Experimental Research On Rheological P Roperties Of Ice Films Between Pile And Freeze Sand Soil

The problem of pile-soil interface is crucial to the study of the bearing capacity of pile foundation, and the interface properties affect the safety and long-term stability of pile foundation. The natural permafrost foundation will be disturbed in variable extent by the various construction methods when the pile foundation is constructed. Under the mutual effects of the various factors, such as the temperature decreases in foundation, the atmospheric temperature and soil temperature from the frozen soil a round the pile, the surrounding soil of the pile and the pile body refreeze together with the ice membrane which is formed from the unfrozen water on the pile surface. The long-term bearing capacity of pile foundation is affected by the special creep properties of frozen soil and ice membrane, and the problem related to the foundation surface is an emphasis in the research on pile foundation. The current domestic and foreign research results are mainly focused on the creep properties of frozen soil, but the study of the creep properties in the frozen soil- structure interface is rare. Therefore, the quick direct shear test and creep test are carried out to study the properties of freeze sand soil-structure interface.All the related tests in this d issertation are conducted in the low temperature laboratory of LanZhou Jiao Tong University. The main equipments used in the experiment includes large-scale low temperature chamber, calorstat, modified strain controlled direct shear apparatus, modified stress controlled direct shear apparatus, temperature detector, temperature sensor and other apparatus. In order to compare the creep property in the indoor temperature with low temperature, the test temperature is 18℃、-1℃、-2℃. The thickness of ice membrane is 0.5mm, 1mm and 2mm. The normal stress is 50 kPa, 100 kPa, 200 kPa and 400 kPa. The soil is fine sand, and its moisture content is 15%. The structure material is C40 concrete.By quick direct shear test and creep test, the stress-strain curve, the Mohr-Coulomb shear strength envelope and the generalized cohesion in negative temperature of the sandy soil and concrete contact surface are obtained. The failure types of sandy soil-concrete interface at indoor temperature and frozen temperature is analyzed. Further, the creep strength is determined by gradation loading test.The test results showed that the shear test of frozen soil concrete contact surface damage type is different from the normal soil, and the characteristic of brittle failure is presented. The existence of generalized cohesion is mainly caused by the ice cementation. Growth of the generalized cohesion strength measured in creep test is faster than that in quick direct shear test, and the lower the temperature, the greater the difference. The reason of this phenomenon is due to the slower shear speed in the creep test, and in the long process the ice cementation is cracked and formed at the same time.Under the same conditions of the temperature and the thickness of ice membrane, the shear strength and creep strength are both increased with the increase of normal stress. Under the same conditions of the thickness of ice membrane and the normal stress, the shear strength and creep strength are both increased with the decrease of temperature. Under the same conditions, the creep strength is approximately half of the shear strength.