阿拉斯加输油管的设计和施工方式方案变更过程及其背后的原因和哲学思想

阿拉斯加输油管道公司曾经研发和使用了3种主要施工方案和技术:传统地埋式、特殊埋设和地上敷设方式.在传统地埋式施工方案中,管顶埋深变化于0.9~2.7 m.这主要是考虑了地形变化,而不是沿途的岩性和土壤类型.在特殊埋设方案中,在原油管道必须埋设的地段,如大规模动物迁徙常用地段则使用通道冷液循环降(保)温系统和(或)热管(桩)降(保)温,来保护多年冻土.地上敷设方案包括桩基架设和地上洁净砾石管堤(垫护层).后者只在管道进入和离开多年冻土时采用.架设桩基横梁方案中使用有或没有热管保温的垂直支架梁(单元)(VSM).在初步规划和设计阶段,管道的业主公司(即横穿阿拉斯加管道系统,或TAPS)和随后的阿拉斯加管道服务公司(APSC)不容商量的坚决要求100%的埋设方案.但是,随着勘察工作的进展和设计方案的细化,施工设计方案在不断变化.1977年管道施工结束时,只有57%的管道采用了埋设方式.管道运行30 a后的今天(考虑运行期间维护中所产生的问题),很多经验丰富的工程师认为53%的埋设可能更合理.设计和施工方案变更的原因主要有:1)为了获得通过联邦政府所属的土地所需的许可证,政府有特殊的规定和要求;2)管道公司的设计、施工和管理人员进行了现场野外调查、研究,并积极参与了详细设计和研发;3)美国环境政策法案(NEPA)的最新要求(启用了核准制).阿拉斯加管道服务公司是7家主要石油公司的服务机构.由于这个项目的巨大规模和所涉及的高昂费用,致使各大石油公司的工程师非同寻常程度的参与.在文章中,笔者论述了与阿拉斯加管道施工有关的阿拉斯加管道服务公司、美国联邦和阿拉斯加州政府相关组织机构的形成历史,管道设计演变过程及其背后的哲学思想,以及阿拉斯加管道工程项目的经验和教训.

The Change of Design of the Alyeska Pipeline and Construction Modes in Permafrost Areas,and Their Reasons and the Philosophy behind It

Alyeska had developed or used three major modes in the construction: conventional burial,special burial,and above ground modes.Conventional burial depths of the pipeline top vary from 0.9 to 2.7 m in accommodationto topography,but not soil conditions.Circulating coolant system and/or thermosyphons were equipped for the special burial at the animal passage sections where the pipeline has to be buried.The above ground mode include the pile bent and above ground gravel berms.The later was used only when the pipeline dips into ground and comes out of the ground.The elevated pile bent uses the vertical support member(VSM),with or without thermosyphons.During the initial planning and design phases,the owner companies,the Trans-Alyeska Pipeline System(TAPS),and later Alyeska Pipeline Service Company(APSC),staunchly demanded 100% burial.However,with the progress of survey and elaboration of designs,the construction modes had been changing all the time.When the construction was completed in 1977,only 57% of pipeline was buried,and some experienced engineers prefer 53% of burial after 30 years of operations.The "reasons"for the changes of construction modesinclude: 1) that they had to change in order to get the permit to cross Federal lands;2) they performed actual field investigations and participated in the development of the detailed engineering;and 3) National Environmental Policy Act(NEPA).Alyeska was the agent for the seven oil companies,and uncharacteristically,because of the size and costs of the project,the oil companies' engineers individually participated to an unusual extent.In this paper,the authors present the organizational history of Alyeska and the US Federal and Alaska State governments as regards to the construction of the Alyeska Oil Pipeline,the process how the design was evolvedand the reasons and the philosophy behind them,and experiences and lessons learned from theAlyeska project.