Stability Analysis of Inclined Shaft for Oil and Gas Pipeline Traversing Slope

For Lan—Zheng-Chang oil and gas pipeline encountered multiple loess gully or slope, the crossing way of inclined shaft has to be adopted due to the site limiting conditions. First, based on some loess gully slope engineering at Tong-guan in Shaan-xi province, the stability boundary of the gully was determined according to the slope geometry in this paper. Then, the method of three-dimensional numerical simulation was used to discuss the varying laws of the stress, displacement, yield regions of soil mass around the inclined pipeline shaft under the different crossing conditions. The analysis results show that the maximum values of the displacement at vault, side-wall and floor appear in the middle of inclined shaft, and the upward-displacement of the floor is far larger than the subsidence of the vault in the same section, and the value of the down-displacement at the vault is very little in the entrance and the exit of the inclined shaft; the variation of the convergence displacement at middle points of the side-wall, along the direction of the inclined shaft, is very small. During the process of the excavation, the maximum tensile stress appears at the slope shoulder, and the tensile stress zone caused by excavation is very small. After the excavation of the inclined shaft is completed, the maximum shear stress appears at the near of the slope foot, and the maximum shear stress will decrease with the increase of the obliquity of the inclined shaft. The yield region around shaft is mainly caused by shear stress, and concentrated in the section-floor within the 1/4–3/4 range in the axial direction of the inclined shaft. Also the failure region appears at the slope foot. According to the comparative analysis of different schemes, at last, the optimum stable and safety design parameters involved in pipeline crossing the inclined shaft are given. The results provide theoretical basis for the construction safety and reasonable support of the inclined shaft for the oil and gas pipeline.