Study On Effect Of Particle Size Matching On Dynamic Characteristics Of Saturated Tailing Sand

Mineral resources are an indispensable material for human social and economic development,the high-pile fine-grained tailings pond is the inevitable development direction of the tailings pond in our country,hidden dangers of disaster will be more serious.At the same time,our country is an earthquake frequent country a large number of tailings ponds are in strong earthquake area.Therefore,it is urgent to strengthen the basic research on the stability of high-pile fine-grained tailings pond under strong earthquake load,so as to provide a theoretical basis for the construction and detection of tailings pond.This paper takes the deep-buried tailings of Yinshan lead-zinc tailings reservoir in Dexing,Shangrao City,Jiangxi Province as the research object.Starting from the key influencing factor of sand particle size gradation,a series of tests and theoretical studies are carried out systematically.In order to study the influence of particle size grade on dynamic characteristics of saturated deep tailing sand,the undisturbed soil of tailing sand was crushed and screened,and then the tailing sand test samples were configured with different fine particle content and different sand grade.In the first series of tests,the effects of fine grain content on dynamic characteristics of sand were explored by keeping the sand grain gradation unchanged.In the second series of experiments,the influence of sand grading parameters（C_c,C_u）on its dynamic characteristics was explored by controlling the fine particle content as a fixed value.Based on the results of dynamic triaxial test,the development characteristics of dynamic strain and dynamic pore water pressure of tailing sand with different fine particle content,different non-uniformity coefficient C_uand different curvature coefficient C_care summarized.The conclusion is as follows:（1）Taking the appearance of cumulative plastic transition strain point as the sign of tailings sand instability,the variation trend of anti-instability ability of saturated tailings with different grain size gradations is analyzed.For different fine particle content,the anti-instability ability of tailings sand is approximately a downward opening parabola:when the fine particle content is low（FC<30%）,the anti-instability ability of tailings sand becomes weaker with the increase of fine particle content.When the fine particle content is high（FC>30%）,the anti-instability ability of tailings sand increases with the increase of fine particle content,but the increase range is not large.When FC=30%,the anti-instability ability of tailing sand is the weakest,and the critical fine particle content is around 30%.For tailing sand with different sand gradations,when C_uand d₁₀remain unchanged,the smaller the C_cvalue,the finer the intermediate particle size of tailing sand,the easier the pore water pressure is to accumulate,and the instability of tailing sand is more likely to occur.When C_cand d₁₀are maintained unchanged,the smaller the C_u,the smaller the overall particle size of the sand particles formed by tailing sand skeleton,the more prone the tailing sand is to destabilization and failure.（2）Based on cumulative plastic strain,qualitative and quantitative analysis was made on the variation law of hysteresis curves k,S and a/b of different particle size grades（FC,C_cand C_u）with the loading process.The results showed that the closer to the critical fine particle content and the decrease of C_uand C_cwould lead to the greater energy dissipation of tailing sand under the action of single cyclic load.（3）The dynamic pore pressure growth curve of tailing sand with different fine particle content increases roughly as"S",showing four stages of development law:slow growth stage,rapid growth stage,damage growth stage and stable stage.The pore pressure development pattern of different C_cvalues is basically the same as that of different C_uvalues,which roughly presents a reverse"C"type growth.As C_uvalue decreases,the pore pressure development pattern gradually increases to"S"type growth.The overall pore pressure development pattern can be roughly divided into three stages:slow growth stage,rapid growth stage and stable stage.Based on the analysis of dynamic pore pressure growth rule under particle size grading parameters and considering the influence of particle size grading parameters on the development form and rate of dynamic pore pressure,a multi-stage cumulative dynamic pore pressure growth model of saturated tailings was established.（4）By introducing the boundary surface model suitable for cyclic loading of saturated sand,the existence of critical fine particle content is verified by comparing the critical state parameters of tailings with different fine particle content.In addition,a dynamic triaxial numerical model of undrained saturated tailing sand is established in FLAC^3D.By comparing with the experimental data,the simulation ability of boundary model for dynamic characteristics of saturated tailing sand with different soil material properties under high stress conditions is verified,which provides a new means for exploring dynamic characteristics of tailing sand under seismic load.At the same time,it also points out the shortcomings of the boundary surface model to prepare for the follow-up research.