Experimental Study On Overall Carbonization And Solidification Process Of Soft Foundation

Due to the great potential of magnesium oxide in the field of engineering construction,a series of studies on the magnesium carbide carbonization method have been carried out,which proves that it is highly effective and environmentally friendly as a curing agent.The existing researches are mainly focused on sand and silt,but less on soft soils In addition,the existing research methods are mainly laboratory tests or model tests,but few is in-situ application test on the overall carbonization of the soft foundation.Supported by National Natural Science Fund Project(51279032,41330641)and Science and Technology Projects of Jiangsu Provincial Department of Communications(2018T01),and based on the research of the Geotechnical Engineering Institute of Southeast University,this study combined with the methods of laboratory tests,field tests and theoretical analysis to explore the construction technology and mechanism of carbonization.The main contents and conclusions were drawn as follows:(1)The effects of MgO and soil parameters on carbonization were determined by unconfined compressive strength test and overall carbonization model experiment.It is found that when the MgO content is 70%,and the dosage is 15%,the mucky soil can obtain a significant carbonization effect,and when the carbonization process is carried out,the soil moisture content should not exceed 40%.Under these conditions,the carbonized reinforced mucky soil has a bearing capacity up to 300 kPa,and its compressibility is significantly improved.(2)According to the parameters obtained from the indoor tests,the on-site single-point and overall tests were carried out.The parameters were improved and a set of magnesium oxide integrated carbonized solidified soil foundation construction process including pretreatment,magnesium oxide stirring,venting ventilation system,and carbonization was formed.Finally,some factors that may affect the carbonization effect during the construction process were analyzed,and suggestions for future improvement were proposed.(3)Effect evaluation and carbonization mechanism analysis of the soil after solidification were carried out by in-situ test and laboratory test.In-situ testing uses a combination of light dynamic penetration and dynamic rebound modulus tests.The results show that most of the regions can reach or approach the expected intensity in the short term.After the supplementary carbonization,the bearing capacity of all regions is above 140 kPa and the modulus of resilience is about 20 MPa.The physical and chemical indexes and shear strength changes of soils before and after carbonization were tested by laboratory tests.The mechanism of mucky soil carbonization was analyzed by SEM scanning electron microscopy and the reason for the change of soil properties is attributed to the filling,wrapping and cementation of carbonized products on soil particles.