Stability Evolution Law Of Open-Pit Coal Mine Slope In High-altitude Permafrost Area

In this paper,the slope stability of open-pit coal mine in high-altitude permafrost area is studied.The law and model of deterioration of rock mass and the evolution of frozen rock slope stability in freeze-thaw environment are selected as scientific problems.The full text of the main achievements were as follows.(1)Based on the geological and hydrological surveys and ground temperature monitoring of permafrost regions,the occurrence status of slope rock mass in permafrost open-pit coal mine is clarified,and three kinds of geologic and physical generalization models of frozen rock and soil are obtained.Distribution law and generalization model of ground temperature were found including thermal instability layer that the temperature of the seasonally frozen layer in the frozen soil area changes drastically with the atmospheric temperature and thermal relatively stable layer that the temperature of the permafrost layer is between 0? and-1?.According to the type of slope,the freezing and thawing phenomena and failure rules of the slope were obtained,and five basic models of freezing and thawing failure of frozen rock(soil)slope were summarized.(2)The temperature field distribution and the heat transfer law of saturated rock under freezing and thawing environment were studied by indoor temperature control experiment.The freezing and thawing process showed a significant three-stage process in which the phase transition stage was a special stage.The temperature change law of rock can completely described by the proposed temperature change model.The microfracture expansion of the rock during the temperature change process was verified by CT test.The analytical equations of rock temperature field,water field and stress field(fissure field)were obtained by the principle of mass conservation,energy conservation and internal force balance.It was proved that the microfracture expansion of rock was the result of multi-field complex coupling.The coupling mechanism of representative rock temperature field,rock fracture stress field and crack propagation is revealed.(3)The mechanical properties and freezing and thawing deterioration rules of three typical rock samples were studied systematically by the freeze-thaw cycle test.The mechanism of rock freezing and thawing damage was revealed by the CT mesoscopic monitoring,sound wave and microfracture test during the freezing and thawing process.A model of typical rock freezing and thawing deterioration was established by microfracture expansion factor.(4)Based on the well-known rock mass strength criterion of Hoek-Brown at home and abroad,combined with the characteristics of frozen rock slope engineering,a new "freezing and thawing disturbance coefficient" was proposed to replace "Blasting disturbance coefficient"which is the method of no longer meaningful in this field.It can fully reflect the timeliness of freezing and thawing process that the deterioration of rock mass gradually increases with the increase of freezing and thawing time.The calculated law of rock mass intensity was consistent with the law obtained by the experiment,which is proved that the reliability and validity of freezing and thawing strength criterion of rock mass.(5)Acording to the monitoring data of the frozen rock slope in the Muli Coal Mine,the 3G2000 three coupling analysis software developed by the team was calibrated.On the basis of the software and FLAC~3D platform,the numerical simulation experiment was carried out to study the main influencing factors of long-term stability of frozen rock slope:ambient temperature,slope water content,conditions of slope water supply,the number of freezing and thawing cycles,the geometric characteristics of the slope and so on.And on this basis,the paper put forward the method and standard of safety evaluation of frozen rock slope.