# Review on the Influence of Complex Stratum on the Drilling Trajectory of the Drilling Robot
## 1 Instruction
Building a roadway through a fault or having to halt roadway construction will increase the production cost of raw coal, while a mechanized coal mining face will stop production due to faults and face equipment will have to move, which will cause greater losses to the mine. Faults have an impact on coal mine safety. The coal seam and its roof near the fault plane are broken, which may lead to roof fall and wall spalling accidents. A water diversion fault may connect the underground water in the aquifer with the coal seam and cause water damage to mine production [17]. In a coal seam with a large gas content in the mine fault zone, gas may easily accumulate. Some closed faults may lead to large differences in the gas content of the two panels of coal seams, and mine gas accidents may also occur when the ventilation management is unfavorable. In the same way, the geological fault fracture zone can also cause a block and hole collapse accident. For example, a drill hole may pass through the overburden to the dolomite, and encounter the fault fracture zone at a hole depth of 340-373 m, and the total pump volume is lost. When the water level drops to 195 m, block and hole collapses are serious. After each lifting of the hole, the difference between continuing to drill is more than 5 m and less than the hole bottom, and the construction cannot continue [18]. In addition to geological fault factors, a formation with water saturation also has an impact on drilling [19; 20; 21]. The existence of voids in the formation is a prerequisite for water content. According to the water content, the formation can be divided into three types: permeable without water content, containing phreatic water and containing confined water. In the first two cases, drilling fluid leakage often occurs, and leakage is closely related to the permeability of the rock stratum. When drilling into a confined aquifer, water inflow and leakage may occur depending on the pressure of the aquifer and the relative density of the flushing fluid used. To sum up, there are two kinds of complex conditions in the drilling process: a formation with an unstable hole wall is called an unstable formation and a formation in which the flushing fluid in the hole is lost (or water gushing) is called the lost (or water gushing) formation. In addition, there are complex strata that are unstable and leaky. Water content has a significant impact on the properties of rock materials, affecting rock strength and rock deformation mechanisms, leading to many rock engineering disasters, such as landslides and karst collapse. At the same time, water injection is also used to prevent some engineering disasters, such as rock burst. [PERSON] et al. [22] studied the characteristics and changes of the geomechanicalproperties of Carboniferouscytone, and its relationship with mineral composition and immersion time. Research showed the correlation coefficient between physical parameters and mineral composition of most samples after soaking for 6 h is generally higher than that after soaking for 3 h. [PERSON] et al. [23] studied the floor heave mechanism of wet soft rock in a roadway when the water content of rock increases. They found that the reduction in rock elastic modulus caused by saturation will lead to the nonlinear increase in floor heave. This can be explained by the plastic strain of the floor rock to establish a stable correlation between the water content and the wet rock floor heave. [PERSON] et al. [24] comprehensively studied the effect of water content on rock mechanical properties by conducting indoor tests on sandstone samples with different water content during saturation and drying. The compression and tensile tests of sandstone samples with different water contents were carried out using the servo-controlled rock mechanics testing machine and Split Hopkinson compression bar technology. From the laboratory test, it was observed that the compressive strength and tensile strength of sandstone under static and dynamic state decreased during different saturation processes.