Research On Reasonable Width And Stability Of Coal Pillar Under Inclined Tunnel Based On Shield Method

This paper did a series of research based on the long distance inclined tunnel construction using shield method in Shenhua Xinjie coal mine(the following is referred to as shield tunnel).In order to study the stability of the shield tunnel when coal mining as well as the reasonable width of coal pillar after the shield tunnel was put in use,both a 2D physical model test and numerical simulation were carried out.The mechanical reaction of the shield tunnel when coal mining,the collapse of overlying rock mass in goaf and the trend of coal pillar width along the shield tunnel under deep high stress are all talked in this paper.Besides according to the catastrophe theory,the cusp catastrophe model of coal pillar is established,and the instability criterion of coal pillar system is obtained.The long-term stability of coal pillar is predicted according to the results of coal rock creep tests.The main work done in this paper is:1.In order to study the structural stability of the shield tunnel under deep mining activities,a physical model test was adopted by using a self-developed multi-functional model test bench,and the whole process of shield excavation and coal mining are simulated.During the test,tangential force and displacement of the measuring targets around the liner were measured when coal excavating,safety factor method was used to evaluate the structural safety of the inclined tunnel and finally the suitable coal pillar width under deep high stress is determined.In the same time,during the mining process,the vibration effect by the overlying rock mass collapse on the segment was recorded and the influence of deep mining on structural stability of inclined tunnel under high in-situ stress was analysed.2.The coal pillar width trend under the shield tunnel was researched.The finite element software RS2 was used in this paper to carry out the numerical simulation.Three criteria are adopted to select the reasonable coal pillar width,and those criteria are the stress condition of the inclined tunnel segment,the connectivity of surrounding rock plastic zone and the influence area of the displacement angle.The simulation results show that,with the increase of the distance between the coal layer and inclined tunnel,the width of the coal pillar increases in the form of logarithmic function and then keep stable.3.The displacement angle under deep mining was established.In most mining area in our country,the displacement angle used for designing coal pillars is obtained by the observation data of less than 300m,so strictly speaking,those data is only applicable under condition of coal pillar design under depth less than 300m.A new displacement angle is defined by observing the result of numerical simulation.First draw the tangent line between a certain point on the vertical bisector of the two centre of inclined tunneland the edge of the inclined tunnel,and the angle between this tangent line and horizontal line is the new displacement angle under this special engineering background.4.The stability of coal pillar was analysied based on the catastrophe theory.The catastrophic instability process of coal pillar is a typical nonlinear process,which is a progressive destruction from the edge to the interior.According to catastrophe theory,the coal pillar is divided into elastic core area and edge plastic zone,and the cusp catastrophe model of coal pillar is set up,then the criterion of instability of coal pillar is obtained.Combined with the rheological module in the discrete element software UDEC,the evaluation of the stability of the coal pillar is made.5.The coal pillar stability time dependence was researched.By analyzing the creep mechanism of creep rock,it is believed the accelerated creep stage is a catastrophe phenomenon,by replacing the elements in Nishihara Model,a damage-concerned Nishihara Model was established.In this model,a rheid element with fractional calculus and a damage-concerned element were used to improve the Nishihara Model.The rheological constitutive equation and creep equation of the new model were deduced,and the model parameters were obtained through laboratory creep test.Based on that,the catastrophe equation of creep compliance of coal was established,and the long-term stability of coal pillar was predicted.