## 1 Introduction  
Recently, more and more underground engineering with characteristics of long and deep burial will be built in deep, soft surrounding rock areas [1; 2; 3; 4; 5; 6]. In situ stress measurement in these areas is essential to determine the mechanical properties of fractured rock masses, analyze the stability of underground structures (e.g., tunnels, caverns, shafts, and other openings), and design the rock support system [7; 8; 9]. At present, two in situ stress monitoring methods, namely hydraulic fracturing and overcoming [10; 11], are widely used in many fields and have obtained acceptable results. These two methods are generally suitable for hard and intact rock as they are assumed that the rock masses have the characteristics of being homogeneous, continuous, isotropic, and linearly elastic. However, most of surrounding rock masses in underground engineering, especially in deep coal mines, are usually soft, fractured, and show a significant time-dependent behavior [12; 13; 14]. In consequence, these two commonly used methods are hardly applied not only in terms of the theoretical assumption but in implementing the measurements.  
In order to undertake in situ stress measurements in deep soft rock masses, [PERSON] et al. [15] proposed a new stress monitoring theory named the rheological stress recovery method, in which it is suggested that compressive stress transducers are embedded in holes drilled into the surrounding rock and grouted into place. Due to the strong rheological characteristics of soft fractured rock mass, the measured stresses of the transducers will increase gradually and eventually reach a stable value. The initial stress of the rock mass before drilling can be determined by analyzing the measured stress. This method can also be used to obtain the long-term disturbed stress field of the surrounding rock if more than one measuring point is set in the drilling holes.  
A three-dimensional vibrating wire compressive stress transducer was developed, as described in the RSR method statement [15]. The sensor was approximately cubic, including three orthogonal sensor faces, and the measuring range was 0-35 MPa. The measuring performance of the transducer was investigated using physical model tests on cement mortar samples and the results confirmed the linear relationship between the loading stress and the measured stress of transducer [16; 17]. The affecting factors, including rheological properties of the rock mass, the elastic mechanical properties of the cement mortar body, and the grouting time, etc., on the measured stress of the transducers when they are buried into the rheological rock masses were investigated using theoretical analysis and numerical simulation [18].  
In this paper, the in situ stress monitoring method was extended to the field. The measuring instrument and corresponding functions are first introduced. The measuring procedures, including preparations, field measurements, and data analysis, are presented in detail. The initial applications of the RSR method were carried out in soft rock masses at deep levels within the coal mine and the measuring data were collected and used to determine the in situ stresses. Finally, the results obtained from the proposed method and that from the traditional methods are compared.