Effect of organic matter content on physical-mechanicalproperties of sea soft soil
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摘要:
有机质是海相软土的重要组成部分，其对土体物理力学性质的影响有待深入研究。以连云港地区全新世海相软土为例，进行百组土体有机质物理力学试验。结果表明，研究区软土有机质含量平均值为0.98%，在0.90%~1.00%这个区间分布最为广泛。有机质含量在空间上分布不均，平行海岸线较垂直海岸线土体有机质含量变化小，自上向下变化规律复杂，但随着深度的增加有机质含量有增加的趋势；有机质含量与土体天然含水率、塑限、液限在0.01水平上显著正相关，与土体天然密度、干密度和比重在0.01水平上显著负相关，与土体粉粒含量在0.05水平上显著正相关，与土体黏粒含量相关性差；有机质含量与固结压力≤400 kPa阶段的孔隙比在0.01水平上显著正相关，与固结压力>400 kPa时的孔隙比相关性变差，这与有机质形成的复合体被破坏有关；海相软土黏土矿物、含盐量及含水率高，有机质与黏土矿物在碱性环境多通过阳离子键桥的方式来结合，形成有机复合体，可能参与千年及万年尺度的碳循环；研究土层最大埋深达30 m，符合有机质深埋的演化规律，而研究土体沉积时间距今最高才约8000 a，推测研究土体有机质还未达到平衡状态，还在进一步的循环演化过程当中。上述相关研究成果对海相软土分布区工程建设具有一定的参考价值。
Abstract:Soil organic matter (SOM) is an important part of marine soft soil, and its role in the physico-mechanical properties of the soil needs to be studied urgently. The Holocene marine soft soil in the Lianyungang area is taken as an example, and a hundred groups of SOM tests and physico-mechanical tests are carried out. The results show that the average SOM content is 0.98% in the study area. The SOM content is most widely distributed in the interval of 0.90%−1.00%. The SOM content is unevenly distributed in space. The SOM content of the parallel coastline has a smaller change than that of the vertical coastline. The top-down change rule is complicated, but the overall trend of the SOM content increases with the increasing depth. SOM content is significantly positively correlated with natural moisture content, plastic limit and liquid limit at the level of 0.01. The SOM content has a significant negative correlation with the natural density, dry density and specific gravity in the soil at the level of 0.01. The SOM content and the powder content in the soil are significantly positively correlated at the 0.05 level. The SOM content are poorly correlated with clay content. The SOM content is significantly positively correlated with the void ratio at the stage when the consolidation pressure is less than or equal to 400 kPa at the level of 0.01. The correlation between the void ratio and the SOM content becomes worse when the consolidation pressure is greater than 400 kPa, which is related to the destruction of the complex formed by the SOM content. Marine soft clay minerals have high salinity and water content. SOM and clay minerals are mostly combined through cationic bond bridges in alkaline environments to form organic complexes, which may participate in the millennium and 10 000-year scale carbon cycle. The maximum buried depth of the studied soil is 30 m, which is in line with the evolution law of deep burial of SOM. The maximum deposition time of the studied soil is only about 8 000 years. It is speculated that the SOM has not reached the equilibrium state in the study area, and it is still in the process of further cyclic evolution. The relevant research results of this study are of certain reference value for the engineering construction in the marine soft soil distribution areas.
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Key words:
- organic matter /
- humus /
- sedimentary age /
- physical mechanics /
- carbon cycle
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表 1 软土的物理力学特性
Table 1. Physico-mechanical properties of soft clay
项目 有机质
含量/%粉粒
含量/%黏粒
含量/%天然密度
/（g·cm−3）天然含
水率/%天然
孔隙比液限/% 塑性
指数/%液性
指数/%压缩系数
/MPa−1压缩
模量/MPacUU
/MPaφUU
/（°）最大值 1.56 68.7 51.1 1.93 74.9 1.98 56.10 26.60 5.18 2.51 4.10 17.00 2.90 最小值 0.36 45.2 31.1 1.56 30.9 1.00 22.80 10.00 1.00 0.50 1.10 2.00 0.30 平均值 0.98 58.8 39.5 1.70 54.0 1.42 43.54 19.33 1.58 1.28 2.00 7.23 0.87 个数 153 48 48 141 141 141 141 141 141 97 97 31 31 变异系数 0.22 0.09 0.12 0.04 0.16 0.15 0.13 0.18 0.33 0.30 0.26 0.50 0.63 偏度 −0.34 −0.76 0.78 0.73 −0.18 −0.12 −0.25 −0.58 2.98 0.40 1.52 0.88 2.11 峰度 0.84 0.46 0.57 0.24 0.54 0.21 0.67 1.14 16.68 0.34 3.59 0.57 5.56 注：cUU为三轴UU试验得出的黏聚强度； φUU为三轴UU试验得出的内摩擦角。 
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表 2 有机质含量与土体物理指标相关性统计表
Table 2. Correlation statistics of SOM content and soil physical indicators
指标 深度 粉粒含量 黏粒含量 砂粒含量 天然含水率 比重 湿密度 干密度 孔隙比 液限 液限 塑性指数 液性指数 相关性 0.476** 0.342* −0.013 −0.325* 0.604** −0.526** −0.630** −0.626** 0.596** 0.349** 0.425** 0.252* 0.255* 样本数 89 48 48 48 74 74 74 74 74 74 74 74 74 注：**表示在0.01水平（双侧）上显著相关；*表示在0.05水平（双侧）上显著相关。负值表示负相关，反之亦然。
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表 3 有机质含量与土体不同固结压力下孔隙比的相关性
Table 3. Correlation between SOM content and soil void ratio under various pressures
指标 e12.5 e25 e50 e75 e100 e200 e400 e800 e1600 e3200 压缩
系数压缩
模量相关性 0.257 0.606** 0.609** 0.592** 0.595** 0.563** 0.483** 0.311* −0.062 −0.239 0.598** −0.604** 样本数 13 41 74 41 74 74 74 60 41 17 41 74 注：e12.5为固结压力12.5 kPa下的孔隙比，其它依次类推；**表示在0.01水平（双侧）上显著相关；*表示在0.05水平（双侧）上显著相关。负值表示负相关，反之亦然
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