# Study on Mechanical Behavior of a New Three-Dimensional Sensor Under Rock Rheology
## 1 Introduction  
In situ stress is the natural stress without engineering disturbance in the stratum, and it is also the fundamental force that causes the deformation and failure of underground or open-pit engineering. The measurement of ground stress determines the natural three-dimensional stress state of the rock mass to be excavated and the surrounding area, which is usually completed by point-to-point measurement [1, 2]. Since the successful measurement of the Hoover Dam in the United States in the 1930s, a variety of methods have been developed, including the stress relief method, hydraulic fracturing method, Kaiser effect method (acoustic emission method), etc. [3]. Among them, the stress relief method and hydraulic fracturing method have been widely used at home and abroad [4]. The hydraulic fracturing method can only determine the maximum principal stress and the minimum principal stress in the vertical drilling plane, which is only suitable for the complete brittle rock [5] but not suitable for the continuous, homogeneous and linear elastic natural fractured rock. The stress relief method is the most widely used, the most mature technology and the most reliable result in the world [6, 7], and it is also one of the test methods recommended by the International Rock Mechanics Association. Its basic principle is touse the sleeve method to make the rock mass of the measuring point break away from the constraints of the surrounding rock mass so that the core with small holes can completely liberate the stress [8; 9; 10]. On this basis, many measurement methods have been further developed, such as the hole bottom strain method, hole diameter strain method, hole wall strain measurement method and so on. In 1969, [PERSON] conducted the first in situ stress measurement in the Scandinavian Peninsula [11]; in 1971, the South African Scientific and Industrial Research Council developed the CSIR triaxial hole wall strain gauge [12]; in 1973, [PERSON] developed UNSW, a new inclusion strain gauge [13]. [PERSON] and [PERSON] proposed optical holography to measure borehole wall strain in 1983 [14]. In 1991, the US Bureau of Mines developed the USBM aperture strain gauge [15]. In the same year, [PERSON], [PERSON] and others developed the KX-81 hollow inclusion triaxial strain gauge [16]. In 1992, [PERSON] et al. proposed a single-hole piezomagnetic full stress measurement method based on the hole wall strain method and designed a full stress meter [17]; in 2003, the Australian Federal Scientific and Industrial Research Organization developed the CSIRO hollow inclusion triaxial strain gauge [18]. In 2009, [PERSON] et al. successfully measured the magnitude and direction of the three principal stresses using the strain gauge one kilometer underground at the Kamioka mine in Japan [19]. In 2011, [PERSON] et al. proposed the borehole local wall stress relief method (BWSRM) [20]. [PERSON], [PERSON] et al. proposed the deep hole hollow inclusion method in 2013 [21]. [PERSON] et al. designed a three-dimensional force sensor based on the hole wall strain method and the flow stress recovery method in 2016 [22]. In 2020, [PERSON] et al. from China University of Mining and Technology developed hollow inclusion triaxial strain gauges such as YH3B-1 and YH3B-3 [23]; in 2022, [PERSON] and [PERSON] et al. proposed a contact-type aperture deformation measurement device based on the principle of microscopic optical imaging, which further realized the in situ stress measurement [24].