Creep Behavior Of Saturated Soft Clay Under Long-term Cyclic Loading

The regions of Bohai bay, Yangtze estuary and the Zhujiang estuary are the economicengine of China, the economic of these regions are developing rapidly, and thetransportation demand is increasing day by day. A lot of coastal infrastructure is inplanning and construction. Soft clay foundation is widely distributed in these areas. Inaddition to the high water content, high compressibility, low strength, lowpermeability, thixotropy, significant structural and nonuniformity, the soft clay alsohas obvious creep propertiy. It tends to occur constant displacement under long-termcontinuous load. Based on the above situation, this paper took the coastalinfrastructure such as road, port and breakwater engineering as the researchbackground. Through a series of triaxial creep test, the creep properties of saturatedsoft clay under long-term load and long-term circulating load had been studied. Thispaper conducted the following research.(1) The triaxial creep tests on remoulded soft clay in Tianjin port were conducted byusing the SLB-1type triaxial apparatus. On the basis of the test results, the stain-timecurve, the stress-strain curve and the strain rate-time curve under different conditionswas obtained. The influences of different confiing pressure, the deviatoric strss leveland drainage conditions were analyzed.(2) Basised on the theory of empirical model, the creep properties of the remouldedsaturated soft clay have been analyzed. A non-linear rheological model suitable forthese soft clays with the property of Attenuation and stable state is established. Thisempirical model can describe not only the data in this test, but also the typical clays inTianjin.(3) The triaxial cyclic creep tests on remoulded soft clay in Tianjin port wereconducted by using the GDS type triaxial apparatus. Three typical characteristiccurves exist in the cyclic creep curves of saturated soft clay under cyclic loading.They are the peak creep curve, the base and the valley creep curve. The cumulativeplastic strain curve and reversible elastic strain curve were obtained by calculating,the nature and characteristics of two kinds of curve. The study found that cyclic creepcurve can be divided into two kinds according to the load pattern; they are Pull-pressmode creep model and press-press creep model. Press-press creep curve can describe the traffic load, wave load and other long-term cyclic loading creep characteristics ofsoils, two kinds of creep curves have different characteristics, so they should bediscussed respectively.(4) Based on the theory of the cyclic creep explicit model, the function of thecumulative plastic strain rate change with cycles has been established. The couplingeffect of dynamic deviatoric stress and static deviaoric stress has been considered byusing binary regression technique.(5) Taking the theory of the static empirical model to the study of cyclic creepproperty, a cumulative plastic strain empirical model has been established combiningthe critical state theory and explicit model theory, which can describe the couplingeffect of dynamic deviatoric stress and static deviaoric stress. This model normalizedthe influent factors on cumulative plastic strain, and could describe theattenuation-stable state creep properties of cumulative plastic strain under traffic orwave loads.(6) Based on the empirical model built in this paper, the secular subsidence of TianjinBinhai New Region has been calculated. Moreover, the long-term settlement of softclay under the long-term cyclic load of gravity type of break water has beencalculated.