Study On Several Typical Geological Disaster Damage Assessment Method For In Service Pipelines

Pipeline transportation has advantages in one-time investment, transportation cost and safety. It is especially appropriate at long distance natural gas transportation. With the world’s growing demand for energy, nations come under increasing strain in pipeline safety. So pipeline integrity management research has attracted many scholars’attention. Geological disasters is particularly important as a part of pipeline integrity management.Firstly, the formulas of pipeline settlement and inner force underground settlement has been deduced on elastic foundation beam, and formulas of pipeline Von Mises stress with inner pressure was present at ground settlement. The accuracy of formulas was verified by comparing the result of formulas with FEA. While the length of gob is smaller than the critical length, the change of gob length has very little effect on pipeline maximum Von Mises stress; but while the length of gob is larger than the critical length, pipeline maximum Von Mises stress rapidly increases with gob length increasing. While pipe soil friction coefficient is less than0.45, pipeline maximum Von Mises stress linear increases with soil friction coefficient increasing; while pipe soil friction coefficient is greater than0.45, the change of soil friction coefficient has very little effect on pipeline maximum Von Mises stress. The pipeline maximum Von Mises stress can be decreased by keeping proper inner pressure. Pipeline maximum Von Mises stress linear increases with depth of pipeline increasing. Pipeline maximum Von Mises stress decreases while thickness of casing soil on gob increasing.Secondly, theory model of pipe soil interaction under lateral landslide has been deduced on elastic foundation beam, and the formulas of pipeline flexibility was present. The solutions of Interfacial angle and bending moment were acquired via the differential equation. The formulas of pipeline Von Mises stress were present based on elastic foundation beam and the accuracy of formulas was verified by comparing the result of formulas with FEA. while the displacement of landslide is constant, the width have extreme value and critical value; when landslide width is the extreme value, the pipeline maximum Von Mises stress is most caused by landslide; when landslide width greater than the critical value, the change of landslide width has very little effect on pipeline maximum Von Mises stress; when landslide width is less than the extreme value, the pipeline maximum Von Mises stress increases with the width increasing; when landslide width is greater than the extreme value and less than the critical value, the pipeline maximum Von Mises stress decreases with the width increasing. While landslide width is constant, the distance of landslide has critical value; when the distance is less than the critical value, the pipeline maximum Von Mises stress linearly increases with the width increasing; while the distance is greater than the critical value, the change of the distance has very little effect on pipeline maximum Von Mises stress.Besides, only consider the effect of maximum falling rock impact force, put forward the pipe stress calculation formula under the action of falling rock impact force, the upper covering soil and internal pressure; carried out the experimental research of falling rock impacts buried pipe, tested the influence of different falling rock height on pipe displacement and strain; build the falling rock impact numerical calculation model of the buried pipe, compared and analyzed both the numerical calculation results and experimental results. Through the research find that the shear modulus and Poisson’s ratio of the soil have important influence on pipe maximum Mises stress when the pipe impacted by falling rock, so select the upper covering soil that has bigger shear modulus and Poisson’s ratio can effectively reduce the influence of falling rock impact on pipe. The maximum Mises stress with the increase of falling rock diameter, velocity and linear increase; when the distance between falling rock edge and the center line of the pipe is greater than the radius of pipe, the falling rock impact little effect on pipe; the Internal pressure effect on pipe exists an extreme value, the influence of falling rock impact increases with the pipe pressure and reduction when the Internal pressure is less than the extreme value; when the internal pressure is greater than the extreme value, the internal pressure load is the main factor of the Mises stress increases; increase the thickness and buried depth of pipe can effectively reduce the effects of falling rock impact on pipe, but there exists extreme value, more than the extreme value, the change of thickness and buried depth have little influence on pipe stress from falling rock impact. Finally, the geological disasters software was developed. The software has friendly user’s interface. It can calculate in the background using ANSYS software, and can directly display the results in the software interface.In this paper, through theoretical analysis, numerical calculation and experiment test, build the Mises stress calculation formula of pipeline deformation area under subsidence, landslides, and falling rock impact of working conditions, the analysis of the typical related factors on the influence regularity of pipe stress, provide theoretical support of integrity assessment of pipe under typical geological disaster conditions.