Study On Mechanical Properties And Constitutive Relation Of Cemented Mercury Slag

There are many mercury mine in the city of Guizhou, Hubei, Yunnan and etc. Mining formed a large number of accumulation. Cemented mercury slag is generated by complex physical chemical processes for many years.Because cemented mercury slag accumulation is in the goundsurface, it will cause some long-standing geological environmental security. Therefore, basic research about cemented mercury slag is an urgent need.Paper focuses on the mechanical properties and constitutive relationship of cemented mercury slag. It has significance and value for long-term stability evaluation of cemented mercury slag accumulation.The present study selected the existing mercury slag in Tongren area of Guizhou, also known as "the mercury city" of China, as research object. The investigation of its types and cementing conditions, and the application of CT scanning and laboratory test obtained the causes, fabric and physical properties of cemented mercury slag. Selecting typical slag type to put forward mechnanical parameters and its varation by general mechanics test, triaxial test of coarse-grained soil and uniaxial CT test. By analyzing the data from triaxial test of coarse-grained soil and applying mechanical theory, it obtained constitutive relation of cemented mercury slag under typical conditions. Using uniaxial CT test parameters as calibration parameters, and based on discrete element stimulation test, the study acquired failure process of typical types of cemented mercury slag under mesco conditions.At last, using the constitutive relation and Duncan-Chang model to analysize the stability of typical cemented mercury slag accumulation. Then compared with the actual test results to verified the feasibility of its constitutive model.From the above study, the dissertation comes to the following conclusion.1.The fabric of cemented mercury slag is mainly takes on calcareous-magnesian carbonate.And there are some furnace ash and the cementation is carbonate.The factors contributing to the formation of cements are:hydrologic conditions>accumulation years>ventilation conditions>depth of covering layers>types of position>light>porosity ratio. The fabric of the slag presents coarse-grained cementation and big voids, with the diameter of grains and voids shortens as the accumulation year increases. The cementation of mercury slag is classified in seven types, which are argillaceous coarse gravel cementation, argillaceous medium gravel cementation, argillaceous fine gravel cementation, cementitious coarse gravel cementation, cementitious medium gravel cementation, irregular coarse gravel cementation and round coarse gravel cementation. Comparison of discreteness and variability among all types is carried out and reveals that cementitious medium gravel cementation is the typical cementing type.2. In terms of the major physical properties of cemented mercury slag, dump slag, as its main aggregate, enjoys poor grain composition, large proportion of coarse particles and the decrease of average values of particles’ diameters as the elevation increases. With the extension of accumulation year, mercury slag presents lower density, more particles with large diameters, less particles with small diameters and higher in water content in furnace ash, yet lower in its permeability. The permeability of the hardened "crust" gets poorer with the increase of the accumulation years and the decrease of burial depth. Through the study of the major failure mode of slope and the accumulation test and theoretical analysis, the study acquires that the saturation of cementing fracture is the typical condition of cemented mercury slag.3. In the conventional mechanical test of aggregate of cemented mercury slag, the dump slag takes on the properties of gravels; however, the furnace ash on the properties of soils. Uniaxial CT test of the typical type shows that the internal cementation structure tends to become tight, in other words, plastic, when the stress fails to reach its peak value; it takes on initial cracking response when the stress arrives at its peak; with the increase of stress, rapid failure occurs to the structure of cemented mercury slag, including overall and partial failures; its structural response stops when the structure is in complete failure.4. Triaxial test of coarse-grained soil of cemented mercury slag under typical condition finds that the cements increase its cohesion; during the shearing process, its internal structure tends to tight, and its strength tends to increase, presenting the features of hardening. As the original voids are filled by some particles during the shearing, under different confining pressure, contractions, instead of dilatancy, will occur to the cemented mercury slag. Comparative analysis reveals that, under a low stress level, the poisson’s ratio obtained from E-V model is quite similar; while under a high stress level, E-B model can best reflect the actual poisson’s ratio. The stress-strain curve and volumetric strain and line strain curve indicate that deformation is less likely to occur, as the intensity gets higher when the accumulation period grows longer; it is in effect heavily influenced by the consolidated stress.5. Due to the existence of cements, the mechanical properties of mercury slag presents weak cementing to some extent. By applying elastic-plastic mechanics and soil mechanics theory, corrected the poisson’s ratio equation of Duncan-Zhang’s model and obtains the constitutive relation of cemented mercury slag.6. Using irregular particles to establish discrete element stimulation and it reveals the failure process of typical cemented mercury slag in microscopic scale, namely the generation, development, cutthrough and failure process of cracks under the load action.7. Using secondary development of FLAC3D to analyze the stability of cemented mercury slag accumulation in Tongren.Compared with the original Duncan-Zhang’s E-V constitutive model, the revised one can better reveal the actual situation, verifying the correctness as well as the significance of the revised constitutive model.Major innovations of this dissertation:1. Based on geological survey and tests for mercury slag, the study offers a systematic exploration of the material composition and structural characteristics of cemented mercury slag and obtains a regional parameter level.2. Based on triaxial test of coarse-grained soil, the study corrected the poisson’s ratio equation of Duncan-Zhang’s model and obtains the constitutive relation of cemented mercury slag.3. Based on uniaxial CT test and discrete element stimulation analysis, it acquires meso-scopic mechanism of mercury slag during the process of mechanical failure.