Experimental Investigation on Anisotropy of Rocks Using Digital Drilling Technology

Abstract

Accurate determination of rock anisotropy is of great significance for analyzing the safety and stability of engineering rock mass. In this paper, uniaxial compression tests are carried out on four kinds of rocks: slate, gneiss, sandstone and shale, to obtain the uniaxial compressive strength of each rock in the different directions. Digital drilling tests are carried out on four kinds of rocks to study the anisotropy of drilling parameters. According to the working principle of the drill bit, its force balance analysis model is established, and the concept of cutting strength ratio is proposed. Using the drilling parameters (drilling depth, drilling time, torque and thrust, etc.) in the different directions for each rock, the interrelationships between them are analyzed. The anisotropy index of rock is defined according to the ratio of cutting strength in different directions of drill parameters, and a new method for judging rock anisotropy is proposed. The results show that the thrust and torque in all directions of the rock increase with the drilling depth. The torque in all directions of the rock has a positive linear relationship with the thrust. The ranking of the anisotropy degree for the four types of rocks is as follows: gneiss > slate > shale > sandstone. The anisotropy results have been validated by an alternative method utilizing uniaxial compressive strength. The determination results are verified by the uniaxial compressive strength of the rocks, and the degree of anisotropy of the four rocks is consistent with the determination results. This method can help engineers analyze the anisotropy of rock, and provide a new idea for studying the integrity and stability of rock mass.