Development Of Measuring Instrument For Rheological Stress Recovery Method And Engineering Applications

The in-situ stress is the fundamental force that causes the deformation and damage of rock mass in underground engineering.Thus,it's a prerequisite to obtain accurate information of in-situ stress for determining the mechanical properties of engineering rock mass,analyzing the stability of surrounding rock,and achieving the scientization of design and decision-making of engineering rock mass excavation support.To obtain accurater in-situ stress of the deep weak fractured rock mass,a new method,namely the rheological stress recovery(RSR)method,is proposed.By the adoption of borehole embedding compressive stress sensor,the information about the stress and disturbance stress of surrounding rock can be obtained by this RSR method.Based on the RSR method,a fiber grating six-direction pressure transducer,a fiber grating demodulator and a calibration device matched with the sensor for the stress measurement using the RSR method are developed in this paper.In addition,the measurement performance of the six-direction pressure transducer is calibrated by an laboratory test.After the calibration,a numerical simulation is conducted to mimic the measurement of in-situ stress through this RSR method based six-direction pressure transducer.Through numerical simulation,the stress recovery law of six-direction pressure transducer under different rheological mechanical properties of rock mass is studied.Finally,based on the soft rock roadway of Pingmei Coal Mine No.4 and No.8 Mine,the on-site stress measurement through this RSR method based six-direction pressure transducer is carried out,and the characteristics of the in-situ stress in the test site are obtained.The detailed research works are as follows:(1)Based on the principle of RSR method,a fiber grating six-direction pressure transducer is developed.The sensor is spherical in shape and contains six independent pressure sensing units.The sensor adopts the fiber grating wavelength division multiplexing technology and fiber fusion technology,which greatly improves the measurement efficiency of the sensor.The calibration device for the sensor is developed,which is applicable to a wide range of applications,easy to disassemble and transport,and has strong adaptability.An intrinsically safe portable fiber grating demodulation instrument is developed,which has explosion-proof,small and lightweight design to meet the requirements of coal mine environment.(2)Based on the R&D test equipment,the laboratory calibration tests of the six-direction compressive stress sensor was carried out.The measured performance of the sensor satisfies the requirements of the rheological stress recovery method for in-situ stress measurement,and the calibration coefficients of each sensing unit are obtained.(3)A numerical simulation analysis model of fiber grating six-direction pressure transducer is established,and the calibration test process of the sensor was simulated to verify the rationality of the built sensor model.After that,the performace of the developed tensor under the different hydrostatice pressure(up to 30MPa)is studied by numerical simulation.Under the measurement performance,verify that the overall stiffness of the sensor meets the requirements of high stress environment.Base on this numerical simulation,the three-dimensional numerical model of the measuring process of the RSR method is established.Besides this numerical model,different rheological model and paremeters from published references are also introduced to study the stress recovery law of the six-direction compressive stress sensor rock mass for different rock state with different rheological model under different in-situ stress.(4)The experimental equipment to be developed was applied in the Pingdingshan No.4 coal mine and No.8 coal mine deep soft rock roadway.The in-situ stress measurement of the RSR method was carried out and compared with the test results of the traditional core stress relief method.Verify the accuracy and reliability of the six-direction pressure transducer test.