The Laboratory Calibration Experiment Of The Overcoring Of Hollow Inclusion Gauge

In-situ stress is a natural force that is objectively deposited in the earth's crust and is not disturbed by engineering.In-situ stress measurement and research have great theoretical and practical significance for the study of stress activity in the crust,the analysis of tectonic system,the study of crustal movement,the mine exploitation,Hydraulic engineering and other underground engineering design and regional stability.The laboratory calibration experiment of in-situ stress measurement is of great theoretical significance.Based on the research status of in-situ stress measurement methods,this paper analyzes the structure and manufacturing process of hollow inclusion gauge and the basic principle and experimental steps of overcoring of hollow inclusion gauge.Aiming at the problems existing in the previous research,relying on the laboratory in-situ stress biaxial calibration device developed by the Institute of Geomechanics,the new experiment is designed.The laboratory calibration experiment of the overcoring of hollow inclusion gauge is carried out to analyze the reliability of the overcoring of hollow inclusion gauge.Achievements are as follows:(1)Through the study of a large number of relevant literatures at home and abroad,the principle and process of the overcoring of hollow inclusion gauge are sorted out,and the detailed data processing methods and the expression of the related functions are given.At the same time,the development history of the overcoring of hollow inclusion gauge is studied,and the problems of laboratory calibration experiment of the overcoring of hollow inclusion gauge are summarized.(2)The correction factor K will directly affect the measurement results,so the value of the correction factor K is critical.In this paper,the value of the correction coefficient K is analyzed from the experimental point of view by using the results of the simulation cancellation experiment.The correction coefficient K is in the range of 0.70-1.00,with an average of about 0.82.(3)Summarize the results of all the hollow core body stress relief method in the indoor calibration experiment,we may come to the some conclusions.For the simulation overcoring experiment,most of the results of the stress magnitude of the error is less than or equal to 0.4 MPa,azimuth error is less than or equal to 6°,the inclination error is less than or equal to 6 °.For the overcoing experiment,the majority of the results of the stress magnitude of the error is less than or equal to 0.6 MPa,the azimuth error is less than or equal to 6 °,the inclination error is less than or equal to 6 °.(4)A new temperature compensation method was used in which a platinum resistance was installed at the position of the hollow core body near the strain gauges to record the temperature change during the overcoring process.Let's write down the temperature at the beginning.After the overcoring,put the core with the hollow inclusion gauge into the constant temperature water bath and continue reading until the temperature of the temperature of hollow inclusion gauge is constant.The method is simple and reliable and can eliminate the influence of temperature.(5)Compared with the curves of the confining pressure calibration experiment,it can be seen that the linearity of the confining pressure calibration curves of granite and tuff is better,and the linearity of the confining pressure calibration curve of marble is poor.With the pressure increases,the rate curve has a tendency to slow down.Which will result the results of the simulation overcoring is too large in a smaller loading state,the results of the simulation overcoring is too small in a larger loading state.