formation and optical fiber is an important influence parameter of distributed fiber detection.The deformation state of overlying strata can be described by distributed fiber characterization model.The influence mechanism of optical fiber on rock deformation in model test is analyzed.It is shown that the optical fiber embedding has an additional effect on the stress distribution of the rock formation,and the influence degree increases with the increase of the fiber diameter and elastic modulus.The influence of the deformation caused by the optical layer is diamond-shaped,with a radius of about 10 cm,which is not affected by the optical fiber parameters.The distribution of rock strata reveals that the effect of fiber properties on rock deformation is to reduce the deformation of rock formation,and the deformation of rock formation caused by 1?2 mm fiber is less than 5%.When the elastic modulus of the optical fiber is more than two orders of magnitude above the elastic modulus of the rock,the deformation of the optical fiber is more than 25%.The influence of fiber diameter and elastic modulus on the deformation of rock formation is discussed as the relationship between quadratic function and primary function,which provides the basis for the selection of fiber in model test.The model test of deformation of optical fiber for mining overburden was carried out,and a distributed optical fiber characterization model was developed for deformation test of optical fiber and deformation of overburden.The influence of the fixed mode of the bottom of the model on the test results is discussed.The response mechanism of the fiber and the working face is analyzed,and the three-stage and three-step changes of the vertical optical fiber frequency shift curve are revealed.The three stages correspond to the lateral strata of the overlying strata,and the three steps are respectively corresponding.The concept of frequency averaging is proposed,and the physical meaning is the higher the average frequency shift,the higher the deformation degree of rock formation.The distribution law of tensile and compressive stresses in the strata during the excavation of the working face is obtained,and the deformation and damage range and the stability range of the rock strata are distinguished.The model of optical fiber characterization of overburden deformation is proposed,and the quantitative relationship between the deformation and damage range and the frequency shift of the optical fiber is given.The relationship between the optical fiber frequency shift and the deformation and deformation of the overlying strata is described.The optical fiber characterization model consistent with the theoretical model of fiber stress distribution.The three-dimensional model test of deformation law of overlying strata under giant conglomerate was carried out,and the optical fiber detection and characterization of deformation characteristics of giant conglomerate were studied.The results show that the group of giant conglomerates is formed by the formation of a large number of longitudinal non-penetrating fissures near the goaf,and the whole group is composed of the central part of the hollow area forms a non-penetrating horizontal fracture in the horizontal layer and is bent in the layer.The average frequency of optical fiber reveals the breaking rule of giant thick conglomerate layer,which indicates that the deformation process of giant thick conglomerate has experienced weak deformation,small deformation accumulation,initial breakage,periodic large deformation and final collapse stability.Based on the optical fiber characterization model of overburden deformation,the deformation and failure zone and the distribution rule of the three zones are obtained,which shows that the height of the crust in the conglomerate is more than 8 times higher than that of the mining.The displacement and displacement field of the rock mass is constructed,and the deformation and deformation characteristics of the rock mass are verified by FLAC numerical simulation.