Study On Consolidation Mechanism Of Peat Soil In Yunnan Province

Yunnan province is an important area connecting China and Southeast Asian countries.However,the settlement of peat soil foundation of some local railways and highways are large and need a long time to reach stability.The bad engineering properties of peat soil affect the construction and use of traffic infrastructure seriously,and bring a bad impact on economic development.Researchers around the world have carried out lots of research on the consolidation characteristics of peat soil.However,due to the complex composition of peat soil,the consolidation characteristics are affected by many factors,such as the content of organic matter and the degree of decomposition.There is still a lack of unified understanding of the consolidation mechanism of peat soil.Therefore,based on the National Natural Science Foundation Project"consolidation mechanism and settlement calculation method of peat soil foundation under embank-ment",the organic matter composition and micro morphology of undisturbed peat soil in some areas of Yunnan Province were observed and one-dimensional consolidation experiment was carried out.Through the comprehensive analysis of the above experimental results,the main conclusions are as follows:(1)With similar loss on ignition,the higher the fiber content the soil samples con-tain,the lower the humic acid content the soil samples contain,and the better the shape of plant residues is.That means lower degree of decomposition of the plant residue.By comparing the results of SEM and EDS measurements of alkali solution boiling treatment and undisturbed mineral particles,it can be seen that humic acid and other high molecular organic matter exist in the form of adsorption on mineral particles or plant residues.(2)With the increase of loss on ignition,the plant residues in soil samples gradually develop from the state of"inlaying"in mineral particles to the state of being wrapped by mineral particles,and finally appear the state of plant residues aggregate;However,the mineral particles in the soil gradually develop from the flat plate-shaped face-to-face contact state to the micro aggregate state wrapped by humic acid and other polymers,and form a loose"spongy"porous structure;(3)There are three typical pore structures in peat soil:(1)pores between mineral particles which wrapped by high molecular organic matter such as humic acid;(2)pores in plant debris;(3)pores between plant residues.The results show that the area of pores between mineral particles in the soil samples with higher humic acid content accounts for a larger proportion of the area of SEM image,while the area of pores in and between plant residues in the soil samples with higher fiber content accounts for a larger proportion of the area of SEM image.(4)Compared with the pores between mineral particles that coated by humic acid,the pores in and between plant residues are the main factors leading to the large amount of consolidation and long time for reaching the stable state of consolidation of peat soil;Under the same load,the pores between plant residues is compressed more obviously than the internal pores of plant residual in the main consolidation stage,while the internal pores of plant residual is compressed more obviously in the secondary consolidation stage;The pores that between plant residues will be compressed obviously between the load of100～200 k Pa,which resulting in the decrease of C_v and the increase of C_α.(5)Through the observation of micro morphology,it is considered that the separation of plant residues and the wrap of high molecular organic matter such as humic acid are the reasons for the weak structure of peat soil.