Research On The Mechanical Property Of Saturated Silty Clay Under Cyclic Loading

With the rapid development of city transportation in China，we have paid moreattention to the geotechnical problems caused by the traffic loads. A series ofundrained cyclic trial tests are conducted on typical Tianjin clay.Static triaxial and direct shear tests are carried to study the strength developmentof clay under different shearing velocity. The strength will increase under highvelocity in CU triaxial tests, and decrease in direct shearing tests. Research on thecreep testing shows that the creep curve has a great difference in defferent confiningpressures, different load ratioes, and different draining conditions. These results areanalysised.In order to do research in the dynamic features of clay under traffic load, a seriesof dynamic tests are conducted for typical undisturbed silty clay of Binhai area inTianjin using GDS dynamic triaxial. The factors of radial pressure, dynamic stressratio, dynamic-static stress coupling and consolidation ratio affecting the dynamicproperties of saturated clay are considered during the tests. The results indicate thatthe deformation curves are different under different stress ratios; the effects on soildynamic deformation, dynamic pore pressure, dynamic modulus of elasticity anddouble amplitude dynamic strain caused by vibration frequency could not beneglected; softening index has a limiting value, and it would not decrease whenreaching the limiting value; dynamic deformation would develop from tension strainto compression strain with the increase of static stress when dynamic stress is constant,higher dynamic stress increases the compression strain when static stress is constant,when tension stress appears, compression strain would develop for the oppositedirection, and tension strain would be created at last. There will be no deformationwhen the static and dynamic stress ratio reaches the critical one. which fluctuatesfrom0.3to0.5. Dynamic deformation would decrease with the increasing ofconsolidation ratio. Failure criterions are defined for four different axial strain curves.The factors of radial pressure, dynamic stress ratio, dynamic-static stresscoupling and consolidation ratio affecting the dynamic properties of saturated clay areconsidered during the remolded clay tests, and the results are compared withundisturbed silty clay. The results indicate that the axial strain curves developmentmode is bilinear, and the inflection point emerge when the dynamic strain reaches3%. Softening phenomenon and liquefaction occur more easily in the remolded silty clay tests. the effects on soil dynamic deformation, dynamic pore pressure, dynamicmodulus of elasticity and double amplitude dynamic strain caused by vibrationfrequency could not be neglected; softening index researches about0.4; The dynamicdeformations of remolded and undisturbed silty clay conform a similar law underdynamic and static loading; as the consolidation ratio increases, dynamic deformationgoes down firstly, then goes up.Dynamic and static triaxial tests were carried to study the patterns of undrainedstrength development of undisturbed and remolded clay after cyclic loading. The resultsshow that the undrained strength of undisturbed saturated clay can degrade after cyclicloading, the formula is founded between post-undrained strength ratio and dymnamicstrain; with the increase of the reduction factor, the stress paths transform from normalconsolidation to lightly quasi-overconsolidation, then to heavily quasi-overconsolidation,stress path after cyclic loading is proposed. The strength of remolded saturated soft clayhardly changes after cyclic loading.stiffness and dynamic strength will rise after thedissipation stage of excess pore pressure, consolidation degree affect s the stiffness andstrength greatly. permeability coefficient sill decrease woth the increasing of confiningpressure, and will goes up with the increasing of dymanic deformation.