Effects Of Initial Damage On Time-dependent Behavior Of Soft Rock Roadway And Control Countermeasure

With the development of coal mining gradually to the deep,the geological environment is becoming more complicated.The surrounding rock of the roadway often shows the characteristics of large deformation and continuous rheology.Especially,for the rock mass with certain initial damage in the surrounding rock after excavation,it is more likely to have the time-dependent deformation and damage under the long-term load.It not only brings great difficulties to the support and maintenance of roadway,but also brings serious challenges to the safety production of the coal mine.In view of this,this paper firstly carried out the creep test considering initial damage effect of rock,and constructed a corresponding creep damage model;then,based on the constructed creep damage model and the numerical simulation,the evolution characteristics of time-dependent deformation and damage in high stress soft rock roadway under different support conditions were analyzed;finally,a new borehole jack with flexible loading platens was designed to determine the damage zone of surrounding rock,and the dynamic support design method of high stress soft rock roadway based on the quantitative determination of the surrounding rock damage zone was put forward.The main research work and achievements in this paper are as follows:（1）The creep tests considering initial damage effect of rock under different confining pressure were carried out.The effects of initial damage and confining pressure on creep deformation,creep strain rate and creep failure stress of sandstone were studied.Combined with scanning electron microscope test（SEM）,the fracture morphology of sandstone under different conditions was obtained,and the mechanism of creep damage and fracture of sandstone was analysised from two aspects:macroscopic and microscopic.（2）According to the creep test results of sandstone under different initial damage states,improved mechanical components were obtained based on the creep theory,and the evolution equation of creep damage affected by initial damage was proposed based on the damage theory.Then,a creep damage coupled model was proposed,which can well reflect the characteristics of the three stages of creep and can consider the effect of initial damage on the creep failure stress.The L-M nonlinear least squares method was used to identify the model parameters and the rationality of the model was verified.The finite difference form of creep damage model was deduced,and was programmed by embedding it in FLAC^3D.（3）Using the developed creep damage model,the time-dependent deformation characteristics and damage evolution law of soft rock roadway considering the initial damage in surrounding rock under different supporting conditions were analyzed by numerical simulation.The influence of different supporting structures on the long-term stability of roadway was discussed.In view of grouting reinforcement technology of high stress soft rock roadway,based on the evolution law of damage and the characteristics of time-dependent deformation in surrounding rock,the best time of grouting delay and the reasonable grouting range in grouting support were analyzed,and corresponding suggestions were put forward.（4）In order to quantitatively evaluate the damage of roadway surrounding rock,based on the borehole jack testing technology to design a new borehole jack with flexible loading platens.Then,the testing principle was analyzed theoretically,and its reliability was verified by laboratory test.It shows that the test results of borehole jack do not need to be corrected and has strong adaptability.The quantitative evaluation method of surrounding rock damage zone which is based on the elastic modulus of the rock mass was proposed to evaluate the regional geological conditions,and achieved good application results in the field.（5）The dynamic support design method based on the quantitative evaluation of the surrounding rock damage area was put forward by using the new borehole jack and the quantitative evaluation method of the surrounding rock damage zone.The engineering practice has been carried out in Haizi coal mine,and the effect of support shows that the dynamic support design method can effectively control the stability of the surrounding rock of soft rock roadway according to the dynamic regulation support structure of geological conditions.