【作者】 王琳；

【导师】 吴建政；

【作者基本信息】 中国海洋大学 ， 海洋地质， 2007， 硕士

【摘要】 2l世纪是“海洋开发的时代”,随着社会的发展与进步,人类将工程建设的中心转移到了海洋。浅海石油的勘探开发,通讯电(光)缆、油气管线的铺设等项目都要求对工程场址或路由进行细致的地质灾害研究,预防可能发生的各种海洋灾害。乐东22-1/15-1预定路由管线位于北部湾南部陆架,该区油气资源丰富,海上平台、海底管线数量众多,许多学者都对该区的地质灾害进行过大量的研究工作,但将各种灾害性地质现象同海底管道稳定性结合起来的研究较少。本文在各种工程报告、论文、资料的基础上,分析预定管线路由区的工程环境和底质特征,研究了可能影响管线稳定性的不良的工程地质现象,包括活动性沙波,海底滑坡等,同时对海底管线铺设后可能发生的管线冲刷和悬跨问题进行了预测。本文的研究内容对未来海底管道的规划和施工具有一定的指导意义。按照地形地貌、底质和沉积环境特征将研究区由陆向海方向依次划分为近岸平坦区,中部强冲刷剥蚀区和平台平坦区。在中部强冲刷剥蚀区,距岸12km-15km的区域广泛分布大型沙丘和小型沙波,前期调查报告定义该区为沙波区,由测年资料可知该区大型沙丘为残留地貌,形成时代大约在距今8000年;距岸40km-42km和68km-75km两处区域发育走向大致垂直于管线的硬脊,前期调查报告定义该区为硬质海底区,由测年资料可知其为晚更新世河湖沉积粘性土在第四纪海侵过程中的侵蚀残余。沙波区和硬质海底区地形变化复杂,为不良的工程地质区域。硬质海底区由于分布规模较小,管线可考虑在底形平稳处绕过该区,但沙波区分布规模较大,管线无法避让,因此沙波区是本文研究的重点区域。由沙波区沙波的形态和浅部地层特征分析可知,该区沙波活动性较强。在常态条件下,研究区以小型沙波的迁移为主,迁移速率较慢,约为0.2m/a,对海底管线影响不大。在台风等极端气候影响下,中小型沙波移动速率骤增,最大可达1m/h～5m/h;大型沙丘表面松散砂层(活动层)的移动性增强,在活动砂体发生迁移的部位则可能出现冲蚀凹坑或沟槽,通过计算与类比研究表明,沙波区底床冲刷深度约为0.4m,在台风等极端气候影响下可达1.0m。小型沙波的快速移动与冲蚀凹坑的出现都可能产生管线悬跨,威胁管线安全。海底冲刷与沙波移动造成的海底管线悬跨长度在15m～40m之间,在沙波区预定路由的少数区段大于海管容许悬跨值,海管可能发生位置错动、破裂、折断的危险。特别在极端天气影响下,这种危险性增大。为了管线安全,设计路由最好选在沙丘背水坡侧沟槽内穿过,且铺设过程中加大挖沟深度。研究表明在研究区斜坡带(距岸10km-12km)海底土体比较稳定,但不排除在地震或极端气候影响下发生滑坡的可能。更多还原

【Abstract】 The 21 century is the most development time of the exploitation of the ocean. The focus of the construct has been transferred on the ocean, going with the development and advancement of the society. More and more project in the ocean to be explored need research on the engineering geology and hazardous geology environments, in order to prevent all kinds of the ocean hazards.The proposed pipeline of the LD22-1/15-1 lies on the shelf in the Beibu Gulf. In the Yinggehai, oil and gas resource development area were made. Many scholars have carried through lots of the scientific research in this area. But the research is lack, which combine the hazardous geology with the stability of the pipeline. Based on lots of engineering reports paper and data, according to dynamic condition and sediment characteristics, the influencing factors such as transferred sand waves, submarine landslide, burial channel and shallow gas, are discussed in the paper. At the same time, the forecast is made about the erosion and suspended span of the pipeline. The research contents and conclusions in the paper are important to the programming and construction of future pipeline.Based on the side scan sonar records, the Export Pipeline route could be divided into three sections, from land to sea they are offshore flat section; eroded section of the middle route; flat section near platform. In the second section, the area which is 12km-15km off shore is called sand wave zone, where sand dunes and sand waves are bestrewed. The area which is 40km-42km and 68km-75km off shore is called hard seabed zone, where stiff ridges are bestrewed. According to the age dating, the stiff ridges are remnant of the clay soil with river facies which deposit in the Late Pleistocene epoch. The landform is complex on the sand wave and hard seabed zone, which is bad engineering. The pipeline will traverse the hard seabed zone because it is a small area, and the pipeline can’t traverse the sand wave zone because the dimension is lager. So the emphases are made on the sand wave zone.Basis on the configuration and the shallow stratum layer character, the conclusion which the activity of the sand waves is intensive is made. In the usual state, the motion of the little sand wave is dominated, and the migration rate is about 0.2m/a. In typhoon state, the motion of the loose sand is strengthen, and the movement speed increased fast, which will be from 1m/h to 5m/h. the movement of the loose sand will induce the form of the erosion rut and trough. The rut and trough ,and also the transferred sand waves will induce the suspended span of the pipeline. By calculating with the equation and analogy analysis, the depth of the erosion is about 0.4m, and will be 1.0m when the bad weather influences the area. the length of the suspended span will be 15m～35m, that less than the length which the pipeline can endure . In order to recede the influence of the bad weather, the suggested pipeline routing needs to choose the sand dune trench, on the other hand it is suitable to choose the steep slope side in the sand dune. The deeper the trench is the higher safety of the pipeline. As long as the depth of the trench is less than the height of the sand wave, it will not be able to produce the pipeline free span in the near future.In study area which is 10km-12km off shore, There is deposited loose-saturated mucilage fine sand in the steep slope belt it also exist the possibility of the landslide of unconsolidated sediment. The investigation reveals that the soil body is stability, but we can’t eliminate the possibility of the submarine landslide. In addition, the burial channels and shallow gases distribute near the platform area, which may affect the stability of pipeline. Sediments infill within burial channel is clay-silt-fine sand while that around channel is stiff clay, differential settlement may happen because of the different engineering properties between the sediments in and around the channels. Because the depth of burial is deeper, they can’t influence the pipeline in the near future. But the series-detection should be made in the area where the burial channels and shallow gases distribute in coincidence.更多还原