| 无明显压实的滨海相沉积孔隙度识别及其机理与意义 |
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| 引用本文： | 徐起浩.无明显压实的滨海相沉积孔隙度识别及其机理与意义[J].沉积学报,2018,36(6):1091-1104. |
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| 作者姓名： | 徐起浩 |
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| 作者单位： | 广东省地震局, 广州 510070 |
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| 基金项目： | 中国地震局2018年老专家科研基金（2018-05） |
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| 摘 要： | 通过建立沉积压实理论模式和由土体单元压缩前后体积、孔隙比、孔隙度变化的理论关系所导出的压实度与孔隙度关系式表明，沉积过程中下伏沉积压实度不发生变化时，上覆沉积孔隙度变化取决于初始沉积孔隙度，因沉积环境变化导致初始沉积孔隙度发生变化，造成沉积孔隙度与沉积深度不相关，出现下伏沉积孔隙度大于上覆沉积的情况。这是下伏沉积孔隙水不能排出，呈欠压实状态的表现。当无沉积外干扰因素，连续沉积过程中出现土柱下部孔隙度大于土柱上部时，土柱下部一定处于欠压实状态，这是识别滨海相沉积上覆沉积后未被再压实的重要标志。通过广东沿海8个工程场地58个钻孔191个土样相同钻孔相同命名土，及广东和国内其他有关地区不同场地共208个土样不同钻孔相同命名土孔隙度与分布深度比较，分析显示，大约40 m以内或晚更新世中晚期以来滨海相沉积在垂向和横向分布上普遍存在这种欠压实特征。提出沉积压实大致具随序发生的三个阶段:1）最表层的薄层在初始沉积孔隙度影响下的初始沉积压实阶段；2）欠压实阶段；3）再压实阶段。综合研究结果显示，滨海相沉积一般渗透性差，泄水环境不好，除沉积外因素导致再压实的局部相关沉积层外，近地表40 m以内或晚更新世中晚期以来的滨海相沉积压实下沉量不明显，在用滨海相沉积研究古海平面及海岸地壳运动时，一般情况可不考虑沉积压实影响。
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| 关 键 词： | 滨海相沉积 初始沉积孔隙度 初始沉积压实 压实度 欠压实 压实下沉 |
| 收稿时间： | 2017-03-31 |
Porosity Identification,Mechanism and Significance for Littoral Sediments without Obvious Compaction |
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| Institution: | Seismological Bureau of Guangdong Province, Guangzhou 510070, China |
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| Abstract: | The correlation between compaction degree and porosity derived from the theoretical model of sedimentary compaction and the variation of soil volume, pore ratio and porosity of soil units before and after compression shows that the variation of the porosity of overlying sediments depends on the initial sedimentary porosity when compaction degree of underlying sediments does not change during sedimentation. The change of sedimentary environment results in the change of initial sedimentary porosity, which is not related to buried depth, and the underlying sediment porosity is greater than that of the overlying deposits. This is the performance of the underlying-sediment pore water which cannot be discharged and the sediments are under-compacted. When the porosity of the lower part of the soil column is greater than that of the upper part of the soil column, the lower part of the soil column must be under-compacted without any external disturbance besides sedimentation, which is an important sign to identify the under-compacted littoral facies sediments after the overlying sediments is formed. Comparing the porosity and distribution depth of the same named soil in 58 boreholes and 191 soil samples from 8 engineering sites along the coast of Guangdong Province and 208 soil samples from different sites in Guangdong and other related areas in China, the analysis shows that the littoral deposits within about 40 m or sediments since the middle and late Pleistocene are under-compacted vertically and laterally. This kind of under-compaction is ubiquitous in horizontal distribution. Therefore, we proposed that sedimentary compaction generally has three stages in sequence:1) the initial sedimentary compaction stage of the thin layer in the most surface layer under the influence of initial sedimentary porosity; 2) under-compaction stage; 3) re-compaction stage. The results show that the littoral deposits generally have poor permeability and drainage environment. Apart from the local sediments which are re-compacted due to deposition process, the compaction subsidence of littoral deposits within 40 m near the surface or since the middle and Late Pleistocene is not obvious. Therefore, when you conduct the study on Paleo-Sea level and coastal crustal movement in littoral deposits, it is not necessary to take into account the impact of sediment compaction. |
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