Study On Instability Prediction Model Of Tension-Splitting Rock Mass On Slopes

The question of "when is a collapse disaster likely to occur" has always been a pain point for collapse disaster monitoring and early warning.Since there are tens of thousands of collapse disaster hidden danger points in China,the use of practical and effective monitoring technology and prediction theory to make disaster time forecasts that can meet the needs of emergency avoidance is a key research goal at this stage.Tension-splitting collapse is the main type of collapse,and the research progress of prediction is slow because the collapse precursors of tension-splitting rock mass are not obvious.Existing studies point out that tilt deformation is the most important deformation behavior of tension-splitting rock mass,the natural frequency can characterize the change of stability trend of tension-splitting rock mass,and the tilt angle sensor and vibration sensor have the unique advantage of simple and low cost.Therefore,this study aims to solve the key problem of "building→validating→applying" of the collapse prediction model of by starting from the time-varying evolution of tilt deformation and natural frequency of tension-splitting rock mass.The "theoretical analysis→model test→field monitoring" is used as the research program chain,and the main work contents and research results are as follows:(1)The fracture mechanics model is derived by analogizing the collapse evolution process of tensional fractured rock masses under the dominant effect of gravity to the subcritical expansion process of rock masses under the effect of stress erosion,using the fracture mechanics theory,a fracture mechanics model is derived for the time-varying evolution of tilt-deformation of tension-splitting rock mass.In the process that the tilt deformation trend of the tension-splitting rock mass can be monitored,the tilt deformation evolution curve shows a shift from"uniform rise" to "accelerated rise";There is a significant exponential correlation between the accumulative tilt deformation and the tilt deformation rate in the accelerated tilt deformation process of the tension-splitting rock mass,and the"inverse tilt rate method" collapse time prediction model is proposed.(2)By simplifying the tension-fractured rock mass into a vibrating system and applying the theory of vibration mechanics,the equation of the relationship between the natural frequency and the depth of the controlled fissure of the tension-fractured rock mass is solved,and the time-varying dynamics model of the intrinsic frequency evolution is obtained.Through the analysis of theoretical calculations,it is found that the evolution curve of natural frequency of the tension-fractured rock mass shows a continuous "accelerated decline" during the measurable process of the trend of natural frequency of the tension-fractured rock mass;there is a significant linear correlation in logarithmic coordinates between the intrinsic frequency and the approaching collapse time of the tension-fractured rock mass in the accelerated change process,and the "natural frequency trend method" collapse time prediction model and "dynamics stability coefficient"calculation method are proposed.(3)Through a series of physical similar simulation and monitoring tests of tension-splitting collapse,the theoretical evolution law of tilt deformation and natural frequency of tension-splitting rock mass is verified:the accumulative tilt angle-time monitoring curve has a macroscopic change from "uniform rise" to"accelerated rise",but there is a local phenomenon of "step-up" and "accelerated trend update";The accelerated rise of the accumulative tilt angle-time monitoring curve is 1.5 min～37.5 h,during which the cumulative tilt angle and the tilt angle change rate have a significant exponential function relationship;the resonant peak frequency-time monitoring curve has a macroscopic "accelerated decline" trend,and there is a local"step-down" process and corresponds to the "step-up" process of the tilt angle;The acceleration reduction of the resonance peak frequency-time monitoring curve is 17 h～11.1 d,during which there is a significant linear relationship between the resonance peak frequency and the approaching collapse time in logarithmic coordinates.(4)Through a series of physical similarity simulation and monitoring tests of the collapse of tension-splitting collapse,the correctness and validity of the theoretical model were verified:the prediction model of "inverse tilt rate method"can obtain prediction results with an average relative error rate of 3.5%at an average prediction lead time of 3.3 h;The prediction model of "natural frequency trend method" can obtain the prediction result with an average relative error rate of 7.4%at an average prediction lead time of 32.6 h;Under the condition that the depth of the controlled fissure cannot be identified,the "dynamics stability coefficient" can be used to accurately evaluate the stability of the tension-splitting rock mass,and the dynamics stability coefficient is found to be exponentially correlated with the material mechanical stability coefficient.(5)The basic mechanism of "acquisition-computation-transmission" of tilt angle based on MEMS technology is constructed;the "segmental linear correlation" between tilt angle monitoring data and sensor temperature is found through 2 a long-term monitoring of stable slopes,and the "segmental temperature compensation method" is proposed,and the time series composition of the tilt angle field monitoring data is obtained;through the field monitoring of the collapse evolution process of two fractured rock hazards,it is found that there were measurable accelerated tilt deformation precursors at 84 h and 117 h near the collapse respectively;further based on the characteristics of the MEMS tilt angle sensing data,the the lalgorithm of "tilt rate inverse method" collapse time prediction model is established,and the feasibility of the algorithm is verified by the real-time prediction analysis of the collapse monitoring cases.(6)By implanting the resonant peak frequency edge acquisition and calculation module in the base mechanism of MEMS sensing,the calculation of"dynamics stability coefficient" and the evaluation of the stability of the dangerous rock mass are realized in the stage of unmeasurable tilt deformation through 1 a field long-term monitoring of the tension-splitting rock mass.