Experimental Study On The Effect Of Organic Matter Content On The Physical And Mechanical Properties Of Clay

In the natural world,the organic matter content of soil has a relatively large range of change.The level of organic matter has a great influence on the physical and mechanical properties of the soil.The engineering properties of clayey soils with different organic matter contents will also be significantly different.As far as the current research is concerned,there is still a lack of in-depth and systematic understanding of the impact of a large range of organic matter content on clay soils.In addition,there are many technical specifications for classifying soils based on organic matter content at home and abroad,but there is no unified consensus between the various standards,and there is little analysis of the mechanism.This requires further analysis by experimental research.Therefore,the research on the influence of organic matter content on the physical and mechanical properties of cohesive soil has certain theoretical value and engineering significance.In this paper,a certain percentage of high-decomposition peat soil was added to inorganic clay minerals to prepare cohesive soils with different organic matter content.Using static consolidation sampling,a series of laboratory tests were conducted to study the effect of organic matter content on the physical prop erties and mechanical properties of clay soils.The main research work and results are as follows:（1）By testing the physical indexes of each clay soil,it can be seen that with the increase of organic matter content in the clay soil,the density and spec ific gravity decrease linearly,the moisture content of the clay soil increases,and the liquid and plastic limits of the clay sample increase to different degrees.The correlation between physical indexes and organic matter content is good.（2）According to the consolidation shear test,the stress-strain relationship of each soil sample is mainly strain hardening type.With the increase of organic matter content,the shear strength of soil samples decreased,and the difference between soil samples was more obvious.There was a positive correlation between cohesion and organic matter content,and a negative correlation between internal friction Angle and organic matter content.（3）Conventional consolidation test results show that the higher the organic matter content is,the greater the compression deformation of the soil sample will be,the compression coefficient a_1-2 and compression index C_c will increase,the compression modulus E_s will decrease,the t₉₀ of the soil sample will increase,and the consolidation coefficient C_v will decrease.With the increase of consolidation load,the consolidation coefficient C_v of soil sample decreases rapidly and then tends to be stable.The results of consolidation creep test showed that the secondary consolidation coefficient of each clay soil increased with the increase of organic matter content,and the t₉₀/t _P of some soil samples decreased.In addition,after long-term creep,some cohesive soils consolidated three times,which may be closely related to the influence of organic matter.According to the results of the permeability test with variable head,the permeability coefficient decreases with the increase of organic matter content,and decreases from 10^-6 to 10^-8.（4）The soil-water characteristic curve of each soil s ample was obtained by testing.The results showed that the content of organic matter had a great influence on the soil-water characteristic curve of cohesive soil.With the increase of the content of organic matter in the soil sample,the water-holding capacity of cohesive soil became stronger,and the intake value and residual value of the soil sample increased to different degrees.With the same organic matter content,the intake and residual values of the undisturbed soil sample were lower than those of t he remolded soil sample.The good fitting degree of SWCC model was followed by Van Genuchten model,Fredlund&Xing model and Gardner model.In addition,some clay soils with high organic matter content have strong water-holding capacity and their characteris tic values are higher than those of bentonite.