Journal of Pipeline Systems Engineering and Practice

Because loess underground erosion is one of the major engineering geological problems in loess areas of China, foundation loess of the Zichang-Yongping section of West-East Gas Pipelines is taken as the research object. The soil-water characteristic curve (SWCC) and hydraulic conductivity function (HCF) of samples have been obtained by laboratory tests, and on this basis, seepage field numerical simulations of loess foundation with and without the pipelines have been processed by the finite-element method. Critical groundwater seepage velocity of underground erosion and the relationship between groundwater seepage velocity and underground erosion velocity have been tested by self-made instruments. Results of tests and numerical simulation indicate that the pipelines not only change the original seepage field of a loess foundation, but also accelerate the underground erosion of a loess foundation. Loess on the top and upstream groundwater side of pipelines will be eroded first, finally causing the failure of foundation and the exposure of pipelines. The combination of soil solidified material and revegetation is suggested as an effective and durable solution to deal with the underground erosion problem of loess pipeline foundations.

The chemical grouting method presented in this paper can restore the position of a pipeline by precisely and rapidly reinforcing the failed pipeline foundation. The method can also improve the meandering and sagging conditions of a pipeline. A case study found that the method is an effective, rapid, and precise trenchless restoration technology for pipeline position restoration. Moreover, discussion results are presented of some patterns of injection tests that were conducted in the laboratory to determine the relationship between the types of grout material and the soil permeability. According to the experimental results, the grout is injected into the lower permeable soil primarily by fracture grouting. Additionally, numerical analysis was conducted by using finite-element analysis software, and the outcome showed that this numerical analysis can be used as an assessment method for predicting the vertical displacement of a pipeline after applying the chemical grouting pipeline position restoration method.

In order to investigate the safe operation, dynamic characteristics and stability of oil and gas submarine pipelines, the natural characteristics of a pipe span under elastic supporting conditions were studied. The pipe was simulated as a commonly supported beam considering the interaction of not only the fluid inside and outside the pipeline but the elastic coefficients of its supporting soil as well. The differential quadrature method (DQM), an efficient numerical method to solve boundary and initial value problems, was adopted to analyze the natural characteristics of a submarine span pipeline. The differential equation and its corresponding DQM simulation equations and boundary conditions were obtained. The impacts of several factors on natural frequency of free-span submarine pipelines were studied. These factors included soil elastic coefficients at pipeline ends, span length, outer diameter, flow velocity and pressure inside pipeline, flow velocity and fluid damping outside the pipeline, density of conveying fluid, and the axially sectional force. The analytical method and numerical results presented in the paper are of value for theoretical research and engineering applications.

Two river crossing cases are considered in which a pipe is installed beneath the Yangtze River using horizontal directional drilling (HDD). In both cases, a length of pipeline located on the rock strata near the north bank, including a local protrusion, is disrupted by river erosion. A three-dimensional (3D) model is developed to simulate the river erosion based on the finite-element software ABAQUS, which is capable of modeling the properties of the soil and pipelines, as well as their interaction. Results are presented based on an analysis of the stress concentration points at the ends of the rock protrusion, in the vicinity of the erosion. The effect on the pipelines is investigated as a function of the depth, extent, and location of the erosion. The resulting stress and displacement along the crown, spring, and invert lines of the pipelines are shown and compared to the function of the depth, extent, and location. And the stress concentration points occur at the location of rock protrusion and in the vicinity of the eroded soil.

This paper investigates buried gas pipelines impacted by an excavator bucket, in addition to the digging load driven by the hydrocylinder of an excavator, and the impact caused by liquid pressure oscillation and the inertial force of the excavator system. These were taken into account for the impact load subjected by the excavator bucket teeth, and the dynamic load coefficient was suggested theoretically. Then the dynamic stress distribution of the buried gas pipeline and corresponding digging limiting load were evaluated by using the strength criterion and the LS-DYNA commercial finite-element software, in which two excavation sections of perpendicular to and parallel to the longitudinal direction of pipeline were detected respectively. Furthermore, cracks exist in the actual pipeline, and the numerical analysis model of the high-pressure gas pipeline with an elliptical crack at the inner surface was established. The limit digging load while the crack existed was determined by the theory of dynamic fracture and compound fracture criterion, which was 20% lower than that without cracks. The numerical analysis method in this article has certain reference value to the design, construction, and risk assessment of a buried gas pipeline.

ASTM guidelines provide a procedure for estimating pull loads and stresses on polyethylene pipe as primarily a function of the drilled path and buoyant weight of the pipe in the drilled hole. The equations were initially developed assuming a level grade or that the horizontal directional drilling (HDD) entry and exit elevations are the same. In practice, however, it is not uncommon that there would be a finite grade or difference in elevation between the entry and exit points of the drilling operation. The equations and methodology have been expanded to address the placement of polyethylene pipe for the case of a nonlevel grade, including the installation of pipe with and without antibuoyancy measures. The theoretical model and associated results were primarily based on a particular generic borehole geometry, recognizing that specific trends and conclusions may differ somewhat for other possible bore paths. This paper therefore investigates an alternate generic geometry for traversing different entry and exit elevations, representing a reasonable bore path in many practical applications. The results help provide a better understanding of the factors influencing the pull loads in the maxi-HDD installation of pipelines.