Centrifuge Model Test On Lime-Modified Expansive Soil Roadbed Under Wetting-Drying Cycles

Taking the lime-modified expansive soil roadbed of Nanning high-speed railway motor cars as research subject, this thesis researches engineering mechanical properties of lime-modified expansive soil roadbed through three wetting and drying cycles test by the geotechnical centrifuge model test technique. The main research contents and results are as follows:Based on the similarity principle, fluid mass continuity law and heat conduction equation, the evaporation similar principle of centrifuge model test is feasible. It can be used to control the heating time in the centrifuge model test.In order to achieve the artificial rainfall and evaporation uniformly during centrifuge operation, the rainfall device and heating device are designed. Through the calibration test of the rainfall device, the uniform coefficient of rainfall is 84.8%, and the rainfall intensity is 0.7mm/min. The evaporation intensity is 0.13mm/min by the calibration test of the heating device.After three wetting-drying cycles test, there are only a few little cracks on the slope surface, and the deformation of the slope is very slight. But the slope stability is not affected.In the model test, the soil pressure, the suction, moisture content and temperature of the roadbed are monitored. Monitoring results are as follows:(1) The soil pressure changes with the variation of moisture content. The curves between soil pressure and moisture content during wetting process and drying process are not coincident. It shows that the variation of soil pressure equals to the sum of variation of self-weight of soil and variation of its expansive pressure, and both of the latter are induced by the change of moisture content.(2) From the monitoring result of the suction, we could get some insights that soil-water characteristic curve of soil was unstable and related to the variation of soil moisture.(3) The moisture-depths curves show that the closer monitoring points to the roadbed surface, the greater the change range of the moisture content. The rainwater permeating into the soil slope at the rainfall stage can’t evaporate completely at the evaporation stage. Therefore the moisture content has increased after three times heating evaporation.(4) From the temperature-time curves, we could obtain that the temperature changes large in heating phase, but the rainfall impact small on temperature.