Experimental Study On Short-term Creep Behavior Of Over-consolidated Silty Clay

With the clay in optimum water content around Beijing, using hammer excitation method, cylindrical soil samples with dimensions ofΦ39.1mm×80mm were made. Quasi-triaxial creep tests were performed on the samples when they were saturated by vacuum-pumping method.In order to make soil samples experience a variety of loading histories and possess different types of mechanic properties before creeping, preloading which divided into five groups was undertaken before creep loading.(1)Group E. Under the confining pressure of 1.5MPa, consolidation was maintained for 20 minutes, which was equivalent to consolidation with the confining pressure of 1.13MPa. Then drained cyclic consolidation was increased to 5mm, which was remained 5 minutes.The next was 5-minutes drained consolidation. At last undrained cyclic loading was gradually applied to 2.5mm, for 2.5 minutes.(2)Group R. Under the confining pressure of 1.5MPa, consolidation was maintained for 20 minutes, which was equivalent to consolidation with the confining pressure of 1.13MPa. Then drained cyclic consolidation was increased to 2.5mm, which was remained 5 minutes.The next was 5-minutes drained consolidation. At last undrained cyclic loading was gradually applied to 5mm, for 5 minutes.(3)Group DR. Under the confining pressure of 1.5MPa, consolidation was maintained for 20 minutes, which was equivalent to consolidation with the confining pressure of 1.13MPa. Then drained cyclic consolidation was increased to 2.5mm, which was remained 5 minutes. The next was 5-minutes drained consolidation. At last undrained monotonic loading was applied to 5mm, for 5 minutes.(4) Group SE.Under the confining pressure of 1.5MPa, consolidation was maintained for 30 minutes, which was equivalent to consolidation with the confining pressure of 1.28MPa. Then undrained monotonic loading was applied to 7.5mm, for 2.5 minutes.(5) Group T.30 minutes consolidation under 1.5MPa was done, with no other pre-loading histories. Creep tests were conducted on samples that have been preloaded. There were two important parameters, the confining pressure in the triaxial cell while creep loading as well as the axial compression on samples, with which combined with the preloading methods, categorized the tests into groups as many as they could be, and 2-6 specimens for each group.There were 4 types of confining pressures and axial pressures respectively in each of Group E, Group R and Group SE. However, there were 2 types of confining pressure in both Group DR and Group T, yet 2 types in Group DR and 4 in Group T in terms of axial pressures.The tests indicate that:(1)Whether the accelerated creep stage of remoulded clay will be emerge,is related to the over-consolidation ratios, axial pressures in creep stage and load histories applied in preloading process.(2) The rules of volume strain in creep process differ with the difference of preloading methods. The rules of pore pressure-volume strain curves are independent with the loading methods. The relationship between pore pressure and volume strain nearly develops in a similar fashion. With the increase of volume, the pore pressures vary slower, or tend to be constants.