暴风浪作用下海底粉土液化研究

发布时间：2018-01-14 18:34

本文关键词：暴风浪作用下海底粉土液化研究　出处：《国家海洋局第一海洋研究所》2015年硕士论文　论文类型：学位论文

【摘要】：粉土广泛分布在我国各大河流入海口附近,具有易液化性。海底粉土液化容易引发海底电缆中断、海底管道失稳和平台、立管倾倒等事故,对海洋工程危害巨大。本文选择海底地质灾害频发的埕岛油田海域作为研究区,在前人调查研究工作的基础上对暴风浪作用下海底粉土液化开展研究工作。前人已调查发现此区域分布着大量的扰动土层,并分析证明波浪作用下海底粉土液化是其主要成因。本文在此基础上,总结分析了已有的研究区水动力、海底地形地貌及浅地层剖面等资料,搜集了研究区42个地质钻孔资料,并按照钻孔是否位于扰动土层内对其分别统计分析,采用瞬时液化评判方法计算了不同重现期波浪条件下的粉土瞬时液化深度,根据风生波浪要素及扰动土与非扰动土的土工试验参数,采用动三轴试验评判方法计算了扰动土与非扰动土残余液化深度,并对计算结果进行分析讨论。获得的主要认知如下:(1)扰动土层内部无明显层理或层理不清,沉积结构杂乱,与非扰动土层对比明显。相对于研究区的非扰动土,海底扰动土含水量、孔隙比、粘粒含量较小,容重、粉粒含量、中值粒径及标贯击数较大,分选较好,土的抗液化能力较强。(2)在50年重现期的波浪作用下,水深8m处海底粉土的瞬时液化极限深度为1.69m。在其他重现期波浪作用下,海底粉土的瞬时液化极限深度在水深7m附近达到最大值。瞬时液化极限深度总体趋势是在某一特定水深处达到液化深度的最大值。在该水深以浅,土体液化极限深度随水深增加而增大;在该水深以深,土体液化极限深度随水深增加而减小。(3)相同风浪作用下,扰动土的残余液化深度计算值比非扰动土小。7-10级风作用下,海底表层非扰动土出现液化;8级风以上时,海底表层扰动土出现液化。不同等级风作用下,最大残余液化出现深度不同。在暴风浪作用下(8级以上),最大残余液化深度出现在水深8m-9m处。在10级风作用下,水深8m处非扰动土的最大残余液化计算深度达到5.25m,这与物探解译得到的扰动层厚度相吻合。(4)海底粉土最大残余液化深度的计算结果在5m-13m水深处与地球物理探测结果基本一致,但在水深3m-4m以及14m以深海底粉土最大液化计算深度与实测资料有所不同。已有物探结果显示,3m-4m以及14m以深海底粉土未发现液化扰动层。这样的计算结果主要缘于水动力参数和土体参数的选取与实际不一致。
[Abstract]:Silt is widely distributed near the entrance of major rivers in China, which is easy to liquefaction. The liquefaction of subsea silt can easily lead to submarine cable disruption, submarine pipeline instability and platform, toppling of risers, and so on. This paper chooses the sea area of Chengdao Oilfield, which has frequent submarine geological disasters, as the research area. On the basis of previous investigation and research work on the liquefaction of silt under the action of storm wind and wave, it has been found that there are a large number of disturbed soil layers in this area. It is proved that the liquefaction of silt under the action of waves is the main cause of formation. Based on this, this paper summarizes and analyzes the existing data of hydrodynamic, submarine topography and shallow stratum profile in the study area. The data of 42 geological boreholes in the study area were collected and statistically analyzed according to whether the boreholes were located in the disturbed soil layer. The instantaneous liquefaction depth of silt was calculated by using the instantaneous liquefaction evaluation method under the wave conditions of different recurrence periods, according to the wind-induced wave elements and the geotechnical test parameters of disturbed soil and undisturbed soil. The residual liquefaction depth of disturbed and undisturbed soils was calculated by dynamic triaxial test. The main results obtained are as follows: 1) there is no obvious stratification or unclear stratification in disturbed soil layer, and the sedimentary structure is messy. Compared with the undisturbed soil layer, the water content, porosity ratio, clay content, bulk density, silt content, median particle size and standard penetration number of the disturbed soil in the study area are larger, and the separation is better than that of the undisturbed soil in the study area. Under the wave action of 50 years, the instantaneous liquefaction limit depth of the silt is 1.69 m at the depth of 8 m. The instantaneous liquefaction limit depth of subsea silt reaches the maximum near the water depth of 7 m. The general trend of the instantaneous liquefaction limit depth is to reach the maximum liquefaction depth in a specific water depth. The limit depth of soil liquefaction increases with the increase of water depth. Under the same wind and waves, the calculated residual liquefaction depth of disturbed soil is smaller than that of non-disturbed soil. There is liquefaction of undisturbed soil on the surface of seabed. The maximum residual liquefaction depth is different under the action of different grade wind, and the maximum residual liquefaction depth is higher than 8 grade under the action of storm wave. The maximum residual liquefaction depth appears at 8m-9m of water depth, and the maximum residual liquefaction depth of undisturbed soil reaches 5.25m under the action of 10-grade wind. This is consistent with the geophysical results obtained from geophysical interpretation of the maximum residual liquefaction depth of subsea silt in the depth of 5m-13m. But at the depth of 3m-4m and 14m, the calculated depth of maximum liquefaction of deep-sea silt is different from the measured data. No liquefaction disturbance layer was found in 3m-4m and 14m silt. The main reason for this calculation is that the selection of hydrodynamic parameters and soil parameters is inconsistent with the actual conditions.
【学位授予单位】：国家海洋局第一海洋研究所
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TU411;P75

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