Design Of Low Temperature Triaxial Testing Machine And Experimental Study On Cyclic Freeze-thaw On The Mechanical Properties Of Silty Caly

It has become a important subject investigated that freeze-thaw cyclic is a kind of weathering process which considerably changes geotechnical properties of soils due to cryogenic actions. Therefore, the effects of freeze-thaw cyclic on the mechanical properties of soil must be taken into account when selecting soil parameters for stability and deformation analysis of many geotechnical engineering problems in cold area. For the lack of study on the effect of freeze-thaw on the mechanical properties of soil, a low cost and high degree of accuracy low temperature triaxial testing machine was developed based on theory of thermal conduction in this paper . Then, a series of experimental study on cyclic freeze-thaw on the mechanical properties of Qinghai-Tibet silty caly were developed by make use of designed low temperature triaxial testing machine. The research work involves several aspects as follows:1. The research status quo of mechanics of frozen soil in foreign countries and homeland and the status quo of research of frozen soil's cyclic freeze-thaw are depicted in detail. The application exiting state of testing machine of freeze-thaw cyclic in soil mechanics laboratory is analyzed.2. A new idea in design of low temperature triaxial testing machine is put forward that is based on thermal theory and mechanics theory in this paper. The total cost of manufacture about the testing machine is less than ten thousand Yuan RMB.3. The developed testing machine was strict verified through a lot of frozen soil experimental. The result indicate that the precision of constant temperature system is 0.6℃,the time of complete frozen of test sample is less than thirty minutes, the temperature difference between upper and lower end face of test sample is less than 0.2℃.4. The freeze-thaw characteristics and the variation rules of their mechanical properties after freeze-thaw are studied considering two influencing factors, the different mechanics experimental mode and different frozen mode. Experiments disclosed the internal relations between test method and test result. 5. The variation rules of saturated soil's mechanical properties after freeze-thaw are analyzed in detail based on the experimental of a lot of triaxial tests. And on the basis of a lot of testing result, a test model of internal friction angle that can be used to describe the variation rules of internal friction angle as increase of cyclic freeze-thaw.6. The variation rules of pore water pressure in saturated soil's laboratory triaxial tests are studied considering two influencing factors, times of cyclic freeze-thaw and different confining pressure. On the basis of a lot of testing results, a test model about increase of pore water pressure in cyclic freezn-thaw is suggested. At last, a new method about variation rules of saturated soil's mechnical properties after freeze-thaw is suggested.