Experimental Study On Unsaturated Drainage And Reinforcement Of Loess Subgrade By Fly Ash-lime Pile Combined With Electro-osmosis

The increase of subgrade humidity will affect the performance of subgrade and increase the probability of subgrade damage.Unsaturated loess roadbed will produce additional deformation due to humidification,which will reduce the strength of the roadbed.The additional deformation of the loess roadbed in operation will seriously affect the safe operation of roads and railways due to humidity.Traditional dewatering treatment of subgrade drainage such as replacement and heavy hammering are the treatment of collapsible loess roadbed before construction.After the construction is completed,the treatment of the roadbed will affect the operation efficiency of the road and railway.Fly ash-lime pile and electro-osmosis methods are common methods for roadbed treatment.Among them,fly ash-lime pile are widely used in the treatment of collapsible loess roadbeds due to water absorption and swelling as well as compaction characteristics.The electro-osmosis method is mostly used for the drainage of satu-rated soft soil,such as muddy soil.In this paper,the technology of unsaturated drain-age with fly ash-lime pile combined with electro-osmosis is proposed.By combining the settings,the fly ash-lime pile with the characteristics of water absorption and compaction can be used to enhance the drainage performance and the in-situ drainage reinforcement of unsaturated loess roadbed.The self-designed test system was used to conduct indoor model tests.By the means of profile sampling,the water content test,ion chromatography test and shear strength test were carried out to explore the spatial variation laws of water content,ion and soil strength during the drainage process.The EDS test was uesd to study the changes of soil microstructure and chemical composition during the drainage process.The main research and conclusions are as follows:?1?The method of fly ash-lime pile combined with electro-osmosis promotes the moisture in the subgrade to move to the cathode,and the moisture content of the soil near the anode in the middle layer of the model decreases by 25%at most.?2?The fly ash-lime pile combined with electro-osmosis method makes the ions move in the soil,and the anions in the soil move to the anode.The cations combine with the water in the soil to form ionized water and move to the cathode.Ion ex-change increases the Ca²⁺content in the soil,which can increase the strength of the soil.?3?The fly ash-lime pile combined with electro-osmosis significantly improves the strength of the subgrade soil.The cohesion is increased by 50-110%,and the in-ternal friction angle is increased by 8-20%.?4?The ion exchange between the fly ash-lime pile and the soil generates a floc-culent gelled substance,and the diffusion radius of calcium ion and aluminum ion is 3times of the pile diameter.