Triaxial Test Study On Cyclic Characteristics Of Under-consolidated Saturated Soft Clay

The reclamation area along the southeast coast of our country is distributed with a wide range of under-consolidated weak soil layers.With the rapid economic development,major infrastructure construction in the region is in full swing.Although the soft soil foundation will be consolidated by drainage before construction,after treatment,only the surface of the foundation will form a hard shell,and the under-consolidated saturated soft clay in the underlying layer will increase the cumulative deformation and reduce the bearing capacity under the long-term action of static load and cyclic load,resulting in frequent engineering problems such as excessive settlement of subgrade and pavement and rupture of underground pipelines,resulting in economic losses and safety problems.In view of the problems of under-consolidated soft clay,this paper uses the GDS dynamic triaxial test system to study the static and dynamic characteristics of under-consolidated saturated soft clay in Wenzhou,and explores the influence of effective confining pressure on the static characteristics of soft clay under different consolidation degrees,and the influence of cyclic stress ratio and vibration frequency on the dynamic performance of soft clay under different consolidation degrees.The main research contents and results are as follows :(1)Under different effective confining pressures,undrained triaxial shear tests were carried out on under-consolidated saturated soft clay specimens,and the factors such as effective confining pressure and consolidation degree were analyzed in detail.The test results show that under the same strain,the pore pressure and stress of the specimen increase with the increase of consolidation degree,and the undrained shear strength increases.Under different effective confining pressures,the normalized pore pressure-strain relationship and the normalized stress-strain relationship of specimens with the same consolidation degree are similar.(2)A series of one-way cyclic undrained triaxial tests were carried out on under-consolidated saturated soft clay under different cyclic stresses.The research shows that the softening degree of underconsolidated soft clay specimens is higher than that of normal consolidated soft clay specimens,and the corresponding viscoplasticity and hysteresis characteristics are also more obvious.The lower the degree of consolidation,the easier the specimen softens in the later stage of loading.When the cyclic stress ratio exceeds the allowable cyclic stress ratio,the cumulative strain increases exponentially.(3)Cyclic triaxial tests were carried out on saturated soft clay with different consolidation degrees by selecting different combinations of cyclic frequency and cyclic stress.It is found that compared with other frequencies,when the frequency is 0.5 Hz,the cumulative rate of pore pressure and strain of the specimen is faster,the pore pressure and cumulative deformation are larger,and the change degree of hysteresis curve is larger,and the softening characteristics of soil are significantly affected.