Research On Liquefaction Characteristics And Pore Pressure Model Of Graphite Tailings

In mining engineering,tailings ponds are a potential "dangerous source".Heilongjiang Province has the largest reserves of graphite tailings in Asia.With the advancement of processing technology,the tailings particles of the tailings are becoming finer and finer,and at the same time,China is prone to earthquakes,which may cause serious disasters in case of liquefaction,so it is particularly important to conduct research on the liquefaction of graphite tailings.In this thesis,laboratory dynamic triaxial tests were carried out on the graphite tailings taken from Hegang,Heilongjiang,to investigate its dynamic performance and the development of pore water pressure,and establish a growth model of pore pressure.A series of shaking table tests were performed to reveal the macroscopic phenomenon of liquefaction,and the response of acceleration and pore pressure of graphite tailings during the tests were also given.The main research contents are as follows:（1）The main physical properties of graphite tailings were analysed.The graphite tailings used in this thesis was classified as silty sand according to its particle size,difference between the particle size distribution of graphite tailings sand and that of Fujian standard sand was obtained.The maximum and minimum dry density,permeability coefficient and shear strength index of the graphite tailings silty sand were measured,and the liquefaction mechanism and causes of liquefaction were elaborated.（2）Consolidated-undrained dynamic triaxial tests were conducted on graphite tailing specimens to investigate the dynamic stress-strain characteristics,and the development of axial strain development and super-static pore water pressure.There is a critical cyclic stress ratio（CSR）among 0.45 to 0.60,above which the axial strain will reach 5%.The greater the relative density and confining pressure,the less likely it is to be liquefaction.With the gradual increase of CSR,the excess pore water pressure increases rapidly and the liquefaction is more likely to occur.（3）Based on the liquefaction test data,the Seed model,hyperbolic model,exponential model and double S-shaped model were applied to fit the pore pressure curve of graphite tailings.The fitting results of the four models were compared and it can be found that the double-S-shaped model was more suitable for the increase of pore pressure in the tests.The effects of relative density,confining pressure and cyclic stress ratio（CSR）on the parameters of the double-S model were also given.（4）Based on the shaking table model tests,the effect of peak ground accelerations（PGA）on the liquefaction characteristics of graphite tailings was investigated,and the liquefaction phenomenon of graphite tailings was revealed.The larger the PGA,the more obvious the liquefaction was,and the more significant the mobility was.The change laws of graphite tailings acceleration time history and pore water pressure process during the tests were analyzed,and the results showed that the acceleration amplification of acceleration was not the same at different depths,With the depth increase,the amplification of acceleration decreases,while the excess pore water pressure ratio in the upper soil is greater than that in the lower soil.