Study And Application Of UU Cyclic Properties Of Clays

The study of clay's UU cyclic properties is one of the most significant branches in geotechnical engineering. Its application plays an important role in evaluating the cyclic bearing capacity of soft clay foundations. It is necessary for well-drilling engineering to study the cyclic properties of clayey filter cakes to improve mud displacement efficiency. Following researches have been done based on above reasons.Remolded prehydrated bentonite samples with different water content were used to simulate filter cakes with different strength. In order to study the feasibility of removing filter cakes using wall surface shear stress method, falling head permeability tests, direct shear tests and cyclic triaxial tests were conducted to determine permeability properties, shear strengths and cyclic strength of remolded prehydrated bentonite. Results showed that the strength of prehydrated bentonite degraded under cyclic loads. Therefore, clayey filter cakes can be removed by cyclic loads when vibration of drilling-fluid pump is acting on the filter cakes. It is proved to be a potential method removing the filter cakes during the mud displacement.The cyclic properties of soft clays were studied under the UU condition. Cyclic triaxial tests were conducted using undisturbed saturated soft clay samples under three different confining pressures. Cyclic strength curves and the cyclic accumulative strain versus the number of cycles were determined under different combined static and cyclic stresses. Effects of confining pressure on the cyclic strength and the cyclic accumulative strain were further analyzed when the confining pressure was increased to 400kPa. Test results showed that the cyclic strength and cyclic accumulative strain of the soft clay depend on the static stress, the cyclic stress and the number of cycles. The effect of confining pressure on cyclic properties of clays can be ignored.Model tests of the circle plate on soft clay foundation were conducted with cyclic loads and the cyclic bearing capacities were also calculated using the pseudo static elastoplastic FEM. By comparing test results with calculation results, the principles, methods and steps evaluating the cyclic bearing capacity of soft clay foundations were discussed based on UU cyclic properties of soft clays.