High-precision Volumetric Borehole Strainmeter And Its Impact Study Of Observation

Deformation of the crust, tectonic movement within the Earth the and the varieties of geological disasters are closely associated with in-situ stress. The change of crustal stress state can cause the fault fracturing. wrinkles and even an earthquake. Borehole strainmcter observation is installed the strainmeter in the borehole which is tens to hundreds of meters underground, and then precisely monitoring the strata stress-strain state. It is a primary means to study crustal stress states, and it also plays an important part in earthquake precursor observation. The volumetric borehole strainmeters has a clear and concise mechanics, and it has a higher-frequency and sensitivity, low dependence on rock and cement status, makes it easy to obtain more reliable observational data, therefore, it occupies a large proportion of the number of strain observation instrument in the world. This paper studies how this high-precision volumetric strainmeter developed, and the work of in-situ stress measurement of the borehole which would install strainmeters is carried on in this paper, several influencing factors of volumetric strainmeters is studied through data analysis, the earthquake reflecting ability of volumetric strainmeters is analyzed. And coseismic precursory anomaly of volumetric strain curve also is studied in this paper. After nearly two years of study and research, the author has made initial progress and understanding as follows:The series of high-precision volume type borehole strainmeter which is named TY types, is easy to assemble, transport and install, this type of strainmeter has a stable system, which make it get a long serving life. Its’ obse’rvation accuracy is superior to1×10-11ε. and the dynamic range is±2×104, which is over±86dB.The mechanics designing and the relationships between mechanics and electricity is introduced, the technology of data-capture, amplifying circuit, communication method between ground and underground instrument is studied, and contrastive study of different instruments (pressure sensor. solenoid valve) is carried on. It is shown that the TY series strainmeters can work at the depth of1000meters underground through simulation experiments like encapsulation test and voltage withstand tests. The GPRS wireless network data transmission technology and network address of the primary server exchange data processing technology that this series strainmeters used is introuduced. The site selection principle, technical indicators, installation steps is studied, and a cement dispenser for installing the strainments is developed.The deep borehole hollow inclusion strain gauge in-situ stress measuring instrument and its assistive tools which were used for deep borehole in-situ stress measurement.lt integrates hollow inclusion strain gauge, strain recording apparatus and electronic compass into a micro-probe, which can be installed at predesignated position in the borehole when measuring the in-situ stress. We obtained in-situ stress data of Zhangjiang observation borehole at the deepest depth of385m underground by using this technology, the results shows the maximum principal stress direction in surveying area is near EW direction, and the values of maximum principal stresses are between8.5and9.0MPa. The minimum principal stress direction is near vertical, and the values of minimum principal stresses are near to the overburden pressure. Measurement shows that deep borehole hollow inclusion strain gauge in-situ stress measuring instrument is suitable for deep hole of3d in-situ measurement.It shows that1600grid values strain solid tidal is clearly observed by TY series volumetric strainmeters, which proved that its" accuracy is better than10-11ε. The coseismic precursory formula of Shandan volumetric strain observation station is derived. And the relationship of strain curve magnitude,the strain earthquake waves and epicentral distance is studied, according to this relationship we can obtained the earthquake epicenter when we know the information of stain seismic waves maximum amplitude and epicenter. It shows Shandan volumetric strainmeters observation station can record any earthquake over Ms6.5wherever it happen on the planet. The coseismic strain anomaly of Wenchuan8.0earthquake and Honshu, Japan9.0earthquake are studied, Shandan station recorded a significant earthquake coseismic-strain step, but train records of the east coast of Honshu Japan9.0earthquake of Daijiaba station did not have the apparent strain step phenomenon, this may be caused by different mechanisms of the earthquakes. Meanwhile, Japan earthquake caused the concave exception of solid tide day drift trends of Daijiaba observation stations. Shandan and daijiaba observation stations all recorded free oscillation curves of the earth with the cycle from600to1200s, which is caused by earthquake.