The Progress of Technique of In Situ Stress Monitoring in China

Abstract

At present, there are many kinds of in-situ stress measurement techniques, such as Hydraulic fracturing, Over-coring, AE Kaiser effect, ASR, DSCA, Borehole Breakouts, Earthquake focal mechanisms, Fault-slip analysis, that can get crustal surface layer of the original stress state. But it is difficult to observe the stress change and its variation in space and time. The borehole strain meter is effective technology to observe the stress change and its variation in space and time. the borehole deformation in diameter was measured in different direction, then We can get the stress variation by theoretical equation. The multi-component observation is important development way of geoscience in deep borehole. It is favorable to the data quality comparison and verification, and suppressing interference of air pressure, groundwater, and lithosphere heterogeneity. An observation system including multi components is developed for the deep borehole environment, which integrates observation results of strain with four components, tilt with two components, and geothermal. The down hole transducer output digital signal directly, and with data bus technique, it is flexible to integrate various monitoring instruments, implement the observation data transported from down hole to ground and functional controlling from ground data Acquisition System to down hole transducer. We have project that applied to our government, it is Crustal stress-strain observation network in China, which is to monitor stress variation along the main earthquake fault. Before that, we carried small scale experiment, to check the borehole strain meter whether or not work well. The five stations have been arranged along or across Anning-Zemu fault. The depth of borehole is 150m. The BHTV and in-situ stress measurement have carried out in borehole, the borehole strain meter is installed in bottom of borehole. Fault activity can be studied according to the fault friction slip criterion with stress data. According to the Coulomb criteria, when the shear stress τ of fault plane is not less than the friction strength μσn, friction slip would occur along the fault plane. We can derive the average shear with function of friction coefficient, and taking the friction strength μ as 0.6~1.0(from Byerlee law), the critical value is 0.57.