Study On Unsaturated Characteristics Of Expansive Soil Improved By Lime And Its Application

Unsaturated soils are widely distributed in nature,it is a three-phase soil mixed with solid,liquid and gas,which differs from saturated soil.Due to the existence of gas phase,the properties of unsaturated soils become more complex.Most of the soils encountered in geotechnical engineering are unsaturated soils.In the past,saturated soil theory was often used to solve the problems of expansive soil subgrade,slope and other issues,which caused some accidents,most of the reasons for not taking into account factors such as suction in unsaturated soils.With the economic development,the problem of unsaturated soil engineering is increasing day by day.The mechanical properties and engineering characteristics of unsaturated soil have become the focus of research.In the present paper,the typical Hefei unsaturated expansive soil was taken as the research object,and the indoor improvement experiment was carried out.The mechanical properties such as the strength of the lime-dusted soil under the action of suction were studied.The effects of grading rate,water content,and age on the improvement of expansive soil were discussed.At the same time,the experimental results were also analyzed with the theory of unsaturated soil,and some meaningful results are obtained.(1)Conventional indoor tests,free-expansion tests,scanning electron microscopy tests and soil-water characteristic curves of soils with different mixing ratios were carried out on Hefei expansive soils.Through the test results obtained:Hefei area expansive soil intake pressure value;With the continuous increase of the mixing rate of soils,the suction of soil samples with the same water content is also increasing.(2)The triaxial test of modified soil with different mixing ratio of ash was carried out by using triaxial apparatus,and the mechanical properties of improved soil under different normal stresses and confining pressures were discussed.Through the test results obtained:the law of the three factors that affect soil strength;The optimum proportion of lime content in Hefei area.It was found that the strength of soil increased first and then decreased with the increase of water content,and the soil moisture increased greatly when the water content was greater than the optimum water content obtained from laboratory compaction test.With the extension of the curing age,the soil strength increases with the growth rate changing from fast to slow.(3)The unsaturated direct shear tests on plain soil and different proportion of mixed lime soil are carried out by using the soil free shear tester.The results show that with the increase of net normal stress,the peak of shear stress increases linearly while in the high suction section,the peak value of shear stress of soil sample increases nonlinearly.The changes of matrix suction and ash mixing rate can greatly improve the soil strength.The existence of matrix suction greatly contributes to the improvement of soil strength.Besides,a fitting formula for the relationship among the matrix suction,cohesive force of the soil and lime soil is obtained.When the suction value exceeds the air entry value,the value of?~b decreases with the increase of suction.(4)Taking a typical subgrade slope model as an example,the slope stability analysis by Flac3D software is carried out to verify the test results.At the same time,the influence of the matrix suction and the mixing ratio on the slope stability is discussed.