Microcosmic Mechanism And Mechanical Effect Of Swelling And Shrinking Of Expansive Soil In Handan

The expansive soil contains more hydrophilic clay minerals,so when it meets the water,the volume will expand and increase immediately;when the water is lost,it will shrink dry and crack immediately.It is a kind of high plastic clay.This property will greatly reduce the safety of the project.In this paper,the expansive soil in the northwest of Handan city is taken as the research object.In view of the micro mechanism and mechanical effect of expansion and shrinkage of the expansive soil,the expansion and shrinkage characteristics and mechanical effects of two layers expansive soil in the northwest of Handan are studied by consulting relevant data,a large number of laboratory tests and microscopic tests.The main contents and conclusions are as follows:Firstly,through X ray diffraction test,scanning electron microscope test and X ray fluorescence spectrum analysis,the mineral composition,microstructure and oxide content of expansive soil in Handan are obtained,and the expansion and shrinkage and mechanical effects of expansive soil are explained from the micro point of view.Secondly,the physical and mechanical properties of Handan expansive soil can be obtained accurately by the tests of water content,severe,pore ratio and liquid plastic limit of expansive soil,and the two indexes of free expansion rate and one dimensional load expansion rate under 50 kPa load are used to distinguish the expansion and contraction of the two layers expansive soil in the test area of Handan.Thirdly,by the expansion force test and direct shear test,the strength index of expansive soil(expansion force,internal friction angle and cohesive force)is obtained.The test results show that the expansive soil is very high in strength when drying,but once the water is encountered,it will expand rapidly and the strength will decrease rapidly.In addition,through scanning electron microscopy test to analyze the microscopic changes of direct shear,consolidation test of soil samples.Forth,The mechanism of swelling shrinkage and mechanical effect of expansive soil is explained reasonably from the perspective of microstructure.Through a large number of experimental research on expansive soil,it is not difficult to draw the following conclusions: from the microcosmic point of view,the clay minerals of the two layers of expansive soil in the northwest of Handan are mainly montmorillonite.The structural characteristics are mainly floc and granular stacking structure.The lamellar aggregates coexist with single grain.The microfracture is well-developed with obvious directionality and large void ratio.Macroscopically speaking,the expansibility of expansive soil in this area is not very strong.The first layer belongs to the weak expansive soil,and the second layer belongs to the moderately expansive soil.Based on these experimental results,this paper studies the significant swelling shrinkage and mechanical effects of expansive soil in the angle of the composition and structure characteristics of the clay minerals in the expansive soil in Handan.It is hoped that the results of this study will provide some new information for engineers and scientific workers engaged in the design and construction of expansive soil engineering in Handan,and extend and supplement the traditional principles and practices.