Experimental Study On Expansibility Of Expansive Soil Along Nanning To Baise Railway By Considering Its Structure Characteristics

The expansive soil acting on the treatment project will affect the engineering structure's stress and even lead to the failure of the project.However,there is no mature expansion force calculation method in design engineering practice.It is one of the reasons that the failure to consider the structure of soil in laboratory measurement of expansive force,especially the expansibility difference and distribution between the soil mass.This paper rely on the slope treatment project along the NBSG-5 segment of additional construction of second line project in Nanning Kunming railway from Nanning to Baise section,on the basis of field investigation and laboratory tests,different expansive soil masses are selected to make samples according to the structure characteristics of the expansive soil on the site slope,and the expansion force laboratory tests is carried out to explore the influence of the structure on the expansibility of expansive soil.The main research results are as follows:1)The research results of expansive test both at home and abroad are summarized.It is pointed out that the previous expansive force test has not considered the structure of expansive soil slope well.2)The relationship between physical and chemical properties and water-physical properties of expansive soil and material composition of expansive soil is expounded.The soil samples were scanned by X diffractometer and the corresponding qualitative analysis and quantitative analysis were obtained.The microstructure of soil samples was observed and analyzed by scanning electron microscope.The gradation parameters and grain diameters is obtained by laboratory particle analysis test.3)The water-physical and mechanical properties of expansive soil are studied through laboratory geotechnical tests,including free expansion rate,load free expansion and expansion force.The expansion potential of expansive soil under different structures,the time history curves of expansion deformation and expansive force after water expansion are analyzed and studied.Fracture statistics of soil samples taken back from the site and the development degree of the local expansive soil fissure is obtained.4)The mineral composition and physical index of K178+847 slope samples are measured through laboratory tests.Different specimens are made according to the structurecharacteristics of the soil slope,and the laboratory expansion test is carried out.The relationship between the structure of expansive soil and the expansion force is analyzed.