Study Of Deformation Characteristics Of Dredger Fill Under Continuous And Intermittent Dynamic Loads

With the demands of the country’s economic and social development,land resources are becoming increasingly tight,especially along the southeast coast of China,where the scarcity of land resources has led people to carry out land reclamation around the sea to open up new areas.Although a series of strict control measures on land enclosure have been introduced since 2017,there are still many sites with completed blowfills that need to be dealt with urgently.In addition,roads constructed on blowfilled sites are prone to problems such as cracking of blowfilled site roads and settlement of road surfaces due to cyclic loading,which in turn can cause engineering accidents.Therefore,it is very important to strengthen the research of soft clay soil on blowfills for safe operation of the project as well as the adverse effects after work,which can provide objective scientific basis for the actual project.In this paper,the test specimens of blow-fill soft clay are produced by the laboratory’s own design of low-level vacuum pre-pressure equipment;the strength and deformation of blow-fill soft clay under different dynamic stress amplitude and different loading forms are obtained through dynamic triaxial tests;and the characteristics of the accumulated plastic strain behaviour of blowfill soft clay under continuous and intermittent dynamic loading are discussed.The main research contents and related conclusions are as follows.1.The preparation of blown soft clay is introduced,and the hardware composition,sample preparation principle and sample preparation method of the self-developed low-level vacuum stacking precompression device are elaborated to achieve rapid and efficient preparation of several blown soft clay specimens with uniform moisture content and density and more homogeneous specimen strength in one time in the chamber.The CU shear stress-strain curve of the blown soft clay shows strain hardening at low consolidation pressures and strain softening as the consolidation pressure increases.This indicates that the prepared blown soft clay has some structural properties.2.Based on the stability theory,the cumulative plastic behaviour of the blown soft clay under continuous dynamic triaxial test results was classified into three forms: stable,critical and destructive.The middle value of the upper and lower boundary values of plastic strain rate of different plastic behaviour is adopted as the criterion to distinguish different plastic deformation behaviour,and the relevant empirical equation of critical dynamic stress of blown soft clay is established,which can be used to determine the plastic deformation behaviour of blown soft clay specimens under different dynamic stress levels of different surrounding pressure.3.Under the action of continuous dynamic loading,the hysteresis circle curve of the blown soft clay has obvious non-linearity and hysteresis with the number of cycles,in the initial loading stage,under the same vibration,the unloading stage obviously lags behind the loading stage hysteresis circle curve is "oval";with the increase of vibration,the specimen strain development tends to stabilize,then the hysteresis circle is "Crescent-shaped".In the same number of cycles,the greater the cyclic stress ratio,the greater the height and width of the hysteresis circle.The rebound strain of blow-filled soft clay develops faster within the initial few thousand vibrations and gradually stabilises.4.The analysis of the results of the dynamic triaxial tests with different loading forms(single-stage and multi-stage loading)on the blown soft clay soil shows that the interval duration has a suppressive and moderating effect on the plastic deformation of the soil.Under different loading interval settings,the shorter interval lengths slowed down the development of the subsequent cumulative plastic strain of the specimens,but still had a tendency to grow all the time;under higher interval lengths,the cumulative plastic deformation of the specimens developed rapidly and steadily.With different loading duration settings,the higher loading duration per stage allows the specimen to reach a higher initial strain level at the end of the first stage compared to the other specimens,and to stabilise rapidly after the first interval stage;while the shorter loading duration per stage still allows the subsequent cumulative plastic strain of the specimen to develop to a certain extent.5.Based on the stability theory,the plastic stability and plastic creep behaviour of blown plastic soft clay under intermittent loading of different interval durations are subdivided,and the criteria for determining the plastic behaviour and the limits of plastic stability are proposed.Based on the cumulative plastic strain law of blow-filled soft clay under continuous and intermittent loading,a prediction model of cumulative plastic strain of blow-filled soft clay under intermittent and continuous loading is established and validated,which can provide reference for practical engineering applications.