【作者】 赵维霞；

【导师】 杨作升； 冯秀丽；

【作者基本信息】 中国海洋大学 ， 地球探测与信息技术， 2005， 硕士

【摘要】 埕岛海区地处黄河三角洲东北角,是海底地质灾害频发地带。这些地质灾害的存在直接威胁到海上工程设施的安全如海上钻井及采油平台、人工岛、输油管线等。在该区曾开展了大量浅地层地质灾害包括海底滑坡的调查研究,但是大多仅限于对某些重点区域有针对性的声学探测和实测资料的解释,而对于该区域的地质灾害分类及其分布、海底滑坡的定量分析我们还缺乏深入的认识。本文以埕岛海区海底斜坡为研究对象,收集了该区近20份井场调查资料,定性描述了研究区海底特征和地貌形态,在此基础上将本区浅地层地质灾害按水深进行分类,并对其成因进行了详细分析;同时根据研究区沉积物的力学性质、水动力条件等,采用GEO-SLOPE(加拿大GEO-SLOPE LTD)软件,对海底滑坡进行定量分析。 通过对井场调查资料分析发现:研究区水深16米以浅海底浅地层发育了大量地质灾害体,侵蚀残留岗丘、塌陷凹坑、滑坡块体、表层扰动体、古河道、古沼泽、古湖泊等。具体来讲,在2米等值线以浅,由于大量人工构筑物的出现导致近岸流场改变,塌陷凹坑发育;在5米等值线附近,由于潮流冲蚀较强,海底面形成了一系列走向和潮流平行的低缓的冲蚀沟槽,在周期性增水加载条件下,将导致滑坡发生;8.0～12.0米之间由于破波带内波浪能量的快速转换导致滑塌体、塌陷凹坑、侵蚀残留岗丘等地质灾害体以及古河道、古湖沼、古沼泽充填相地层的发育;12～16米区域浅层地质灾害主要为海底表层扰动体、古河道及古沼泽相地层。 对研究区沉积物力学性质的分析发现,该区地层分布在空间上不连续,高压缩性低强度的软弱土层普遍存在,受不均衡的压力作用在倾斜的海底层面上容易发生流动、变形,这是本区浅地层地质灾害的直接诱发因素,更重要的是它的存在是海底滑坡的基础。引起海底滑坡的内在因素包括软弱层抗剪强度、软弱层厚度;外因很复杂,包括静孔隙水压力、波浪、潮流水动力作用、地震、潮位变化引起的超孔隙水压力、浅层气等。采用GEO-SLOPE软件就研究区软弱层进行了海底斜坡稳定性的定量计算。针对软弱层抗剪强度变化、软弱层厚度、孔隙水压更多还原

【Abstract】 Chengdao area, northeast of Huanghe subaqueous delta is typically characterized by the geologic hazards , which will threaten the safety of the offshore engineering such as drilling well and drilling oil platform, man-made island and oil transporting pipelines. Many investigations were carried out in this area for the measurement of geologic hazards using the sonic equipment and the records were interpreted. However, the extensive understandings on the classification and distribution of the shallow geologic hazards are still needed, as well as the intrinsic and extrinsic factors responsible for the submarine landslides. Here the data of about 20 well sites in this area are collected and used to study the soil stratum and consequently to analyze the related geologic hazards. The regional seafloor morphologic features are studied qualitatively. The distribution of the shallow stratum geologic hazards is presented according to water depth. Based on the property of the sediment mechanics and the condition of the hydrodynamics, the submarine landslides were quantitatively analyzed facilitated by the Geo-Slope software (GEO-SLOPE International Ltd. Canada).In the Chengdao area many geologic hazards bodies are developed in the soil stratum with the water depth below 16 meters, such as relic dune, collapse pezograph, landslide block, crust disturbing body, palaeochannel, ancient swamp, fossil lake, et al. Bellow the 2-m isobaths, the collapse pezograph is dominant due to many man-made structures that significantly change the flow field in the coastal area. Around the 5-misobaths, owing to the bed scouring induced by stronger tidal currents, a series of mild erosional furrow were developed parallel to the major axes of the tidal currents. Under the circumstance of periodic setup loading the landslides will easily happen. Between 8-m and 12-m isobaths, due to the energy transferring to the seabed from the breaking waves in the surf zone, it develops some geologic hazards such as slip blocks, collapse pezographs, relic dunes and some filled facies stratum such as palaeochannel, ancient swamp and fossil lake. Between 12-m and 16-m isobaths, geologic hazards are mostly crust disturbing body, palaeochannel and fossil lake.The analysis of sediment mechanics properties suggests that the spatial distribution of stratum is discontinuous. The soft stratum with properties of high compressibility and low-intensity is generally detected in the study area that will flow and deform on the declining slope due to the unbalanced pressures. This is the direct triggering factor to the geologic hazards of the shallow stratum, and it is also the base of submarine landslides in this region. The intrinsic factors controlling the submarine landslides are the shearing strength and the thickness of the soft stratum. The extrinsic factors are including many other external conditions such as static pore-water pressure, the actions of wave and tidal current, the excess pore pressure induced by earthquake and the tidal fluctuation. The stability of the subaqueous slope is calculated quantitatively through analyzing the soft stratum using the GEO-SLOPE software. The degree of reliability is analyzed in contrast to soft stratum parametric variation, soft stratum thickness, pore-water pressure and the actions of wave and tidal current. The experimental results show that when the soft stratum shearing strength approaches its minimum, the submarine landslides will happen with failure possibility of 71. 02%; when the soft stratum shearing strength approaches its maximum,the probability for submarine landslides will decrease drastically, even it never happen. The results also indicate that the thickness of the soft stratum is another important factor influencing the submarine landslides. As the thickness increasing, the probability of the slope failure enhances. The critical value of the buckling is founded through analyzing the softstratum shearing strength index, that is c = 10.0、 φ =2.5.In this thesis the distribution of the geologic hazards in the Chengdao areas is comprehensively analyzed. The analysis shows that under the circumstance of different hydrodynamics the geologic hazards types are multiple. The submarine landslides are quantitatively analyzed for the first time using the GEO-SLOPE software and the related factors affecting the submarine landslides are discussed.This study extended the understanding on the shallow geologic hazards and the conclusions presented in this thesis are of importance to the offshore engineering and the route design of the oil transporting pipelines.更多还原