Effect of organic matter content on physical-mechanicalproperties of sea soft soil

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.