Investigation of pull-out behaviour of small diameter medium density polyethylene pipes

管道在现代社会中发挥着重要作用，将液体和气体从源头输送到用户。根据加拿大自然资源部的数据，大约有82.5万公里的石油和天然气传输、收集和分配管道穿越加拿大。这些管道中有许多经过易发生山体滑坡的地区。**由于滑坡引起的土壤移动可能对管道造成纵向、横向或组合载荷，**视管道相对于移动地面的方向而定。现有的滑坡地区管道结构完整性评估设计指南是基于对刚性管道的观察而制定的，可能不适用于柔性管道，如中密度聚乙烯（MDPE）管道。然而，在过去的几十年里，包括MDPE管在内的柔性聚乙烯管由于其各种优点而被广泛使用。MDPE管道在滑坡荷载作用下的性能评价设计方法尚不完善。MDPE的全尺寸测试和有限元（FE）建模也非常有限。在拟议的研究中，将利用纽芬兰纪念大学**(MUN)的设施，对**小直径MDPE管道进行一套全尺寸测试，以建立一个数据库，并更好地了解管道在**地面运动载荷下的行为。试验程序包括以下内容：1)平面管轴向拉拔试验；ii)带三通管（分支管）的轴向拉拔试验；iii)埋在松散致密砂中的管道横向拔管试验。将进行实验室单元测试，以寻找岩土参数和开发砂的本构模型，以及MDPE管道材料的应变率依赖行为。**有限元建模技术将使用Abaqus有限元软件来模拟从**全尺寸管道试验中观察到的响应。这项研究的结果将对加拿大管道行业**有用，使他们能够评估不稳定地层中的管道状况，从而做出更有效的管理决策，以确保管道的结构完整性，并将管道故障的风险降至最低。

Pipelines play an important role in modern society through transporting liquids and gases from the source to the**users. According to Natural Resources Canada, about 825,000 kilometers of oil and gas transmission, gathering**and distribution pipelines traverse Canada. Many of these pipelines pass through the areas prone to landslides.**Soil movement due to landslides may cause longitudinal, transverse or combined loads on the pipelines,**depending upon the orientation of the pipeline with respect to the moving ground. The existing design**guidelines for structural integrity assessment of pipelines in landslide areas were developed based on the**observations for rigid pipes, which may not be applicable to flexible pipes, such as Medium Density**Polyethylene (MDPE) pipes. However, flexible polyethylene pipes including MDPE pipes have been widely**used over the last few decades due to their various advantages. The design method for the assessment of the**performance of MDPE pipelines subjected to landslide loading is not well-developed. Full-scale tests and finite**element (FE) modelling of MDPE are also very limited. In the proposed research, a set of full-scale tests of**small diameter MDPE pipe will be conducted using the facility at Memorial University of Newfoundland**(MUN) to develop a database and an improved understanding on the behaviour of pipes under the loads from**ground movements. The test program will consists of following: i) axial pullout testing of plane pipes; ii) axial**pullout testing of pipes with Tee-junctions (branched pipes); and iii) lateral pullout testing for pipes, buried in**loose and dense sand. Laboratory element testing will be conducted to find geotechnical parameters and**development of constitutive models for sand and the strain rate dependent behavior of MDPE pipe materials.**FE modelling techniques will be developed using Abaqus FE software to simulate the observed response from**the full-scale pipe tests. The findings from this research will be useful to the Canadian pipeline industry,**enabling them to assess pipeline conditions in unstable ground and thus to make more effective management**decisions to ensure structural integrity of the pipeline and minimize the risk of pipeline failure.