多年冻土区输油管道工程中的(差异性)融沉和冻胀问题

多年冻土区石油和经济开发不断推动输油管道技术的发展,但是多年冻土区输油管道的(差异性)融沉和冻胀问题仍是关键性难题.寒区管道设计和施工必须考虑沿线的地形和环境条件对冻胀和融沉,以及相应的管道工程基础和结构整体性的影响.阿拉斯加输油管道工程取得成功的原因在于充足的科研投入、讨论和决策时间,以及最终采用的一系列创新设计来保护多年冻土和抑制融沉.这些研究围绕的关键问题是温热油管在多年冻土中的水热效应和差异性融沉和冻胀所导致的管道变形破坏,这些研究对可能出现问题的及早发现、充分理解和正确预测以及最终合理的设计、施工和维护至关重要.罗曼井和格拉线环境温度输油管道在20a左右的运营中,冻胀和融沉都比较显著.准确预测管道和围岩土的冻胀和融沉需要详细的观测研究和模拟试验相结合.在预测的基础上,针对具体问题抑制融沉和冻胀.成功设计、施工和运行寒区输油管道需要科学家、工程师、业界人士和管理部门密切合作.

(Differential) Frost Heave and Thaw Settlement in the Engineering Design and Construction of Oil Pipelines in Permafrost Regions: A Review

With the rapid development of oil pipeline technologies, the length, diameter, construction difficulty, complicity and risks of pipelines in permafrost regions have been increasing steadily. Some key oil pipelines have to traverse extensive expanse of permafrost, which provide great challenges for engineering deign and construction. The key issues in the engineering stability of oil pipelines are frost heave and subsequent thaw settlement in permafrost foundations. Therefore, design and construction in cold regions have to carefully consider the impacts of topography and environments on frost heave and thaw settlement, and their impacts on the engineering foundations and the integrity of pipelines. The environmental movements since the 1960s have greatly influenced the design and construction of oil pipelines in cold regions, which further complicated the issue, but also facilitated the research programs on these issues.;The success of the Trans-Alaska Oil Pipeline are attributed to the substantial investments in research and experiments, sufficient time for project evaluation, debating, and decision-making, as well as extensive participation of the public. The solutions of the permafrost problems include series of creative and innovative designs for reducing thaw settlement and environmental damages. The key scientific questions are focused on the impacts of the heated pipeline on the thermal and moisture regimes of permafrost, among which the most dangerous hazards would be potential differential thaw settlement and its impacts on pipeline deformation and integrity. The secondary hazards include the changes of micro-topography, drainage and vegetation after the construction of the pipeline, and the possible damages of the induced thaw settlement on pipeline stability and its ambient eco-environments. The 17-year observations on the temperatures, thaw penetration and surface thaw settlement within the right of way (ROW) regions and undisturbed sites along the Norman Wells Oil Pipeline indicate that the thaw penetration is still within the design predictions while the surface settlement in the trench in organic and ice-rich mineral soils has reached or exceeded design predictions in some locations. Along the Golmud to Lhasa ambient temperature product pipeline, frost heave and thaw settlement, as well as worn out, damaged or inadequate cathodic protection, and natural hazards such as strong earthquakes and flash floods have caused significant deformation of pipes and leaks many times during the past 28 years, necessitating a major renovation. Most of the frost heaving and thaw settlement occurred in ice-rich, fine-grained lacustrine sediments with shallow water table.;The observations and unique long-term data sets on oil pipeline engineering have greatly increased the body of knowledge in geocryology. They have supported the modification of operations, mitigation of frost hazards, and formulation of emergency response measures. In these studies, permafrost researchers, cold regions and pipeline engineers and project decision-makers need to discover, fully understand and correctly forecast potential problems as soon as possible, through careful investigations, close cooperation and mutual trust. If designed properly and the construction closely followed the designed specifications, all these problems would not necessarily produce significant consequences.