Research On In-situ Thermal Reinforcement Method Of Dispersive Soil

Dispersive soil is a type of water-sensitive soil that is often modified with lime and other soil solidification materials.However,for slope engineering,the complex construction process of modification treatment results in high modification costs and often fails to meet design requirements.Thermal reinforcement technology,a long-standing in-situ soil treatment technology,is often used for the treatment of weak or special foundations.Due to its high energy consumption characteristics,it has only recently been given renewed attention and has shown promising results in thermal remediation of contaminated soil and improving poor engineering properties such as soil collapse and expansion.This paper conducted a detailed analysis of the influence factors,construction parameters,action mechanism,and changes of engineering properties of dispersive soil after in-situ thermal reinforcement,based on the dispersion mechanism of dispersive soil,through tests such as dispersion discrimination,engineering mechanical property detection,soil heat transfer simulation,microstructure determination,and physical & chemical property determination.Subsequently,the feasibility of modifying dispersive soil by high temperature heating combined with in-situ grouting was explored based on the changes in soil properties under high temperature.The research conclusions are as follows:(1)Temperature,heating time,compaction degree,existing state of soil,clay content,and other factors have a significant impact on the effectiveness of thermal consolidation of dispersive soil.For compacted soil,as the heating temperature,heating time,and compaction degree increase,the dispersity of dispersive soil gradually decreases until it is eliminated.However,when the heating temperature is lower than 200℃,the weakening of soil dispersity is reversible.Above 200℃,the soil mass completely loses its dispersity and is irreversible.Compared to compacted soil,granular soil can only be modified by high temperatures.Affected by the plastic change of soil,the temperature range should be controlled between 200～400℃,and the critical modification temperature will increase with the decrease of clay content.Thermal reinforcement technology is no longer applicable when the clay content is less than 10%.(2)As the heating temperature increases,the shear strength,cohesion,and internal friction angle of the soil increase,while the anti-disintegration ability first decreases and then increases,and the disintegration curve gradually becomes flat.The permeability coefficient increases,the plastic limit increases,and the plasticity decreases.The failure mode of the soil mass changes to brittle failure.After vacuum saturation treatment,the shear strength parameters of the soil mass decrease significantly,but the overall trend remains unchanged.After high-temperature treatment above 200℃,the soil still exhibits relatively obvious brittle failure characteristics.(3)The heating efficiency of soil increases as the heat source temperature,heating time,and spacing between heat sources all increase.To meet modification temperature and energy consumption requirements,a 900℃ heat source should be used and arranged in a regular triangle pattern with a spacing of less than 0.4m.In addition,exploratory tests have shown that modifying dispersive soil through a combination of high temperature and a modifier is feasible.As the heating temperature,heating time,and modifier dosage increase,the range of complete improvement of the dispersive soil also expands.(4)After being treated at high temperature,the dispersive soil undergoes physical particle agglomeration and chemical melting bonding,which enhances the particle aggregation structure,improves the soil’s mechanical strength,reduces the amount of water-soluble ions dissolved,lowers the soil’s alkalinity,and decreases the thickness of the double electric layer.As a result,the gravitational force between soil particles becomes greater than the repulsive force,weakening or even eliminating dispersion.Simultaneously,the water loss and dry shrinkage of the soil mass increase the permeability coefficient,providing favorable conditions for the infiltration of modifiers.