Deformation Characteristics Of Buried Pipeline In Liquefied Site

Sand Liquefaction was a usual soil failure form in earthquake. It could cause large soil deformation and huge floating pressure which are the most dangerous damage factors in buried pipeline system. Studing the design theory and methods against sand liquefaction is an essential part to ensure the safety of the buried pipelines in liquefied site. Sand liquefaction could cause huge buoyant force during the process of liquefaction and vertical settlements occures in the process of post liquefaction. Based on the two phenomenons, this paper explores the deformation characteristics of the continuous and discontinuous buried pipelines under two conditions which could provide reliable guidance for reasonable design of the buried pipelines. Herein, the main researches and conclusions are concluded as follows:Firstly, based on ansys platform, non-linear contact model is used in the non-liquefied area and non-linear spring model is used in the liquefied area. The stress distribution and deformation characteristics of the continuous and discontinuous buried pipelines are analyzed systematically. The results show that the non-linear contact model used in the liquefied area and the non-linear contact model used in the non-liquefied area could simulate the laws of interaction between the soil and the buried pipelines.Secondly, the continuous and discontinuous buried pipelines models under bouyant force in liquefied soil are established. Material nonlinearity and geometrical nonlinearity are taken into consideration. The pipeline is simulated using shell element. The flexible joint is simulated using spring element. The result shows t hat the most dangerous place appears at the junction of the un-liquefied and the liquefied area and the middle position of the liquefied area. The liquefied zone is the key factor that affects the flotation of the continuous pipelines. Controlling the length of the liquefied zone is an effective measure to avoid the damage of the continuous pipelines. The uplift displacement of the discontinuous pipelines is much bigger than the continuous pipelines. The stress mainly concentrates near the joint position. The maximum pull out length and angle increases with the increase of the number of joints in liquefied soil.Lastly, the continuous and discontinuous buried pipelines models under post-liquefaction settlement are established. Compare the reaction of the con tinuous and discontinuous buried pipelines under different soil properties. The result shows that when the soil stiffness in un-liquefied soil is small, the discontinuous buried pipelines could absorb big post-liquefaction settlement through the rotation of the joint. When the soil stiffness in un-liquefied soil is large, the damage of the discontinuous buried pipelines are more likely to happen than the continuous buried pipelines. Reducing the length of the segment is an effective measure to prevent the damage of the body of the pipelines.