Based on the concept of porous media, a dynamic evolution model between porosity, permeability coefficient and damage variable volumetric strain is established. The strength reduction factor conversion relationship between the Mohr-Coulomb criterion and Drucker-Prager criterion is given. Based on the Abaqus platform, the dynamic evolution model combined with the finite element strength reduction coefficient method is used to investigate the horizontal directional drilling wall stability. Engineering case calculations show that using different yield criteria may result in different safety factors. However, under certain conditions, they can be equivalent, or the numerical results are consistent with the theoretical analysis. Different effects of pressure on the slurry stability of the hole wall are studied, and it is found that under certain mud pressure, the safety factor continuously decreases with the increase of the mud pressure. At the end of expanding, the mud pressure is 2.4 MPa, the biggest plastic radius is 2.34 m and the maximum plastic strain reaches 0.393 at the hole-wall. In the limit equilibrium state, when the mud pressure is 2.4 MPa, the maximum plastic strain increases to 1.208 around the hole-wall, which is greater than the maximum strain value of expanding. The radius of plastic reaches 5.68 m, which is about 15 times the aperture.

horizontal directional drilling  /  hole wall stability  /  flow-solid coupling  /  strength reduction