## 1 Introduction  
With the continuous exploitation of global resources, the number of deep and ultradeep holes is increasing, and the pressure and temperature of the occurrence environment at the bottom of holes are also increasing [1; 2; 3; 4]. Because the physical and chemical properties of rocks in deep in-situ environments are quite different from those under normal temperature and pressure [5], it is very important to obtain in-situ rock samples and study their related properties to realize effective evaluation of deep resources [6; 7; 8]. At the same time, a high-temperature and high-pressure environment will impact the engineering of deep drilling projects. When the resource mining depth exceeds 1000 m, a series of mining accidents will occur because existing rock theory cannot provide theoretical support for the development of deep mining technology [9; 10]. Therefore, it is urgent to evaluate rock theory in a deep in-situ state to promote the development of deep mining technology. During the exploration of deep rock, it is important to retrieve cores with their in-situ pressure conditions to more accurately simulate the occurrence environment (temperatureand pressure) of deep rock samples [11; 12; 13; 14]. According to cores obtained in recent decades, deep cores undergo cracking and destruction as they are brought to the surface, which changes their original composition and characteristics. This phenomenon is caused by the lack of means necessary to maintain the pressure environment of the core as it is raised from the bottom of the hole to the surface and exposed on the ground; this changes the environment of the core, results in the release of internal stress, and alters the composition [15; 16; 17; 18; 19; 20; 21]. Therefore, it is of great significance to study the physical and mechanical properties of bottom-hole rock with deep cores for which the in-situ pressure is preserved. To achieve this goal, it is necessary to simulate the deep temperature and pressure environment first, because this provides an experimental environment for the development of coring tools compatible with high pressures and solves the problems of high-risk and high-cost for on-site coring tests. The simulation of a high-temperature and ultrahigh-pressure environment can be used to verify the performance of a pressure-preserving coring tools in deep environments. At present, research institutions have carried out considerable research on downhole simulation test devices and have made some progress [22; 23; 24; 25; 26]. [PERSON] et al. used an indoor micro-drill to conduct drilling tests on rock samples subjected to lithostatic pressure, pore pressure, and drilling fluid column pressure at the same time, and studied the effects of fluid properties and pressure on the drilling speed of rock samples [27]. Schlumberger Cambridge Research Center in the UK has established a drilling simulation test facility that can be used to study the mechanical properties of drill bits and rocks [28]. This facility can provide a pressure environment with a maximum overburden pressure of 17.9 MPa, a lithostatic pressure of 103.5 MPa, and a pore pressure and drilling fluid column pressure of 69 MPa, and achieve the highest simulation temperature of 200 \({}^{\circ}\)C. Terra Tek, Inc. [29; 30] has developed a full-scale simulation drilling test device to simulate downhole pressure, which is as follows: overburden pressure of 207 MPa, lithostatic pressure of 138 MPa, pore pressure of 27.6 MPa, and liquid column pressure of 103 MPa. A series of important conclusions in the field of drilling have been obtained by using standard tricone bits to drill rock samples.