At present, borehole strain observations are generally in the horizontal longitudinal components of the strain. These observations take stress concentration model of an infinite flat plate with hole as their theoretical basis and are used for measuring stress distribution and stress change. Measuring both horizontal and vertical normal components of the stress, we can perform three-dimensional stress distribution. This article describes the horizontal and vertical strain measurement units of a deep-seated RZB-type integrated wideband deformation observing system, especially focusing on the measuring principle of the vertical longitudinal strain and technological breakthrough. Finite element method has been used to test the robust of the equipment.
The earth's crust has differential movement and deformation under the action of tectonic stress field. While the accumulated energy eventually leading to quick destruction of a place of the earths brittle crust, there is an earthquake. Employing the measured data of crust deformation, we can better understand the crust movement, which is important to establish the dynamics model of earthquakes and to reveal tectonic stress field. Since the 70s of last century, China has exerted strain observation and has already accumulated a large number of borehole strain data. Nowever, for technical limitations, the observation only limited to the horizontal strain measurements, which are difficult to carry out three-dimensional stress inversion. Japanese scholars exerted vertical strain measurements, which were used to achieve three-dimensional strain observation together with horizontal strain measurements. However, its magnetic sensor prevent them from having large dynamic range of measurement and high sensitivity. Large magnetic drift is also a severe problem. In 2009, Prof. Zuxi Ouyang and his coworkers designed and manufactured deep-seated RZB-type integrated wideband deformation observing system. The system has been accepted by the National Science and Technology.