Experimental Study On Rheological Properties Of Frozen Silty Clay-concrete Pile Interface

With the rapid development of capital construction, pile foundation has been widely used in construction of cold region, which exists a large amount of problems about pile-frozen soil interface in the cold region. The property of the pile-frozen soil interface is the key influencing factor of the security and stability of pile structure.In order to obtain major influencing factors and essential principle in the study of pile-frozen soil interface, the horizontal and normal stress-strain tests of contact interface were carried on, which is limited by the lack of relevant experimental research means.Therefore, the development of equipment and testing system become the premise of the research on the contact surface of frozen soil.Combined with the current research results of the soil-structure contact interface test equipment at home and abroad, and based on National Natural Science Foundation of China "Theoretical and Experimental Study of permafrost foundation pile-frozen soil interface formation mechanism"(No.51268033), a new apparatus called large-scale flowing deformation direct shear apparatus for frozen soil-structure interface is developed, which could accurately perform and reproduce the mechanical and deformational behaviors of the interface layer between frozen soil and structure. In addition, taking need of actual test into account, the shear box applied in the test is designed as a square shear box with the size of200×200×100mm.The experiment materials are silty clay samples taken in Lanzhou with controlled moisture 20% and C35 concrete. Based on this test system, the shear test and creep test were carried on under different temperatures(15℃、-0.7℃、-2℃、-3.5℃) and different normal stresses(50kPa、100kPa、150kPa、200kPa). The stress-strain curve under different temperature was drawn through analysis of shear test result, and shear strength of contact interface at different temperatures and different normal stresses was obtained, and friction angle and cohesion of contact interface under different temperatures were obtained through calculation on strength parameters of interface. According to the “Boltzmann superposition principle”,stress-strain curve is transformed to creep curve with “coordinate shift” method, which turns out to be the creep curve under different temperatures and normal stresses.Shear test of contact surface results show that the shape of shear curves under different temperatures are similar to that at normal stresses. Under the same temperature and shear displacement conditions, shear force and shear strength of contact interface increase with the augment of normal stress. Under the same normal stress, the shear strength of the contact surface increases with the decrease of temperature. Internal friction angle and cohesionincrease with the decrease of temperature. Compared with friction angle, cohesion increases are sensitive with the change of temperature.The creep test of contact surface results show that the interfacial shear displacement-time curve develops at state of ladder shape under multi-stage loading condition. Under the condition of low shear stress, the type of creep is mainly attenuational, and the creep curve of contact interface gradually changes from attenuation creep to non-attenuation creep with the increase of shear stress. Force time of each level is related to temperature, normal stress and level of shear stress, which is mostly concentrated in the range of 300~700 min. For attenuation creep, non-steady creep stage lasts shorter time and steady creep stage time increases with the increase of shear stress.