Three-stage consolidation characteristics of highly organic peaty soil

Previous studies fail to provide consistent information on the division method of consolidation process of peat soil. Some scholars think that the consolidation process of peat soil is the same as that of common clay, which is two-stage consolidation. Some scholars also propose that the consolidation process of peat soil is three-stage or four-stage consolidation. In order to describe the consolidation process of peat soil accurately, this paper focuses on the peaty soil with high organic content in Dali, Yunnan Province, China. The unidirectional consolidation tests and consolidation- permeability tests were conducted. At the same time, water content, loss on ignition (LOI), and total nitrogen (TN) were measured at different time during the consolidation process. The results show that the consolidation process of peaty soil in Dali area of Yunnan Province should be divided into three stages. A method for dividing the three-stage consolidation process is proposed in this paper. The relationship between the consolidation completion time of the peaty soil at each stage and the load level is exponential function. When the load is greater than 50 kPa, the proportion of consolidation deformation of peaty soil at each stage under different load does not change with the load level. The results of water content, LOI, and TN content showed that deformation during primary and secondary consolidation stages was mainly caused by drainage, accounting for 99.67% and 98.39% respectively. The deformation during the tertiary consolidation stage was due to drainage and organic matter decomposition. Through the analysis of the relationship between deformation and permeability coefficient, the influence of permeability on the consolidation process of highly organic peaty soil mainly occurs in the primary and secondary consolidation stage, and has little effect on the tertiary consolidation process.