Study On Soil Swelling And Shrinkage Characteristics And Improvement Of The Site Of The Ancient City Of CAI

There is a lot of soil sites in the central plains,Zhumadian CAI ancient sites is one of them.CAI city is located in zhumadian shangcai county area,is the western zhou dynasty to the spring and autumn period in the history of a city,the soil in zhumadian is mostly expansive soil.Expansive soil due to contain hydrophilic minerals such as montmorillonite,illite,it has the characteristics of shrinkage due to water loss and expansion due to water absorption,expansion of soil deformation,shrinkage deformation and drying shrinkage cracks,so the stability and bearing capacity of soil is reduced,which may make the soil landslide,collapse,surface spalling damage;In addition,soil sites in the natural environment will also be subject to freeze-thaw,acid and alkali erosion and other natural disasters,these diseases are very adverse to the repair and protection of soil sites.In this paper,the soil of the ancient city of CAI was taken as the research object,and a series of tests were conducted to explore the methods to improve the characteristics of soil swelling and shrinkage deformation,dry shrinkage crack and water absorption at the expansive site.The conclusions are as follows:1.In order to study the development law of the dry shrinkage crack in the site and improve it,the dry shrinkage crack test was carried out.Experimental study on the particle size,thickness,dry-wet circulation these three factors of site soil drying shrinkage crack law of development.MATLAB was used to carry out binarization processing on soil drying shrinkage crack images to obtain the crack rate and draw the curve of crack rate changing with time for quantitative analysis of drying shrinkage crack.Dry shrinkage crack was improved by adding calcium ash powder and water-proofing agent.The experimental results show that the moisture content of the expansive soil with small particle size decreases faster than that of the expansive soil with large particle size,and the fracture rate increases faster than that of the expansive soil with large particle size.The thicker the soil sample is,the wider the crack width will be.With the increase of the number of dry and wet cycles,the surface crack rate increased gradually.The dry shrinkage crack rate,water resistance and water loss of expansive soil were improved obviously.2.In order to study the law of the dry shrinkage deformation of the site soil under different initial conditions and improve the dry shrinkage deformation,the dry shrinkage deformation test of the site soil was carried out with the soil shrinkage tester,the vertical deformation and moisture content changes were measured,and the curve of linear shrinkage and moisture content changes with time was drawn.By adding different ratio of the improved material to improvement of drying shrinkage deformation,and the water absorption test to explore to improve materials on the improvement of the site soil water imbibition.According to the test results,a kind of improved material ratio with the best effect on dry shrinkage deformation and water absorption of soil sample was determined.The results show that the dry shrinkage deformation increases with the initial moisture content with the same dry density.With the same initial moisture content,the dry shrinkage deformation decreases with the increase of initial dry density.With the addition of modified calcium grey powder and water-proofing agent,the dry shrinkage deformation decreased with the increase of calcium grey powder content and decreased with the increase of water-proofing agent content.Both calcium ash powder and water repellent can effectively improve the water absorption of the site soil.In order to improve the dry shrinkage deformation and water absorption of the site,the best content of the improved material is 5% calcium ash powder and 5% water-proofing agent,the final linear shrinkage rate and the final water absorption rate of the improved soil were 1.7% and 6.03% respectively,the final linear shrinkage of unimproved soil is 7.35% and the final water absorption is 29.2%.It can be seen that the improved material can significantly improve the dry shrinkage deformation and water absorption of the site soil.3.In order to study the expansion and deformation law of unimproved soil and improved soil,the expansion and deformation test of site soil was carried out with soil dilatometer.The vertical expansion and deformation of soil samples under different initial conditions were measured,and the curve of linear expansion rate with time was drawn.The results show that the higher the initial moisture content,the slower the expansion and deformation rate,and the smaller the final expansion and deformation.The higher the initial dry density,the slower the expansion and deformation rate,and the smaller the final expansion and deformation.Adding calcium ash powder and waterproofing agent to improve the material can significantly reduce the site soil swelling deformation,the final expansion rate of improved soil is 0.3% and that of unimproved soil is 3.25%.4.In order to explore the influence of the improved materials on the mechanical properties and durability of the site soil,the direct shear test,freeze-thaw cycle test and acid and alkali resistance test were carried out.In the test,the shear strength index and compressive strength of the improved soil and the plain soil were obtained.Unimproved soil cohesive force and friction Angle of 15.69 kPa and 3.5°,respectively,improved soil cohesive force and friction Angle of 88.11 kPa、25.85°respectively.After the freeze-thaw cycle,the shear strength index of both the improved soil and the unimproved soil decreased,after 3 times of freeze-thaw cycle of unimproved soil cohesive force and friction Angle of 12.02 kPa、2°,respectively,cohesive force and friction Angle of improved soil was 55.59 kPa、24.1°,respectively,but the improved soil still maintained high cohesion and friction Angle.After soaking in acid and alkali solution,the plain soil sample obviously does not have strength,while the improved soil can still keep its appearance intact.Then the compressive strength was tested.The compressive strength of the improved soil slightly decreased after soaking in acid and alkali,but it was still higher than that of the plain soil sample.The compressive strength of the improved plain soil and the improved soil were 3.31 MPa and 4.83 MPa,respectively.The compressive strength of the improved soil after acid and alkali erosion was 4.48 MPa and 4.55 MPa,respectively.It can be seen that the improved soil sample also has good acid and alkali corrosion resistance.